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0.7904–0.7928 g·cm −3 (10 °C) [ 4 ]
Acetaldehyde (IUPAC systematic name ethanal ) is an organic chemical compound with the formula CH 3 CH=O , sometimes abbreviated as Me CH=O . It is a colorless liquid or gas, boiling near room temperature. It is one of the most important aldehydes , occurring widely in nature and being produced on a large scale in industry. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, [ 11 ] and is produced by plants. It is also produced by the partial oxidation of ethanol by the liver enzyme alcohol dehydrogenase and is a contributing cause of hangover after alcohol consumption. [ 12 ] Pathways of exposure include air, water, land, or groundwater, as well as drink and smoke. [ 13 ] Consumption of disulfiram inhibits acetaldehyde dehydrogenase , the enzyme responsible for the metabolism of acetaldehyde, thereby causing it to build up in the body.
The International Agency for Research on Cancer (IARC) has listed acetaldehyde as a Group 1 carcinogen . [ 14 ] Acetaldehyde is "one of the most frequently found air toxins with cancer risk greater than one in a million". [ 15 ]
Acetaldehyde was first observed by the Swedish pharmacist/chemist Carl Wilhelm Scheele (1774); [ 16 ] it was then investigated by the French chemists Antoine François, comte de Fourcroy and Louis Nicolas Vauquelin (1800), [ 17 ] and the German chemists Johann Wolfgang Döbereiner (1821, 1822, 1832) [ 18 ] and Justus von Liebig (1835). [ 19 ] [ 20 ]
In 1835, Liebig named it "aldehyde", [ 21 ] and in the middle of the century the name was altered to "acetaldehyde". [ 22 ]
In 2013, global production was about 438 thousand tons. [ 23 ] Before 1962, ethanol and acetylene were the major sources of acetaldehyde. Since then, ethylene is the dominant feedstock . [ 24 ]
The main method of production is the oxidation of ethene by the Wacker process , which involves oxidation of ethene using a homogeneous palladium/copper catalyst system:
In the 1970s, the world capacity of the Wacker-Hoechst direct oxidation process exceeded 2 million tonnes annually.
Smaller quantities can be prepared by the partial oxidation of ethanol in an exothermic reaction. This process typically is conducted over a silver catalyst at about 500–650 °C (932–1,202 °F). [ 24 ]
This method is one of the oldest routes for the industrial preparation of acetaldehyde.
Prior to the Wacker process and the availability of cheap ethylene, acetaldehyde was produced by the hydration of acetylene . [ 25 ] This reaction is catalyzed by mercury(II) salts:
The mechanism involves the intermediacy of vinyl alcohol , which tautomerizes to acetaldehyde. The reaction is conducted at 90–95 °C (194–203 °F), and the acetaldehyde formed is separated from water and mercury and cooled to 25–30 °C (77–86 °F). In the wet oxidation process, iron(III) sulfate is used to reoxidize the mercury back to the mercury(II) salt. The resulting iron(II) sulfate is oxidized in a separate reactor with nitric acid . [ 24 ]
The enzyme Acetylene hydratase discovered in the strictly anaerobic bacterium Pelobacter acetylenicus can catalyze an analogous reaction without involving any compounds of mercury. [ 26 ] However, it has thus far not been brought to any large-scale or commercial use.
Traditionally, acetaldehyde was produced by the partial dehydrogenation of ethanol:
In this endothermic process, ethanol vapor is passed at 260–290 °C over a copper-based catalyst. The process was once attractive because of the value of the hydrogen coproduct, [ 24 ] but in modern times is not economically viable.
The hydroformylation of methanol with catalysts like cobalt, nickel, or iron salts also produces acetaldehyde, although this process is of no industrial importance. Similarly noncompetitive, acetaldehyde arises from synthesis gas with modest selectivity. [ 24 ]
Like many other carbonyl compounds , acetaldehyde tautomerizes to give an enol ( vinyl alcohol ; IUPAC name: ethenol):
The equilibrium constant is 6 × 10 −7 at room temperature, thus that the relative amount of the enol form in a sample of acetaldehyde is very small. [ 27 ] At room temperature, acetaldehyde ( CH 3 CH=O ) is more stable than vinyl alcohol ( CH 2 =CHOH ) by 42.7 kJ/mol: [ 28 ] Overall the keto-enol tautomerization occurs slowly but is catalyzed by acids.
Photo-induced keto-enol tautomerization is viable under atmospheric or stratospheric conditions. This photo-tautomerization is relevant to the Earth's atmosphere, because vinyl alcohol is thought to be a precursor to carboxylic acids in the atmosphere. [ 29 ] [ 30 ]
Acetaldehyde is a common electrophile in organic synthesis . [ 31 ] In addition reactions acetaldehyde is prochiral . It is used primarily as a source of the " CH 3 C + H(OH) " synthon in aldol reactions and related condensation reactions . [ 32 ] Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives. [ 33 ] In one of the more spectacular addition reactions, formaldehyde in the presence of calcium hydroxide adds to MeCHO to give pentaerythritol , C(CH 2 OH) 4 and formate . [ 34 ]
In a Strecker reaction , acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis , the amino acid alanine . [ 35 ] Acetaldehyde can condense with amines to yield imines ; for example, with cyclohexylamine to give N - ethylidenecyclohexylamine . These imines can be used to direct subsequent reactions like an aldol condensation. [ 36 ]
It is also a building block in the synthesis of heterocyclic compounds . In one example, it converts, upon treatment with ammonia , to 5-ethyl-2-methylpyridine ("aldehyde-collidine"). [ 37 ]
Three molecules of acetaldehyde condense to form " paraldehyde ", a cyclic trimer containing C-O single bonds. Similarly condensation of four molecules of acetaldehyde give the cyclic molecule metaldehyde . Paraldehyde can be produced in good yields, using a sulfuric acid catalyst. Metaldehyde is only obtained in a few percent yield and with cooling, often using HBr rather than H 2 SO 4 as the catalyst. At −40 °C (−40 °F) in the presence of acid catalysts, polyacetaldehyde is produced. [ 24 ] There are two stereomers of paraldehyde and four of metaldehyde.
The German chemist Valentin Hermann Weidenbusch (1821–1893) synthesized paraldehyde in 1848 by treating acetaldehyde with acid (either sulfuric or nitric acid) and cooling to 0 °C (32 °F). He found it quite remarkable that when paraldehyde was heated with a trace of the same acid, the reaction went the other way, recreating acetaldehyde. [ 38 ]
Although vinyl alcohol is a polymeric form of acetaldehyde ( § Tautomerization to vinyl alcohol ), polyvinyl alcohol cannot be produced from acetaldehyde.
Acetaldehyde forms a stable acetal upon reaction with ethanol under conditions that favor dehydration. The product, CH 3 CH(OCH 2 CH 3 ) 2 , is formally named 1,1-diethoxyethane but is commonly referred to as "acetal". [ 39 ] This can cause confusion as "acetal" is more commonly used to describe compounds with the functional groups RCH(OR') 2 or RR'C(OR'') 2 rather than referring to this specific compound — in fact, 1,1-diethoxyethane is also described as the diethyl acetal of acetaldehyde.
Acetaldehyde is a precursor to vinylphosphonic acid , which is used to make adhesives and ion conductive membranes. The synthesis sequence begins with a reaction with phosphorus trichloride : [ 40 ]
In the liver , the enzyme , alcohol dehydrogenase oxidizes ethanol into acetaldehyde, which is then further oxidized into harmless acetic acid by acetaldehyde dehydrogenase . These two oxidation reactions are coupled with the reduction of NAD + to NADH . [ 41 ] In the brain, the enzyme catalase is primarily responsible for oxidizing ethanol to acetaldehyde, and alcohol dehydrogenase plays a minor role. [ 41 ] The last steps of alcoholic fermentation in bacteria, plants, and yeast involve the conversion of pyruvate into acetaldehyde and carbon dioxide by the enzyme pyruvate decarboxylase , followed by the conversion of acetaldehyde into ethanol. The latter reaction is again catalyzed by an alcohol dehydrogenase, now operating in the opposite direction.
Many East Asian people have an ALDH2 mutation which makes them significantly less efficient at oxidizing acetaldehyde. On consuming alcohol, their bodies tend to accumulate excessive amounts of acetaldehyde, causing the so-called alcohol flush reaction . [ 42 ] They develop a characteristic flush on the face and body, along with "nausea, headache and general physical discomfort". [ 43 ] Ingestion of the drug disulfiram , which inhibits ALDH2, leads to a similar reaction (see: § Aggravating factors below) . [ 44 ]
Traditionally, acetaldehyde was mainly used as a precursor to acetic acid. This application has declined because acetic acid is produced more efficiently from methanol by the Monsanto and Cativa processes . Acetaldehyde is an important precursor to pyridine derivatives, pentaerythritol , and crotonaldehyde . Urea and acetaldehyde combine to give a useful resin . Acetic anhydride reacts with acetaldehyde to give ethylidene diacetate , a precursor to vinyl acetate , which is used to produce polyvinyl acetate . [ 24 ]
The global market for acetaldehyde is declining. Demand has been impacted by changes in the production of plasticizer alcohols, which has shifted because n -butyraldehyde is less often produced from acetaldehyde, instead being generated by hydroformylation of propylene . Likewise, acetic acid , once produced from acetaldehyde, is made predominantly by the lower-cost methanol carbonylation process. [ 45 ] The impact on demand has led to increase in prices and thus slowdown in the market.
China is the largest consumer of acetaldehyde in the world, accounting for almost half of global consumption in 2012. Major use has been the production of acetic acid. Other uses such as pyridines and pentaerythritol are expected to grow faster than acetic acid, but the volumes are not large enough to offset the decline in acetic acid. As a consequence, overall acetaldehyde consumption in China may grow slightly at 1.6% per year through 2018. Western Europe is the second-largest consumer of acetaldehyde worldwide, accounting for 20% of world consumption in 2012. As with China, the Western European acetaldehyde market is expected to increase only very slightly at 1% per year during 2012–2018. However, Japan could emerge as a potential consumer for acetaldehyde in the next five years due to newfound use in commercial production of butadiene . The supply of butadiene has been volatile in Japan and the rest of Asia. This should provide the much needed boost to the flat market, as of 2013. [ 46 ]
The threshold limit value is 25ppm (STEL/ceiling value) and the MAK (Maximum Workplace Concentration) is 50 ppm. At 50 ppm acetaldehyde, no irritation or local tissue damage in the nasal mucosa is observed. When taken up by the organism, acetaldehyde is metabolized rapidly in the liver to acetic acid. Only a small proportion is exhaled unchanged. After intravenous injection, the half-life in the blood is approximately 90 seconds. [ 24 ]
Many serious cases of acute intoxication have been recorded. [ 24 ] Acetaldehyde naturally breaks down in the human body. [ 13 ] [ 47 ]
Acetaldehyde is an irritant of the skin, eyes, mucous membranes, throat, and respiratory tract. This occurs at concentrations as low as 1000 ppm. Symptoms of exposure to this compound include nausea , vomiting , and headache . These symptoms may not happen immediately. The perception threshold for acetaldehyde in air is in the range between 0.07 and 0.25 ppm. [ 24 ] At such concentrations, the fruity odor of acetaldehyde is apparent. Conjunctival irritations have been observed after a 15-minute exposure to concentrations of 25 and 50 ppm, but transient conjunctivitis and irritation of the respiratory tract have been reported after exposure to 200 ppm acetaldehyde for 15 minutes.
Acetaldehyde is carcinogenic in humans. [ 48 ] [ 49 ] In 1988 the International Agency for Research on Cancer stated, "There is sufficient evidence for the carcinogenicity of acetaldehyde (the major metabolite of ethanol) in experimental animals ." [ 50 ] In October 2009 the International Agency for Research on Cancer updated the classification of acetaldehyde stating that acetaldehyde included in and generated endogenously from alcoholic beverages is a Group I human carcinogen. [ 51 ] In addition, acetaldehyde is damaging to DNA [ 52 ] and causes abnormal muscle development as it binds to proteins. [ 53 ]
Acetaldehyde induces DNA interstrand crosslinks, a form of DNA damage. These can be repaired by either of two replication-coupled DNA repair pathways. [ 54 ] The first is referred to as the FA pathway, because it employs gene products defective in Fanconi's anemia patients. This repair pathway results in increased mutation frequency and altered mutational spectrum. [ 54 ] The second repair pathway requires replication fork convergence, breakage of the acetaldehyde crosslink, translesion synthesis by a Y-family DNA polymerase and homologous recombination. [ 54 ]
People with a genetic deficiency for the enzyme responsible for the conversion of acetaldehyde into acetic acid may have a greater risk of Alzheimer's disease . "These results indicate that the ALDH2 deficiency is a risk factor for LOAD [late-onset Alzheimer's disease] ..." [ 55 ]
A study of 818 heavy drinkers found that those exposed to more acetaldehyde than normal through a genetic variant of the gene encoding for ADH1C , ADH1C*1, are at greater risk of developing cancers of the upper gastrointestinal tract and liver. [ 56 ]
The drug disulfiram (Antabuse) inhibits acetaldehyde dehydrogenase, an enzyme that oxidizes the compound into acetic acid. Metabolism of ethanol forms acetaldehyde before acetaldehyde dehydrogenase forms acetic acid, but with the enzyme inhibited, acetaldehyde accumulates. If one consumes ethanol while taking disulfiram, the hangover effect of ethanol is felt more rapidly and intensely ( disulfiram-alcohol reaction ). As such, disulfiram is sometimes used as a deterrent for alcoholics wishing to stay sober. [ 44 ]
Acetaldehyde is a potential contaminant in workplace, indoors, and ambient environments. Moreover, the majority of humans spend more than 90% of their time in indoor environments, increasing any exposure and the risk to human health. [ 57 ]
In a study in France , the mean indoor concentration of acetaldehydes measured in 16 homes was approximately seven times higher than the outside acetaldehyde concentration. The living room had a mean of 18.1±17.5 μg m −3 and the bedroom was 18.2±16.9 μg m −3 , whereas the outdoor air had a mean concentration of 2.3±2.6 μg m −3 . [ citation needed ]
It has been concluded that volatile organic compounds (VOC) such as benzene, formaldehyde, acetaldehyde, toluene, and xylenes have to be considered priority pollutants with respect to their health effects. It has been pointed that in renovated or completely new buildings, the VOCs concentration levels are often several orders of magnitude higher. The main sources of acetaldehydes in homes include building materials, laminate, PVC flooring, varnished wood flooring, and varnished cork/pine flooring (found in the varnish, not the wood). It is also found in plastics, oil-based and water-based paints, in composite wood ceilings, particle-board, plywood, treated pine wood, and laminated chipboard furniture. [ 58 ]
The use of acetaldehyde is widespread in different industries, and it may be released into waste water or the air during production, use, transportation and storage. Sources of acetaldehyde include fuel combustion emissions from stationary internal combustion engines and power plants that burn fossil fuels, wood, or trash, oil and gas extraction, refineries, cement kilns, lumber and wood mills and paper mills. [ 59 ] Acetaldehyde is also present in automobile and diesel exhaust . [ 60 ] As a result, acetaldehyde is "one of the most frequently found air toxics with cancer risk greater than one in a million". [ 15 ]
Natural tobacco polysaccharides , including cellulose , have been shown to be the primary precursors making acetaldehyde a significant constituent of tobacco smoke . [ 61 ] [ 62 ] It has been demonstrated to have a synergistic effect with nicotine in rodent studies of addiction . [ 63 ] [ 64 ] Acetaldehyde is also the most abundant carcinogen in tobacco smoke; it is dissolved into the saliva while smoking.
Acetaldehyde has been found in cannabis smoke . This finding emerged through the use of new chemical techniques that demonstrated the acetaldehyde present was causing DNA damage in laboratory settings. [ 65 ]
Many microbes produce acetaldehyde from ethanol, but they have a lower capacity to eliminate the acetaldehyde, which can lead to the accumulation of acetaldehyde in saliva, stomach acid, and intestinal contents. Fermented food and many alcoholic beverages can also contain significant amounts of acetaldehyde. Acetaldehyde, derived from mucosal or microbial oxidation of ethanol, tobacco smoke, and diet, appears to act as a cumulative carcinogen in the upper digestive tract of humans. [ 66 ] According to European Commission's Scientific Committee on Consumer Safety's (SCCS) "Opinion on Acetaldehyde" (2012) the cosmetic products special risk limit is 5 mg/L and acetaldehyde should not be used in mouth-washing products. [ 67 ]
Acetaldehyde can be produced by the photo-oxidation of polyethylene terephthalate (PET), via a Type II Norrish reaction . [ 68 ]
Although the levels produced by this process are minute acetaldehyde has an exceedingly low taste/ odor threshold of around 20–40 ppb and can cause an off-taste in bottled water. [ 69 ] The level at which an average consumer could detect acetaldehyde is still considerably lower than any toxicity. [ 70 ]
Candida albicans in patients with potentially carcinogenic oral diseases has been shown to produce acetaldehyde in quantities sufficient to cause problems. [ 71 ] | https://en.wikipedia.org/wiki/H3C-CHO |
Acetone ( 2-propanone or dimethyl ketone ) is an organic compound with the formula (CH 3 ) 2 CO . [ 22 ] It is the simplest and smallest ketone ( R−C(=O)−R' ). It is a colorless, highly volatile , and flammable liquid with a characteristic pungent odor. [ 23 ]
Acetone is miscible with water and serves as an important organic solvent in industry, home, and laboratory. About 6.7 million tonnes were produced worldwide in 2010, mainly for use as a solvent and for production of methyl methacrylate and bisphenol A , which are precursors to widely used plastics . [ 24 ] [ 25 ] It is a common building block in organic chemistry . It serves as a solvent in household products such as nail polish remover and paint thinner . It has volatile organic compound (VOC)-exempt status in the United States. [ 26 ]
Acetone is produced and disposed of in the human body through normal metabolic processes. Small quantities of it are present naturally in blood and urine. People with diabetic ketoacidosis produce it in larger amounts. Ketogenic diets that increase ketone bodies (acetone, β-hydroxybutyric acid and acetoacetic acid ) in the blood are used to counter epileptic attacks in children who suffer from refractory epilepsy. [ 27 ]
From the 17th century, and before modern developments in organic chemistry nomenclature , acetone was given many different names. They included "spirit of Saturn", which was given when it was thought to be a compound of lead and, later, "pyro-acetic spirit" and "pyro-acetic ester". [ 6 ]
Prior to the name "acetone" being coined by French chemists (see below ), it was named "mesit" (from the Greek μεσίτης, meaning mediator) by Carl Reichenbach , who also claimed that methyl alcohol consisted of mesit and ethyl alcohol . [ 28 ] [ 6 ] Names derived from mesit include mesitylene and mesityl oxide which were first synthesised from acetone.
In 1839, the name "acetone" began to be used and the term was composed of “daughter of” and acetum (acetic acid) because it was obtained from acetic acid. [ 23 ] Unlike many compounds with the acet- prefix which have a 2-carbon chain, acetone has a 3-carbon chain. That has caused confusion because there cannot be a ketone with 2 carbons. The prefix refers to acetone's relation to vinegar ( acetum in Latin , also the source of the words "acid" and "acetic"), rather than its chemical structure. [ 29 ]
Acetone was first produced by Andreas Libavius in 1606 by distillation of lead(II) acetate . [ 30 ] [ 31 ]
In 1832, French chemist Jean-Baptiste Dumas and German chemist Justus von Liebig determined the empirical formula for acetone. [ 32 ] [ 33 ] In 1833, French chemists Antoine Bussy and Michel Chevreul decided to name acetone by adding the suffix -one to the stem of the corresponding acid (viz, acetic acid ) just as a similarly prepared product of what was then confused with margaric acid was named margarone. [ 34 ] [ 29 ] By 1852, English chemist Alexander William Williamson realized that acetone was methyl acetyl ; [ 35 ] the following year, the French chemist Charles Frédéric Gerhardt concurred. [ 36 ] In 1865, the German chemist August Kekulé published the modern structural formula for acetone. [ 37 ] [ 38 ] Johann Josef Loschmidt had presented the structure of acetone in 1861, [ 39 ] but his privately published booklet received little attention. During World War I , Chaim Weizmann developed the process for industrial production of acetone (Weizmann Process). [ 40 ]
In 2010, the worldwide production capacity for acetone was estimated at 6.7 million tonnes per year. [ 41 ] With 1.56 million tonnes per year, the United States had the highest production capacity, [ 42 ] followed by Taiwan and China . The largest producer of acetone is INEOS Phenol , owning 17% of the world's capacity, with also significant capacity (7–8%) by Mitsui , Sunoco and Shell in 2010. [ 41 ] INEOS Phenol also owns the world's largest production site (420,000 tonnes/annum) in Beveren (Belgium). Spot price of acetone in summer 2011 was 1100–1250 USD/tonne in the United States. [ 43 ]
Acetone is produced directly or indirectly from propene . Approximately 83% of acetone is produced via the cumene process ; [ 25 ] as a result, acetone production is tied to phenol production. In the cumene process, benzene is alkylated with propylene to produce cumene , which is oxidized by air to produce phenol and acetone:
Other processes involve the direct oxidation of propylene ( Wacker-Hoechst process ), or the hydration of propylene to give 2-propanol , which is oxidized (dehydrogenated) to acetone. [ 25 ]
Previously, acetone was produced by the dry distillation of acetates , for example calcium acetate in ketonic decarboxylation .
After that time, during World War I , acetone was produced using acetone-butanol-ethanol fermentation with Clostridium acetobutylicum bacteria , which was developed by Chaim Weizmann (later the first president of Israel ) in order to help the British war effort, [ 25 ] [ 44 ] in the preparation of Cordite . [ 45 ] This acetone-butanol-ethanol fermentation was eventually abandoned when newer methods with better yields were found. [ 25 ]
Acetone is reluctant to form a hydrate: [ 46 ]
Like most ketones, acetone exhibits the keto–enol tautomerism in which the nominal keto structure (CH 3 ) 2 C=O of acetone itself is in equilibrium with the enol isomer (CH 3 )C(OH)=(CH 2 ) ( prop-1-en-2-ol ). In acetone vapor at ambient temperature, only 2.4 × 10 −7 % of the molecules are in the enol form. [ 47 ]
In the presence of suitable catalysts , two acetone molecules also combine to form the compound diacetone alcohol (CH 3 )C=O(CH 2 )C(OH)(CH 3 ) 2 , which on dehydration gives mesityl oxide (CH 3 )C=O(CH)=C(CH 3 ) 2 . This product can further combine with another acetone molecule, with loss of another molecule of water, yielding phorone and other compounds. [ 48 ]
Acetone is a weak Lewis base that forms adducts with soft acids like I 2 and hard acids like phenol . Acetone also forms complexes with divalent metals. [ 49 ] [ 50 ]
Under ultraviolet light, acetone fluoresces. [ 51 ]
The flame temperature of pure acetone is 1980 °C. [ 52 ]
At its melting point (−96 °C) is claimed to polymerize to give a white elastic solid, soluble in acetone, stable for several hours at room temperature. To do so, a vapor of acetone is co-condensed with magnesium as a catalyst onto a very cold surface. [ 53 ] [ 54 ] [ 55 ]
Humans exhale several milligrams of acetone per day. It arises from decarboxylation of acetoacetate . [ 56 ] [ 57 ] Small amounts of acetone are produced in the body by the decarboxylation of ketone bodies . Certain dietary patterns, including prolonged fasting and high-fat low-carbohydrate dieting, can produce ketosis , in which acetone is formed in body tissue. Certain health conditions, such as alcoholism and diabetes, can produce ketoacidosis , uncontrollable ketosis that leads to a sharp, and potentially fatal, increase in the acidity of the blood. Since it is a byproduct of fermentation, acetone is a byproduct of the distillery industry. [ 56 ]
Acetone can then be metabolized either by CYP2E1 via methylglyoxal to D -lactate and pyruvate , and ultimately glucose /energy, or by a different pathway via propylene glycol to pyruvate , lactate , acetate (usable for energy) and propionaldehyde . [ 58 ] [ 59 ] [ 60 ]
About a third of the world's acetone is used as a solvent, and a quarter is consumed as acetone cyanohydrin , a precursor to methyl methacrylate . [ 24 ]
Acetone is used to synthesize methyl methacrylate . It begins with the initial conversion of acetone to acetone cyanohydrin via reaction with hydrogen cyanide (HCN):
In a subsequent step, the nitrile is hydrolyzed to the unsaturated amide , which is esterified :
The third major use of acetone (about 20%) [ 24 ] is synthesizing bisphenol A . Bisphenol A is a component of many polymers such as polycarbonates , polyurethanes , and epoxy resins . The synthesis involves the condensation of acetone with phenol :
Many millions of kilograms of acetone are consumed in the production of the solvents methyl isobutyl alcohol and methyl isobutyl ketone . These products arise via an initial aldol condensation to give diacetone alcohol . [ 25 ]
Condensation with acetylene gives 2-methylbut-3-yn-2-ol , precursor to synthetic terpenes and terpenoids . [ 61 ]
Acetone is a good solvent for many plastics and some synthetic fibers. It is used for thinning polyester resin , cleaning tools used with it, and dissolving two-part epoxies and superglue before they harden. It is used as one of the volatile components of some paints and varnishes . [ 23 ] As a heavy-duty degreaser, it is useful in the preparation of metal prior to painting or soldering , and to remove rosin flux after soldering (to prevent adhesion of dirt and electrical leakage and perhaps corrosion or for cosmetic reasons), although it may attack some electronic components, such as polystyrene capacitors. [ 62 ]
Although itself flammable , acetone is used extensively as a solvent for the safe transportation and storage of acetylene , which cannot be safely pressurized as a pure compound. Vessels containing a porous material are first filled with acetone followed by acetylene, which dissolves into the acetone. One litre of acetone can dissolve around 250 litres of acetylene at a pressure of 10 bars (1.0 MPa). [ 63 ] [ 64 ]
Acetone is used as a solvent by the pharmaceutical industry and as a denaturant in denatured alcohol . [ 65 ] Acetone is also present as an excipient in some pharmaceutical drugs . [ 66 ] [ needs update ]
A variety of organic reactions employ acetone as a polar , aprotic solvent , e.g. the Jones oxidation .
Because acetone is cheap, volatile, and dissolves or decomposes with most laboratory chemicals, an acetone rinse is the standard technique to remove solid residues from laboratory glassware before a final wash. [ 67 ] Despite common desiccatory use, acetone dries only via bulk displacement and dilution. It forms no azeotropes with water (see azeotrope tables ). [ 68 ] Acetone also removes certain stains from microscope slides . [ 69 ]
Acetone freezes well below −78 °C. An acetone/dry ice mixture cools many low-temperature reactions. [ 70 ] Make-up artists use acetone to remove skin adhesive from the netting of wigs and mustaches by immersing the item in an acetone bath, then removing the softened glue residue with a stiff brush. [ 71 ] Acetone is a main ingredient in many nail polish removers because it breaks down nail polish. [ 72 ] It is used for all types of nail polish removal, like gel nail polish, dip powder and acrylic nails. [ 73 ]
Proteins precipitate in acetone. [ 74 ] The chemical modifies peptides, both at α- or ε-amino groups, and in a poorly understood but rapid modification of certain glycine residues. [ 74 ]
In pathology , acetone helps find lymph nodes in fatty tissues (such as the mesentery ) for tumor staging . [ 75 ] The liquid dissolves the fat and hardens the nodes, making them easier to find. [ 76 ]
Dermatologists use acetone with alcohol for acne treatments to chemically peel dry skin. Common agents used today for chemical peeling are salicylic acid , glycolic acid , azelaic acid , 30% salicylic acid in ethanol , and trichloroacetic acid (TCA). Prior to chemexfoliation, the skin is cleaned and excess fat removed in a process called defatting. Acetone, hexachlorophene , or a combination of these agents was used in this process. [ 77 ]
Acetone has been shown to have anticonvulsant effects in animal models of epilepsy , in the absence of toxicity, when administered in millimolar concentrations. [ 78 ] It has been hypothesized that the high-fat low-carbohydrate ketogenic diet used clinically to control drug-resistant epilepsy in children works by elevating acetone in the brain. [ 78 ] Because of their higher energy requirements, children have higher acetone production than most adults – and the younger the child, the higher the expected production. This indicates that children are not uniquely susceptible to acetone exposure. External exposures are small compared to the exposures associated with the ketogenic diet. [ 79 ]
Acetone's most hazardous property is its extreme flammability. In small amounts, acetone burns with a dull blue flame ; in larger amounts, fuel evaporation causes incomplete combustion and a bright yellow flame . When hotter than acetone's flash point of −20 °C (−4 °F), air mixtures of 2.5‑12.8% acetone (by volume) may explode or cause a flash fire . Vapors can flow along surfaces to distant ignition sources and flash back.
Static discharge may also ignite acetone vapors, though acetone has a very high ignition initiation energy and accidental ignition is rare. [ 80 ] Acetone's auto-ignition temperature is the relatively high 465 °C (869 °F); [ 19 ] moreover, auto-ignition temperature depends upon experimental conditions, such as exposure time, and has been quoted as high as 535 °C. [ 81 ] Even pouring or spraying acetone over red-glowing coal will not ignite it, due to the high vapour concentration and the cooling effect of evaporation. [ 80 ]
Acetone should be stored away from strong oxidizers, such as concentrated nitric and sulfuric acid mixtures. [ 82 ] It may also explode when mixed with chloroform in the presence of a base. [ 83 ] [ clarification needed ] When oxidized without combustion, for example with hydrogen peroxide , acetone may form acetone peroxide , a highly unstable primary explosive . Acetone peroxide may be formed accidentally, e.g. when waste peroxide is poured into waste solvents. [ 84 ]
Acetone occurs naturally as part of certain metabolic processes in the human body, and has been studied extensively and is believed to exhibit only slight toxicity in normal use. There is no strong evidence of chronic health effects if basic precautions are followed. [ 85 ] It is generally recognized to have low acute and chronic toxicity if ingested and/or inhaled. [ 86 ] Acetone is not currently regarded as a carcinogen , a mutagen , or a concern for chronic neurotoxicity effects. [ 80 ]
Acetone can be found as an ingredient in a variety of consumer products ranging from cosmetics to processed and unprocessed foods. Acetone has been rated as a generally recognized as safe (GRAS) substance when present in drinks, baked foods, desserts, and preserves at concentrations ranging from 5 to 8 mg/L. [ 86 ]
Acetone is however an irritant, causing mild skin and moderate-to-severe eye irritation. At high vapor concentrations, it may depress the central nervous system like many other solvents. [ 87 ] Acute toxicity for mice by ingestion (LD 50 ) is 3 g/kg, and by inhalation (LC 50 ) is 44 g/m 3 over 4 hours. [ 88 ]
Although acetone occurs naturally in the environment in plants, trees, volcanic gases, forest fires, and as a product of the breakdown of body fat, [ 89 ] the majority of the acetone released into the environment is of industrial origin. [ clarification needed ] Acetone evaporates rapidly, even from water and soil. Once in the atmosphere, it has a 22-day half-life and is degraded by UV light via photolysis (primarily into methane and ethane . [ 90 ] ) Consumption by microorganisms contributes to the dissipation of acetone in soil, animals, or waterways. [ 89 ]
In 1995, the United States Environmental Protection Agency (EPA) removed acetone from the list of volatile organic compounds . The companies requesting the removal argued that it would "contribute to the achievement of several important environmental goals and would support EPA's pollution prevention efforts", and that acetone could be used as a substitute for several compounds that are listed as hazardous air pollutants (HAP) under section 112 of the Clean Air Act . [ 91 ] In making its decision EPA conducted an extensive review of the available toxicity data on acetone, which was continued through the 2000s. It found that the evaluable "data are inadequate for an assessment of the human carcinogenic potential of acetone". [ 9 ]
On 30 July 2015, scientists reported that upon the first touchdown of the Philae lander on comet 67P 's surface, measurements by the COSAC and Ptolemy instruments revealed sixteen organic compounds , four of which were seen for the first time on a comet, including acetamide , acetone, methyl isocyanate , and propionaldehyde . [ 92 ] [ 93 ] [ 94 ] | https://en.wikipedia.org/wiki/H3C-CO-CH3 |
Propylene , also known as propene , is an unsaturated organic compound with the chemical formula CH 3 CH=CH 2 . It has one double bond , and is the second simplest member of the alkene class of hydrocarbons . It is a colorless gas with a faint petroleum-like odor. [ 4 ]
Propylene is a product of combustion from forest fires, cigarette smoke, and motor vehicle and aircraft exhaust. [ 5 ] It was discovered in 1850 by A. W. von Hoffmann 's student Captain (later Major General [ 6 ] ) John Williams Reynolds as the only gaseous product of thermal decomposition of amyl alcohol to react with chlorine and bromine . [ 7 ]
The dominant technology for producing propylene is steam cracking , using propane as the feedstock . Cracking propane yields a mixture of ethylene , propylene, methane , hydrogen gas , and other related compounds. The yield of propylene is about 15%. The other principal feedstock is naphtha , especially in the Middle East and Asia. [ 8 ] Propylene can be separated by fractional distillation from the hydrocarbon mixtures obtained from cracking and other refining processes; refinery-grade propene is about 50 to 70%. [ 9 ] In the United States, shale gas is a major source of propane.
In the Phillips triolefin or olefin conversion technology , propylene is interconverted with ethylene and 2-butenes . Rhenium and molybdenum catalysts are used: [ 10 ]
The technology is founded on an olefin metathesis reaction discovered at Phillips Petroleum Company . [ 11 ] [ 12 ] Propylene yields of about 90 wt% are achieved.
Related is the Methanol-to-Olefins/Methanol-to-Propene process. It converts synthesis gas (syngas) to methanol , and then converts the methanol to ethylene and/or propene . The process produces water as a by-product. Synthesis gas is produced from the reformation of natural gas or by the steam-induced reformation of petroleum products such as naphtha, or by gasification of coal or natural gas.
High severity fluid catalytic cracking (FCC) uses traditional FCC technology under severe conditions (higher catalyst-to-oil ratios, higher steam injection rates, higher temperatures, etc.) in order to maximize the amount of propene and other light products. A high severity FCC unit is usually fed with gas oils (paraffins) and residues, and produces about 20–25% (by mass) of propene on feedstock together with greater volumes of motor gasoline and distillate byproducts. These high temperature processes are expensive and have a high carbon footprint. For these reasons, alternative routes to propylene continue to attract attention. [ 13 ]
On-purpose propylene production technologies were developed throughout the twentieth century. Of these, propane dehydrogenation technologies such as the CATOFIN and OLEFLEX processes have become common, although they still make up a minority of the market, with most of the olefin being sourced from the above mentioned cracking technologies. Platinum, chromia, and vanadium catalysts are common in propane dehydrogenation processes.
Propene production has remained static at around 35 million tonnes (Europe and North America only) from 2000 to 2008, but it has been increasing in East Asia, most notably Singapore and China. [ 14 ] Total world production of propene is currently about half that of ethylene.
The use of engineered enzymes has been explored but has not been commercialized. [ 15 ]
There is ongoing research into the use of oxygen carrier catalysts for the oxidative dehydrogenation of propane. This poses several advantages, as this reaction mechanism can occur at lower temperatures than conventional dehydrogenation, and may not be equilibrium-limited because oxygen is used to combust the hydrogen by-product. [ 16 ]
Propylene is the second most important starting product in the petrochemical industry after ethylene . It is the raw material for a wide variety of products. Polypropylene manufacturers consume nearly two thirds of global production. [ 17 ] Polypropylene end uses include films, fibers, containers, packaging, and caps and closures. Propene is also used for the production of chemicals such as propylene oxide , acrylonitrile , cumene , butyraldehyde , and acrylic acid . In the year 2013 about 85 million tonnes of propylene were processed worldwide. [ 17 ]
Propylene and benzene are converted to acetone and phenol via the cumene process .
Propylene is also used to produce isopropyl alcohol (propan-2-ol), acrylonitrile , propylene oxide , and epichlorohydrin . [ 18 ] The industrial production of acrylic acid involves the catalytic partial oxidation of propylene. [ 19 ] Propylene is an intermediate in the oxidation to acrylic acid.
In industry and workshops, propylene is used as an alternative fuel to acetylene in Oxy-fuel welding and cutting , brazing and heating of metal for the purpose of bending. It has become a standard in BernzOmatic products and others in MAPP substitutes, [ 20 ] now that true MAPP gas is no longer available.
Propylene resembles other alkenes in that it undergoes electrophilic addition reactions relatively easily at room temperature. The relative weakness of its double bond explains its tendency to react with substances that can achieve this transformation. Alkene reactions include:
Foundational to hydroformylation, alkene metathesis, and polymerization are metal-propylene complexes , which are intermediates in these processes. Propylene is prochiral , meaning that binding of a reagent (such as a metal electrophile) to the C=C group yields one of two enantiomers .
The majority of propylene is used to form polypropylene, a very important commodity thermoplastic , through chain-growth polymerization . [ 17 ] In the presence of a suitable catalyst (typically a Ziegler–Natta catalyst ), propylene will polymerize. There are multiple ways to achieve this, such as using high pressures to suspending the catalyst in a solution of liquid propylene, or running gaseous propylene through a fluidized bed reactor . [ 21 ]
In the presence of catalysts , propylene will form various short oligomers . It can dimerizes to give 2,3-dimethyl-1-butene and/or 2,3-dimethyl-2-butene . [ 22 ] or trimerise to form tripropylene .
Propene is a product of combustion from forest fires, cigarette smoke, and motor vehicle and aircraft exhaust. [ 5 ] It is an impurity in some heating gases. Observed concentrations have been in the range of 0.1–4.8 parts per billion ( ppb ) in rural air, 4–10.5 ppb in urban air, and 7–260 ppb in industrial air samples. [ 9 ]
In the United States and some European countries a threshold limit value of 500 parts per million ( ppm ) was established for occupational (8-hour time-weighted average ) exposure. It is considered a volatile organic compound (VOC) and emissions are regulated by many governments, but it is not listed by the U.S. Environmental Protection Agency (EPA) as a hazardous air pollutant under the Clean Air Act . With a relatively short half-life, it is not expected to bioaccumulate. [ 9 ]
Propene has low acute toxicity from inhalation and is not considered to be carcinogenic. Chronic toxicity studies in mice did not yield significant evidence suggesting adverse effects. Humans briefly exposed to 4,000 ppm did not experience any noticeable effects. [ 23 ] Propene is dangerous from its potential to displace oxygen as an asphyxiant gas , and from its high flammability/explosion risk.
Bio-propylene is the bio-based propylene. [ 24 ] [ 25 ] It has been examined, motivated by diverse interests such a carbon footprint . Production from glucose has been considered. [ 26 ] More advanced ways of addressing such issues focus on electrification alternatives to steam cracking .
Propene is flammable. Propene is usually stored as liquid under pressure, although it is also possible to store it safely as gas at ambient temperature in approved containers. [ 27 ]
Propene is detected in the interstellar medium through microwave spectroscopy. [ 28 ] On September 30, 2013, NASA announced the detection of small amounts of naturally occurring propene in the atmosphere of Titan using infrared spectroscopy. [ 29 ] [ 30 ] [ 31 ] The detection was made by a team led by NASA GSFC scientist Conor Nixon using data from the CIRS instrument [ 32 ] [ 33 ] on the Cassini orbiter spacecraft, part of the Cassini-Huygens mission. Its confirmation solved a 32-year old mystery by filling a predicted gap in Titan's detected hydrocarbons , adding the C 3 H 6 species (propene) to the already-detected C 3 H 4 ( propyne ) and C 3 H 8 ( propane ). [ 34 ] | https://en.wikipedia.org/wiki/H3C-HC=CH2 |
Acetone ( 2-propanone or dimethyl ketone ) is an organic compound with the formula (CH 3 ) 2 CO . [ 22 ] It is the simplest and smallest ketone ( R−C(=O)−R' ). It is a colorless, highly volatile , and flammable liquid with a characteristic pungent odor. [ 23 ]
Acetone is miscible with water and serves as an important organic solvent in industry, home, and laboratory. About 6.7 million tonnes were produced worldwide in 2010, mainly for use as a solvent and for production of methyl methacrylate and bisphenol A , which are precursors to widely used plastics . [ 24 ] [ 25 ] It is a common building block in organic chemistry . It serves as a solvent in household products such as nail polish remover and paint thinner . It has volatile organic compound (VOC)-exempt status in the United States. [ 26 ]
Acetone is produced and disposed of in the human body through normal metabolic processes. Small quantities of it are present naturally in blood and urine. People with diabetic ketoacidosis produce it in larger amounts. Ketogenic diets that increase ketone bodies (acetone, β-hydroxybutyric acid and acetoacetic acid ) in the blood are used to counter epileptic attacks in children who suffer from refractory epilepsy. [ 27 ]
From the 17th century, and before modern developments in organic chemistry nomenclature , acetone was given many different names. They included "spirit of Saturn", which was given when it was thought to be a compound of lead and, later, "pyro-acetic spirit" and "pyro-acetic ester". [ 6 ]
Prior to the name "acetone" being coined by French chemists (see below ), it was named "mesit" (from the Greek μεσίτης, meaning mediator) by Carl Reichenbach , who also claimed that methyl alcohol consisted of mesit and ethyl alcohol . [ 28 ] [ 6 ] Names derived from mesit include mesitylene and mesityl oxide which were first synthesised from acetone.
In 1839, the name "acetone" began to be used and the term was composed of “daughter of” and acetum (acetic acid) because it was obtained from acetic acid. [ 23 ] Unlike many compounds with the acet- prefix which have a 2-carbon chain, acetone has a 3-carbon chain. That has caused confusion because there cannot be a ketone with 2 carbons. The prefix refers to acetone's relation to vinegar ( acetum in Latin , also the source of the words "acid" and "acetic"), rather than its chemical structure. [ 29 ]
Acetone was first produced by Andreas Libavius in 1606 by distillation of lead(II) acetate . [ 30 ] [ 31 ]
In 1832, French chemist Jean-Baptiste Dumas and German chemist Justus von Liebig determined the empirical formula for acetone. [ 32 ] [ 33 ] In 1833, French chemists Antoine Bussy and Michel Chevreul decided to name acetone by adding the suffix -one to the stem of the corresponding acid (viz, acetic acid ) just as a similarly prepared product of what was then confused with margaric acid was named margarone. [ 34 ] [ 29 ] By 1852, English chemist Alexander William Williamson realized that acetone was methyl acetyl ; [ 35 ] the following year, the French chemist Charles Frédéric Gerhardt concurred. [ 36 ] In 1865, the German chemist August Kekulé published the modern structural formula for acetone. [ 37 ] [ 38 ] Johann Josef Loschmidt had presented the structure of acetone in 1861, [ 39 ] but his privately published booklet received little attention. During World War I , Chaim Weizmann developed the process for industrial production of acetone (Weizmann Process). [ 40 ]
In 2010, the worldwide production capacity for acetone was estimated at 6.7 million tonnes per year. [ 41 ] With 1.56 million tonnes per year, the United States had the highest production capacity, [ 42 ] followed by Taiwan and China . The largest producer of acetone is INEOS Phenol , owning 17% of the world's capacity, with also significant capacity (7–8%) by Mitsui , Sunoco and Shell in 2010. [ 41 ] INEOS Phenol also owns the world's largest production site (420,000 tonnes/annum) in Beveren (Belgium). Spot price of acetone in summer 2011 was 1100–1250 USD/tonne in the United States. [ 43 ]
Acetone is produced directly or indirectly from propene . Approximately 83% of acetone is produced via the cumene process ; [ 25 ] as a result, acetone production is tied to phenol production. In the cumene process, benzene is alkylated with propylene to produce cumene , which is oxidized by air to produce phenol and acetone:
Other processes involve the direct oxidation of propylene ( Wacker-Hoechst process ), or the hydration of propylene to give 2-propanol , which is oxidized (dehydrogenated) to acetone. [ 25 ]
Previously, acetone was produced by the dry distillation of acetates , for example calcium acetate in ketonic decarboxylation .
After that time, during World War I , acetone was produced using acetone-butanol-ethanol fermentation with Clostridium acetobutylicum bacteria , which was developed by Chaim Weizmann (later the first president of Israel ) in order to help the British war effort, [ 25 ] [ 44 ] in the preparation of Cordite . [ 45 ] This acetone-butanol-ethanol fermentation was eventually abandoned when newer methods with better yields were found. [ 25 ]
Acetone is reluctant to form a hydrate: [ 46 ]
Like most ketones, acetone exhibits the keto–enol tautomerism in which the nominal keto structure (CH 3 ) 2 C=O of acetone itself is in equilibrium with the enol isomer (CH 3 )C(OH)=(CH 2 ) ( prop-1-en-2-ol ). In acetone vapor at ambient temperature, only 2.4 × 10 −7 % of the molecules are in the enol form. [ 47 ]
In the presence of suitable catalysts , two acetone molecules also combine to form the compound diacetone alcohol (CH 3 )C=O(CH 2 )C(OH)(CH 3 ) 2 , which on dehydration gives mesityl oxide (CH 3 )C=O(CH)=C(CH 3 ) 2 . This product can further combine with another acetone molecule, with loss of another molecule of water, yielding phorone and other compounds. [ 48 ]
Acetone is a weak Lewis base that forms adducts with soft acids like I 2 and hard acids like phenol . Acetone also forms complexes with divalent metals. [ 49 ] [ 50 ]
Under ultraviolet light, acetone fluoresces. [ 51 ]
The flame temperature of pure acetone is 1980 °C. [ 52 ]
At its melting point (−96 °C) is claimed to polymerize to give a white elastic solid, soluble in acetone, stable for several hours at room temperature. To do so, a vapor of acetone is co-condensed with magnesium as a catalyst onto a very cold surface. [ 53 ] [ 54 ] [ 55 ]
Humans exhale several milligrams of acetone per day. It arises from decarboxylation of acetoacetate . [ 56 ] [ 57 ] Small amounts of acetone are produced in the body by the decarboxylation of ketone bodies . Certain dietary patterns, including prolonged fasting and high-fat low-carbohydrate dieting, can produce ketosis , in which acetone is formed in body tissue. Certain health conditions, such as alcoholism and diabetes, can produce ketoacidosis , uncontrollable ketosis that leads to a sharp, and potentially fatal, increase in the acidity of the blood. Since it is a byproduct of fermentation, acetone is a byproduct of the distillery industry. [ 56 ]
Acetone can then be metabolized either by CYP2E1 via methylglyoxal to D -lactate and pyruvate , and ultimately glucose /energy, or by a different pathway via propylene glycol to pyruvate , lactate , acetate (usable for energy) and propionaldehyde . [ 58 ] [ 59 ] [ 60 ]
About a third of the world's acetone is used as a solvent, and a quarter is consumed as acetone cyanohydrin , a precursor to methyl methacrylate . [ 24 ]
Acetone is used to synthesize methyl methacrylate . It begins with the initial conversion of acetone to acetone cyanohydrin via reaction with hydrogen cyanide (HCN):
In a subsequent step, the nitrile is hydrolyzed to the unsaturated amide , which is esterified :
The third major use of acetone (about 20%) [ 24 ] is synthesizing bisphenol A . Bisphenol A is a component of many polymers such as polycarbonates , polyurethanes , and epoxy resins . The synthesis involves the condensation of acetone with phenol :
Many millions of kilograms of acetone are consumed in the production of the solvents methyl isobutyl alcohol and methyl isobutyl ketone . These products arise via an initial aldol condensation to give diacetone alcohol . [ 25 ]
Condensation with acetylene gives 2-methylbut-3-yn-2-ol , precursor to synthetic terpenes and terpenoids . [ 61 ]
Acetone is a good solvent for many plastics and some synthetic fibers. It is used for thinning polyester resin , cleaning tools used with it, and dissolving two-part epoxies and superglue before they harden. It is used as one of the volatile components of some paints and varnishes . [ 23 ] As a heavy-duty degreaser, it is useful in the preparation of metal prior to painting or soldering , and to remove rosin flux after soldering (to prevent adhesion of dirt and electrical leakage and perhaps corrosion or for cosmetic reasons), although it may attack some electronic components, such as polystyrene capacitors. [ 62 ]
Although itself flammable , acetone is used extensively as a solvent for the safe transportation and storage of acetylene , which cannot be safely pressurized as a pure compound. Vessels containing a porous material are first filled with acetone followed by acetylene, which dissolves into the acetone. One litre of acetone can dissolve around 250 litres of acetylene at a pressure of 10 bars (1.0 MPa). [ 63 ] [ 64 ]
Acetone is used as a solvent by the pharmaceutical industry and as a denaturant in denatured alcohol . [ 65 ] Acetone is also present as an excipient in some pharmaceutical drugs . [ 66 ] [ needs update ]
A variety of organic reactions employ acetone as a polar , aprotic solvent , e.g. the Jones oxidation .
Because acetone is cheap, volatile, and dissolves or decomposes with most laboratory chemicals, an acetone rinse is the standard technique to remove solid residues from laboratory glassware before a final wash. [ 67 ] Despite common desiccatory use, acetone dries only via bulk displacement and dilution. It forms no azeotropes with water (see azeotrope tables ). [ 68 ] Acetone also removes certain stains from microscope slides . [ 69 ]
Acetone freezes well below −78 °C. An acetone/dry ice mixture cools many low-temperature reactions. [ 70 ] Make-up artists use acetone to remove skin adhesive from the netting of wigs and mustaches by immersing the item in an acetone bath, then removing the softened glue residue with a stiff brush. [ 71 ] Acetone is a main ingredient in many nail polish removers because it breaks down nail polish. [ 72 ] It is used for all types of nail polish removal, like gel nail polish, dip powder and acrylic nails. [ 73 ]
Proteins precipitate in acetone. [ 74 ] The chemical modifies peptides, both at α- or ε-amino groups, and in a poorly understood but rapid modification of certain glycine residues. [ 74 ]
In pathology , acetone helps find lymph nodes in fatty tissues (such as the mesentery ) for tumor staging . [ 75 ] The liquid dissolves the fat and hardens the nodes, making them easier to find. [ 76 ]
Dermatologists use acetone with alcohol for acne treatments to chemically peel dry skin. Common agents used today for chemical peeling are salicylic acid , glycolic acid , azelaic acid , 30% salicylic acid in ethanol , and trichloroacetic acid (TCA). Prior to chemexfoliation, the skin is cleaned and excess fat removed in a process called defatting. Acetone, hexachlorophene , or a combination of these agents was used in this process. [ 77 ]
Acetone has been shown to have anticonvulsant effects in animal models of epilepsy , in the absence of toxicity, when administered in millimolar concentrations. [ 78 ] It has been hypothesized that the high-fat low-carbohydrate ketogenic diet used clinically to control drug-resistant epilepsy in children works by elevating acetone in the brain. [ 78 ] Because of their higher energy requirements, children have higher acetone production than most adults – and the younger the child, the higher the expected production. This indicates that children are not uniquely susceptible to acetone exposure. External exposures are small compared to the exposures associated with the ketogenic diet. [ 79 ]
Acetone's most hazardous property is its extreme flammability. In small amounts, acetone burns with a dull blue flame ; in larger amounts, fuel evaporation causes incomplete combustion and a bright yellow flame . When hotter than acetone's flash point of −20 °C (−4 °F), air mixtures of 2.5‑12.8% acetone (by volume) may explode or cause a flash fire . Vapors can flow along surfaces to distant ignition sources and flash back.
Static discharge may also ignite acetone vapors, though acetone has a very high ignition initiation energy and accidental ignition is rare. [ 80 ] Acetone's auto-ignition temperature is the relatively high 465 °C (869 °F); [ 19 ] moreover, auto-ignition temperature depends upon experimental conditions, such as exposure time, and has been quoted as high as 535 °C. [ 81 ] Even pouring or spraying acetone over red-glowing coal will not ignite it, due to the high vapour concentration and the cooling effect of evaporation. [ 80 ]
Acetone should be stored away from strong oxidizers, such as concentrated nitric and sulfuric acid mixtures. [ 82 ] It may also explode when mixed with chloroform in the presence of a base. [ 83 ] [ clarification needed ] When oxidized without combustion, for example with hydrogen peroxide , acetone may form acetone peroxide , a highly unstable primary explosive . Acetone peroxide may be formed accidentally, e.g. when waste peroxide is poured into waste solvents. [ 84 ]
Acetone occurs naturally as part of certain metabolic processes in the human body, and has been studied extensively and is believed to exhibit only slight toxicity in normal use. There is no strong evidence of chronic health effects if basic precautions are followed. [ 85 ] It is generally recognized to have low acute and chronic toxicity if ingested and/or inhaled. [ 86 ] Acetone is not currently regarded as a carcinogen , a mutagen , or a concern for chronic neurotoxicity effects. [ 80 ]
Acetone can be found as an ingredient in a variety of consumer products ranging from cosmetics to processed and unprocessed foods. Acetone has been rated as a generally recognized as safe (GRAS) substance when present in drinks, baked foods, desserts, and preserves at concentrations ranging from 5 to 8 mg/L. [ 86 ]
Acetone is however an irritant, causing mild skin and moderate-to-severe eye irritation. At high vapor concentrations, it may depress the central nervous system like many other solvents. [ 87 ] Acute toxicity for mice by ingestion (LD 50 ) is 3 g/kg, and by inhalation (LC 50 ) is 44 g/m 3 over 4 hours. [ 88 ]
Although acetone occurs naturally in the environment in plants, trees, volcanic gases, forest fires, and as a product of the breakdown of body fat, [ 89 ] the majority of the acetone released into the environment is of industrial origin. [ clarification needed ] Acetone evaporates rapidly, even from water and soil. Once in the atmosphere, it has a 22-day half-life and is degraded by UV light via photolysis (primarily into methane and ethane . [ 90 ] ) Consumption by microorganisms contributes to the dissipation of acetone in soil, animals, or waterways. [ 89 ]
In 1995, the United States Environmental Protection Agency (EPA) removed acetone from the list of volatile organic compounds . The companies requesting the removal argued that it would "contribute to the achievement of several important environmental goals and would support EPA's pollution prevention efforts", and that acetone could be used as a substitute for several compounds that are listed as hazardous air pollutants (HAP) under section 112 of the Clean Air Act . [ 91 ] In making its decision EPA conducted an extensive review of the available toxicity data on acetone, which was continued through the 2000s. It found that the evaluable "data are inadequate for an assessment of the human carcinogenic potential of acetone". [ 9 ]
On 30 July 2015, scientists reported that upon the first touchdown of the Philae lander on comet 67P 's surface, measurements by the COSAC and Ptolemy instruments revealed sixteen organic compounds , four of which were seen for the first time on a comet, including acetamide , acetone, methyl isocyanate , and propionaldehyde . [ 92 ] [ 93 ] [ 94 ] | https://en.wikipedia.org/wiki/H3CCOCH3 |
H3K36me is an epigenetic modification to the DNA packaging protein Histone H3 , specifically, the mono- methylation at the 36th lysine residue of the histone H3 protein.
There are diverse modifications at H3K36, such as phosphorylation, methylation, acetylation, and ubiquitylation, which have many important biological processes. [ 1 ] The methylation of H3K36 has particularly had effects in transcriptional repression, alternative splicing, dosage compensation, DNA replication and repair, DNA methylation, and the transmission of the memory of gene expression from parents to offspring during development. [ 1 ]
H3K36me2 indicates dimethylation of lysine 36 on histone H3 protein subunit: [ 2 ]
(counting from N-terminus)
This diagram shows the progressive methylation of a lysine residue. The mono-methylation (second from left) denotes the methylation present in H3K36me1.
Lysine methylation is the addition of a methyl group to the lysine of histone proteins. [ 3 ] This occurs via histone lysine methyltransferase (HMTase) that utilize S -adenosylmethionine to specifically place the methyl group on histone Lys or Arg residues. [ 1 ] So far, there have only been eight specific mammalian enzymes discovered that can methylate H3K36 in vitro and/or in vivo, all of which have identical catalytic SET domains but, different preferences for Lys36 residues in different methylation states. [ 1 ]
The genomic DNA of eukaryotic cells is wrapped around special protein molecules known as histones . The complexes formed by the looping of the DNA are known as chromatin . The basic structural unit of chromatin is the nucleosome , which consists of the core octamer of histones ( H2A , H2B , H3 , and H4 ) as well as a linker histone and about 180 base pairs of DNA wrapped around it. These core histones are rich in lysine and arginine residues. The carboxyl (C) terminal end of these histones contribute to histone-histone interactions, as well as histone-DNA interactions. The amino (N) terminal charged tails are the site of the post-translational modifications, such as the one seen in H3K36me3. [ 4 ] [ 5 ]
The post-translational modification of histone tails by either histone-modifying complexes or chromatin remodeling complexes is interpreted by the cell and leads to the complex, combinatorial transcriptional output. It is thought that a histone code dictates the expression of genes by a complex interaction between the histones in a particular region. [ 6 ] The current understanding and interpretation of histones come from two large scale projects: ENCODE and the Epigenomic roadmap. [ 7 ] The purpose of the epigenomic study was to investigate epigenetic changes across the entire genome. This led to chromatin states which define genomic regions by grouping the interactions of different proteins and/or histone modifications together. Chromatin states were investigated in Drosophila cells by looking at the binding location of proteins in the genome. The use of ChIP-sequencing revealed regions in the genome characterized by different banding. [ 8 ] Different developmental stages were profiled in Drosophila as well, an emphasis was placed on histone modification relevance. [ 9 ] A look into the data obtained led to the definition of chromatin states based on histone modifications. [ 10 ] Certain modifications were mapped and enrichment was seen to localize in certain genomic regions. Five core histone modifications were found with each respective one being linked to various cell functions.
The human genome was annotated with chromatin states. These annotated states can be used as new ways to annotate a genome independently of the underlying genome sequence. This independence from the DNA sequence enforces the epigenetic nature of histone modifications. Chromatin states are also useful in identifying regulatory elements that have no defined sequence, such as enhancers. This additional level of annotation allows for a deeper understanding of cell-specific gene regulation. [ 11 ]
The histone mark H3K36me can be detected in a variety of ways: | https://en.wikipedia.org/wiki/H3K36me |
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the formula N H 3 . A stable binary hydride and the simplest pnictogen hydride , ammonia is a colourless gas with a distinctive pungent smell. Biologically, it is a common nitrogenous waste , and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to fertilisers . [ 13 ] Around 70% of ammonia produced industrially is used to make fertilisers [ 14 ] in various forms and composition, such as urea and diammonium phosphate . Ammonia in pure form is also applied directly into the soil.
Ammonia, either directly or indirectly, is also a building block for the synthesis of many chemicals.
Ammonia occurs in nature and has been detected in the interstellar medium. In many countries, it is classified as an extremely hazardous substance . [ 15 ]
Ammonia is toxic, causing damage to cells and tissues. For this reason it is excreted by most animals in the urine, in the form of dissolved urea.
Ammonia is produced biologically in a process called nitrogen fixation , but even more is generated industrially by the Haber process . The process helped revolutionize agriculture by providing cheap fertilizers. The global industrial production of ammonia in 2021 was 235 million tonnes. [ 16 ] [ 17 ] Industrial ammonia is transported by road in tankers , by rail in tank wagons , by sea in gas carriers , or in cylinders . [ 18 ]
Ammonia boils at −33.34 °C (−28.012 °F) at a pressure of one atmosphere , but the liquid can often be handled in the laboratory without external cooling. Household ammonia or ammonium hydroxide is a solution of ammonia in water.
Pliny , in Book XXXI of his Natural History , refers to a salt named hammoniacum , so called because of the proximity of its source to the Temple of Jupiter Amun ( Greek Ἄμμων Ammon ) in the Roman province of Cyrenaica . [ 19 ] However, the description Pliny gives of the salt does not conform to the properties of ammonium chloride . According to Herbert Hoover 's commentary in his English translation of Georgius Agricola 's De re metallica , it is likely to have been common sea salt. [ 20 ] In any case, that salt ultimately gave ammonia and ammonium compounds their name.
Traces of ammonia/ammonium are found in rainwater. Ammonium chloride ( sal ammoniac ), and ammonium sulfate are found in volcanic districts. Crystals of ammonium bicarbonate have been found in Patagonia guano . [ 21 ]
Ammonia is found throughout the Solar System on Mars , Jupiter , Saturn , Uranus , Neptune , and Pluto , among other places: on smaller, icy bodies such as Pluto, ammonia can act as a geologically important antifreeze, as a mixture of water and ammonia can have a melting point as low as −100 °C (−148 °F; 173 K) if the ammonia concentration is high enough and thus allow such bodies to retain internal oceans and active geology at a far lower temperature than would be possible with water alone. [ 22 ] [ 23 ] Substances containing ammonia, or those that are similar to it, are called ammoniacal . [ 24 ]
Ammonia is a colourless gas with a characteristically pungent smell . It is lighter than air , its density being 0.589 times that of air . It is easily liquefied due to the strong hydrogen bonding between molecules. Gaseous ammonia turns to a colourless liquid , which boils at −33.1 °C (−27.58 °F), and freezes to colourless crystals [ 21 ] at −77.7 °C (−107.86 °F). Little data is available at very high temperatures and pressures, but the liquid-vapor critical point occurs at 405 K and 11.35 MPa. [ 25 ]
The crystal symmetry is cubic, Pearson symbol cP16, space group P2 1 3 No.198, lattice constant 0.5125 nm . [ 26 ]
Liquid ammonia possesses strong ionising powers reflecting its high ε of 22 at −35 °C (−31 °F). [ 27 ] Liquid ammonia has a very high standard enthalpy change of vapourization (23.5 kJ/mol ; [ 28 ] for comparison, water 's is 40.65 kJ/mol, methane 8.19 kJ/mol and phosphine 14.6 kJ/mol) and can be transported in pressurized or refrigerated vessels; however, at standard temperature and pressure liquid anhydrous ammonia will vaporize. [ 29 ]
Ammonia readily dissolves in water. In an aqueous solution, it can be expelled by boiling. The aqueous solution of ammonia is basic , and may be described as aqueous ammonia or ammonium hydroxide . [ 30 ] The maximum concentration of ammonia in water (a saturated solution ) has a specific gravity of 0.880 and is often known as '.880 ammonia'. [ 31 ]
Liquid ammonia is a widely studied nonaqueous ionising solvent. Its most conspicuous property is its ability to dissolve alkali metals to form highly coloured, electrically conductive solutions containing solvated electrons . Apart from these remarkable solutions, much of the chemistry in liquid ammonia can be classified by analogy with related reactions in aqueous solutions . Comparison of the physical properties of NH 3 with those of water shows NH 3 has the lower melting point, boiling point, density, viscosity , dielectric constant and electrical conductivity . These differences are attributed at least in part to the weaker hydrogen bonding in NH 3 . The ionic self- dissociation constant of liquid NH 3 at −50 °C is about 10 −33 .
Liquid ammonia is an ionising solvent, although less so than water, and dissolves a range of ionic compounds, including many nitrates , nitrites , cyanides , thiocyanates , metal cyclopentadienyl complexes and metal bis(trimethylsilyl)amides . [ 32 ] Most ammonium salts are soluble and act as acids in liquid ammonia solutions. The solubility of halide salts increases from fluoride to iodide . A saturated solution of ammonium nitrate ( Divers' solution , named after Edward Divers ) contains 0.83 mol solute per mole of ammonia and has a vapour pressure of less than 1 bar even at 25 °C (77 °F). However, few oxyanion salts with other cations dissolve. [ 34 ]
Liquid ammonia will dissolve all of the alkali metals and other electropositive metals such as Ca , [ 35 ] Sr , Ba , Eu and Yb (also Mg using an electrolytic process [ 33 ] ). At low concentrations (<0.06 mol/L), deep blue solutions are formed: these contain metal cations and solvated electrons , free electrons that are surrounded by a cage of ammonia molecules.
These solutions are strong reducing agents. At higher concentrations, the solutions are metallic in appearance and in electrical conductivity. At low temperatures, the two types of solution can coexist as immiscible phases.
The range of thermodynamic stability of liquid ammonia solutions is very narrow, as the potential for oxidation to dinitrogen, E ° ( N 2 + 6 [NH 4 ] + + 6 e − ⇌ 8 NH 3 ), is only +0.04 V. In practice, both oxidation to dinitrogen and reduction to dihydrogen are slow. This is particularly true of reducing solutions: the solutions of the alkali metals mentioned above are stable for several days, slowly decomposing to the metal amide and dihydrogen. Most studies involving liquid ammonia solutions are done in reducing conditions; although oxidation of liquid ammonia is usually slow, there is still a risk of explosion, particularly if transition metal ions are present as possible catalysts.
The ammonia molecule has a trigonal pyramidal shape, as predicted by the valence shell electron pair repulsion theory (VSEPR theory) with an experimentally determined bond angle of 106.7°. [ 36 ] The central nitrogen atom has five outer electrons with an additional electron from each hydrogen atom. This gives a total of eight electrons, or four electron pairs that are arranged tetrahedrally . Three of these electron pairs are used as bond pairs, which leaves one lone pair of electrons. The lone pair repels more strongly than bond pairs; therefore, the bond angle is not 109.5°, as expected for a regular tetrahedral arrangement, but 106.7°. [ 36 ] This shape gives the molecule a dipole moment and makes it polar . The molecule's polarity, and especially its ability to form hydrogen bonds , makes ammonia highly miscible with water. The lone pair makes ammonia a base , a proton acceptor. Ammonia is moderately basic; a 1.0 M aqueous solution has a pH of 11.6, and if a strong acid is added to such a solution until the solution is neutral ( pH = 7 ), 99.4% of the ammonia molecules are protonated . Temperature and salinity also affect the proportion of ammonium [NH 4 ] + . The latter has the shape of a regular tetrahedron and is isoelectronic with methane .
The ammonia molecule readily undergoes nitrogen inversion at room temperature; a useful analogy is an umbrella turning itself inside out in a strong wind. The energy barrier to this inversion is 24.7 kJ/mol, and the resonance frequency is 23.79 GHz , corresponding to microwave radiation of a wavelength of 1.260 cm. The absorption at this frequency was the first microwave spectrum to be observed [ 37 ] and was used in the first maser .
One of the most characteristic properties of ammonia is its basicity . Ammonia is considered to be a weak base. It combines with acids to form ammonium salts ; thus, with hydrochloric acid it forms ammonium chloride (sal ammoniac); with nitric acid , ammonium nitrate , etc. Perfectly dry ammonia gas will not combine with perfectly dry hydrogen chloride gas; moisture is necessary to bring about the reaction. [ 38 ] [ 39 ]
As a demonstration experiment under air with ambient moisture, opened bottles of concentrated ammonia and hydrochloric acid solutions produce a cloud of ammonium chloride , which seems to appear 'out of nothing' as the salt aerosol forms where the two diffusing clouds of reagents meet between the two bottles.
The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion ( [NH 4 ] + ). [ 38 ]
Although ammonia is well known as a weak base, it can also act as an extremely weak acid. It is a protic substance and is capable of formation of amides (which contain the NH − 2 ion). For example, lithium dissolves in liquid ammonia to give a blue solution ( solvated electron ) of lithium amide :
Like water, liquid ammonia undergoes molecular autoionisation to form its acid and base conjugates :
Ammonia often functions as a weak base , so it has some buffering ability. Shifts in pH will cause more or fewer ammonium cations ( NH + 4 ) and amide anions ( NH − 2 ) to be present in solution . At standard pressure and temperature,
Ammonia does not burn readily or sustain combustion , except under narrow fuel-to-air mixtures of 15–28% ammonia by volume in air. [ 40 ] When mixed with oxygen , it burns with a pale yellowish-green flame. Ignition occurs when chlorine is passed into ammonia, forming nitrogen and hydrogen chloride ; if chlorine is present in excess, then the highly explosive nitrogen trichloride ( NCl 3 ) is also formed.
The combustion of ammonia to form nitrogen and water is exothermic :
The standard enthalpy change of combustion , Δ H ° c , expressed per mole of ammonia and with condensation of the water formed, is −382.81 kJ/mol. Dinitrogen is the thermodynamic product of combustion : all nitrogen oxides are unstable with respect to N 2 and O 2 , which is the principle behind the catalytic converter . Nitrogen oxides can be formed as kinetic products in the presence of appropriate catalysts , a reaction of great industrial importance in the production of nitric acid :
A subsequent reaction leads to NO 2 :
The combustion of ammonia in air is very difficult in the absence of a catalyst (such as platinum gauze or warm chromium(III) oxide ), due to the relatively low heat of combustion , a lower laminar burning velocity, high auto-ignition temperature , high heat of vapourization , and a narrow flammability range . However, recent studies have shown that efficient and stable combustion of ammonia can be achieved using swirl combustors, thereby rekindling research interest in ammonia as a fuel for thermal power production. [ 41 ] The flammable range of ammonia in dry air is 15.15–27.35% and in 100% relative humidity air is 15.95–26.55%. [ 42 ] [ clarification needed ] For studying the kinetics of ammonia combustion, knowledge of a detailed reliable reaction mechanism is required, but this has been challenging to obtain. [ 43 ]
Ammonia is a direct or indirect precursor to most manufactured nitrogen-containing compounds . It is the precursor to nitric acid, which is the source for most N-substituted aromatic compounds.
Amines can be formed by the reaction of ammonia with alkyl halides or, more commonly, with alcohols :
Its ring-opening reaction with ethylene oxide give ethanolamine , diethanolamine , and triethanolamine .
Amides can be prepared by the reaction of ammonia with carboxylic acid and their derivatives. For example, ammonia reacts with formic acid (HCOOH) to yield formamide ( HCONH 2 ) when heated. Acyl chlorides are the most reactive, but the ammonia must be present in at least a twofold excess to neutralise the hydrogen chloride formed. Esters and anhydrides also react with ammonia to form amides. Ammonium salts of carboxylic acids can be dehydrated to amides by heating to 150–200 °C as long as no thermally sensitive groups are present.
Other organonitrogen compounds include alprazolam , ethanolamine , ethyl carbamate and hexamethylenetetramine .
Nitric acid is generated via the Ostwald process by oxidation of ammonia with air over a platinum catalyst at 700–850 °C (1,292–1,562 °F), ≈9 atm. Nitric oxide and nitrogen dioxide are intermediate in this conversion: [ 44 ]
Nitric acid is used for the production of fertilisers , explosives , and many organonitrogen compounds.
The hydrogen in ammonia is susceptible to replacement by a myriad substituents.
Ammonia gas reacts with metallic sodium to give sodamide , NaNH 2 . [ 38 ]
With chlorine, monochloramine is formed.
Pentavalent ammonia is known as λ 5 -amine, nitrogen pentahydride decomposes spontaneously into trivalent ammonia (λ 3 -amine) and hydrogen gas at normal conditions. This substance was once investigated as a possible solid rocket fuel in 1966. [ 45 ]
Ammonia is also used to make the following compounds:
Ammonia is a ligand forming metal ammine complexes . For historical reasons, ammonia is named ammine in the nomenclature of coordination compounds . One notable ammine complex is cisplatin ( Pt(NH 3 ) 2 Cl 2 , a widely used anticancer drug. Ammine complexes of chromium (III) formed the basis of Alfred Werner 's revolutionary theory on the structure of coordination compounds. Werner noted only two isomers ( fac - and mer -) of the complex [CrCl 3 (NH 3 ) 3 ] could be formed, and concluded the ligands must be arranged around the metal ion at the vertices of an octahedron .
Ammonia forms 1:1 adducts with a variety of Lewis acids such as I 2 , phenol , and Al(CH 3 ) 3 . Ammonia is a hard base (HSAB theory) and its E & C parameters are E B = 2.31 and C B = 2.04. Its relative donor strength toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots .
Ammonia and ammonium salts can be readily detected, in very minute traces, by the addition of Nessler's solution , which gives a distinct yellow colouration in the presence of the slightest trace of ammonia or ammonium salts. The amount of ammonia in ammonium salts can be estimated quantitatively by distillation of the salts with sodium (NaOH) or potassium hydroxide (KOH), the ammonia evolved being absorbed in a known volume of standard sulfuric acid and the excess of acid then determined volumetrically ; or the ammonia may be absorbed in hydrochloric acid and the ammonium chloride so formed precipitated as ammonium hexachloroplatinate , [NH 4 ] 2 [PtCl 6 ] . [ 46 ]
Sulfur sticks are burnt to detect small leaks in industrial ammonia refrigeration systems. Larger quantities can be detected by warming the salts with a caustic alkali or with quicklime , when the characteristic smell of ammonia will be at once apparent. [ 46 ] Ammonia is an irritant and irritation increases with concentration; the permissible exposure limit is 25 ppm , and lethal above 500 ppm by volume. [ 47 ] Higher concentrations are hardly detected by conventional detectors, the type of detector is chosen according to the sensitivity required (e.g. semiconductor, catalytic, electrochemical). Holographic sensors have been proposed for detecting concentrations up to 12.5% in volume. [ 48 ]
In a laboratorial setting, gaseous ammonia can be detected by using concentrated hydrochloric acid or gaseous hydrogen chloride. A dense white fume (which is ammonium chloride vapor) arises from the reaction between ammonia and HCl(g). [ 49 ]
Ammoniacal nitrogen (NH 3 –N) is a measure commonly used for testing the quantity of ammonium ions, derived naturally from ammonia, and returned to ammonia via organic processes, in water or waste liquids. It is a measure used mainly for quantifying values in waste treatment and water purification systems, as well as a measure of the health of natural and man-made water reserves. It is measured in units of mg/L ( milligram per litre ).
The ancient Greek historian Herodotus mentioned that there were outcrops of salt in an area of Libya that was inhabited by a people called the 'Ammonians' (now the Siwa oasis in northwestern Egypt, where salt lakes still exist). [ 50 ] [ 51 ] The Greek geographer Strabo also mentioned the salt from this region. However, the ancient authors Dioscorides , Apicius , Arrian , Synesius , and Aëtius of Amida described this salt as forming clear crystals that could be used for cooking and that were essentially rock salt . [ 52 ] Hammoniacus sal appears in the writings of Pliny , [ 53 ] although it is not known whether the term is equivalent to the more modern sal ammoniac (ammonium chloride). [ 21 ] [ 54 ] [ 55 ]
The fermentation of urine by bacteria produces a solution of ammonia ; hence fermented urine was used in Classical Antiquity to wash cloth and clothing, to remove hair from hides in preparation for tanning, to serve as a mordant in dyeing cloth, and to remove rust from iron. [ 56 ] It was also used by ancient dentists to wash teeth. [ 57 ] [ 58 ] [ 59 ]
In the form of sal ammoniac (نشادر, nushadir ), ammonia was important to the Muslim alchemists . It was mentioned in the Book of Stones , likely written in the 9th century and attributed to Jābir ibn Hayyān . [ 60 ] It was also important to the European alchemists of the 13th century, being mentioned by Albertus Magnus . [ 21 ] It was also used by dyers in the Middle Ages in the form of fermented urine to alter the colour of vegetable dyes. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal ammoniac. [ 61 ] At a later period, when sal ammoniac was obtained by distilling the hooves and horns of oxen and neutralizing the resulting carbonate with hydrochloric acid , the name 'spirit of hartshorn' was applied to ammonia. [ 21 ] [ 62 ]
Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting sal ammoniac ( ammonium chloride ) with calcined magnesia ( magnesium oxide ). [ 63 ] [ 64 ] It was isolated again by Peter Woulfe in 1767, [ 65 ] [ 66 ] by Carl Wilhelm Scheele in 1770 [ 67 ] and by Joseph Priestley in 1773 and was termed by him 'alkaline air'. [ 21 ] [ 68 ] Eleven years later in 1785, Claude Louis Berthollet ascertained its composition. [ 69 ] [ 21 ]
The production of ammonia from nitrogen in the air (and hydrogen) was invented by Fritz Haber and Robert LeRossignol. The patent was sent in 1909 (USPTO Nr 1,202,995) and awarded in 1916. Later, Carl Bosch developed the industrial method for ammonia production ( Haber–Bosch process ). It was first used on an industrial scale in Germany during World War I , [ 70 ] following the allied blockade that cut off the supply of nitrates from Chile . The ammonia was used to produce explosives to sustain war efforts. [ 71 ] The Nobel Prize in Chemistry 1918 was awarded to Fritz Haber "for the synthesis of ammonia from its elements".
Before the availability of natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process .
With the advent of the steel industry in the 20th century, ammonia became a byproduct of the production of coking coal.
In the US as of 2019 [update] , approximately 88% of ammonia was used as fertilisers either as its salts, solutions or anhydrously . [ 72 ] When applied to soil, it helps provide increased yields of crops such as maize and wheat . [ 73 ] 30% of agricultural nitrogen applied in the US is in the form of anhydrous ammonia, and worldwide, 110 million tonnes are applied each year. [ 74 ] Solutions of ammonia ranging from 16% to 25% are used in the fermentation industry as a source of nitrogen for microorganisms and to adjust pH during fermentation. [ 75 ]
Because of ammonia's vapourization properties, it is a useful refrigerant . [ 70 ] It was commonly used before the popularisation of chlorofluorocarbons (Freons). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. It suffers from the disadvantage of toxicity, and requiring corrosion resistant components, which restricts its domestic and small-scale use. Along with its use in modern vapour-compression refrigeration it is used in a mixture along with hydrogen and water in absorption refrigerators . The Kalina cycle , which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia–water mixture.
Ammonia coolant is also used in the radiators aboard the International Space Station in loops that are used to regulate the internal temperature and enable temperature-dependent experiments. [ 76 ] [ 77 ] The ammonia is under sufficient pressure to remain liquid throughout the process. Single-phase ammonia cooling systems also serve the power electronics in each pair of solar arrays.
The potential importance of ammonia as a refrigerant has increased with the discovery that vented CFCs and HFCs are potent and stable greenhouse gases. [ 78 ]
As early as in 1895, it was known that ammonia was 'strongly antiseptic ; it requires 1.4 grams per litre to preserve beef tea (broth).' [ 79 ] In one study, anhydrous ammonia destroyed 99.999% of zoonotic bacteria in three types of animal feed , but not silage . [ 80 ] [ 81 ] Anhydrous ammonia is currently used commercially to reduce or eliminate microbial contamination of beef . [ 82 ] [ 83 ] Lean finely textured beef (popularly known as ' pink slime ') in the beef industry is made from fatty beef trimmings (c. 50–70% fat) by removing the fat using heat and centrifugation , then treating it with ammonia to kill E. coli . The process was deemed effective and safe by the US Department of Agriculture based on a study that found that the treatment reduces E. coli to undetectable levels. [ 84 ] There have been safety concerns about the process as well as consumer complaints about the taste and smell of ammonia-treated beef. [ 85 ]
Ammonia has been used as fuel, and is a proposed alternative to fossil fuels and hydrogen. Being liquid at ambient temperature under its own vapour pressure and having high volumetric and gravimetric energy density, ammonia is considered a suitable carrier for hydrogen, [ 86 ] and may be cheaper than direct transport of liquid hydrogen. [ 87 ]
Compared to hydrogen, ammonia is easier to store. Compared to hydrogen as a fuel , ammonia is much more energy efficient, and could be produced, stored and delivered at a much lower cost than hydrogen, which must be kept compressed or as a cryogenic liquid. [ 88 ] [ 89 ] The raw energy density of liquid ammonia is 11.5 MJ/L, [ 88 ] which is about a third that of diesel .
Ammonia can be converted back to hydrogen to be used to power hydrogen fuel cells, or it may be used directly within high-temperature solid oxide direct ammonia fuel cells to provide efficient power sources that do not emit greenhouse gases . [ 90 ] [ 91 ] Ammonia to hydrogen conversion can be achieved through the sodium amide process [ 92 ] or the catalytic decomposition of ammonia using solid catalysts. [ 93 ]
Ammonia engines or ammonia motors, using ammonia as a working fluid , have been proposed and occasionally used. [ 94 ] The principle is similar to that used in a fireless locomotive , but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and the St. Charles Streetcar Line in New Orleans in the 1870s and 1880s, [ 95 ] and during World War II ammonia was used to power buses in Belgium . [ 96 ]
Ammonia is sometimes proposed as a practical alternative to fossil fuel for internal combustion engines . [ 96 ] [ 97 ] [ 98 ] [ 99 ] However, ammonia cannot be easily used in existing Otto cycle engines because of its very narrow flammability range . Despite this, several tests have been run. [ 100 ] [ 101 ] [ 102 ] Its high octane rating of 120 [ 103 ] and low flame temperature [ 104 ] allows the use of high compression ratios without a penalty of high NO x production. Since ammonia contains no carbon, its combustion cannot produce carbon dioxide , carbon monoxide , hydrocarbons , or soot .
Ammonia production currently creates 1.8% of global CO 2 emissions. 'Green ammonia' is ammonia produced by using green hydrogen (hydrogen produced by electrolysis with electricity from renewable energy), whereas 'blue ammonia' is ammonia produced using blue hydrogen (hydrogen produced by steam methane reforming) where the carbon dioxide has been captured and stored. [ 105 ]
Rocket engines have also been fueled by ammonia. The Reaction Motors XLR99 rocket engine that powered the X-15 hypersonic research aircraft used liquid ammonia. Although not as powerful as other fuels, it left no soot in the reusable rocket engine, and its density approximately matches the density of the oxidiser, liquid oxygen , which simplified the aircraft's design.
In 2020, Saudi Arabia shipped 40 metric tons of liquid 'blue ammonia' to Japan for use as a fuel. [ 106 ] It was produced as a by-product by petrochemical industries, and can be burned without giving off greenhouse gases . Its energy density by volume is nearly double that of liquid hydrogen. If the process of creating it can be scaled up via purely renewable resources, producing green ammonia, it could make a major difference in avoiding climate change . [ 107 ] The company ACWA Power and the city of Neom have announced the construction of a green hydrogen and ammonia plant in 2020. [ 108 ]
Green ammonia is considered as a potential fuel for future container ships. In 2020, the companies DSME and MAN Energy Solutions announced the construction of an ammonia-based ship, DSME plans to commercialize it by 2025. [ 109 ] The use of ammonia as a potential alternative fuel for aircraft jet engines is also being explored. [ 110 ]
Japan intends to implement a plan to develop ammonia co-firing technology that can increase the use of ammonia in power generation, as part of efforts to assist domestic and other Asian utilities to accelerate their transition to carbon neutrality . [ 111 ] In October 2021, the first International Conference on Fuel Ammonia (ICFA2021) was held. [ 112 ] [ 113 ]
In June 2022, IHI Corporation succeeded in reducing greenhouse gases by over 99% during combustion of liquid ammonia in a 2,000-kilowatt-class gas turbine achieving truly CO 2 -free power generation. [ 114 ] In July 2022, Quad nations of Japan, the U.S., Australia and India agreed to promote technological development for clean-burning hydrogen and ammonia as fuels at the security grouping's first energy meeting. [ 115 ] As of 2022 [update] , however, significant amounts of NO x are produced. [ 116 ] Nitrous oxide may also be a problem as it is a " greenhouse gas that is known to possess up to 300 times the Global Warming Potential (GWP) of carbon dioxide ". [ 117 ]
The IEA forecasts that ammonia will meet approximately 45% of shipping fuel demands by 2050. [ 118 ]
At high temperature and in the presence of a suitable catalyst ammonia decomposes into its constituent elements. [ 119 ] Decomposition of ammonia is a slightly endothermic process requiring 23 kJ/mol (5.5 kcal/mol ) of ammonia, and yields hydrogen and nitrogen gas.
Ammonia is used to scrub SO 2 from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertiliser. Ammonia neutralises the nitrogen oxide ( NO x ) pollutants emitted by diesel engines. This technology, called SCR ( selective catalytic reduction ), relies on a vanadia -based catalyst. [ 120 ]
Ammonia may be used to mitigate gaseous spills of phosgene . [ 121 ]
Ammonia, as the vapour released by smelling salts , has found significant use as a respiratory stimulant. Ammonia is commonly used in the illegal manufacture of methamphetamine through a Birch reduction . [ 123 ] The Birch method of making methamphetamine is dangerous because the alkali metal and liquid ammonia are both extremely reactive, and the temperature of liquid ammonia makes it susceptible to explosive boiling when reactants are added. [ 124 ]
Liquid ammonia is used for treatment of cotton materials, giving properties like mercerisation , using alkalis. In particular, it is used for prewashing of wool. [ 125 ]
At standard temperature and pressure, ammonia is less dense than atmosphere and has approximately 45–48% of the lifting power of hydrogen or helium . Ammonia has sometimes been used to fill balloons as a lifting gas . Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast). [ 126 ]
Ammonia has been used to darken quartersawn white oak in Arts & Crafts and Mission-style furniture. Ammonia fumes react with the natural tannins in the wood and cause it to change colour. [ 127 ]
The US Occupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia of 35 ppm by volume in the environmental air and an 8-hour exposure limit of 25 ppm by volume. [ 129 ] The National Institute for Occupational Safety and Health (NIOSH) recently reduced the IDLH (Immediately Dangerous to Life or Health, the level to which a healthy worker can be exposed for 30 minutes without suffering irreversible health effects) from 500 to 300 ppm based on recent more conservative interpretations of original research in 1943. Other organisations have varying exposure levels. US Navy Standards [U.S. Bureau of Ships 1962] maximum allowable concentrations (MACs): for continuous exposure (60 days) is 25 ppm; for exposure of 1 hour is 400 ppm. [ 130 ]
Ammonia vapour has a sharp, irritating, pungent odor that acts as a warning of potentially dangerous exposure. The average odor threshold is 5 ppm, well below any danger or damage. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death. [ 129 ] Ammonia is regulated in the US as a non-flammable gas, but it meets the definition of a material that is toxic by inhalation and requires a hazardous safety permit when transported in quantities greater than 3,500 US gallons (13,000 L; 2,900 imp gal). [ 131 ]
Liquid ammonia is dangerous because it is hygroscopic and because it can cause caustic burns . See Gas carrier § Health effects of specific cargoes carried on gas carriers for more information.
The toxicity of ammonia solutions does not usually cause problems for humans and other mammals, as a specific mechanism exists to prevent its build-up in the bloodstream. Ammonia is converted to carbamoyl phosphate by the enzyme carbamoyl phosphate synthetase , and then enters the urea cycle to be either incorporated into amino acids or excreted in the urine. [ 132 ] Fish and amphibians lack this mechanism, as they can usually eliminate ammonia from their bodies by direct excretion. Ammonia even at dilute concentrations is highly toxic to aquatic animals, and for this reason it is classified as "dangerous for the environment" . Atmospheric ammonia plays a key role in the formation of fine particulate matter . [ 133 ]
Ammonia is a constituent of tobacco smoke . [ 134 ]
Ammonia is present in coking wastewater streams, as a liquid by-product of the production of coke from coal . [ 135 ] In some cases, the ammonia is discharged to the marine environment where it acts as a pollutant. The Whyalla Steelworks in South Australia is one example of a coke-producing facility that discharges ammonia into marine waters. [ 136 ]
Ammonia toxicity is believed to be a cause of otherwise unexplained losses in fish hatcheries . Excess ammonia may accumulate and cause alteration of metabolism or increases in the body pH of the exposed organism. Tolerance varies among fish species. [ 137 ] At lower concentrations, around 0.05 mg/L, un-ionised ammonia is harmful to fish species and can result in poor growth and feed conversion rates, reduced fecundity and fertility and increase stress and susceptibility to bacterial infections and diseases. [ 138 ] Exposed to excess ammonia, fish may suffer loss of equilibrium, hyper-excitability, increased respiratory activity and oxygen uptake and increased heart rate. [ 137 ] At concentrations exceeding 2.0 mg/L, ammonia causes gill and tissue damage, extreme lethargy, convulsions, coma, and death. [ 137 ] [ 139 ] Experiments have shown that the lethal concentration for a variety of fish species ranges from 0.2 to 2.0 mg/L. [ 139 ]
During winter, when reduced feeds are administered to aquaculture stock, ammonia levels can be higher. Lower ambient temperatures reduce the rate of algal photosynthesis so less ammonia is removed by any algae present. Within an aquaculture environment, especially at large scale, there is no fast-acting remedy to elevated ammonia levels. Prevention rather than correction is recommended to reduce harm to farmed fish [ 139 ] and in open water systems, the surrounding environment.
Similar to propane , anhydrous ammonia boils below room temperature when at atmospheric pressure. A storage vessel capable of 250 psi (1.7 MPa ) is suitable to contain the liquid. [ 140 ] Ammonia is used in numerous different industrial applications requiring carbon or stainless steel storage vessels. Ammonia with at least 0.2% by weight water content is not corrosive to carbon steel. NH 3 carbon steel construction storage tanks with 0.2% by weight or more of water could last more than 50 years in service. [ 141 ] Experts warn that ammonium compounds not be allowed to come in contact with bases (unless in an intended and contained reaction), as dangerous quantities of ammonia gas could be released.
The hazards of ammonia solutions depend on the concentration: 'dilute' ammonia solutions are usually 5–10% by weight (< 5.62 mol/L); 'concentrated' solutions are usually prepared at >25% by weight. A 25% (by weight) solution has a density of 0.907 g/cm 3 , and a solution that has a lower density will be more concentrated. The European Union classification of ammonia solutions is given in the table.
The ammonia vapour from concentrated ammonia solutions is severely irritating to the eyes and the respiratory tract , and experts warn that these solutions only be handled in a fume hood . Saturated ('0.880'–see § Properties ) solutions can develop a significant pressure inside a closed bottle in warm weather, and experts also warn that the bottle be opened with care. This is not usually a problem for 25% ('0.900') solutions.
Experts warn that ammonia solutions not be mixed with halogens , as toxic and/or explosive products are formed. Experts also warn that prolonged contact of ammonia solutions with silver , mercury or iodide salts can also lead to explosive products: such mixtures are often formed in qualitative inorganic analysis , and that it needs to be lightly acidified but not concentrated (<6% w/v) before disposal once the test is completed.
Anhydrous ammonia is classified as toxic ( T ) and dangerous for the environment ( N ). The gas is flammable ( autoignition temperature : 651 °C) and can form explosive mixtures with air (16–25%). The permissible exposure limit (PEL) in the United States is 50 ppm (35 mg/m 3 ), while the IDLH concentration is estimated at 300 ppm. Repeated exposure to ammonia lowers the sensitivity to the smell of the gas: normally the odour is detectable at concentrations of less than 50 ppm, but desensitised individuals may not detect it even at concentrations of 100 ppm. Anhydrous ammonia corrodes copper - and zinc -containing alloys , which makes brass fittings not appropriate for handling the gas. Liquid ammonia can also attack rubber and certain plastics.
Ammonia reacts violently with the halogens . Nitrogen triiodide , a primary high explosive , is formed when ammonia comes in contact with iodine . Ammonia causes the explosive polymerisation of ethylene oxide . It also forms explosive fulminating compounds with compounds of gold , silver , mercury , germanium or tellurium , and with stibine . Violent reactions have also been reported with acetaldehyde , hypochlorite solutions, potassium ferricyanide and peroxides .
Ammonia has one of the highest rates of production of any inorganic chemical. Production is sometimes expressed in terms of 'fixed nitrogen'. Global production was estimated as being 160 million tonnes in 2020 (147 tons of fixed nitrogen). [ 143 ] China accounted for 26.5% of that, followed by Russia at 11.0%, the United States at 9.5%, and India at 8.3%. [ 143 ]
Before the start of World War I , most ammonia was obtained by the dry distillation [ 144 ] of nitrogenous vegetable and animal waste products, including camel dung , where it was distilled by the reduction of nitrous acid and nitrites with hydrogen; in addition, it was produced by the distillation of coal , and also by the decomposition of ammonium salts by alkaline hydroxides [ 145 ] such as quicklime : [ 21 ]
For small scale laboratory synthesis, one can heat urea and calcium hydroxide or sodium hydroxide :
The Haber process , [ 146 ] also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia . [ 147 ] [ 148 ] It converts atmospheric nitrogen (N 2 ) to ammonia (NH 3 ) by a reaction with hydrogen (H 2 ) using finely divided iron metal as a catalyst:
N 2 + 3 H 2 ↽ − − ⇀ 2 NH 3 Δ H 298 K ∘ = − 92.28 kJ per mole of N 2 {\displaystyle {\ce {N2 + 3H2 <=> 2NH3}}\qquad {\Delta H_{\mathrm {298~K} }^{\circ }=-92.28~{\text{kJ per mole of }}{\ce {N2}}}}
This reaction is exothermic but disfavored in terms of entropy because four equivalents of reactant gases are converted into two equivalents of product gas. As a result, high pressures and temperatures that are not too high are needed to drive the reaction forward .
The German chemists Fritz Haber and Carl Bosch developed the process in the first decade of the 20th century, and its improved efficiency over existing methods such as the Birkeland-Eyde and Frank-Caro processes was a major advancement in the industrial production of ammonia. [ 149 ] [ 150 ] [ 151 ]
The electrochemical synthesis of ammonia involves the reductive formation of lithium nitride , which can be protonated to ammonia, given a proton source. The first use of this chemistry was reported in 1930, where lithium solutions in ethanol were used to produce ammonia at pressures of up to 1000 bar, with ethanol acting as the proton source. [ 152 ] Beyond simply mediating proton transfer to the nitrogen reduction reaction, ethanol has been found to play a multifaceted role, influencing electrolyte transformations and contributing to the formation of the solid electrolyte interphase, which enhances overall reaction efficiency. [ 153 ] [ 154 ]
In 1994, Tsuneto et al. used lithium electrodeposition in tetrahydrofuran to synthesize ammonia at more moderate pressures with reasonable Faradaic efficiency . [ 155 ] Subsequent studies have further explored the ethanol–tetrahydrofuran system for electrochemical ammonia synthesis. [ 154 ] [ 156 ]
In 2020, a solvent-agnostic gas diffusion electrode was shown to improve nitrogen transport to the reactive lithium. NH 3 production rates of up to 30 ± 5 nmol/(s⋅cm 2 ) and Faradaic efficiencies of up to 47.5 ± 4% at ambient temperature and 1 bar pressure were achieved. [ 157 ]
In 2021, it was demonstrated that ethanol could be replaced with a tetraalkyl phosphonium salt . [ 158 ] The study observed NH 3 production rates of 53 ± 1 nmol/(s⋅cm 2 ) at 69 ± 1% Faradaic efficiency experiments under 0.5 bar hydrogen and 19.5 bar nitrogen partial pressure at ambient temperature. [ 158 ] Technology based on this electrochemistry is being developed for commercial fertiliser and fuel production. [ 159 ] [ 160 ]
In 2022, ammonia was produced via the lithium mediated process in a continuous-flow electrolyzer also demonstrating the hydrogen gas as proton source. The study synthesized ammonia at 61 ± 1% Faradaic efficiency at a current density of −6 mA/cm 2 at 1 bar and room temperature. [ 161 ]
Ammonia is essential for life. [ 163 ] For example, it is required for the formation of amino acids and nucleic acids , fundamental building blocks of life. Ammonia is however quite toxic. Nature thus uses carriers for ammonia. Within a cell, glutamate serves this role. In the bloodstream, glutamine is a source of ammonia. [ 164 ]
Ethanolamine, required for cell membranes, is the substrate for ethanolamine ammonia-lyase , which produces ammonia: [ 165 ]
Ammonia is both a metabolic waste and a metabolic input throughout the biosphere . It is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds (more than 75%), few living creatures are capable of using atmospheric nitrogen in its diatomic form, N 2 gas. Therefore, nitrogen fixation is required for the synthesis of amino acids, which are the building blocks of protein . Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixing legumes , benefit from symbiotic relationships with rhizobia bacteria that create ammonia from atmospheric nitrogen. [ 166 ]
In humans, inhaling ammonia in high concentrations can be fatal. Exposure to ammonia can cause headaches , edema , impaired memory, seizures and coma as it is neurotoxic in nature. [ 167 ]
In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases . The overall process is called nitrogen fixation . Intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. The scientific interest in this problem is motivated by the unusual structure of the active site of the enzyme, which consists of an Fe 7 MoS 9 ensemble. [ 168 ]
Ammonia is also a metabolic product of amino acid deamination catalyzed by enzymes such as glutamate dehydrogenase 1 . Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea (by liver ), which is much less toxic, particularly less basic . This urea is a major component of the dry weight of urine . Most reptiles, birds, insects, and snails excrete uric acid solely as nitrogenous waste.
Ammonia plays a role in both normal and abnormal animal physiology . It is biosynthesised through normal amino acid metabolism and is toxic in high concentrations. The liver converts ammonia to urea through a series of reactions known as the urea cycle . Liver dysfunction, such as that seen in cirrhosis , may lead to elevated amounts of ammonia in the blood ( hyperammonemia ). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase , lead to hyperammonemia . Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy , as well as the neurological disease common in people with urea cycle defects and organic acidurias . [ 169 ]
Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine , α-ketoglutarate may be degraded to produce two bicarbonate ions, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules , combine with a hydrogen ion, and thus allow for further acid excretion . [ 170 ]
Ammonium ions are a toxic waste product of metabolism in animals . In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in the urea cycle to urea , which is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid , which is solid and can therefore be excreted with minimal water loss. [ 171 ]
Ammonia has been detected in the atmospheres of the giant planets Jupiter , Saturn , Uranus and Neptune , along with other gases such as methane , hydrogen , and helium . The interior of Saturn may include frozen ammonia crystals. [ 172 ] It is found on Deimos and Phobos –the two moons of Mars . [ citation needed ]
Ammonia was first detected in interstellar space in 1968, based on microwave emissions from the direction of the galactic core . [ 173 ] This was the first polyatomic molecule to be so detected. The sensitivity of the molecule to a broad range of excitations and the ease with which it can be observed in a number of regions has made ammonia one of the most important molecules for studies of molecular clouds . [ 174 ] The relative intensity of the ammonia lines can be used to measure the temperature of the emitting medium.
The following isotopic species of ammonia have been detected: NH 3 , 15 NH 3 , NH 2 D , NHD 2 , and ND 3 . The detection of triply deuterated ammonia was considered a surprise as deuterium is relatively scarce. It is thought that the low-temperature conditions allow this molecule to survive and accumulate. [ 175 ]
Since its interstellar discovery, NH 3 has proved to be an invaluable spectroscopic tool in the study of the interstellar medium. With a large number of transitions sensitive to a wide range of excitation conditions, NH 3 has been widely astronomically detected–its detection has been reported in hundreds of journal articles. Listed below is a sample of journal articles that highlights the range of detectors that have been used to identify ammonia.
The study of interstellar ammonia has been important to a number of areas of research in the last few decades. Some of these are delineated below and primarily involve using ammonia as an interstellar thermometer.
The interstellar abundance for ammonia has been measured for a variety of environments. The [ NH 3 ]/[ H 2 ] ratio has been estimated to range from 10 −7 in small dark clouds [ 176 ] up to 10 −5 in the dense core of the Orion molecular cloud complex . [ 177 ] Although a total of 18 total production routes have been proposed, [ 178 ] the principal formation mechanism for interstellar NH 3 is the reaction:
The rate constant, k , of this reaction depends on the temperature of the environment, with a value of 5.2 × 10 − 6 {\displaystyle 5.2\times 10^{-6}} at 10 K. [ 179 ] The rate constant was calculated from the formula k = a ( T / 300 ) B {\displaystyle k=a(T/300)^{B}} . For the primary formation reaction, a = 1.05 × 10 −6 and B = −0.47 . Assuming an NH + 4 abundance of 3 × 10 − 7 {\displaystyle 3\times 10^{-7}} and an electron abundance of 10 −7 typical of molecular clouds, the formation will proceed at a rate of 1.6 × 10 −9 cm −3 s −1 in a molecular cloud of total density 10 5 cm −3 . [ 180 ]
All other proposed formation reactions have rate constants of between two and 13 orders of magnitude smaller, making their contribution to the abundance of ammonia relatively insignificant. [ 181 ] As an example of the minor contribution other formation reactions play, the reaction:
has a rate constant of 2.2 × 10 −15 . Assuming H 2 densities of 10 5 and [ NH 2 ]/[ H 2 ] ratio of 10 −7 , this reaction proceeds at a rate of 2.2 × 10 −12 , more than three orders of magnitude slower than the primary reaction above.
Some of the other possible formation reactions are:
There are 113 total proposed reactions leading to the destruction of NH 3 . Of these, 39 were tabulated in extensive tables of the chemistry among C, N and O compounds. [ 182 ] A review of interstellar ammonia cites the following reactions as the principal dissociation mechanisms: [ 174 ]
with rate constants of 4.39×10 −9 [ 183 ] and 2.2×10 −9 , [ 184 ] respectively. The above equations ( 1 , 2 ) run at a rate of 8.8×10 −9 and 4.4×10 −13 , respectively. These calculations assumed the given rate constants and abundances of [ NH 3 ]/[ H 2 ] = 10 −5 , [ [H 3 ] + ]/[ H 2 ] = 2×10 −5 , [ HCO + ]/[ H 2 ] = 2×10 −9 , and total densities of n = 10 5 , typical of cold, dense, molecular clouds. [ 185 ] Clearly, between these two primary reactions, equation ( 1 ) is the dominant destruction reaction, with a rate ≈10,000 times faster than equation ( 2 ). This is due to the relatively high abundance of [H 3 ] + .
Radio observations of NH 3 from the Effelsberg 100-m Radio Telescope reveal that the ammonia line is separated into two components–a background ridge and an unresolved core. The background corresponds well with the locations previously detected CO. [ 186 ] The 25 m Chilbolton telescope in England detected radio signatures of ammonia in H II regions , HNH 2 O masers , H–H objects, and other objects associated with star formation. A comparison of emission line widths indicates that turbulent or systematic velocities do not increase in the central cores of molecular clouds. [ 187 ]
Microwave radiation from ammonia was observed in several galactic objects including W3(OH), Orion A , W43 , W51 , and five sources in the galactic centre. The high detection rate indicates that this is a common molecule in the interstellar medium and that high-density regions are common in the galaxy. [ 188 ]
VLA observations of NH 3 in seven regions with high-velocity gaseous outflows revealed condensations of less than 0.1 pc in L1551, S140, and Cepheus A . Three individual condensations were detected in Cepheus A, one of them with a highly elongated shape. They may play an important role in creating the bipolar outflow in the region. [ 189 ]
Extragalactic ammonia was imaged using the VLA in IC 342 . The hot gas has temperatures above 70 K, which was inferred from ammonia line ratios and appears to be closely associated with the innermost portions of the nuclear bar seen in CO. [ 190 ] NH 3 was also monitored by VLA toward a sample of four galactic ultracompact HII regions: G9.62+0.19, G10.47+0.03, G29.96−0.02, and G31.41+0.31. Based upon temperature and density diagnostics, it is concluded that in general such clumps are probably the sites of massive star formation in an early evolutionary phase prior to the development of an ultracompact HII region. [ 191 ]
Absorption at 2.97 micrometres due to solid ammonia was recorded from interstellar grains in the Becklin–Neugebauer Object and probably in NGC 2264-IR as well. This detection helped explain the physical shape of previously poorly understood and related ice absorption lines. [ 192 ]
A spectrum of the disk of Jupiter was obtained from the Kuiper Airborne Observatory , covering the 100 to 300 cm −1 spectral range. Analysis of the spectrum provides information on global mean properties of ammonia gas and an ammonia ice haze. [ 193 ]
A total of 149 dark cloud positions were surveyed for evidence of 'dense cores' by using the (J,K) = (1,1) rotating inversion line of NH 3 . In general, the cores are not spherically shaped, with aspect ratios ranging from 1.1 to 4.4. It is also found that cores with stars have broader lines than cores without stars. [ 194 ]
Ammonia has been detected in the Draco Nebula and in one or possibly two molecular clouds, which are associated with the high-latitude galactic infrared cirrus . The finding is significant because they may represent the birthplaces for the Population I metallicity B-type stars in the galactic halo that could have been borne in the galactic disk. [ 195 ]
By balancing and stimulated emission with spontaneous emission, it is possible to construct a relation between excitation temperature and density. Moreover, since the transitional levels of ammonia can be approximated by a 2-level system at low temperatures, this calculation is fairly simple. This premise can be applied to dark clouds, regions suspected of having extremely low temperatures and possible sites for future star formation. Detections of ammonia in dark clouds show very narrow lines – indicative not only of low temperatures, but also of a low level of inner-cloud turbulence. Line ratio calculations provide a measurement of cloud temperature that is independent of previous CO observations. The ammonia observations were consistent with CO measurements of rotation temperatures of ≈10 K. With this, densities can be determined, and have been calculated to range between 10 4 and 10 5 cm −3 in dark clouds. Mapping of NH 3 gives typical clouds sizes of 0.1 pc and masses near 1 solar mass. These cold, dense cores are the sites of future star formation.
Ultra-compact HII regions are among the best tracers of high-mass star formation. The dense material surrounding UCHII regions is likely primarily molecular. Since a complete study of massive star formation necessarily involves the cloud from which the star formed, ammonia is an invaluable tool in understanding this surrounding molecular material. Since this molecular material can be spatially resolved, it is possible to constrain the heating/ionising sources, temperatures, masses, and sizes of the regions. Doppler-shifted velocity components allow for the separation of distinct regions of molecular gas that can trace outflows and hot cores originating from forming stars.
Ammonia has been detected in external galaxies, [ 196 ] [ 197 ] and by simultaneously measuring several lines, it is possible to directly measure the gas temperature in these galaxies. Line ratios imply that gas temperatures are warm (≈50 K), originating from dense clouds with sizes of tens of parsecs. This picture is consistent with the picture within our Milky Way galaxy – hot dense molecular cores form around newly forming stars embedded in larger clouds of molecular material on the scale of several hundred parsecs (giant molecular clouds; GMCs). | https://en.wikipedia.org/wiki/H3N |
Ammonia borane (also systematically named ammoniotrihydroborate [ citation needed ] ), also called borazane , is the chemical compound with the formula H 3 NBH 3 . The colourless or white solid is the simplest molecular boron - nitrogen - hydride compound. It has attracted attention as a source for hydrogen fuel, but is otherwise primarily of academic interest.
Reaction of diborane with ammonia mainly gives the diammoniate salt [H 2 B(NH 3 ) 2 ] + [BH 4 ] − (diammoniodihydroboronium tetrahydroborate). Ammonia borane is the main product when an adduct of borane is employed in place of diborane: [ 5 ]
It can also be synthesized from sodium borohydride . [ 6 ] [ 7 ] [ 8 ]
The molecule adopts a structure similar to that of ethane , with which it is isoelectronic . The B−N distance is 1.58(2) Å. The B−H and N−H distances are 1.15 and 0.96 Å, respectively. Its similarity to ethane is tenuous since ammonia borane is a solid and ethane is a gas: their melting points differing by 284 °C. This difference is consistent with the highly polar nature of ammonia borane. The H atoms attached to boron are hydridic (negatively charged) and those attached to nitrogen are acidic (positively charged). [ 9 ]
The structure of the solid indicates a close association of the N H and the B H centers. The closest H−H distance is 1.990 Å, which can be compared with the H−H bonding distance of 0.74 Å. This interaction is called a dihydrogen bond . [ 10 ] [ 11 ] The original crystallographic analysis of this compound reversed the assignments of B and N. The updated structure was arrived at with improved data using the technique of neutron diffraction that allowed the hydrogen atoms to be located with greater precision.
Ammonia borane has been suggested as a storage medium for hydrogen , e.g. for when the gas is used to fuel motor vehicles. It can be made to release hydrogen on heating, being polymerized first to (NH 2 BH 2 ) n , then to (NHBH) n , [ 15 ] which ultimately decomposes to boron nitride (BN) at temperatures above 1000 °C. [ 16 ] It is more hydrogen-dense than liquid hydrogen and also able to exist at normal temperatures and pressures. [ 17 ]
Ammonia borane finds some use in organic synthesis as an air-stable derivative of diborane. [ 18 ] It can be used as a reducing agent in transfer hydrogenation reactions, often in the presence of a transition metal catalyst. [ 19 ]
Many analogues have been prepared from primary, secondary, and even tertiary amines :
The first amine adduct of borane was derived from trimethylamine . Borane tert-butylamine complex is prepared by the reaction of sodium borohydride with t-butylammonium chloride. Generally adduct are more robust with more basic amines. Variations are also possible for the boron component, although primary and secondary boranes are less common. [ 8 ] | https://en.wikipedia.org/wiki/H3NBH3 |
Sulfamic acid , also known as amidosulfonic acid , amidosulfuric acid , aminosulfonic acid , sulphamic acid and sulfamidic acid , is a molecular compound with the formula H 3 NSO 3 . This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water , sulfur trioxide , sulfur dioxide and nitrogen . [ 2 ]
Sulfamic acid (H 3 NSO 3 ) may be considered an intermediate compound between sulfuric acid (H 2 SO 4 ), and sulfamide (H 4 N 2 SO 2 ), effectively replacing a hydroxyl (–OH) group with an amine (–NH 2 ) group at each step. This pattern can extend no further in either direction without breaking down the sulfonyl (–SO 2 –) moiety. Sulfamates are derivatives of sulfamic acid.
Sulfamic acid is produced industrially by treating urea with a mixture of sulfur trioxide and sulfuric acid (or oleum ). The conversion is conducted in two stages, the first being sulfamation :
In this way, approximately 96,000 tonnes were produced in 1995. [ 3 ]
The compound is well described by the formula H 3 NSO 3 , not the tautomer H 2 NSO 2 (OH). The relevant bond distances are 1.44 Å for the S=O and 1.77 Å for the S–N. The greater length of the S–N is consistent with a single bond. [ 5 ] Furthermore, a neutron diffraction study located the hydrogen atoms, all three of which are 1.03 Å distant from the nitrogen. [ 4 ] In the solid state, the molecule of sulfamic acid is well described by a zwitterionic form.
The crystalline solid is indefinitely stable under ordinary storage conditions, however, aqueous solutions of sulfamic acid slowly hydrolyse to ammonium bisulfate , according to the following reaction:
Its behaviour resembles that of urea , (H 2 N) 2 CO. Both feature amino groups linked to electron-withdrawing centres that can participate in delocalised bonding . Both liberate ammonia upon heating in water, with urea releasing CO 2 while sulfamic acid releases sulfuric acid .
Sulfamic acid is a moderately strong acid, K a = 0.101 (p K a = 0.995). Because the solid is not hygroscopic , it is used as a standard in acidimetry (quantitative assays of acid content).
Double deprotonation can be effected in liquid ammonia to give the anion HNSO 2− 3 . [ 6 ]
With nitrous acid , sulfamic acid reacts to give nitrogen :
while with concentrated nitric acid , it affords nitrous oxide : [ 7 ]
The reaction of excess hypochlorite ions with sulfamic acid or a sulfamate salt gives rise reversibly to both N -chlorosulfamate and N , N -dichlorosulfamate ions. [ 8 ] [ 9 ] [ 10 ]
Consequently, sulfamic acid is used as hypochlorite scavenger in the oxidation of aldehydes with chlorite such as the Pinnick oxidation .
Upon heating sulfamic acid will react with alcohols to form the corresponding organosulfates . It is more expensive than other reagents for doing this, such as chlorosulfonic acid or oleum , but is also significantly milder and will not sulfonate aromatic rings. Products are produced as their ammonium salts. Such reactions can be catalyzed by the presence of urea . [ 10 ] Without the presence of any catalysts, sulfamic acid will not react with ethanol at temperatures below 100 °C.
An example of this reaction is the production 2-ethylhexyl sulfate, a wetting agent used in the mercerisation of cotton, by combining sulfamic acid with 2-ethylhexanol .
Sulfamic acid is mainly a precursor to sweet-tasting compounds. Reaction with cyclohexylamine followed by addition of NaOH gives C 6 H 11 NHSO 3 Na, sodium cyclamate . Related compounds are also sweeteners , such as acesulfame potassium .
Sulfamates have been used in the design of many types of therapeutic agents such as antibiotics , nucleoside/nucleotide human immunodeficiency virus (HIV) reverse transcriptase inhibitors , HIV protease inhibitors (PIs), anticancer drugs ( steroid sulfatase and carbonic anhydrase inhibitors), anti-epileptic drugs, and weight loss drugs . [ 11 ]
Sulfamic acid is used as an acidic cleaning agent and descaling agent sometimes pure or as a component of proprietary mixtures, typically for metals and ceramics . For cleaning purposes, there are different grades based on application such as GP Grade, SR Grade and TM Grade. It is frequently used for removing rust and limescale , replacing the more volatile and irritating hydrochloric acid , which is cheaper. It is often a component of household descalant, for example, Lime-A-Way Thick Gel contains up to 8% sulfamic acid and has pH 2.0–2.2, [ 12 ] or detergents used for removal of limescale . When compared to most of the common strong mineral acids , sulfamic acid has desirable water descaling properties, low volatility, and low toxicity. It forms water-soluble salts of calcium, nickel, and ferric iron.
Sulfamic acid is preferable to hydrochloric acid in household use, due to its intrinsic safety. If inadvertently mixed with hypochlorite based products such as bleach , it does not form chlorine gas, whereas the most common acids would; the reaction ( neutralisation ) with ammonia , produces a salt, as depicted in the section above.
It also finds applications in the industrial cleaning of dairy and brewhouse equipment. Although it is considered less corrosive than hydrochloric acid , corrosion inhibitors are often added to the commercial cleansers of which it is a component. It can be used as a descalant for descaling home coffee and espresso machines and in denture cleaners.
According to the label on the consumer product, the silver cleaning product TarnX contains thiourea , a detergent , and sulfamic acid. | https://en.wikipedia.org/wiki/H3NO3S |
Orthonitrate is a tetrahedral anion of nitrogen with the formula NO 3− 4 . It was first identified in 1977 [ 1 ] and is currently known in only two compounds, sodium orthonitrate (Na 3 NO 4 ) and potassium orthonitrate (K 3 NO 4 ). The corresponding oxoacid, orthonitric acid (H 3 NO 4 ), is hypothetical and has never been observed. Sodium and potassium orthonitrate can be prepared by fusion of the nitrate and metal oxide under high temperatures [ 2 ] and ideally high pressures (several GPa ). [ 3 ]
The resulting orthonitrates are white solids which are extremely sensitive to moisture and CO 2 , decomposing within minutes to hydroxides, carbonates, and nitrates upon exposure to air. [ 1 ]
The orthonitrate ion is tetrahedral with N–O bond lengths of 139 pm, which is unexpectedly short, indicating that polar interactions are shortening the bond. [ 4 ] This short bond length parallels that of hypervalent oxyanions containing third-row elements like PO 3− 4 and SO 2− 4 , for which pπ–dπ bonding was previously proposed as the explanation for the short bond length. Since 3d orbitals of nitrogen are much too high in energy to be involved in the case of orthonitrate, the shortness of the N–O bond in orthonitrate indicates that pπ–dπ bonding is likely not the most important explanation for the bond lengths of these heavier anions either. [ 2 ] | https://en.wikipedia.org/wiki/H3NO4 |
In chemistry , hydronium ( hydroxonium in traditional British English ) is the cation [H 3 O] + , also written as H 3 O + , the type of oxonium ion produced by protonation of water . It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton (a positive hydrogen ion, H + ) to the surrounding water molecules ( H 2 O ). In fact, acids must be surrounded by more than a single water molecule in order to ionize, yielding aqueous H + and conjugate base.
Three main structures for the aqueous proton have garnered experimental support:
Spectroscopic evidence from well-defined IR spectra overwhelmingly supports the Stoyanov cation as the predominant form. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ non-primary source needed ] For this reason, it has been suggested that wherever possible, the symbol H + (aq) should be used instead of the hydronium ion. [ 2 ]
The molar concentration of hydronium or H + ions determines a solution's pH according to
where M = mol/L. The concentration of hydroxide ions analogously determines a solution's pOH . The molecules in pure water auto-dissociate into aqueous protons and hydroxide ions in the following equilibrium:
In pure water, there is an equal number of hydroxide and H + ions, so it is a neutral solution. At 25 °C (77 °F), pure water has a pH of 7 and a pOH of 7 (this varies when the temperature changes: see self-ionization of water ). A pH value less than 7 indicates an acidic solution, and a pH value more than 7 indicates a basic solution. [ 7 ]
According to IUPAC nomenclature of organic chemistry , the hydronium ion should be referred to as oxonium . [ 8 ] Hydroxonium may also be used unambiguously to identify it. [ citation needed ]
An oxonium ion is any cation containing a trivalent oxygen atom.
Since O + and N have the same number of electrons, H 3 O + is isoelectronic with ammonia . As shown in the images above, H 3 O + has a trigonal pyramidal molecular geometry with the oxygen atom at its apex. The H−O−H bond angle is approximately 113°, [ 9 ] [ 10 ] and the center of mass is very close to the oxygen atom. Because the base of the pyramid is made up of three identical hydrogen atoms, the H 3 O + molecule's symmetric top configuration is such that it belongs to the C 3v point group . Because of this symmetry and the fact that it has a dipole moment, the rotational selection rules are Δ J = ±1 and Δ K = 0. The transition dipole lies along the c -axis and, because the negative charge is localized near the oxygen atom, the dipole moment points to the apex, perpendicular to the base plane.
The hydrated proton is very acidic: at 25 °C, its p K a is approximately 0. [ 11 ] The values commonly given for p K a aq (H 3 O + ) are 0 or −1.74. The former uses the convention that the activity of the solvent in a dilute solution (in this case, water) is 1, while the latter uses the value of the concentration of water in the pure liquid of 55.5 M. Silverstein has shown that the latter value is thermodynamically unsupportable. [ 12 ] The disagreement comes from the ambiguity that to define p K a of H 3 O + in water, H 2 O has to act simultaneously as a solute and the solvent. The IUPAC has not given an official definition of p K a that would resolve this ambiguity. Burgot has argued that H 3 O + (aq) + H 2 O (l) ⇄ H 2 O (aq) + H 3 O + (aq) is simply not a thermodynamically well-defined process. For an estimate of p K a aq (H 3 O + ), Burgot suggests taking the measured value p K a EtOH (H 3 O + ) = 0.3, the p K a of H 3 O + in ethanol, and applying the correlation equation p K a aq = p K a EtOH − 1.0 (± 0.3) to convert the ethanol p K a to an aqueous value, to give a value of p K a aq (H 3 O + ) = −0.7 (± 0.3). [ 13 ] On the other hand, Silverstein has shown that Ballinger and Long's experimental results [ 14 ] support a p K a of 0.0 for the aqueous proton. [ 15 ] Neils and Schaertel provide added arguments for a p K a of 0.0 [ 16 ]
The aqueous proton is the most acidic species that can exist in water (assuming sufficient water for dissolution): any stronger acid will ionize and yield a hydrated proton. The acidity of H + (aq) is the implicit standard used to judge the strength of an acid in water: strong acids must be better proton donors than H + (aq), as otherwise a significant portion of acid will exist in a non-ionized state (i.e.: a weak acid). Unlike H + (aq) in neutral solutions that result from water's autodissociation, in acidic solutions, H + (aq) is long-lasting and concentrated, in proportion to the strength of the dissolved acid.
pH was originally conceived to be a measure of the hydrogen ion concentration of aqueous solution. [ 17 ] Virtually all such free protons are quickly hydrated; acidity of an aqueous solution is therefore more accurately characterized by its concentration of H + (aq). In organic syntheses, such as acid catalyzed reactions, the hydronium ion ( H 3 O + ) is used interchangeably with the H + ion; choosing one over the other has no significant effect on the mechanism of reaction.
Researchers have yet to fully characterize the solvation of hydronium ion in water, in part because many different meanings of solvation exist. A freezing-point depression study determined that the mean hydration ion in cold water is approximately H 3 O + (H 2 O) 6 : [ 18 ] on average, each hydronium ion is solvated by 6 water molecules which are unable to solvate other solute molecules.
Some hydration structures are quite large: the H 3 O + (H 2 O) 20 magic ion number structure (called magic number because of its increased stability with respect to hydration structures involving a comparable number of water molecules – this is a similar usage of the term magic number as in nuclear physics ) might place the hydronium inside a dodecahedral cage. [ 19 ] However, more recent ab initio method molecular dynamics simulations have shown that, on average, the hydrated proton resides on the surface of the H 3 O + (H 2 O) 20 cluster. [ 20 ] Further, several disparate features of these simulations agree with their experimental counterparts suggesting an alternative interpretation of the experimental results.
Two other well-known structures are the Zundel cation and the Eigen cation . The Eigen solvation structure has the hydronium ion at the center of an H 9 O + 4 complex in which the hydronium is strongly hydrogen-bonded to three neighbouring water molecules. [ 21 ] In the Zundel H 5 O + 2 complex the proton is shared equally by two water molecules in a symmetric hydrogen bond . [ 22 ] A work in 1999 indicates that both of these complexes represent ideal structures in a more general hydrogen bond network defect. [ 23 ]
Isolation of the hydronium ion monomer in liquid phase was achieved in a nonaqueous, low nucleophilicity superacid solution ( HF − SbF 5 SO 2 ). The ion was characterized by high resolution 17 O nuclear magnetic resonance . [ 24 ]
A 2007 calculation of the enthalpies and free energies of the various hydrogen bonds around the hydronium cation in liquid protonated water [ 25 ] at room temperature and a study of the proton hopping mechanism using molecular dynamics showed that the hydrogen-bonds around the hydronium ion (formed with the three water ligands in the first solvation shell of the hydronium) are quite strong compared to those of bulk water.
A new model was proposed by Stoyanov based on infrared spectroscopy in which the proton exists as an H 13 O + 6 ion. The positive charge is thus delocalized over 6 water molecules. [ 26 ]
For many strong acids , it is possible to form crystals of their hydronium salt that are relatively stable. These salts are sometimes called acid monohydrates . As a rule, any acid with an ionization constant of 10 9 or higher may do this. Acids whose ionization constants are below 10 9 generally cannot form stable H 3 O + salts. For example, nitric acid has an ionization constant of 10 1.4 , and mixtures with water at all proportions are liquid at room temperature. However, perchloric acid has an ionization constant of 10 10 , and if liquid anhydrous perchloric acid and water are combined in a 1:1 molar ratio, they react to form solid hydronium perchlorate ( H 3 O + ·ClO − 4 ). [ citation needed ]
The hydronium ion also forms stable compounds with the carborane superacid H(CB 11 H(CH 3 ) 5 Br 6 ) . [ 27 ] X-ray crystallography shows a C 3v symmetry for the hydronium ion with each proton interacting with a bromine atom each from three carborane anions 320 pm apart on average. The [H 3 O] [H(CB 11 HCl 11 )] salt is also soluble in benzene . In crystals grown from a benzene solution the solvent co-crystallizes and a H 3 O·(C 6 H 6 ) 3 cation is completely separated from the anion. In the cation three benzene molecules surround hydronium forming pi-cation interactions with the hydrogen atoms. The closest (non-bonding) approach of the anion at chlorine to the cation at oxygen is 348 pm.
There are also many known examples of salts containing hydrated hydronium ions, such as the H 5 O + 2 ion in HCl·2H 2 O , the H 7 O + 3 and H 9 O + 4 ions both found in HBr·4H 2 O . [ 28 ]
Sulfuric acid is also known to form a hydronium salt H 3 O + HSO − 4 at temperatures below 8.49 °C (47.28 °F). [ 29 ]
Hydronium is an abundant molecular ion in the interstellar medium and is found in diffuse [ 30 ] and dense [ 31 ] molecular clouds as well as the plasma tails of comets. [ 32 ] Interstellar sources of hydronium observations include the regions of Sagittarius B2, Orion OMC-1, Orion BN–IRc2, Orion KL, and the comet Hale–Bopp.
Interstellar hydronium is formed by a chain of reactions started by the ionization of H 2 into H + 2 by cosmic radiation. [ 33 ] H 3 O + can produce either OH − or H 2 O through dissociative recombination reactions, which occur very quickly even at the low (≥10 K) temperatures of dense clouds. [ 34 ] This leads to hydronium playing a very important role in interstellar ion-neutral chemistry.
Astronomers are especially interested in determining the abundance of water in various interstellar climates due to its key role in the cooling of dense molecular gases through radiative processes. [ 35 ] However, H 2 O does not have many favorable transitions for ground-based observations. [ 36 ] Although observations of HDO (the deuterated version of water [ 37 ] ) could potentially be used for estimating H 2 O abundances, the ratio of HDO to H 2 O is not known very accurately. [ 36 ]
Hydronium, on the other hand, has several transitions that make it a superior candidate for detection and identification in a variety of situations. [ 36 ] This information has been used in conjunction with laboratory measurements of the branching ratios of the various H 3 O + dissociative recombination reactions [ 34 ] to provide what are believed to be relatively accurate OH − and H 2 O abundances without requiring direct observation of these species. [ 38 ] [ 39 ]
As mentioned previously, H 3 O + is found in both diffuse and dense molecular clouds. By applying the reaction rate constants ( α , β , and γ ) corresponding to all of the currently available characterized reactions involving H 3 O + , it is possible to calculate k ( T ) for each of these reactions. By multiplying these k ( T ) by the relative abundances of the products, the relative rates (in cm 3 /s) for each reaction at a given temperature can be determined. These relative rates can be made in absolute rates by multiplying them by the [H 2 ] 2 . [ 40 ] By assuming T = 10 K for a dense cloud and T = 50 K for a diffuse cloud, the results indicate that most dominant formation and destruction mechanisms were the same for both cases. It should be mentioned that the relative abundances used in these calculations correspond to TMC-1, a dense molecular cloud, and that the calculated relative rates are therefore expected to be more accurate at T = 10 K . The three fastest formation and destruction mechanisms are listed in the table below, along with their relative rates. Note that the rates of these six reactions are such that they make up approximately 99% of hydronium ion's chemical interactions under these conditions. [ 32 ] All three destruction mechanisms in the table below are classified as dissociative recombination reactions. [ 41 ]
It is also worth noting that the relative rates for the formation reactions in the table above are the same for a given reaction at both temperatures. This is due to the reaction rate constants for these reactions having β and γ constants of 0, resulting in k = α which is independent of temperature.
Since all three of these reactions produce either H 2 O or OH, these results reinforce the strong connection between their relative abundances and that of H 3 O + . The rates of these six reactions are such that they make up approximately 99% of hydronium ion's chemical interactions under these conditions.
As early as 1973 and before the first interstellar detection, chemical models of the interstellar medium (the first corresponding to a dense cloud) predicted that hydronium was an abundant molecular ion and that it played an important role in ion-neutral chemistry. [ 42 ] However, before an astronomical search could be underway there was still the matter of determining hydronium's spectroscopic features in the gas phase, which at this point were unknown. The first studies of these characteristics came in 1977, [ 43 ] which was followed by other, higher resolution spectroscopy experiments. Once several lines had been identified in the laboratory, the first interstellar detection of H 3 O + was made by two groups almost simultaneously in 1986. [ 31 ] [ 36 ] The first, published in June 1986, reported observation of the J vt K = 1 − 1 − 2 + 1 transition at 307 192 .41 MHz in OMC-1 and Sgr B2 . The second, published in August, reported observation of the same transition toward the Orion-KL nebula.
These first detections have been followed by observations of a number of additional H 3 O + transitions. The first observations of each subsequent transition detection are given below in chronological order:
In 1991, the 3 + 2 − 2 − 2 transition at 364 797 .427 MHz was observed in OMC-1 and Sgr B2. [ 44 ] One year later, the 3 + 0 − 2 − 0 transition at 396 272 .412 MHz was observed in several regions, the clearest of which was the W3 IRS 5 cloud. [ 39 ]
The first far-IR 4 − 3 − 3 + 3 transition at 69.524 μm (4.3121 THz) was made in 1996 near Orion BN -IRc2. [ 45 ] In 2001, three additional transitions of H 3 O + in were observed in the far infrared in Sgr B2; 2 − 1 − 1 + 1 transition at 100.577 μm (2.98073 THz), 1 − 1 − 1 + 1 at 181.054 μm (1.65582 THz) and 2 − 0 − 1 + 0 at 100.869 μm (2.9721 THz). [ 46 ] | https://en.wikipedia.org/wiki/H3O |
Hydroxy- λ 5 -phosphanone Oxo- λ 5 -phosphanol Oxo- λ 5 -phosphinous acid
1.22 g/cm 3 (50 wt% aq. solution)
Hypophosphorous acid ( HPA ), or phosphinic acid , is a phosphorus oxyacid and a powerful reducing agent with molecular formula H 3 PO 2 . It is a colorless low-melting compound, which is soluble in water, dioxane and alcohols. The formula for this acid is generally written H 3 PO 2 , but a more descriptive presentation is HOP(O)H 2 , which highlights its monoprotic character. Salts derived from this acid are called hypophosphites . [ 3 ]
HOP(O)H 2 exists in equilibrium with the minor tautomer HP(OH) 2 . Sometimes the minor tautomer is called hypophosphorous acid and the major tautomer is called phosphinic acid.
Hypophosphorous acid was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838). [ 4 ]
The acid is prepared industrially via a two step process: Firstly, elemental white phosphorus reacts with alkali and alkaline earth hydroxides to give an aqueous solution of hypophosphites:
Any phosphites produced in this step can be selectively precipitated out by treatment with calcium salts. The purified material is then treated with a strong, non-oxidizing acid (often sulfuric acid ) to give the free hypophosphorous acid:
HPA is usually supplied as a 50% aqueous solution. Anhydrous acid cannot be obtained by simple evaporation of the water, as the acid readily oxidises to phosphorous acid and phosphoric acid and also disproportionates to phosphorous acid and phosphine . Pure anhydrous hypophosphorous acid can be formed by the continuous extraction of aqueous solutions with diethyl ether . [ 5 ]
The molecule displays P(═O)H to P–OH tautomerism similar to that of phosphorous acid ; the P(═O) form is strongly favoured. [ 6 ]
HPA is usually supplied as a 50% aqueous solution and heating at low temperatures (up to about 90 °C) prompts it to react with water to form phosphorous acid and hydrogen gas.
Heating above 110 °C causes hypophosphorous acid to undergo disproportionation to give phosphorous acid and phosphine . [ 7 ]
Hypophosphorous acid can reduce chromium(III) oxide to chromium(II) oxide :
Most metal-hypophosphite complexes are unstable, owing to the tendency of hypophosphites to reduce metal cations back into the bulk metal. Some examples have been characterised, [ 8 ] [ 9 ] including the important nickel salt [Ni(H 2 O) 6 ](H 2 PO 2 ) 2 . [ 10 ]
Because hypophosphorous acid can reduce elemental iodine to form hydroiodic acid , which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine , [ 11 ] the United States Drug Enforcement Administration designated hypophosphorous acid (and its salts) as a List I precursor chemical effective November 16, 2001. [ 12 ] Accordingly, handlers of hypophosphorous acid or its salts in the United States are subject to stringent regulatory controls including registration, recordkeeping, reporting, and import/export requirements pursuant to the Controlled Substances Act and 21 CFR §§ 1309 and 1310. [ 12 ] [ 13 ] [ 14 ]
In organic chemistry, H 3 PO 2 can be used for the reduction of arenediazonium salts , converting Ar− + N≡N to Ar−H . [ 15 ] [ 16 ] [ 17 ] When diazotized in a concentrated solution of hypophosphorous acid, an amine substituent can be removed from arenes.
Owing to its ability to function as a mild reducing agent and oxygen scavenger it is sometimes used as an additive in Fischer esterification reactions, where it prevents the formation of colored impurities.
It is used to prepare phosphinic acid derivatives. [ 18 ]
Hypophosphorous acid (and its salts) are used to reduce metal salts back into bulk metals. It is effective for various transition metals ions (i.e. those of: Co, Cu, Ag, Mn, Pt) but is most commonly used to reduce nickel . [ 19 ] This forms the basis of electroless nickel plating (Ni–P), which is the single largest industrial application of hypophosphites. For this application it is principally used as a salt ( sodium hypophosphite ). [ 20 ]
[ 1 ] | https://en.wikipedia.org/wiki/H3O2P |
Dihydroxy(oxo)- λ 5 -phosphane Dihydroxy- λ 5 -phosphanone Orthophosphorous acid Oxo- λ 5 -phosphanediol Oxo- λ 5 -phosphonous acid
Phosphorous acid (or phosphonic acid ) is the compound described by the formula H 3 PO 3 . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO 3 H 2 , are called phosphonic acids .
Solid HP(O)(OH) 2 has tetrahedral geometry about the central phosphorus atom, with a P−H bond of 132 pm , one P=O double bond of 148 pm and two longer P−OH single bonds of 154 pm. In common with other phosphorus oxides with P−H bonds (e.g. hypophosphorous acid and dialkyl phosphites ), [ 2 ] it exists in equilibrium with an extremely minor tautomer P(OH) 3 . (In contrast, arsenous acid 's major tautomer is the trihydroxy form.) IUPAC recommends that the trihydroxy form P(OH) 3 be called phosphorous acid, and the dihydroxy form HP(O)(OH) 2 phosphonic acid. [ 3 ] Only the reduced phosphorus compounds are spelled with an " -ous " ending.
On an industrial scale, the acid is prepared by hydrolysis of phosphorus trichloride with water or steam: [ 5 ]
HPO(OH) 2 could be produced by the hydrolysis of phosphorus trioxide :
Phosphorous acid has a p K a in the range 1.26–1.3. [ 6 ] [ 7 ]
It is a diprotic acid , the hydrogenphosphite ion, HP(O) 2 (OH) − is a weak acid:
The conjugate base HP(O) 2 (OH) − is called hydrogen phosphite, and the second conjugate base, HPO 2− 3 , is the phosphite ion. [ 8 ] (Note that the IUPAC recommendations are hydrogen phosphonate and phosphonate respectively).
The hydrogen atom bonded directly to the phosphorus atom is not readily ionizable. Chemistry examinations often test students' appreciation of the fact that not all three hydrogen atoms are acidic under aqueous conditions, in contrast with H 3 PO 4 .
On heating at 200 °C, phosphorous acid disproportionates to phosphoric acid and phosphine : [ 9 ]
This reaction is used for laboratory-scale preparations of PH 3 .
Phosphorous acid slowly oxidizes in air to phosphoric acid. [ 5 ]
Both phosphorous acid and its deprotonated forms are good reducing agents , although not necessarily quick to react. They are oxidized to phosphoric acid or its salts. It reduces solutions of noble metal cations to the metals. When phosphorous acid is treated with a cold solution of mercuric chloride , a white precipitate of mercurous chloride forms:
Mercurous chloride is reduced further by phosphorous acid to mercury on heating or on standing:
Upon treatment with metals of d 6 configuration, phosphorous acid is known to coordinate as the otherwise rare P(OH) 3 tautomer. Examples include Mo(CO) 5 (P(OH) 3 ) and [Ru(NH 3 ) 4 (H 2 O)(P(OH) 3 )] 2+ . [ 10 ] [ 11 ]
Heating a mixture of potassium tetrachloroplatinate and phosphorous acid gives the luminescent salt potassium diplatinum(II) tetrakispyrophosphite : [ 12 ]
The most important use of phosphorous acid (phosphonic acid) is the production of basic lead phosphite , which is a stabilizer in PVC and related chlorinated polymers. [ 5 ]
It is used in the production of basic lead phosphonate PVC stabilizer, aminomethylene phosphonic acid and hydroxyethane diphosphonic acid.
It is also used as a strong reducing agent and in the production of synthetic fibres, organophosphorus pesticides, and the highly efficient water treatment agent ATMP .
Ferrous materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using phosphoric acid and further protected by surface coating. (See: Passivation (chemistry) ).
The IUPAC (mostly organic) name is phosphonic acid . This nomenclature is commonly reserved for substituted derivatives, that is, organic group bonded to phosphorus, not simply an ester. For example, (CH 3 )PO(OH) 2 is " methylphosphonic acid ", which may of course form "methyl phosphonate " esters . | https://en.wikipedia.org/wiki/H3O3P |
Phosphotungstic acid ( PTA ) or tungstophosphoric acid ( TPA ), is a heteropoly acid with the chemical formula H 3 P W 12 O 40 ] . It forms hydrates H 3 [PW 12 O 40 ]· n H 2 O . It is normally isolated as the n = 24 hydrate but can be desiccated to the hexahydrate ( n = 6). [ 2 ] EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 H 2 O hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of names and acronyms (see 'other names' section of infobox).
In these names the "12" or "dodeca" reflects the fact that the anion contains 12 tungsten atoms. Some early workers who did not know the structure [ 3 ] called it phospho-24-tungstic acid, formulating it as 3H 2 O·P 2 O 5 24WO 3 ·59H 2 O, (P 2 W 24 O 80 H 6 )·29H 2 O , which correctly identifies the atomic ratios of P, W and O. This formula was still quoted in papers as late as 1970. [ 4 ]
Phosphotungstic acid is used in histology as a component for staining of cell specimens, often together with haematoxylin as PTAH . It binds to fibrin , collagen , and fibres of connective tissues , and replaces the anions of dyes from these materials, selectively decoloring them.
Phosphotungstic acid is electron dense, opaque for electrons . It is a common negative stain for viruses , nerves , polysaccharides , and other biological tissue materials for imaging by a transmission electron microscope .
Gouzerh [ 5 ] summarises the historical views on the structure of phosphotungstic acid leading up to Keggin's determination of the structure as:
The structure was determined by J.F Keggin first published in 1933 [ 6 ] and then in 1934 [ 7 ] and is generally known as the Keggin structure . The anion has full tetrahedral symmetry and comprises a cage of twelve tungsten atoms linked by oxygen atoms with the phosphorus atom at its centre. The picture on the right shows the octahedral coordination of oxygen atoms around the tungsten atoms, and that the surface of the anion has both bridging and terminal oxygen atoms. Further investigation showed that the compound was a hexahydrate not a pentahydrate as Keggin had proposed. [ 8 ]
Phosphotungstic acid can be prepared by the reaction of sodium tungstate dihydrate, Na 2 WO 4 ·2H 2 O , with phosphoric acid , H 3 PO 4 , acidified with hydrochloric acid , HCl. [ 9 ] This procedure has been updated. [ 2 ]
Phosphotungstic acid solutions decompose as the pH is increased. A step-wise decomposition has been determined and the approximate compositions at various pH values are as follows: [ 10 ]
The species [PW 11 O 39 ] 7− is a lacunary, or defective Keggin ion. The [P 2 W 18 O 62 ] 6− has a Dawson structure . At pH less than 8, the presence of ethanol or acetone stabilises the anion, [PW 12 O 40 ] 3− , reducing decomposition. [ 10 ]
Tungstophosphoric acid is thermally stable up to 400 °C, and is more stable than the analogous silicotungstic acid , H 4 [SiW 12 O 40 ] . [ 11 ]
Large quantities of polar molecules such as pyridine are absorbed into the bulk phase and not simply adsorbed onto the surface. Solid state NMR studies of ethanol absorbed in the bulk phase show that both protonated dimers, (C 2 H 5 OH) 2 H + , and monomers, C 2 H 5 OH + 2 , are present.
Phosphotungstic acid is less sensitive to reduction than phosphomolybdic acid. Reduction with uric acid or iron(II) sulfate produces a brown coloured compound. the related silicotungstic acid when reduced forms a similar brown compound where one of the four W 3 units in the Keggin structure becomes a metal-metal bonded cluster of three edge shared W IV octahedra. [ 12 ]
Phosphotungstic acid is the strongest of heteropolyacids . Its conjugate base is the [PW 12 O 40 ] 3− anion. [ 13 ] Its acidity in acetic acid has been investigated and shows that the three protons dissociate independently rather than sequentially, and the acid sites are of the same strength. [ 14 ] One estimate of the acidity is that the solid has an acidity stronger than H 0 = −13.16, [ 11 ] which would qualify the compound as a superacid . This acidic strength means that even at low pH the acid is fully dissociated.
In common with the other heteropolyacids phosphotungstic acid is a catalyst and its high acidity and thermal stability make it a catalyst of choice according to some researchers. [ 15 ] It is in solution as a homogeneous catalyst , and as a heterogeneous catalyst "supported" on a substrate e.g. alumina , silica . Some acid catalysed reactions include:
Phosphotungstic acid has been used to precipitate different types of dyes as " lakes ". [ 16 ] Examples are basic dyes and triphenylmethane dyes, e.g. pararosaniline derivatives. [ 17 ]
Phosphotungstic acid is used in histology for staining specimens, as a component of phosphotungstic acid haematoxylin, PTAH , and “trichrome” reagents, and as a negative stain for imaging by a transmission electron microscope . [ citation needed ]
The potassium salt is only slightly soluble, unlike most other phosphotungstate salts, and has been proposed as a method for the gravimetric analysis of potassium. [ 24 ]
In a number of analytical procedures one of the roles of phosphotungstic acid is to precipitate out proteins. It has been termed a "universal" precipitant for polar proteins. [ 25 ] Further studies showed that no precipitation occurred with α-amino groups but did occur with guanidino, ε-amino and imidazole groups. [ 26 ]
Very little work appears to have been carried out in this area. One example relates to liver necrosis in rats. [ 27 ]
The heteropoly acids, including phosphotungstic acid, are being investigated as materials in composite proton exchange membranes , such as Nafion . The interest lies in the potential of these composite materials in the manufacture of fuel cells as they have improved operating characteristics. [ 28 ] | https://en.wikipedia.org/wiki/H3O40PW12 |
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus -containing solid , and inorganic compound with the chemical formula H 3 P O 4 . It is commonly encountered as an 85% aqueous solution , which is a colourless, odourless, and non- volatile syrupy liquid. It is a major industrial chemical, being a component of many fertilizers.
The compound is an acid . Removal of all three H + ions gives the phosphate ion PO 3− 4 . Removal of one or two protons gives dihydrogen phosphate ion H 2 PO − 4 , and the hydrogen phosphate ion HPO 2− 4 , respectively. Phosphoric acid forms esters , called organophosphates . [ 17 ]
The name "orthophosphoric acid" can be used to distinguish this specific acid from other " phosphoric acids ", such as pyrophosphoric acid . Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current IUPAC nomenclature .
Phosphoric acid is produced industrially by one of two routes, wet processes and dry. [ 18 ] [ 19 ] [ 20 ]
In the wet process, a phosphate-containing mineral such as calcium hydroxyapatite and fluorapatite are treated with sulfuric acid . [ 21 ]
Calcium sulfate (gypsum, CaSO 4 ) is a by-product, which is removed as phosphogypsum . The hydrogen fluoride (HF) gas is streamed into a wet (water) scrubber producing hydrofluoric acid . In both cases the phosphoric acid solution usually contains 23–33% P 2 O 5 (32–46% H 3 PO 4 ). It may be concentrated to produce commercial- or merchant-grade phosphoric acid, which contains about 54–62% P 2 O 5 (75–85% H 3 PO 4 ). Further removal of water yields superphosphoric acid with a P 2 O 5 concentration above 70% (corresponding to nearly 100% H 3 PO 4 ). The phosphoric acid from both processes may be further purified by removing compounds of arsenic and other potentially toxic impurities.
To produce food-grade phosphoric acid, phosphate ore is first reduced with coke in an electric arc furnace , to give elemental phosphorus . This process is also known as the thermal process or the electric furnace process. Silica is also added, resulting in the production of calcium silicate slag. Elemental phosphorus is distilled out of the furnace and burned with air to produce high-purity phosphorus pentoxide , which is dissolved in water to make phosphoric acid. [ 22 ] The thermal process produces phosphoric acid with a very high concentration of P 2 O 5 (about 85%) and a low level of impurities.
However, this process is more expensive and energy-intensive than the wet process, which produces phosphoric acid with a lower concentration of P 2 O 5 (about 26–52%) and a higher level of impurities. The wet process is the most common method of producing phosphoric acid for fertilizer use. [ 23 ] Even in China, where the thermal process is still used quite widely due to relatively cheap coal as opposed to the sulfuric acid, over 7/8 of phosphoric acid is produced with wet process. [ 24 ]
Phosphoric acids produced from phosphate rock or thermal processes often requires purification. A common purification methods is liquid–liquid extraction, which involves the separation of phosphoric acids from water and other impurities using organic solvents, such as tributyl phosphate (TBP), methyl isobutyl ketone (MIBK), or n -octanol . Nanofiltration involves the use of a premodified nanofiltration membrane, which is functionalized by a deposit of a high molecular weight polycationic polymer of polyethyleneimines. Nanofiltration has been shown to significantly reduce the concentrations of various impurities, including cadmium, aluminum, iron, and rare earth elements. The laboratory and industrial pilot scale results showed that this process allows the production of food-grade phosphoric acid. [ 25 ]
Fractional crystallization can achieve highest purities typically used for semiconductor applications. Usually a static crystallizer is used. A static crystallizer uses vertical plates, which are suspended in the molten feed and which are alternatingly cooled and heated by a heat transfer medium. The process begins with the slow cooling of the heat transfer medium below the freezing point of the stagnant melt. This cooling causes a layer of crystals to grow on the plates. Impurities are rejected from the growing crystals and are concentrated in the remaining melt. After the desired fraction has been crystallized, the remaining melt is drained from the crystallizer. The purer crystalline layer remains adhered to the plates. In a subsequent step, the plates are heated again to liquify the crystals and the purified phosphoric acid drained into the product vessel. The crystallizer is filled with feed again and the next cooling cycle is started. [ 26 ]
In aqueous solution phosphoric acid behaves as a triprotic acid.
The difference between successive p K a values is sufficiently large so that salts of either monohydrogen phosphate, HPO 2− 4 or dihydrogen phosphate, H 2 PO − 4 , can be prepared from a solution of phosphoric acid by adjusting the pH to be mid-way between the respective p K a values.
Aqueous solutions up to 62.5% H 3 PO 4 are eutectic , exhibiting freezing-point depression as low as −85 °C. When the concentration of acid rises above 62.5% the freezing-point increases, reaching 21 °C by 85% H 3 PO 4 (w/w; the monohydrate ). Beyond this the phase diagram becomes complicated, with significant local maxima and minima. For this reason phosphoric acid is rarely sold above 85%, as beyond this adding or removing small amounts of moisture risks the entire mass freezing solid, which would be a major problem on a large scale. A local maximum at 91.6% which corresponds to the hemihydrate 2H 3 PO 4 •H 2 O, freezing at 29.32 °C. [ 27 ] [ 28 ] There is a second smaller eutectic depression at a concentration of 94.75% with a freezing point of 23.5 °C. At higher concentrations the freezing point rapidly increases. Concentrated phosphoric acid tends to supercool before crystallization occurs, and may be relatively resistant to crystallisation even when stored below the freezing point. [ 13 ]
Phosphoric acid is commercially available as aqueous solutions of various concentrations, not usually exceeding 85%. If concentrated further it undergoes slow self-condensation, forming an equilibrium with pyrophosphoric acid :
Even at 90% concentration the amount of pyrophosphoric acid present is negligible, but beyond 95% it starts to increase, reaching 15% at what would have otherwise been 100% orthophosphoric acid. [ 29 ]
As the concentration is increased higher acids are formed, culminating in the formation of polyphosphoric acids . [ 30 ] It is not possible to fully dehydrate phosphoric acid to phosphorus pentoxide , instead the polyphosphoric acid becomes increasingly polymeric and viscous. Due to the self-condensation, pure orthophosphoric acid can only be obtained by a careful fractional freezing/melting process. [ 13 ] [ 12 ]
The dominant use of phosphoric acid is for fertilizers , consuming approximately 90% of production. [ 31 ]
Food-grade phosphoric acid (additive E338 [ 32 ] ) is used to acidify foods and beverages such as various colas and jams, providing a tangy or sour taste. The phosphoric acid also serves as a preservative . [ 33 ] Soft drinks containing phosphoric acid, which would include Coca-Cola , are sometimes called phosphate sodas or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion. [ 34 ] Phosphoric acid also has the potential to contribute to the formation of kidney stones , especially in those who have had kidney stones previously. [ 35 ]
Specific applications of phosphoric acid include:
Phosphoric acid may also be used for chemical polishing ( etching ) of metals like aluminium or for passivation of steel products in a process called phosphatization . [ 41 ]
Phosphoric acid is not a strong acid . However, at moderate concentrations phosphoric acid solutions are irritating to the skin. Contact with concentrated solutions can cause severe skin burns and permanent eye damage. [ 42 ]
A link has been shown between long-term regular cola intake and osteoporosis in later middle age in women (but not men). [ 43 ] | https://en.wikipedia.org/wiki/H3O4P |
Hydroxy- λ 5 -phosphanone Oxo- λ 5 -phosphanol Oxo- λ 5 -phosphinous acid
1.22 g/cm 3 (50 wt% aq. solution)
Hypophosphorous acid ( HPA ), or phosphinic acid , is a phosphorus oxyacid and a powerful reducing agent with molecular formula H 3 PO 2 . It is a colorless low-melting compound, which is soluble in water, dioxane and alcohols. The formula for this acid is generally written H 3 PO 2 , but a more descriptive presentation is HOP(O)H 2 , which highlights its monoprotic character. Salts derived from this acid are called hypophosphites . [ 3 ]
HOP(O)H 2 exists in equilibrium with the minor tautomer HP(OH) 2 . Sometimes the minor tautomer is called hypophosphorous acid and the major tautomer is called phosphinic acid.
Hypophosphorous acid was first prepared in 1816 by the French chemist Pierre Louis Dulong (1785–1838). [ 4 ]
The acid is prepared industrially via a two step process: Firstly, elemental white phosphorus reacts with alkali and alkaline earth hydroxides to give an aqueous solution of hypophosphites:
Any phosphites produced in this step can be selectively precipitated out by treatment with calcium salts. The purified material is then treated with a strong, non-oxidizing acid (often sulfuric acid ) to give the free hypophosphorous acid:
HPA is usually supplied as a 50% aqueous solution. Anhydrous acid cannot be obtained by simple evaporation of the water, as the acid readily oxidises to phosphorous acid and phosphoric acid and also disproportionates to phosphorous acid and phosphine . Pure anhydrous hypophosphorous acid can be formed by the continuous extraction of aqueous solutions with diethyl ether . [ 5 ]
The molecule displays P(═O)H to P–OH tautomerism similar to that of phosphorous acid ; the P(═O) form is strongly favoured. [ 6 ]
HPA is usually supplied as a 50% aqueous solution and heating at low temperatures (up to about 90 °C) prompts it to react with water to form phosphorous acid and hydrogen gas.
Heating above 110 °C causes hypophosphorous acid to undergo disproportionation to give phosphorous acid and phosphine . [ 7 ]
Hypophosphorous acid can reduce chromium(III) oxide to chromium(II) oxide :
Most metal-hypophosphite complexes are unstable, owing to the tendency of hypophosphites to reduce metal cations back into the bulk metal. Some examples have been characterised, [ 8 ] [ 9 ] including the important nickel salt [Ni(H 2 O) 6 ](H 2 PO 2 ) 2 . [ 10 ]
Because hypophosphorous acid can reduce elemental iodine to form hydroiodic acid , which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine , [ 11 ] the United States Drug Enforcement Administration designated hypophosphorous acid (and its salts) as a List I precursor chemical effective November 16, 2001. [ 12 ] Accordingly, handlers of hypophosphorous acid or its salts in the United States are subject to stringent regulatory controls including registration, recordkeeping, reporting, and import/export requirements pursuant to the Controlled Substances Act and 21 CFR §§ 1309 and 1310. [ 12 ] [ 13 ] [ 14 ]
In organic chemistry, H 3 PO 2 can be used for the reduction of arenediazonium salts , converting Ar− + N≡N to Ar−H . [ 15 ] [ 16 ] [ 17 ] When diazotized in a concentrated solution of hypophosphorous acid, an amine substituent can be removed from arenes.
Owing to its ability to function as a mild reducing agent and oxygen scavenger it is sometimes used as an additive in Fischer esterification reactions, where it prevents the formation of colored impurities.
It is used to prepare phosphinic acid derivatives. [ 18 ]
Hypophosphorous acid (and its salts) are used to reduce metal salts back into bulk metals. It is effective for various transition metals ions (i.e. those of: Co, Cu, Ag, Mn, Pt) but is most commonly used to reduce nickel . [ 19 ] This forms the basis of electroless nickel plating (Ni–P), which is the single largest industrial application of hypophosphites. For this application it is principally used as a salt ( sodium hypophosphite ). [ 20 ]
[ 1 ] | https://en.wikipedia.org/wiki/H3PO2 |
Dihydroxy(oxo)- λ 5 -phosphane Dihydroxy- λ 5 -phosphanone Orthophosphorous acid Oxo- λ 5 -phosphanediol Oxo- λ 5 -phosphonous acid
Phosphorous acid (or phosphonic acid ) is the compound described by the formula H 3 PO 3 . It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO 3 H 2 , are called phosphonic acids .
Solid HP(O)(OH) 2 has tetrahedral geometry about the central phosphorus atom, with a P−H bond of 132 pm , one P=O double bond of 148 pm and two longer P−OH single bonds of 154 pm. In common with other phosphorus oxides with P−H bonds (e.g. hypophosphorous acid and dialkyl phosphites ), [ 2 ] it exists in equilibrium with an extremely minor tautomer P(OH) 3 . (In contrast, arsenous acid 's major tautomer is the trihydroxy form.) IUPAC recommends that the trihydroxy form P(OH) 3 be called phosphorous acid, and the dihydroxy form HP(O)(OH) 2 phosphonic acid. [ 3 ] Only the reduced phosphorus compounds are spelled with an " -ous " ending.
On an industrial scale, the acid is prepared by hydrolysis of phosphorus trichloride with water or steam: [ 5 ]
HPO(OH) 2 could be produced by the hydrolysis of phosphorus trioxide :
Phosphorous acid has a p K a in the range 1.26–1.3. [ 6 ] [ 7 ]
It is a diprotic acid , the hydrogenphosphite ion, HP(O) 2 (OH) − is a weak acid:
The conjugate base HP(O) 2 (OH) − is called hydrogen phosphite, and the second conjugate base, HPO 2− 3 , is the phosphite ion. [ 8 ] (Note that the IUPAC recommendations are hydrogen phosphonate and phosphonate respectively).
The hydrogen atom bonded directly to the phosphorus atom is not readily ionizable. Chemistry examinations often test students' appreciation of the fact that not all three hydrogen atoms are acidic under aqueous conditions, in contrast with H 3 PO 4 .
On heating at 200 °C, phosphorous acid disproportionates to phosphoric acid and phosphine : [ 9 ]
This reaction is used for laboratory-scale preparations of PH 3 .
Phosphorous acid slowly oxidizes in air to phosphoric acid. [ 5 ]
Both phosphorous acid and its deprotonated forms are good reducing agents , although not necessarily quick to react. They are oxidized to phosphoric acid or its salts. It reduces solutions of noble metal cations to the metals. When phosphorous acid is treated with a cold solution of mercuric chloride , a white precipitate of mercurous chloride forms:
Mercurous chloride is reduced further by phosphorous acid to mercury on heating or on standing:
Upon treatment with metals of d 6 configuration, phosphorous acid is known to coordinate as the otherwise rare P(OH) 3 tautomer. Examples include Mo(CO) 5 (P(OH) 3 ) and [Ru(NH 3 ) 4 (H 2 O)(P(OH) 3 )] 2+ . [ 10 ] [ 11 ]
Heating a mixture of potassium tetrachloroplatinate and phosphorous acid gives the luminescent salt potassium diplatinum(II) tetrakispyrophosphite : [ 12 ]
The most important use of phosphorous acid (phosphonic acid) is the production of basic lead phosphite , which is a stabilizer in PVC and related chlorinated polymers. [ 5 ]
It is used in the production of basic lead phosphonate PVC stabilizer, aminomethylene phosphonic acid and hydroxyethane diphosphonic acid.
It is also used as a strong reducing agent and in the production of synthetic fibres, organophosphorus pesticides, and the highly efficient water treatment agent ATMP .
Ferrous materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using phosphoric acid and further protected by surface coating. (See: Passivation (chemistry) ).
The IUPAC (mostly organic) name is phosphonic acid . This nomenclature is commonly reserved for substituted derivatives, that is, organic group bonded to phosphorus, not simply an ester. For example, (CH 3 )PO(OH) 2 is " methylphosphonic acid ", which may of course form "methyl phosphonate " esters . | https://en.wikipedia.org/wiki/H3PO3 |
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus -containing solid , and inorganic compound with the chemical formula H 3 P O 4 . It is commonly encountered as an 85% aqueous solution , which is a colourless, odourless, and non- volatile syrupy liquid. It is a major industrial chemical, being a component of many fertilizers.
The compound is an acid . Removal of all three H + ions gives the phosphate ion PO 3− 4 . Removal of one or two protons gives dihydrogen phosphate ion H 2 PO − 4 , and the hydrogen phosphate ion HPO 2− 4 , respectively. Phosphoric acid forms esters , called organophosphates . [ 17 ]
The name "orthophosphoric acid" can be used to distinguish this specific acid from other " phosphoric acids ", such as pyrophosphoric acid . Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current IUPAC nomenclature .
Phosphoric acid is produced industrially by one of two routes, wet processes and dry. [ 18 ] [ 19 ] [ 20 ]
In the wet process, a phosphate-containing mineral such as calcium hydroxyapatite and fluorapatite are treated with sulfuric acid . [ 21 ]
Calcium sulfate (gypsum, CaSO 4 ) is a by-product, which is removed as phosphogypsum . The hydrogen fluoride (HF) gas is streamed into a wet (water) scrubber producing hydrofluoric acid . In both cases the phosphoric acid solution usually contains 23–33% P 2 O 5 (32–46% H 3 PO 4 ). It may be concentrated to produce commercial- or merchant-grade phosphoric acid, which contains about 54–62% P 2 O 5 (75–85% H 3 PO 4 ). Further removal of water yields superphosphoric acid with a P 2 O 5 concentration above 70% (corresponding to nearly 100% H 3 PO 4 ). The phosphoric acid from both processes may be further purified by removing compounds of arsenic and other potentially toxic impurities.
To produce food-grade phosphoric acid, phosphate ore is first reduced with coke in an electric arc furnace , to give elemental phosphorus . This process is also known as the thermal process or the electric furnace process. Silica is also added, resulting in the production of calcium silicate slag. Elemental phosphorus is distilled out of the furnace and burned with air to produce high-purity phosphorus pentoxide , which is dissolved in water to make phosphoric acid. [ 22 ] The thermal process produces phosphoric acid with a very high concentration of P 2 O 5 (about 85%) and a low level of impurities.
However, this process is more expensive and energy-intensive than the wet process, which produces phosphoric acid with a lower concentration of P 2 O 5 (about 26–52%) and a higher level of impurities. The wet process is the most common method of producing phosphoric acid for fertilizer use. [ 23 ] Even in China, where the thermal process is still used quite widely due to relatively cheap coal as opposed to the sulfuric acid, over 7/8 of phosphoric acid is produced with wet process. [ 24 ]
Phosphoric acids produced from phosphate rock or thermal processes often requires purification. A common purification methods is liquid–liquid extraction, which involves the separation of phosphoric acids from water and other impurities using organic solvents, such as tributyl phosphate (TBP), methyl isobutyl ketone (MIBK), or n -octanol . Nanofiltration involves the use of a premodified nanofiltration membrane, which is functionalized by a deposit of a high molecular weight polycationic polymer of polyethyleneimines. Nanofiltration has been shown to significantly reduce the concentrations of various impurities, including cadmium, aluminum, iron, and rare earth elements. The laboratory and industrial pilot scale results showed that this process allows the production of food-grade phosphoric acid. [ 25 ]
Fractional crystallization can achieve highest purities typically used for semiconductor applications. Usually a static crystallizer is used. A static crystallizer uses vertical plates, which are suspended in the molten feed and which are alternatingly cooled and heated by a heat transfer medium. The process begins with the slow cooling of the heat transfer medium below the freezing point of the stagnant melt. This cooling causes a layer of crystals to grow on the plates. Impurities are rejected from the growing crystals and are concentrated in the remaining melt. After the desired fraction has been crystallized, the remaining melt is drained from the crystallizer. The purer crystalline layer remains adhered to the plates. In a subsequent step, the plates are heated again to liquify the crystals and the purified phosphoric acid drained into the product vessel. The crystallizer is filled with feed again and the next cooling cycle is started. [ 26 ]
In aqueous solution phosphoric acid behaves as a triprotic acid.
The difference between successive p K a values is sufficiently large so that salts of either monohydrogen phosphate, HPO 2− 4 or dihydrogen phosphate, H 2 PO − 4 , can be prepared from a solution of phosphoric acid by adjusting the pH to be mid-way between the respective p K a values.
Aqueous solutions up to 62.5% H 3 PO 4 are eutectic , exhibiting freezing-point depression as low as −85 °C. When the concentration of acid rises above 62.5% the freezing-point increases, reaching 21 °C by 85% H 3 PO 4 (w/w; the monohydrate ). Beyond this the phase diagram becomes complicated, with significant local maxima and minima. For this reason phosphoric acid is rarely sold above 85%, as beyond this adding or removing small amounts of moisture risks the entire mass freezing solid, which would be a major problem on a large scale. A local maximum at 91.6% which corresponds to the hemihydrate 2H 3 PO 4 •H 2 O, freezing at 29.32 °C. [ 27 ] [ 28 ] There is a second smaller eutectic depression at a concentration of 94.75% with a freezing point of 23.5 °C. At higher concentrations the freezing point rapidly increases. Concentrated phosphoric acid tends to supercool before crystallization occurs, and may be relatively resistant to crystallisation even when stored below the freezing point. [ 13 ]
Phosphoric acid is commercially available as aqueous solutions of various concentrations, not usually exceeding 85%. If concentrated further it undergoes slow self-condensation, forming an equilibrium with pyrophosphoric acid :
Even at 90% concentration the amount of pyrophosphoric acid present is negligible, but beyond 95% it starts to increase, reaching 15% at what would have otherwise been 100% orthophosphoric acid. [ 29 ]
As the concentration is increased higher acids are formed, culminating in the formation of polyphosphoric acids . [ 30 ] It is not possible to fully dehydrate phosphoric acid to phosphorus pentoxide , instead the polyphosphoric acid becomes increasingly polymeric and viscous. Due to the self-condensation, pure orthophosphoric acid can only be obtained by a careful fractional freezing/melting process. [ 13 ] [ 12 ]
The dominant use of phosphoric acid is for fertilizers , consuming approximately 90% of production. [ 31 ]
Food-grade phosphoric acid (additive E338 [ 32 ] ) is used to acidify foods and beverages such as various colas and jams, providing a tangy or sour taste. The phosphoric acid also serves as a preservative . [ 33 ] Soft drinks containing phosphoric acid, which would include Coca-Cola , are sometimes called phosphate sodas or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion. [ 34 ] Phosphoric acid also has the potential to contribute to the formation of kidney stones , especially in those who have had kidney stones previously. [ 35 ]
Specific applications of phosphoric acid include:
Phosphoric acid may also be used for chemical polishing ( etching ) of metals like aluminium or for passivation of steel products in a process called phosphatization . [ 41 ]
Phosphoric acid is not a strong acid . However, at moderate concentrations phosphoric acid solutions are irritating to the skin. Contact with concentrated solutions can cause severe skin burns and permanent eye damage. [ 42 ]
A link has been shown between long-term regular cola intake and osteoporosis in later middle age in women (but not men). [ 43 ] | https://en.wikipedia.org/wiki/H3PO4 |
Phosphotungstic acid ( PTA ) or tungstophosphoric acid ( TPA ), is a heteropoly acid with the chemical formula H 3 P W 12 O 40 ] . It forms hydrates H 3 [PW 12 O 40 ]· n H 2 O . It is normally isolated as the n = 24 hydrate but can be desiccated to the hexahydrate ( n = 6). [ 2 ] EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 H 2 O hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of names and acronyms (see 'other names' section of infobox).
In these names the "12" or "dodeca" reflects the fact that the anion contains 12 tungsten atoms. Some early workers who did not know the structure [ 3 ] called it phospho-24-tungstic acid, formulating it as 3H 2 O·P 2 O 5 24WO 3 ·59H 2 O, (P 2 W 24 O 80 H 6 )·29H 2 O , which correctly identifies the atomic ratios of P, W and O. This formula was still quoted in papers as late as 1970. [ 4 ]
Phosphotungstic acid is used in histology as a component for staining of cell specimens, often together with haematoxylin as PTAH . It binds to fibrin , collagen , and fibres of connective tissues , and replaces the anions of dyes from these materials, selectively decoloring them.
Phosphotungstic acid is electron dense, opaque for electrons . It is a common negative stain for viruses , nerves , polysaccharides , and other biological tissue materials for imaging by a transmission electron microscope .
Gouzerh [ 5 ] summarises the historical views on the structure of phosphotungstic acid leading up to Keggin's determination of the structure as:
The structure was determined by J.F Keggin first published in 1933 [ 6 ] and then in 1934 [ 7 ] and is generally known as the Keggin structure . The anion has full tetrahedral symmetry and comprises a cage of twelve tungsten atoms linked by oxygen atoms with the phosphorus atom at its centre. The picture on the right shows the octahedral coordination of oxygen atoms around the tungsten atoms, and that the surface of the anion has both bridging and terminal oxygen atoms. Further investigation showed that the compound was a hexahydrate not a pentahydrate as Keggin had proposed. [ 8 ]
Phosphotungstic acid can be prepared by the reaction of sodium tungstate dihydrate, Na 2 WO 4 ·2H 2 O , with phosphoric acid , H 3 PO 4 , acidified with hydrochloric acid , HCl. [ 9 ] This procedure has been updated. [ 2 ]
Phosphotungstic acid solutions decompose as the pH is increased. A step-wise decomposition has been determined and the approximate compositions at various pH values are as follows: [ 10 ]
The species [PW 11 O 39 ] 7− is a lacunary, or defective Keggin ion. The [P 2 W 18 O 62 ] 6− has a Dawson structure . At pH less than 8, the presence of ethanol or acetone stabilises the anion, [PW 12 O 40 ] 3− , reducing decomposition. [ 10 ]
Tungstophosphoric acid is thermally stable up to 400 °C, and is more stable than the analogous silicotungstic acid , H 4 [SiW 12 O 40 ] . [ 11 ]
Large quantities of polar molecules such as pyridine are absorbed into the bulk phase and not simply adsorbed onto the surface. Solid state NMR studies of ethanol absorbed in the bulk phase show that both protonated dimers, (C 2 H 5 OH) 2 H + , and monomers, C 2 H 5 OH + 2 , are present.
Phosphotungstic acid is less sensitive to reduction than phosphomolybdic acid. Reduction with uric acid or iron(II) sulfate produces a brown coloured compound. the related silicotungstic acid when reduced forms a similar brown compound where one of the four W 3 units in the Keggin structure becomes a metal-metal bonded cluster of three edge shared W IV octahedra. [ 12 ]
Phosphotungstic acid is the strongest of heteropolyacids . Its conjugate base is the [PW 12 O 40 ] 3− anion. [ 13 ] Its acidity in acetic acid has been investigated and shows that the three protons dissociate independently rather than sequentially, and the acid sites are of the same strength. [ 14 ] One estimate of the acidity is that the solid has an acidity stronger than H 0 = −13.16, [ 11 ] which would qualify the compound as a superacid . This acidic strength means that even at low pH the acid is fully dissociated.
In common with the other heteropolyacids phosphotungstic acid is a catalyst and its high acidity and thermal stability make it a catalyst of choice according to some researchers. [ 15 ] It is in solution as a homogeneous catalyst , and as a heterogeneous catalyst "supported" on a substrate e.g. alumina , silica . Some acid catalysed reactions include:
Phosphotungstic acid has been used to precipitate different types of dyes as " lakes ". [ 16 ] Examples are basic dyes and triphenylmethane dyes, e.g. pararosaniline derivatives. [ 17 ]
Phosphotungstic acid is used in histology for staining specimens, as a component of phosphotungstic acid haematoxylin, PTAH , and “trichrome” reagents, and as a negative stain for imaging by a transmission electron microscope . [ citation needed ]
The potassium salt is only slightly soluble, unlike most other phosphotungstate salts, and has been proposed as a method for the gravimetric analysis of potassium. [ 24 ]
In a number of analytical procedures one of the roles of phosphotungstic acid is to precipitate out proteins. It has been termed a "universal" precipitant for polar proteins. [ 25 ] Further studies showed that no precipitation occurred with α-amino groups but did occur with guanidino, ε-amino and imidazole groups. [ 26 ]
Very little work appears to have been carried out in this area. One example relates to liver necrosis in rats. [ 27 ]
The heteropoly acids, including phosphotungstic acid, are being investigated as materials in composite proton exchange membranes , such as Nafion . The interest lies in the potential of these composite materials in the manufacture of fuel cells as they have improved operating characteristics. [ 28 ] | https://en.wikipedia.org/wiki/H3PW12O40 |
H3 is a pyrotechnic composition which is used mostly as a burst charge for small diameter shells. It is friction and shock sensitive, as are most compositions containing chlorates. For this reason, H3 should be mixed using the "diaper method" and not with a ball mill. The composition consists of:
Due to the potassium chlorate, H3 should not be mixed with sulfur or compositions containing sulfur, as sulfur increases the sensitivity of the mixture.
This pyrotechnics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/H3_(pyrotechnics) |
Methane ( US : / ˈ m ɛ θ eɪ n / METH -ayn , UK : / ˈ m iː θ eɪ n / MEE -thayn ) is a chemical compound with the chemical formula CH 4 (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride , the simplest alkane , and the main constituent of natural gas . The abundance of methane on Earth makes it an economically attractive fuel , although capturing and storing it is difficult because it is a gas at standard temperature and pressure . In the Earth's atmosphere methane is transparent to visible light but absorbs infrared radiation , acting as a greenhouse gas . Methane is an organic compound , and among the simplest of organic compounds. Methane is also a hydrocarbon .
Naturally occurring methane is found both below ground and under the seafloor and is formed by both geological and biological processes. The largest reservoir of methane is under the seafloor in the form of methane clathrates . When methane reaches the surface and the atmosphere , it is known as atmospheric methane . [ 10 ]
The Earth's atmospheric methane concentration has increased by about 160% since 1750, with the overwhelming percentage caused by human activity. [ 11 ] It accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases , according to the 2021 Intergovernmental Panel on Climate Change report. [ 12 ] Strong, rapid and sustained reductions in methane emissions could limit near-term warming and improve air quality by reducing global surface ozone. [ 13 ]
Methane has also been detected on other planets, including Mars , which has implications for astrobiology research. [ 14 ]
Methane is a tetrahedral molecule with four equivalent C–H bonds . Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H . The lowest-energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements.
Methane is an odorless, colourless and transparent gas at standard temperature and pressure . [ 15 ] It does absorb visible light, especially at the red end of the spectrum, due to overtone bands , but the effect is only noticeable if the light path is very long. This is what gives Uranus and Neptune their blue or bluish-green colors, as light passes through their atmospheres containing methane and is then scattered back out. [ 16 ]
The familiar smell of natural gas as used in homes is achieved by the addition of an odorant , usually blends containing tert -butylthiol , as a safety measure. Methane has a boiling point of −161.5 °C at a pressure of one atmosphere . [ 3 ] As a gas, it is flammable over a range of concentrations (5.4%–17%) in air at standard pressure .
Solid methane exists in several modifications , of which nine are known. [ 17 ] Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system ( space group Fm 3 m). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it is a plastic crystal . [ 18 ]
The primary chemical reactions of methane are combustion , steam reforming to syngas , and halogenation . In general, methane reactions are difficult to control.
Partial oxidation of methane to methanol ( C H 3 O H ), a more convenient, liquid fuel, is challenging because the reaction typically progresses all the way to carbon dioxide and water even with an insufficient supply of oxygen . The enzyme methane monooxygenase produces methanol from methane, but cannot be used for industrial-scale reactions. [ 19 ] Some homogeneously catalyzed systems and heterogeneous systems have been developed, but all have significant drawbacks. These generally operate by generating protected products which are shielded from overoxidation. Examples include the Catalytica system , copper zeolites , and iron zeolites stabilizing the alpha-oxygen active site. [ 20 ]
One group of bacteria catalyze methane oxidation with nitrite as the oxidant in the absence of oxygen , giving rise to the so-called anaerobic oxidation of methane . [ 21 ]
Like other hydrocarbons , methane is an extremely weak acid . Its p K a in DMSO is estimated to be 56. [ 22 ] It cannot be deprotonated in solution, but the conjugate base is known in forms such as methyllithium .
A variety of positive ions derived from methane have been observed, mostly as unstable species in low-pressure gas mixtures. These include methenium or methyl cation CH + 3 , methane cation CH + 4 , and methanium or protonated methane CH + 5 . Some of these have been detected in outer space . Methanium can also be produced as diluted solutions from methane with superacids . Cations with higher charge, such as CH 2+ 6 and CH 3+ 7 , have been studied theoretically and conjectured to be stable. [ 23 ]
Despite the strength of its C–H bonds, there is intense interest in catalysts that facilitate C–H bond activation in methane (and other lower numbered alkanes ). [ 24 ]
Methane's heat of combustion is 55.5 MJ/kg. [ 25 ] Combustion of methane is a multiple step reaction summarized as follows:
Peters four-step chemistry is a systematically reduced four-step chemistry that explains the burning of methane.
Given appropriate conditions, methane reacts with halogen radicals as follows:
where X is a halogen : fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). This mechanism for this process is called free radical halogenation . It is initiated when UV light or some other radical initiator (like peroxides ) produces a halogen atom . A two-step chain reaction ensues in which the halogen atom abstracts a hydrogen atom from a methane molecule, resulting in the formation of a hydrogen halide molecule and a methyl radical ( •CH 3 ). The methyl radical then reacts with a molecule of the halogen to form a molecule of the halomethane, with a new halogen atom as byproduct. [ 26 ] Similar reactions can occur on the halogenated product, leading to replacement of additional hydrogen atoms by halogen atoms with dihalomethane , trihalomethane , and ultimately, tetrahalomethane structures, depending upon reaction conditions and the halogen-to-methane ratio.
This reaction is commonly used with chlorine to produce dichloromethane and chloroform via chloromethane . Carbon tetrachloride can be made with excess chlorine.
Methane may be transported as a refrigerated liquid (liquefied natural gas, or LNG ). While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of the cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component.
Methane is used as a fuel for ovens, homes, water heaters, kilns, automobiles, [ 27 ] [ 28 ] turbines, etc.
As the major constituent of natural gas , methane is important for electricity generation by burning it as a fuel in a gas turbine or steam generator . Compared to other hydrocarbon fuels , methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than that of any other hydrocarbon, but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) than other complex hydrocarbons. In many areas with a dense enough population, methane is piped into homes and businesses for heating , cooking, and industrial uses. In this context it is usually known as natural gas , which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot . Liquefied natural gas (LNG) is predominantly methane ( CH 4 ) converted into liquid form for ease of storage or transport.
Refined liquid methane as well as LNG is used as a rocket fuel , [ 29 ] when combined with liquid oxygen , as in the TQ-12 , BE-4 , Raptor , YF-215 , and Aeon engines. [ 30 ] Due to the similarities between methane and LNG such engines are commonly grouped together under the term methalox .
As a liquid rocket propellant , a methane/ liquid oxygen combination offers the advantage over kerosene / liquid oxygen combination, or kerolox, of producing small exhaust molecules, reducing coking or deposition of soot on engine components. Methane is easier to store than hydrogen due to its higher boiling point and density, as well as its lack of hydrogen embrittlement . [ 31 ] [ 32 ] The lower molecular weight of the exhaust also increases the fraction of the heat energy which is in the form of kinetic energy available for propulsion, increasing the specific impulse of the rocket. Compared to liquid hydrogen , the specific energy of methane is lower but this disadvantage is offset by methane's greater density and temperature range, allowing for smaller and lighter tankage for a given fuel mass. Liquid methane has a temperature range (91–112 K) nearly compatible with liquid oxygen (54–90 K). The fuel currently sees use in operational launch vehicles such as Zhuque-2 , Vulcan and New Glenn as well as in-development launchers such as Starship , Neutron , Terran R , Nova , and Long March 9 . [ 33 ]
Natural gas , which is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. Steam methane reforming (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50 million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas. [ 34 ] Much of this hydrogen is used in petroleum refineries , in the production of chemicals and in food processing. Very large quantities of hydrogen are used in the industrial synthesis of ammonia .
At high temperatures (700–1100 °C) and in the presence of a metal -based catalyst ( nickel ), steam reacts with methane to yield a mixture of CO and H 2 , known as "water gas" or " syngas ":
This reaction is strongly endothermic (consumes heat, Δ H r = 206 kJ/mol).
Additional hydrogen is obtained by the reaction of CO with water via the water-gas shift reaction :
This reaction is mildly exothermic (produces heat, Δ H r = −41 kJ/mol).
Methane is also subjected to free-radical chlorination in the production of chloromethanes, although methanol is a more typical precursor. [ 35 ]
Hydrogen can also be produced via the direct decomposition of methane, also known as methane pyrolysis , which, unlike steam reforming, produces no greenhouse gases (GHG). The heat needed for the reaction can also be GHG emission free, e.g. from concentrated sunlight, renewable electricity, or burning some of the produced hydrogen. If the methane is from biogas then the process can be a carbon sink . Temperatures in excess of 1200 °C are required to break the bonds of methane to produce hydrogen gas and solid carbon. [ 36 ]
However, through the use of a suitable catalyst the reaction temperature can be reduced to between 550 and 900 °C depending on the chosen catalyst. Dozens of catalysts have been tested, including unsupported and supported metal catalysts, carbonaceous and metal-carbon catalysts. [ 37 ]
The reaction is moderately endothermic as shown in the reaction equation below. [ 38 ]
As a refrigerant , methane has the ASHRAE designation R-50 .
Methane can be generated through geological, biological or industrial routes.
The two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic ( abiotic ). [ 14 ] Thermogenic methane occurs due to the breakup of organic matter at elevated temperatures and pressures in deep sedimentary strata . Most methane in sedimentary basins is thermogenic; therefore, thermogenic methane is the most important source of natural gas. Thermogenic methane components are typically considered to be relic (from an earlier time). Generally, formation of thermogenic methane (at depth) can occur through organic matter breakup, or organic synthesis. Both ways can involve microorganisms ( methanogenesis ), but may also occur inorganically. The processes involved can also consume methane, with and without microorganisms.
The more important source of methane at depth (crystalline bedrock) is abiotic. Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes [ example needed ] or via water-rock reactions that occur at low temperatures and pressures, like serpentinization . [ 39 ] [ 40 ]
Most of Earth's methane is biogenic and is produced by methanogenesis , [ 41 ] [ 42 ] a form of anaerobic respiration only known to be conducted by some members of the domain Archaea . [ 43 ] Methanogens occur in landfills and soils , [ 44 ] ruminants (for example, cattle ), [ 45 ] the guts of termites, and the anoxic sediments below the seafloor and the bottom of lakes.
This multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is:
The final step in the process is catalyzed by the enzyme methyl coenzyme M reductase (MCR). [ 46 ]
Wetlands are the largest natural sources of methane to the atmosphere, [ 47 ] accounting for approximately 20 – 30% of atmospheric methane. [ 48 ] Climate change is increasing the amount of methane released from wetlands due to increased temperatures and altered rainfall patterns. This phenomenon is called wetland methane feedback . [ 49 ]
Rice cultivation generates as much as 12% of total global methane emissions due to the long-term flooding of rice fields. [ 50 ]
Ruminants such as cattle belch out methane, accounting for about 22% of the U.S. annual methane emissions to the atmosphere. [ 51 ] One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane. [ 52 ] A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions. [ 53 ] Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments, [ 54 ] [ 55 ] and to trap the gas to use its combustion energy. [ 56 ]
Most of the subseafloor is anoxic because oxygen is removed by aerobic microorganisms within the first few centimeters of the sediment . Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in gas hydrates . [ 43 ] These other organisms that utilize methane for energy are known as methanotrophs ('methane-eating'), and are the main reason why little methane generated at depth reaches the sea surface. [ 43 ] Consortia of Archaea and Bacteria have been found to oxidize methane via anaerobic oxidation of methane (AOM); the organisms responsible for this are anaerobic methanotrophic Archaea (ANME) and sulfate-reducing bacteria (SRB). [ 57 ]
Given its cheap abundance in natural gas, there is little incentive to produce methane industrially. Methane can be produced by hydrogenating carbon dioxide through the Sabatier process . Methane is also a side product of the hydrogenation of carbon monoxide in the Fischer–Tropsch process , which is practiced on a large scale to produce longer-chain molecules than methane.
An example of large-scale coal-to-methane gasification is the Great Plains Synfuels plant, started in 1984 in Beulah, North Dakota as a way to develop abundant local resources of low-grade lignite , a resource that is otherwise difficult to transport for its weight, ash content, low calorific value and propensity to spontaneous combustion during storage and transport. A number of similar plants exist around the world, although mostly these plants are targeted towards the production of long chain alkanes for use as gasoline , diesel , or feedstock to other processes.
Power to methane is a technology that uses electrical power to produce hydrogen from water by electrolysis and uses the Sabatier reaction to combine hydrogen with carbon dioxide to produce methane.
Methane can be produced by protonation of methyl lithium or a methyl Grignard reagent such as methylmagnesium chloride . It can also be made from anhydrous sodium acetate and dry sodium hydroxide , mixed and heated above 300 °C (with sodium carbonate as byproduct). [ citation needed ] In practice, a requirement for pure methane can easily be fulfilled by steel gas bottle from standard gas suppliers.
Methane is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields , with coal seam gas extraction becoming a major source (see coal bed methane extraction , a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other hydrocarbon fuels, and sometimes accompanied by helium and nitrogen . Methane is produced at shallow levels (low pressure) by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain oil .
Methane is generally transported in bulk by pipeline in its natural gas form, or by LNG carriers in its liquefied form; few countries transport it by truck.
Methane is an important greenhouse gas , responsible for around 30% of the rise in global temperatures since the industrial revolution. [ 58 ]
Methane has a global warming potential (GWP) of 29.8 ± 11 compared to CO 2 (potential of 1) over a 100-year period, and 82.5 ± 25.8 over a 20-year period. [ 59 ] This means that, for example, a leak of one tonne of methane is equivalent to emitting 82.5 tonnes of carbon dioxide. Burning methane and producing carbon dioxide also reduces the greenhouse gas impact compared to simply venting methane to the atmosphere.
As methane is gradually converted into carbon dioxide (and water) in the atmosphere, these values include the climate forcing from the carbon dioxide produced from methane over these timescales.
Annual global methane emissions are currently approximately 580 Mt, [ 60 ] 40% of which is from natural sources and the remaining 60% originating from human activity, known as anthropogenic emissions. The largest anthropogenic source is agriculture , responsible for around one quarter of emissions, closely followed by the energy sector , which includes emissions from coal, oil, natural gas and biofuels. [ 61 ]
Historic methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages , and between 600 and 700 nmol/mol during the warm interglacial periods. A 2012 NASA website said the oceans were a potential important source of Arctic methane, [ 62 ] but more recent studies associate increasing methane levels as caused by human activity. [ 11 ]
Global monitoring of atmospheric methane concentrations began in the 1980s. [ 11 ] The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century. [ 11 ] In 2013, atmospheric methane accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. [ 63 ] Between 2011 and 2019 the annual average increase of methane in the atmosphere was 1866 ppb. [ 12 ] From 2015 to 2019 sharp rises in levels of atmospheric methane were recorded. [ 64 ] [ 65 ]
In 2019, the atmospheric methane concentration was higher than at any time in the last 800,000 years. As stated in the AR6 of the IPCC , "Since 1750, increases in CO 2 (47%) and CH 4 (156%) concentrations far exceed, and increases in N 2 O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence)". [ 12 ] [ a ] [ 66 ]
In February 2020, it was reported that fugitive emissions and gas venting from the fossil fuel industry may have been significantly underestimated. [ 67 ] [ 68 ] The largest annual increase occurred in 2021 with the overwhelming percentage caused by human activity. [ 11 ]
Climate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a climate change feedback . [ 43 ] [ 69 ] Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere. [ 70 ]
Over 100 countries have signed the Global Methane Pledge , launched in 2021, promising to cut their methane emissions by 30% by 2030. [ 71 ] This could avoid 0.2 °C of warming globally by 2050, although there have been calls for higher commitments in order to reach this target. [ 72 ] The International Energy Agency 's 2022 report states "the most cost-effective opportunities for methane abatement are in the energy sector, especially in oil and gas operations". [ 73 ]
Methane clathrates (also known as methane hydrates) are solid cages of water molecules that trap single molecules of methane. Significant reservoirs of methane clathrates have been found in arctic permafrost and along continental margins beneath the ocean floor within the gas clathrate stability zone , located at high pressures (1 to 100 MPa; lower end requires lower temperature) and low temperatures (< 15 °C; upper end requires higher pressure). [ 74 ] Methane clathrates can form from biogenic methane, thermogenic methane, or a mix of the two. These deposits are both a potential source of methane fuel as well as a potential contributor to global warming. [ 75 ] [ 76 ] The global mass of carbon stored in gas clathrates is still uncertain and has been estimated as high as 12,500 Gt carbon and as low as 500 Gt carbon. [ 49 ] The estimate has declined over time with a most recent estimate of ≈1800 Gt carbon. [ 77 ] A large part of this uncertainty is due to our knowledge gap in sources and sinks of methane and the distribution of methane clathrates at the global scale. For example, a source of methane was discovered relatively recently in an ultraslow spreading ridge in the Arctic. [ 48 ] Some climate models suggest that today's methane emission regime from the ocean floor is potentially similar to that during the period of the Paleocene–Eocene Thermal Maximum ( PETM ) around 55.5 million years ago, although there are no data indicating that methane from clathrate dissociation currently reaches the atmosphere. [ 77 ] Arctic methane release from permafrost and seafloor methane clathrates is a potential consequence and further cause of global warming ; this is known as the clathrate gun hypothesis . [ 78 ] [ 79 ] [ 80 ] [ 81 ] Data from 2016 indicate that Arctic permafrost thaws faster than predicted. [ 82 ]
Methane "degrades air quality and adversely impacts human health, agricultural yields, and ecosystem productivity". [ 83 ]
Methane is extremely flammable and may form explosive mixtures with air. Methane gas explosions are responsible for many deadly mining disasters. [ 84 ] A methane gas explosion was the cause of the Upper Big Branch coal mine disaster in West Virginia on April 5, 2010, killing 29. [ 85 ] Natural gas accidental release has also been a major focus in the field of safety engineering , due to past accidental releases that concluded in the formation of jet fire disasters. [ 86 ] [ 87 ]
The 2015–2016 methane gas leak in Aliso Canyon, California was considered to be the worst in terms of its environmental effect in American history. [ 88 ] [ 89 ] [ 90 ] It was also described as more damaging to the environment than Deepwater Horizon 's leak in the Gulf of Mexico. [ 91 ]
In May 2023 The Guardian published a report blaming Turkmenistan as the worst in the world for methane super emitting . The data collected by Kayrros researchers indicate that two large Turkmen fossil fuel fields leaked 2.6 million and 1.8 million metric tonnes of methane in 2022 alone, pumping the CO 2 equivalent of 366 million tonnes into the atmosphere, surpassing the annual CO 2 emissions of the United Kingdom . [ 92 ]
Methane is also an asphyxiant if the oxygen concentration is reduced to below about 16% by displacement, as most people can tolerate a reduction from 21% to 16% without ill effects . The concentration of methane at which asphyxiation risk becomes significant is much higher than the 5–15% concentration in a flammable or explosive mixture. Methane off-gas can penetrate the interiors of buildings near landfills and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture this gas and vent it away from the building. [ citation needed ]
Methane is abundant in many parts of the Solar System and potentially could be harvested on the surface of another Solar System body (in particular, using methane production from local materials found on Mars [ 93 ] or Titan ), providing fuel for a return journey. [ 29 ] [ 94 ]
Negative methane , the negative ion of methane, is also known to exist in interstellar space . [ 95 ] Its mechanism of formation is not fully understood.
Methane has been detected on all planets of the Solar System and most of the larger moons. [ citation needed ] With the possible exception of Mars , it is believed to have come from abiotic processes. [ 96 ] [ 97 ]
The Curiosity rover has documented seasonal fluctuations of atmospheric methane levels on Mars. These fluctuations peaked at the end of the Martian summer at 0.6 parts per billion. [ 98 ] [ 99 ] [ 100 ] [ 101 ] [ 102 ] [ 103 ] [ 104 ] [ 105 ]
Methane has been proposed as a possible rocket propellant on future Mars missions due in part to the possibility of synthesizing it on the planet by in situ resource utilization . [ 106 ] An adaptation of the Sabatier methanation reaction may be used with a mixed catalyst bed and a reverse water-gas shift in a single reactor to produce methane and oxygen from the raw materials available on Mars, utilizing water from the Martian subsoil and carbon dioxide in the Martian atmosphere . [ 93 ]
Methane could be produced by a non-biological process called serpentinization [ b ] involving water, carbon dioxide, and the mineral olivine , which is known to be common on Mars. [ 107 ]
Methane has been detected in vast abundance on Titan , the largest moon of Saturn . It comprises a significant portion of its atmosphere and also exists in a liquid form on its surface, where it comprises the majority of the liquid in Titan's vast lakes of hydrocarbons, the second largest of which is believed to be almost pure methane in composition. [ 108 ]
The presence of stable lakes of liquid methane on Titan, as well as the surface of Titan being highly chemically active and rich in organic compounds, has led scientists to consider the possibility of life existing within Titan's lakes, using methane as a solvent in the place of water for Earth-based life [ 109 ] and using hydrogen in the atmosphere to derive energy with acetylene . [ 110 ]
The discovery of methane is credited to Italian physicist Alessandro Volta , who characterized numerous properties including its flammability limit and origin from decaying organic matter. [ 111 ]
Volta was initially motivated by reports of inflammable air present in marshes by his friend Father Carlo Guiseppe Campi. While on a fishing trip to Lake Maggiore straddling Italy and Switzerland in November 1776, he noticed the presence of bubbles in the nearby marshes and decided to investigate. Volta collected the gas rising from the marsh and demonstrated that the gas was inflammable. [ 111 ] [ 112 ]
Volta notes similar observations of inflammable air were present previously in scientific literature, including a letter written by Benjamin Franklin . [ 113 ]
Following the Felling mine disaster of 1812 in which 92 men perished, Sir Humphry Davy established that the feared firedamp was in fact largely methane. [ 114 ]
The name "methane" was coined in 1866 by the German chemist August Wilhelm von Hofmann . [ 115 ] [ 116 ] The name was derived from methanol .
Etymologically, the word methane is coined from the chemical suffix " -ane ", which denotes substances belonging to the alkane family; and the word methyl , which is derived from the German Methyl (1840) or directly from the French méthyle , which is a back-formation from the French méthylène (corresponding to English "methylene"), the root of which was coined by Jean-Baptiste Dumas and Eugène Péligot in 1834 from the Greek μέθυ méthy (wine) (related to English "mead") and ὕλη hýlē (meaning "wood"). The radical is named after this because it was first detected in methanol , an alcohol first isolated by distillation of wood. The chemical suffix -ane is from the coordinating chemical suffix -ine which is from Latin feminine suffix -ina which is applied to represent abstracts. The coordination of "-ane", " -ene ", " -one ", etc. was proposed in 1866 by German chemist August Wilhelm von Hofmann . [ 117 ]
The abbreviation CH 4 -C can mean the mass of carbon contained in a mass of methane, and the mass of methane is always 1.33 times the mass of CH 4 -C. [ 118 ] [ 119 ] CH 4 -C can also mean the methane-carbon ratio, which is 1.33 by mass. [ 120 ] Methane at scales of the atmosphere is commonly measured in teragrams (Tg CH 4 ) or millions of metric tons (MMT CH 4 ), which mean the same thing. [ 121 ] Other standard units are also used, such as nanomole (nmol, one billionth of a mole), mole (mol), kilogram , and gram . | https://en.wikipedia.org/wiki/H4C |
Orthocarbonic acid , carbon hydroxide , methanetetrol is the name given to a hypothetical compound with the chemical formula H 4 CO 4 or C(OH) 4 . Its molecular structure consists of a single carbon atom bonded to four hydroxyl groups. It would be therefore a fourfold alcohol . In theory it could lose four protons to give the hypothetical oxocarbon anion orthocarbonate CO 4− 4 , and is therefore considered an oxoacid of carbon.
Orthocarbonic acid is highly unstable. Calculations show that it decomposes into carbonic acid and water: [ 2 ] [ 3 ]
Orthocarbonic acid is one of the group of ortho acids that have the general structure of RC(OH) 3 . The term ortho acid is also used to refer to the most hydroxylated acid in a set of oxoacids .
Researchers predict that orthocarbonic acid is stable at high pressure; hence it may form in the interior of the ice giant planets Uranus and Neptune , where water and methane are common. [ 4 ]
By loss of one through four protons, orthocarbonic acid could yield four anions: H 3 CO − 4 (trihydrogen orthocarbonate), H 2 CO 2− 4 (dihydrogen orthocarbonate), HCO 3− 4 (hydrogen orthocarbonate), and CO 4− 4 (orthocarbonate).
Numerous salts of fully deprotonated CO 4− 4 , such as Ca 2 CO 4 (calcium orthocarbonate) or Sr 2 CO 4 (strontium orthocarbonate), have been synthesized under high pressure conditions and structurally characterized by X-ray diffraction. [ 5 ] [ 6 ] [ 7 ] Strontium orthocarbonate, Sr 2 CO 4 , is stable at atmospheric pressure. Orthocarbonate is tetrahedral in shape, and is isoelectronic to orthonitrate . The C-O distance is 1.41 Å . [ 8 ] Sr 3 (CO 4 )O is an oxide orthocarbonate (tristrontium orthocarbonate oxide), also stable at atmospheric pressure . [ 9 ]
The tetravalent moiety CO 4 is found in stable organic compounds ; they are formally esters of orthocarbonic acid, and therefore are called orthocarbonates . For example, tetraethoxymethane can be prepared by the reaction between chloropicrin and sodium ethoxide in ethanol . [ 10 ] Polyorthocarbonates are stable polymers that might have applications in absorbing organic solvents in waste treatment processes, [ 11 ] or in dental restorative materials . [ 12 ] The explosive trinitroethylorthocarbonate possesses an orthocarbonate core.
A linear polymer which can be described as a ( spiro ) orthocarbonate ester of pentaerythritol , whose formula could be written as [(−CH 2 ) 2 C(CH 2 −) 2 (−O) 2 C(O−) 2 ] n , was synthesized in 2002. [ 13 ]
The carbon atom in the spiro ester bis- catechol orthocarbonate was found to have tetrahedral bond geometry, contrasting with the square planar geometry of the silicon atom in the analogous orthosilicate ester. [ 14 ]
Orthocarbonates may exist in several conformers , that differ by the relative rotation of the C–O–C bridges. The conformation structures of some esters, such as tetraphenoxymethane , tetrakis(3,5-dimethyl-phenoxy)methane , and tetrakis(4-bromophenoxy)methane have been determined by X-ray diffraction . [ 15 ] | https://en.wikipedia.org/wiki/H4CO4 |
Ammonium nitrate is a chemical compound with the formula NH 4 NO 3 . It is a white crystalline salt consisting of ions of ammonium and nitrate . It is highly soluble in water and hygroscopic as a solid, but does not form hydrates . It is predominantly used in agriculture as a high-nitrogen fertilizer . [ 5 ]
Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction. It is the major constituent of ANFO , an industrial explosive which accounts for 80% of explosives used in North America; similar formulations have been used in improvised explosive devices .
Many countries are phasing out its use in consumer applications due to concerns over its potential for misuse. [ 6 ] Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century. [ 6 ] [ 7 ] Global production was estimated at 21.6 million tonnes in 2017. [ 8 ] By 2021, global production of ammonium nitrate was down to 16.7 million tonnes. [ 7 ]
Ammonium nitrate is found as the natural mineral gwihabaite (formerly known as nitrammite) [ 9 ] – the ammonium analogue of saltpetre (mineralogical name: niter) [ 10 ] [ 11 ] – in the driest regions of the Atacama Desert in Chile , often as a crust on the ground or in conjunction with other nitrate, iodate , and halide minerals . Ammonium nitrate was mined there until the Haber–Bosch process made it possible to synthesize nitrates from atmospheric nitrogen, rendering nitrate mining obsolete.
The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid : [ 12 ]
The ammonia required for this process is obtained by the Haber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidized to nitric acid by the Ostwald process . Ammonia is used in its anhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highly exothermic nature. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in a spray tower , or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.
Another production method is a variant of the nitrophosphate process :
The products, calcium carbonate and ammonium nitrate, may be separately purified or sold combined as calcium ammonium nitrate .
Ammonium nitrate can also be made via metathesis reactions :
As ammonium nitrate is a salt , both the cation, NH + 4 , and the anion, NO − 3 , may take part in chemical reactions.
Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly produces nitrous oxide and water:
At higher temperatures, the following reaction predominates. [ 13 ]
Both decomposition reactions are exothermic and their products are gases. Under certain conditions, this can lead to a runaway reaction , with the decomposition process becoming explosive. [ 14 ] See § Disasters for details. Many ammonium nitrate disasters , with loss of lives, have occurred.
The red–orange colour in an explosion cloud is due to nitrogen dioxide , a secondary reaction product. [ 14 ]
Several crystalline phases of ammonium nitrate have been observed. The following occur under atmospheric pressure.
The transition between β-rhombic to α-rhombic forms (at 32.3 °C) occurs at ambient temperature in many parts of the world. These forms have a 3.6% difference in density and hence transition between them causes a change in volume. One practical consequence of this is that ammonium nitrate cannot be used as a solid rocket motor propellant, as it develops cracks. Stabilized ammonium nitrate (PSAN) was developed as a solution to this and incorporates metal halides stabilisers, which prevent density fluctuations. [ 16 ]
Ammonium nitrate is an important fertilizer with NPK rating 34-0-0 (34% nitrogen). [ 17 ] It is less concentrated than urea (46-0-0), giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not rapidly lose nitrogen to the atmosphere.
Ammonium nitrate readily forms explosive mixtures with varying properties when combined with explosives such as TNT or with fuels like aluminium powder or fuel oil.
Examples of explosives containing ammonium nitrate include:
ANFO is a mixture of 94% ammonium nitrate ("AN") and 6% fuel oil ("FO") widely used as a bulk industrial explosive . [ 18 ] : 1 It is used in coal mining , quarrying , metal mining , and civil construction in undemanding applications where the advantages of ANFO's low cost, relative safety, and ease of use matter more than the benefits offered by conventional industrial explosives, such as water resistance, oxygen balance , high detonation velocity, and performance in small diameters. [ 18 ] : 2
Ammonium nitrate-based explosives were used in the Sterling Hall bombing in Madison, Wisconsin, 1970, the Oklahoma City bombing in 1995, the 2011 Delhi bombings , the 2011 bombing in Oslo , the Myyrmanni bombing and the 2013 Hyderabad blasts .
In November 2009, the government of the KPK (previously termed as NWFP) of Pakistan imposed a ban on ammonium sulfate , ammonium nitrate, and calcium ammonium nitrate fertilizers in the former Malakand Division – comprising the Upper Dir , Lower Dir , Swat , Chitral , and Malakand districts of the NWFP – following reports that those chemicals were used by militants to make explosives. Due to these bans, " Potassium chlorate – the material which allows safety matches to catch fire – has surpassed fertilizer as the explosive of choice for insurgents." [ 19 ]
Ammonium nitrate is used in some instant cold packs , as its dissolution in water is highly endothermic . In 2021, King Abdullah University of Science and Technology in Saudi Arabia conducted experiments to study the potential for dissolving ammonium nitrate in water for off-grid cooling systems and as a refrigerant. They suggested that the water could be distilled and reused using solar energy to avoid water wastage in severe environments. [ 20 ]
It was once used, in combination with independently explosive "fuels" such as guanidine nitrate , [ 21 ] [ 22 ] as a cheaper (but less stable) alternative to 5-aminotetrazole in the inflators of airbags manufactured by Takata Corporation , which were recalled as unsafe after killing 14 people. [ 23 ] The current USA death total is 27. [ 24 ]
Numerous safety guidelines are available for storing and handling ammonium nitrate. Health and safety data are shown on the safety data sheets available from suppliers and from various governments. [ 25 ] [ 26 ] [ 27 ]
Pure ammonium nitrate does not burn, but as a strong oxidizer, it supports and accelerates the combustion of organic (and some inorganic) material. [ 25 ] [ 28 ] [ 29 ] It should not be stored near combustible substances.
While ammonium nitrate is stable at ambient temperature and pressure under many conditions, it may detonate from a strong initiation charge. It should not be stored near high explosives or blasting agents.
Molten ammonium nitrate is very sensitive to shock and detonation, particularly if it becomes contaminated with incompatible materials such as combustibles, flammable liquids, acids, chlorates, chlorides, sulfur, metals, charcoal and sawdust. [ 30 ] [ 25 ]
Contact with certain substances such as chlorates , mineral acids and metal sulfides , can lead to vigorous or even violent decomposition capable of igniting nearby combustible material or detonating. [ 31 ] [ 32 ]
Ammonium nitrate begins decomposition after melting, releasing NO x , HNO 3 , NH 3 and H 2 O . It should not be heated in a confined space. [ 25 ] The resulting heat and pressure from decomposition increases the sensitivity to detonation and increases the speed of decomposition. Detonation may occur at 80 atmospheres . Contamination can reduce this to 20 atmospheres. [ 30 ]
Ammonium nitrate has a critical relative humidity of 59.4% at 30 °C. At higher humidity it will absorb moisture from the atmosphere. Therefore, it is important to store ammonium nitrate in a tightly sealed container. Otherwise, it can coalesce into a large, solid mass. Ammonium nitrate can absorb enough moisture to liquefy. Blending ammonium nitrate with certain other fertilizers can lower the critical relative humidity. [ 33 ]
The potential for use of the material as an explosive has prompted regulatory measures. For example, in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances. [ 34 ] Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse. [ 35 ] Additional uses such as education and research purposes may also be considered, but individual use will not. Employees of those with licenses to deal with the substance are still required to be supervised by authorized personnel and are required to pass a security and national police check before a license may be granted.
Ammonium nitrate is not hazardous to health and is usually used in fertilizer products. [ 36 ] [ 37 ] [ 38 ]
Ammonium nitrate has an LD 50 of 2217 mg/kg, [ 39 ] which for comparison is about two-thirds that of table salt .
Ammonium nitrate decomposes, non-explosively, into the gases nitrous oxide and water vapor when heated. However, it can be induced to decompose explosively by detonation . [ 40 ] Large stockpiles of the material can also be a major fire risk due to their supporting oxidation , a situation which can easily escalate to detonation. Explosions are not uncommon: relatively minor incidents occur most years, and several large and devastating explosions have also occurred. Examples include the Oppau explosion of 1921 (one of the largest artificial non-nuclear explosions ), the Texas City disaster of 1947, the 2015 Tianjin explosions in China, and the 2020 Beirut explosion . [ 41 ]
Ammonium nitrate can explode through two mechanisms: | https://en.wikipedia.org/wiki/H4N2O3 |
Diphosphane , or diphosphine , is an inorganic compound with the chemical formula P 2 H 4 . This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air.
Diphosphane adopts the gauche conformation (like hydrazine , less symmetrical than shown in the image) with a P−P distance of 2.219 angstroms . It is nonbasic, unstable at room temperature, and spontaneously flammable in air . It is only poorly soluble in water but dissolves in organic solvents. Its 1 H NMR spectrum consists of 32 lines resulting from an A 2 XX'A' 2 splitting system. [ 1 ]
Diphosphane is produced by the hydrolysis of calcium monophosphide , which can be described as the Ca 2+ derivative of P 4− 2 . According to an optimized procedure, hydrolysis of 400 g of CaP at −30 °C gives about 20 g of product, slightly contaminated with phosphine .
Reaction of diphosphane with butyllithium affords a variety of condensed polyphosphine compounds.
A variety of organic derivatives of diphosphane are known, but asymmetric diphosphanes are only stable at cryogenic temperatures. Otherwise, the substituents facily redistribute on the phosphorus centers to give a mixture of products. On the other hand, there appears to be a substantial barrier to chiral inversion . [ 2 ]
The central bond is weak, and easily adds substituents. [ 3 ]
The simplest synthesis method heats a phosphorus halide and a phosphane:
Alkali metals can replace the hydrogen in that reaction (i.e., a dialkyl phosphide ), and in some rare cases a dialkylamine can replace the halide. Symmetric diphosphanes are easily prepared by reductive coupling, e.g. tetraphenyldiphosphine from chlorodiphenylphosphine :
Ultraviolet radiation decomposes mercury(II) dialkylphosphides to the metal and a dialkylphosphane. [ 4 ]
The methyl compound P 2 Me 4 is prepared by the reduction of Me 2 P(S)−P(S)Me 2 , which is produced by methylation of thiophosphoryl chloride with methylmagnesium bromide. [ 5 ] | https://en.wikipedia.org/wiki/H4P2 |
Pyrophosphoric acid , also known as diphosphoric acid , is the inorganic compound with the formula H 4 P 2 O 7 or, more descriptively, [(HO) 2 P(O)] 2 O. Colorless and odorless, it is soluble in water , diethyl ether , and ethyl alcohol . The anhydrous acid crystallizes in two polymorphs , which melt at 54.3 and 71.5 °C. The compound is a component of polyphosphoric acid, an important source of phosphoric acid. [ 1 ] Anions , salts , and esters of pyrophosphoric acid are called pyrophosphates .
It can be prepared by reaction of phosphoric acid with phosphoryl chloride : [ 2 ]
It can also be prepared by ion exchange from sodium pyrophosphate or by treating lead pyrophosphate with hydrogen sulfide . [ 1 ]
Boiling the water from orthophosphoric acid will not dehydrate it to pure pyrophosphoric acid, instead a mixture of ortho, pyro, and polyphosphoric acids are produced, the maximum pyrophosphoric acid concentration remains below 50% and occurs slightly before what would otherwise be pure pyrophosphoric acid. [ 3 ]
Pyrophosphoric acid is a tetraprotic acid, with four distinct pKa's: [ 4 ]
The pKa's occur in two distinct ranges because deprotonations occur on separate phosphate groups. For comparison with the pKa's for phosphoric acid are 2.14, 7.20, and 12.37.
At physiological pH's, pyrophosphate exists as a mixture of doubly and singly protonated forms.
When molten, pyrophosphoric acid rapidly converts to an equilibrium mixture of phosphoric acid, pyrophosphoric acid and polyphosphoric acids. The percentage by weight of pyrophosphoric acid is around 40% and it is difficult to recrystallise from the melt.
Even in cold water, pyrophosphoric acid hydrolyses to phosphoric acid. All polyphosphoric acids behave similarly. [ 5 ]
While pyrophosphoric acid is corrosive, it is not known to be otherwise toxic. [ 6 ]
The name pyrophosphoric acid was given by a "Mr. Clarke of Glasgow" in 1827 who is credited with its discovery following the heating to red heat of a sodium phosphate salt. It was found that phosphoric acid when heated to red heat formed pyrophosphoric acid that was readily converted to phosphoric acid by hot water. [ 7 ] | https://en.wikipedia.org/wiki/H4P2O7 |
Orthosilicic acid ( / ˌ ɔːr θ ə s ɪ ˈ l ɪ s ɪ k / ) is an inorganic compound with the formula Si ( O H ) 4 . Although rarely observed, it is the key compound of silica and silicates and the precursor to other silicic acids [H 2 x SiO x +2 ] n . Silicic acids play important roles in biomineralization and technology. [ 2 ] [ 3 ] [ 4 ] It is the parent acid of the orthosilicate anion SiO 4− 4 .
Typically orthosilicic acid is assumed to be a product of the hydrolysis of its esters, Si(OR) 4 , where R stands for organyl group, as is practiced in sol-gel syntheses. [ 2 ] These conditions are however too vigorous to allow isolation of the parent acid.
Orthosilicic acid can be produced by Pd - catalyzed hydrogenolysis of tetrabenzoxysilicon: [ 5 ]
The acid was crystallized from a solution of dimethylacetamide and tetrabutylammonium chloride . As established by X-ray crystallography , the chloride anions interact with the acid via hydrogen bonds . Otherwise, the structure consists of the expected tetrahedral silicon center.
Silicic acid readily condenses to give "higher" silicic acids including disilicic (pyrosilicic) and cyclo -tetrasilicic acid, (−O−Si(OH) 2 −) 4 : [ 5 ]
These derivatives have also been characterized crystallographically .
Silicon has been explored as a nutrient for plant growth, with silica constituting up to 10% of plant weight on a dry matter basis. [ 6 ] Orthosilicic acid is of particular interest as it is thought to be the form in which plants acquire silicon from the soil, [ 7 ] [ 8 ] before being deposited as phytoliths throughout the plant, leading to research in the application of orthosilicic acid through foliar sprays to supplement plant growth. [ 9 ] Studies have demonstrated that foliar application of stabilized orthosilicic acid can alleviate abiotic stressors such as drought, [ 10 ] [ 11 ] heavy metal toxicity, [ 12 ] [ 13 ] and salinity, [ 14 ] resulting in increased yields. [ 15 ] Additionally, applications of orthosilicic acid have been demonstrated to reduce fungal infections and disease in plants, [ 16 ] suggesting the possibility of using stabilized orthosilicic acid as an alternative or complement to existing disease control measures. The mechanisms by which orthosilicic acid alleviates abiotic stress and controls diseases is not well understood; current theories advanced include the activation of plant defense reactions [ 17 ] and the precipitation of silica in the apoplast of the plant. [ 18 ]
Dissolved silica (DSi) is a term used in the field of oceanography to describe the form of water-soluble silica , which is assumed to be Si(OH) 4 (orthosilicic acid) or its conjugate bases (orthosilicate anions) such as − O−Si(OH) 3 and ( − O−) 2 Si(OH) 2 . Theoretical computations indicate that the dissolution of silica in water proceeds through the formation of a SiO 2 ·2H 2 O complex and then orthosilicic acid. [ 20 ] The biogeochemical cycle of silica is regulated by the algae known as the diatoms . [ 21 ] [ 22 ] These algae polymerise the silicic acid to so-called biogenic silica , used to construct their cell walls (called frustules ). [ 23 ]
In the uppermost water column the surface ocean is undersaturated with respect to dissolved silica, except for the Antarctic Circumpolar Current south of 55°S.
The dissolved silica concentration increases with increasing water depth, and along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean. [ 24 ] [ 25 ] | https://en.wikipedia.org/wiki/H4SiO4 |
Periodic acid ( / ˌ p ɜːr aɪ ˈ ɒ d ɪ k / per-eye- OD -ik ) is an oxoacid of iodine . It can exist in two forms: orthoperiodic acid, with the chemical formula H 5 IO 6 , and metaperiodic acid, which has the formula HIO 4 . Periodic acids are colourless crystals. Periodic acid features iodine in the highest oxidation state of +7.
Periodic acid was discovered by Heinrich Gustav Magnus and C. F. Ammermüller in 1833. [ 3 ]
Modern industrial scale production involves the oxidation of a solution of sodium iodate under alkaline conditions , either electrochemically on a PbO 2 anode , or by treatment with chlorine : [ 4 ]
A standard laboratory preparation involves treating a mixture of tribarium dihydrogen orthoperiodate with nitric acid . Upon concentrating the mixture, the barium nitrate , which is less soluble, is separated from periodic acid: [ 6 ]
Orthoperiodic acid has a number of acid dissociation constants . [ 7 ] [ 8 ] The p K a of metaperiodic acid has not been determined.
There being two forms of periodic acid, it follows that two types of periodate salts are formed. For example, sodium metaperiodate , NaIO 4 , can be synthesised from HIO 4 while sodium orthoperiodate , Na 5 IO 6 can be synthesised from H 5 IO 6 .
Orthoperiodic acid forms monoclinic crystals ( space group P2 1 / n ) consisting of a slightly deformed IO 6 octahedron interlinked via bridging hydrogens. Five I–O bond distances are in the range 1.87–1.91 Å and one I–O bond is 1.78 Å. [ 9 ] [ 10 ] The structure of metaperiodic acid also includes IO 6 octahedra, however these are connected via cis -edge-sharing with bridging oxygens to form one-dimensional infinite chains. [ 11 ]
Orthoperiodic acid can be dehydrated to give metaperiodic acid by heating to 100 °C under reduced pressure.
Further heating to around 150 °C gives iodine pentoxide ( I 2 O 5 ) rather than the expected anhydride diiodine heptoxide ( I 2 O 7 ). Metaperiodic acid can also be prepared from various orthoperiodates by treatment with dilute nitric acid . [ 12 ]
Like all periodates periodic acid can be used to cleave various 1,2-difunctional compounds. Most notably periodic acid will cleave vicinal diols into two aldehyde or ketone fragments ( Malaprade reaction ).
This can be useful in determining the structure of carbohydrates as periodic acid can be used to open saccharide rings. This process is often used in labeling saccharides with fluorescent molecules or other tags such as biotin . Because the process requires vicinal diols, periodate oxidation is often used to selectively label the 3′-termini of RNA ( ribose has vicinal diols) instead of DNA as deoxyribose does not have vicinal diols.
Periodic acid is also used as an oxidising agent of moderate strength, as exemplified in the Babler oxidation of secondary allyl alcohols which are oxidised to enones by stoichiometric amounts of orthoperiodic acid with catalyst PCC . [ 13 ]
Periodic acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.
Compounds with a similar structure:
Compounds with similar chemistry: | https://en.wikipedia.org/wiki/H5IO6 |
Triphosphane (IUPAC systematic name) or triphosphine is an inorganic compound having the chemical formula HP(PH 2 ) 2 . It can be generated from diphosphine but is highly unstable at room temperature: [ 3 ]
Samples have been isolated by gas chromatography . The compound rapidly converts to PH 3 and the cyclophosphine cyclo - P 5 H 5 . [ 4 ] | https://en.wikipedia.org/wiki/H5P3 |
A hydrogen molecular ion cluster or hydrogen cluster ion is a positively charged cluster of hydrogen molecules. The hydrogen molecular ion ( H + 2 ) and trihydrogen ion ( H + 3 ) are well defined molecular species. However hydrogen also forms singly charged clusters ( H + n ) with n up to 120.
Hydrogen ion clusters can be formed in liquid helium or with lesser cluster size in pure hydrogen. H + 6 is far more common than higher even numbered clusters. [ 1 ] H + 6 is stable in solid hydrogen . The positive charge is balanced by a solvated electron. It is formed when ionizing radiation impinges on solid hydrogen , and so is formed in radioactive solid tritium . In natural hydrogen treated with radiation, the positive charge transfers to HD molecules, in preference to H 2 , with the ultimate most stable arrangement being HD(HD) + HD. [ 2 ] H + 6 can migrate through solid hydrogen by linking a hydrogen molecule at one end and losing it at the other: H 2 + H + 6 → H + 6 + H 2 . This migration stops once an HD molecule is added resulting in a lower energy level. [ 3 ] HD or D 2 is added in preference over H 2 . [ 4 ]
Clampitt and Gowland found clusters with an odd number of hydrogen atoms H + 3+2 n [ 5 ] and later showed that H + 15 was relatively stable. H + 3 formed the core of this cluster with six H 2 molecules surrounding it. [ 6 ] Hiroka studied the stability of the odd numbered clusters in gas up to H + 21 . [ 7 ] Bae determined that H + 15 was especially stable amongst the odd numbered clusters. [ 8 ]
Kirchner discovered even numbered atomic clusters in gas at lower concentrations than the odd numbered atom clusters. H + 6 was twenty times less abundant than H + 5 . H + 4 , H + 8 and H + 10 were detected at lesser amounts than H + 6 . [ 9 ] Kurosaki and Takayanagi showed that H + 6 is much more stable than other even clusters and showed antiprismatic symmetry of order 4 ( D 2d molecular symmetry ). [ 10 ] This turnstile structured molecule was computationally found to be more energetically stable than a ring of five hydrogen atoms around a proton. [ 11 ]
Negative hydrogen clusters have not been found to exist. H − 3 is theoretically unstable, but D − 3 in theory is bound at 0.003 eV. [ 8 ]
H + 6 in the free gas state decays by giving off H atoms and H 2 molecules. Different energies of decay occur with levels averaging at 0.038 eV and peaking at 0.14 eV. [ 9 ]
Hydrogen molecular ion clusters can be formed through different kinds of ionizing radiation. High energy electrons capable of ionizing the material can perform this task. When hydrogen dissolved in liquid helium is irradiated with electrons their energy must be sufficient to ionize helium to produce significant hydrogen clusters. Irradiation of solid hydrogen by gamma rays or X-rays also produces H + 6 . [ 12 ]
Positive ion clusters are also formed when compressed hydrogen expands though a nozzle. [ 13 ]
Kirchner's theory for the formation of even numbered clusters was that neutral H 3 molecules reacted with the H + 3 ion (or other odd clusters) to make H + 6 . [ 9 ]
Solvation of H + 6 in solid hydrogen had little effect on its spectrum. [ 10 ]
SRI International studied solid ionic hydrogen fuel. They believed that a solid containing H + 3 and H − ions could be manufactured. If it could be made it would have a higher energy than other rocket fuels with only 2% concentration of ions. However they could not contain the H − in a stable way, but determined that other negative ions would do as well. [ 8 ] This theoretical impulse exceeds that of solid and liquid fuel rockets. [ 8 ] SRI developed a cluster ion gun that could make positive and negative ion clusters at a current of 500 pA . [ 8 ]
Nuclear fusion using ion clusters can impact far more atoms than single ions in one hit. This concept is called cluster ion fusion (CIF). Lithium deuteride (LiD) is a potential starter material for generating the ions. [ 8 ] | https://en.wikipedia.org/wiki/H6+ |
The histocompatibility 60 (H60) was originally identified as a transplant rejection antigen [ 1 ] and it is a family of murine cell surface glycoproteins contains three members: H60a, H60b, H60c. The genes encoding these proteins are located on murine chromosome 10. [ 2 ] H60 family members are related to MHC class I . [ 2 ] [ 3 ] H60a and H60b consist of external α1α2 domain, a transmembrane segment, and a cytoplasmic domain. [ 2 ] [ 3 ] H60c is made up of α1α2 domain which is linked to the cell membrane by GPI anchor. [ 2 ] All these proteins function as stress-induced ligands for NKG2D receptor. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/H60_family |
Chloroplatinic acid (also known as hexachloroplatinic acid ) is an inorganic compound with the formula [H 3 O] 2 [PtCl 6 ](H 2 O) x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum , usually as an aqueous solution . Although often written in shorthand as H 2 PtCl 6 , it is the hydronium (H 3 O + ) salt of the hexachloroplatinate anion ( PtCl 2− 6 ). [ 1 ] [ 2 ] [ 3 ] Hexachloroplatinic acid is highly hygroscopic .
Hexachloroplatinic acid may be produced via a variety of methods. The most common of these methods involves dissolution of platinum in aqua regia . Other methods include exposing an aqueous suspension of platinum particles to chlorine gas, or via electrolysis.
When produced by the aqua regia route, hexachloroplatinic acid is thought to arise by the following equation: [ 4 ] [ 5 ]
The resulting orange/red solution can be evaporated to produce brownish red crystals. Some authors suggest that hexachloroplatinic acid produced using this method is contaminated with nitrosonium hexachloroplatinate. Newer literature indicates that this is not the case, and that once the nitric acid has been driven off, samples prepared via this method contain no detectable nitrogen.
Alternative methods have been investigated and described, often motivated by the avoidance of nitrogen contamination. [ 6 ]
According to X-ray crystallography , hexachloroplatinic acid consists of octahedral PtCl 2− 6 ions linked by hydrogen bonding. The cubic array of these octahedra encase water molecules. [ citation needed ]
When heated, hexachloroplatinic acid decomposes to platinum(IV) chloride . [ 1 ]
Chloroplatinic acid was popularized for the quantitative analysis of potassium. The potassium is selectively precipitated from solution as potassium hexachloroplatinate. Determinations were done in 85% (v/v) alcohol solutions with excess platinate ions, and the precipitated product was weighed. Potassium could be detected for solutions as dilute as 0.02 to 0.2% (m/v). [ 7 ]
This method for determination of potassium was advantageous compared to the sodium cobaltinitrite method used previously, since it required a single precipitation reaction. [ 7 ] Gravimetric analysis of precipitated products has been supplanted by modern instrumental analysis methods such as ion selective electrodes , flame photometry , ICP-AES or ICP-MS .
Upon treatment with an ammonium salt, such as ammonium chloride , chloroplatinic acid converts to ammonium hexachloroplatinate , which precipitates as a solid. [ 4 ] Upon heating in an atmosphere of hydrogen , the ammonium salt converts to elemental platinum. Platinum is often isolated from ores or recycled from residues using this method. [ 8 ]
Like many platinum compounds, chloroplatinic acid is a catalyst (or precatalyst) for hydrogenation and related reactions. As first reported by John Speier and colleagues from Dow Corning , it catalyzes the addition of hydrosilanes to olefins, i.e. hydrosilylation . Early demonstration reactions used isopropanol solutions of trichlorosilane (SiHCl 3 ) with pentenes . Prior work on the addition of silanes to alkenes required radical reactions that were inefficient. [ 9 ] [ 10 ] As well as with Karstedt's catalyst , Speier's catalyst enjoys widespread use for hydrosilylation, the main drawback is the deliquescent properties of the catalyst. [ 11 ]
It is generally agreed that chloroplatinic acid is a precursor to the actual catalyst. A possible role for colloidal platinum or zero-valent complexes has also been considered. [ 12 ]
Chloroplatinic acid prepared from aqua regia is proposed to contain nitrosonium hexachloroplatinate, (NO) 2 PtCl 6 . Nitrosonium hexachloroplatinate is obtained by the reaction of nitrosyl chloride (NOCl) and platinum metal. [ 13 ] Nitrosonium hexachloroplatinate has been found to react vigorously with water and hydrochloric acid, making contamination of chloroplatinic acid prepared with aqua regia with nitrosonium hexachloroplatinate unlikely. [ citation needed ] | https://en.wikipedia.org/wiki/H6Cl6O2Pt |
Ammonium sulfamate (or ammonium sulphamate ) is a white crystalline solid, readily soluble in water. It is commonly used as a broad spectrum herbicide , with additional uses as a compost accelerator, flame retardant and in industrial processes.
It is a salt formed from ammonia and sulfamic acid .
Ammonium sulfamate is distributed under the following tradenames, which are principally herbicidal product names: Amicide, Amidosulfate, Ammate, Amcide, Ammate X-NI, AMS, Fyran 206k, Ikurin, Sulfamate, AMS and Root-Out.
Ammonium sulfamate is considered to be particularly useful in controlling tough woody weeds , tree stumps and brambles .
Ammonium sulfamate has been successfully used in several major UK projects by organisations like the British Trust for Conservation Volunteers , English Heritage , the National Trust , and various railway, canal and waterways authorities.
Several years ago the Henry Doubleday Research Association (HDRA) (known as Garden Organic), published an article on ammonium sulfamate after a successful set of herbicide trials. [ citation needed ] Though not approved for use by organic growers it does provide an option when alternatives have failed.
The following problem weeds / plants can be controlled:
Japanese Knotweed ( Reynoutria japonica , syn. Fallopia japonica ),
Marestail / Horsetail ( Equisetum ),
Ground-elder ( Aegopodium podagraria ), Rhododendron ponticum ,
Brambles,
Brushwood,
Ivy ( Hedera species), Senecio /Ragwort, Honey fungus ( Armillaria ), and
felled tree stumps and most other tough woody specimens. [ citation needed ]
Ammonium sulfamate is used as a composting accelerator in horticultural settings. It is especially effective in breaking down the tougher and woodier weeds put onto the compost heap.
Ammonium sulfamate (like other ammonium salts, e.g. Ammonium dihydrogen phosphate , Ammonium sulfate ) is a useful flame retardant . [ 4 ] These salt based flame retardants offer advantages over other metal/mineral-based flame retardants in that they are water processable. Their relatively low decomposition temperature makes them suitable for flame retarding cellulose based materials (paper/wood). Ammonium sulfamate (like Ammonium dihydrogen phosphate ) is sometimes used in conjunction with Magnesium sulfate or Ammonium sulfate (in ratios of approximately 2:1) for enhanced flame retardant properties.
Within industry ammonium sulfamate is used as a flame retardant, a plasticiser and in electro-plating . Within the laboratory it is used as a reagent.
Ammonium sulfamate is considered to be only slightly toxic to humans and other animals, making it appropriate for amateur home garden, professional and forestry uses. [ 5 ] It is generally accepted to be safe for use on plots of land that will be used for growing fruit and vegetables intended for consumption.
It corrodes brass, copper, and iron. Its contact with eyes or skin can be harmful unless it is quickly washed off. [ 6 ]
In the United States, the Occupational Safety and Health Administration has set a permissible exposure limit at 15 mg/m 3 over an eight-hour time-weighted average, while the National Institute for Occupational Safety and Health recommends exposures no greater than 10 mg/m 3 over an eight-hour time-weighted average. [ 7 ] These occupational exposure limits are protective values, given the IDLH concentration is set at 1500 mg/m 3 . [ 8 ]
It is also considered to be environmentally friendly due to its degradation to non-harmful residues.
The pesticides review by the European Union led to herbicides containing ammonium sulfamate becoming unlicensed, and therefore effectively banned, from 2008. [ 9 ]
Its availability and use as a compost accelerator is unaffected by the EU's pesticide legislation. | https://en.wikipedia.org/wiki/H6N2O3S |
Hydrazine sulfate , more properly hydrazinium hydrogensulfate , is a salt of the cation hydrazinium and the anion bisulfate (hydrogensulfate), with the formula N 2 H 6 SO 4 or more properly [N 2 H 5 ] + [HSO 4 ] − . It is a white, water-soluble solid at room temperature .
Hydrazine sulfate has a number of uses in chemical laboratories and in the chemical industry , including analytical chemistry and the synthesis of organic compounds . In those uses it is usually preferred to pure hydrazine, because it is not volatile and is less susceptible to atmospheric oxidation on storage.
The compound can be prepared by treating an aqueous solution of hydrazine ( N 2 H 4 ) with sulfuric acid ( H 2 SO 4 ). [ 1 ]
Besides its general use as a safe source of hydrazine, the compound is used as a catalyst in making fibers out of acetate , in the analysis and synthesis of minerals, and testing for arsenic in metals. [ 2 ]
Hydrazine sulfate can be used as a fungicide and antiseptic . [ 2 ]
Hydrazine sulfate has been used as an alternative medical treatment for the loss of appetite ( anorexia ) and rapid weight loss ( cachexia ), which are often associated with cancer . [ 3 ] [ 4 ] [ 5 ]
Although it has been marketed as a dietary supplement , [ 6 ] [ 7 ] hydrazine sulfate has never been approved in the United States as safe and effective in treating any medical condition.
Hydrazine sulfate was first proposed as an anti-cancer agent by U.S. physician Joseph Gold in the mid-1970s. [ 8 ] Gold's arguments were based on the fact that cancer cells are often unusually dependent on glycolysis for energy (the Warburg effect ). Gold proposed that the body might offset this increased glycolysis using gluconeogenesis , which is the pathway that is the reverse of glycolysis. Since this process would require a great deal of energy, Gold thought that inhibiting gluconeogenesis might reverse this energy requirement and be an effective treatment for cancer cachexia. [ 9 ] Hydrazine is a reactive chemical that in the test tube can inactivate one of the enzymes needed for gluconeogenesis, phosphoenolpyruvate carboxykinase (PEP-CK). It was also postulated that if tumor energy gain (glycolysis) and host-energy loss (gluconeogenesis) were functionally interrelated, inhibition of gluconeogenesis at PEP CK could result in actual tumor regression in addition to reversal or arrest of cancer cachexia. [ 10 ] In this model, hydrazine sulfate is therefore thought to act by irreversibly inhibiting the enzyme phosphoenolpyruvate carboxykinase.
The use of hydrazine sulfate as a cancer remedy was popularized by the magazine Penthouse in the mid-1990s, when Kathy Keeton , wife and business partner of the magazine's publisher Bob Guccione , used it in an attempt to treat her metastatic breast cancer . [ 11 ] Alternative medicine nutritionist Gary Null wrote three of the articles about alternative cancer treatments, including one titled "The Great Cancer Fraud." [ 12 ] Keeton (until her death in 1997) and other supporters of hydrazine sulfate treatment accused the U.S. National Cancer Institute (NCI) of deliberately hiding the beneficial effects of the compound, and threatened to launch a class action lawsuit. [ 13 ] [ 14 ] The NCI denied the claims, [ 15 ] and says that there is little to no evidence that hydrazine sulfate has any beneficial effects whatsoever. [ 6 ] The position of the NCI was supported by an inquiry held by the General Accounting Office . [ 16 ]
A review of the clinical research concluded that hydrazine sulfate has never been shown to act as an anticancer agent; patients do not experience remissions or regressions of their cancer, and patients do not live longer than non-treated patients. [ 6 ] [ 17 ] [ 18 ] Some academic reviews of alternative cancer treatments have described the compound as a "disproved and ineffective treatment for cancer". [ 19 ] [ 20 ]
Joseph Gold's claims [ 8 ] have been questioned by the American Cancer Society , and other investigators have been unable to repeat or confirm these results. [ 17 ] [ 21 ] Gold is reported not to trust the motives or results of other investigators, with CNN quoting him as stating that "they've been out to get hydrazine sulfate, and I don't know why". [ 22 ]
In response to these results, an uncontrolled clinical trial was carried out at the Petrov Research Institute of Oncology in St. Petersburg over a period of 17 years, [ 17 ] [ 23 ] and a controlled trial was carried out at the Harbor-UCLA Medical Center in California over period of 10 years, respectively. The Russian trial reported complete tumor regression in about 1% of cases, a partial response in about 3% of cases and some subjective improvement of symptoms in about half of the patients. [ 23 ] The National Cancer Institute analysis of this trial notes that interpretation of these data is difficult, due to the absence of controls, the lack of information on prior treatment and the study's reliance on subjective assessments of symptoms ( i.e. asking patients if the drug had made them feel any better). [ 24 ] Overall, the trials in California saw no statistically significant effect on survival from hydrazine sulfate treatment, but noted increased calorie intake in treated patients versus controls. [ 25 ] The authors also performed a post-hoc analysis on one or more subgroups of these patients, which they reported as suggesting a beneficial effect from treatment. The design and interpretation of this trial, and in particular the validity of this subgroup analysis, was criticized in detail in an editorial in the Journal of Clinical Oncology . [ 26 ]
Later randomized controlled trials failed to find any improvement in survival, [ 27 ] [ 28 ] For example, in a trial of the treatment of advanced lung cancer , with either cisplatin and vinblastine or these drugs plus hydrazine sulfate, saw complete tumor regression in 4% of the hydrazine group, versus 3% in the control group, and tumor progression in 36% of the hydrazine group, versus 30% of the control group; however, none of these differences were statistically significant. [ 29 ] Some trials even found both significantly decreased survival and significantly poorer quality of life in those patients receiving hydrazine sulfate. [ 30 ] These consistently negative results have resulted in hydrazine sulfate being described as a "disproven cancer therapy" in a recent medical review. [ 20 ] Similarly, other reviews have concluded that there is "strong evidence" against the use of hydrazine sulfate to treat anorexia or weight loss in cancer patients. [ 31 ] [ 32 ]
Hydrazine sulfate is toxic and potentially carcinogenic . [ 33 ] [ 34 ] Nevertheless, the short-term side effects reported in various clinical trials are relatively mild: [ 7 ] minor nausea and vomiting, dizziness and excitement, polyneuritis (inflammation of the nerves) and difficulties in fine muscle control (such as writing). However, more serious, even fatal side effects have been reported in rare cases: one patient developed fatal liver and kidney failure, [ 35 ] and another developed serious symptoms of neurotoxicity. [ 36 ] These side effects and other reports of hydrazine toxicity [ 25 ] [ 26 ] are consistent with the hypothesis that hydrazine may play a role in the toxicity of the antibiotic isoniazid , which is thought to be metabolized to hydrazine in the body. [ 7 ]
Hydrazine sulfate is also a monoamine oxidase inhibitor (MAOI), [ 37 ] and is incompatible with alcohol , tranquilizers and sleeping pills ( benzodiazepines and barbiturates ), and other psycho-active drugs, with pethidine (meperidine, Demerol), and with foods containing significant amounts of the amino acid breakdown product tyramine , such as aged cheeses, raisins, avocados, processed and cured fish and meats, fermented products, and others. | https://en.wikipedia.org/wiki/H6N2O4S |
Ammonia borane (also systematically named ammoniotrihydroborate [ citation needed ] ), also called borazane , is the chemical compound with the formula H 3 NBH 3 . The colourless or white solid is the simplest molecular boron - nitrogen - hydride compound. It has attracted attention as a source for hydrogen fuel, but is otherwise primarily of academic interest.
Reaction of diborane with ammonia mainly gives the diammoniate salt [H 2 B(NH 3 ) 2 ] + [BH 4 ] − (diammoniodihydroboronium tetrahydroborate). Ammonia borane is the main product when an adduct of borane is employed in place of diborane: [ 5 ]
It can also be synthesized from sodium borohydride . [ 6 ] [ 7 ] [ 8 ]
The molecule adopts a structure similar to that of ethane , with which it is isoelectronic . The B−N distance is 1.58(2) Å. The B−H and N−H distances are 1.15 and 0.96 Å, respectively. Its similarity to ethane is tenuous since ammonia borane is a solid and ethane is a gas: their melting points differing by 284 °C. This difference is consistent with the highly polar nature of ammonia borane. The H atoms attached to boron are hydridic (negatively charged) and those attached to nitrogen are acidic (positively charged). [ 9 ]
The structure of the solid indicates a close association of the N H and the B H centers. The closest H−H distance is 1.990 Å, which can be compared with the H−H bonding distance of 0.74 Å. This interaction is called a dihydrogen bond . [ 10 ] [ 11 ] The original crystallographic analysis of this compound reversed the assignments of B and N. The updated structure was arrived at with improved data using the technique of neutron diffraction that allowed the hydrogen atoms to be located with greater precision.
Ammonia borane has been suggested as a storage medium for hydrogen , e.g. for when the gas is used to fuel motor vehicles. It can be made to release hydrogen on heating, being polymerized first to (NH 2 BH 2 ) n , then to (NHBH) n , [ 15 ] which ultimately decomposes to boron nitride (BN) at temperatures above 1000 °C. [ 16 ] It is more hydrogen-dense than liquid hydrogen and also able to exist at normal temperatures and pressures. [ 17 ]
Ammonia borane finds some use in organic synthesis as an air-stable derivative of diborane. [ 18 ] It can be used as a reducing agent in transfer hydrogenation reactions, often in the presence of a transition metal catalyst. [ 19 ]
Many analogues have been prepared from primary, secondary, and even tertiary amines :
The first amine adduct of borane was derived from trimethylamine . Borane tert-butylamine complex is prepared by the reaction of sodium borohydride with t-butylammonium chloride. Generally adduct are more robust with more basic amines. Variations are also possible for the boron component, although primary and secondary boranes are less common. [ 8 ] | https://en.wikipedia.org/wiki/H6NB |
Ammonium phosphinate is a chemical compound with the chemical formula NH 4 PH 2 O 2 . [ 3 ] [ 4 ] This is a salt of ammonium and phosphoric acid.
The effect of ammonia solution on phosphoric acid solution:
Ammonium phosphonate forms colorless crystals of rhombic system , spatial group C mma , cell parameters a = 0.757 nm, b = 1.147 nm, c = 0.398 nm, Z = 4. [ 5 ]
The compound is soluble in water and ethanol , but insoluble in acetone . [ 6 ]
The compound is usually used as a catalyst for the production of polyamide . [ 2 ] | https://en.wikipedia.org/wiki/H6NO2P |
Telluric acid , or more accurately orthotelluric acid , is a chemical compound with the formula Te(OH) 6 , often written as H 6 TeO 6 . It is a white crystalline solid made up of octahedral Te(OH) 6 molecules which persist in aqueous solution. [ 3 ] In the solid state, there are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH) 6 molecules, [ 4 ] containing one hexavalent tellurium (Te) atom in the +6 oxidation state, attached to six hydroxyl (–OH) groups, thus, it can be called tellurium(VI) hydroxide.
Telluric acid is a weak acid which is dibasic , forming tellurate salts with strong bases and hydrogen tellurate salts with weaker bases or upon hydrolysis of tellurates in water. [ 4 ] [ 5 ] It is used as tellurium-source in the synthesis of oxidation catalysts.
Telluric acid is formed by the oxidation of tellurium or tellurium dioxide with a powerful oxidising agent such as hydrogen peroxide , chromium trioxide or sodium peroxide . [ 4 ]
Crystallization of telluric acid solutions below 10 °C gives telluric acid tetrahydrate Te(OH) 6 ·4H 2 O . [ 3 ] It is an oxidising agent, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations. [ 4 ]
Chlorine , by comparison, is +1.36 V and selenous acid is +0.74 V in oxidizing conditions.
The anhydrous acid is stable in air at 100 °C but above this it dehydrates to form polymetatelluric acid, a white hygroscopic powder (approximate composition (H 2 TeO 4 ) 10 ), and allotelluric acid, an acid syrup of unknown structure (approximate composition 3·H 2 TeO 4 ·4H 2 O ). [ 6 ] [ 3 ]
Typical salts of the acid contains the anions [Te(O)(OH) 5 ] − and [Te(O) 2 (OH) 4 ] 2− . The presence of the tellurate ion TeO 2− 4 has been confirmed in the solid state structure of Rb 6 [TeO 5 ][TeO 4 ] . [ 7 ] Strong heating at over 300 °C produces the α crystalline modification of tellurium trioxide , α- TeO 3 . [ 5 ] Reaction with diazomethane gives the hexamethyl ester, Te(OCH 3 ) 6 . [ 3 ]
Telluric acid and its salts mostly contain hexacoordinate tellurium . [ 4 ] This is true even for salts such as magnesium tellurate, MgTeO 4 , which is isostructural with magnesium molybdate and contains TeO 6 octahedra. [ 4 ]
Metatelluric acid, H 2 TeO 4 , the tellurium analogue of sulfuric acid , H 2 SO 4 , is unknown. Allotelluric acid of approximate composition 3·H 2 TeO 4 ·4H 2 O , is not well characterised and may be a mixture of Te(OH) 6 and (H 2 TeO 4 ) n . [ 3 ]
Tellurous acid H 2 TeO 3 , containing tellurium in its +4 oxidation state, is known but not well characterised. Hydrogen telluride is an unstable gas that forms hydrotelluric acid upon addition to water. | https://en.wikipedia.org/wiki/H6O6Te |
Disilane is a chemical compound with general chemical formula Si 2 R 6 that was first identified in 1902 by Henri Moissan and Samuel Smiles (1877–1953) where R = H. Moissan and Smiles reported disilane as being among the products formed by the action of dilute acids on metal silicides. Although these reactions had been previously investigated by Friedrich Woehler and Heinrich Buff between 1857 and 1858, Moissan and Smiles were the first to explicitly identify disilane. They referred to disilane as silicoethane . Higher members of the homologous series Si n H 2 n +2 formed in these reactions were subsequently identified by Carl Somiesky (sometimes spelled "Karl Somieski") and Alfred Stock .
At standard temperature and pressure , disilane is a colourless, acrid gas. Disilane and ethane have similar structures, although disilane is much more reactive. Other compounds of the general formula Si 2 X 6 (X = hydrogen , halogen , alkyl , aryl , and mixtures of these groups) are called disilanes. Disilane is a group 14 hydride .
Disilane is usually prepared by the hydrolysis of magnesium silicide . This reaction produces silane , disilane, and even trisilane . The method has been abandoned for the production of silane, but it remains viable for generating disilane. [ 3 ] The presence of traces of disilane is responsible for the spontaneous flammability of silane produced by hydrolysis by this method (analogously diphosphine is often the spontaneously pyrophoric contaminant in samples of phosphine ).
It also arises by thermal decomposition disilane via both photochemical [ 4 ] and thermal decomposition of silane.
The reduction of Si 2 Cl 6 with lithium aluminium hydride affords disilane in modest yield. [ 5 ]
Disilane and silane thermally decompose around 640 °C, depositing amorphous silicon . This chemical vapor deposition process is relevant to the manufacture of photovoltaic devices . [ 3 ] Specifically it is utilized in the production of silicon wafers . [ 6 ]
More generally, diorganosilanes are produced by reductive coupling of silyl chlorides , e.g.
Disilane gas can be used to control pressure of Si vapors during process of graphene growth by thermal decomposition of SiC . Pressure of Si vapors influences quality of produced graphene. [ 7 ] | https://en.wikipedia.org/wiki/H6Si2 |
Telluric acid , or more accurately orthotelluric acid , is a chemical compound with the formula Te(OH) 6 , often written as H 6 TeO 6 . It is a white crystalline solid made up of octahedral Te(OH) 6 molecules which persist in aqueous solution. [ 3 ] In the solid state, there are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH) 6 molecules, [ 4 ] containing one hexavalent tellurium (Te) atom in the +6 oxidation state, attached to six hydroxyl (–OH) groups, thus, it can be called tellurium(VI) hydroxide.
Telluric acid is a weak acid which is dibasic , forming tellurate salts with strong bases and hydrogen tellurate salts with weaker bases or upon hydrolysis of tellurates in water. [ 4 ] [ 5 ] It is used as tellurium-source in the synthesis of oxidation catalysts.
Telluric acid is formed by the oxidation of tellurium or tellurium dioxide with a powerful oxidising agent such as hydrogen peroxide , chromium trioxide or sodium peroxide . [ 4 ]
Crystallization of telluric acid solutions below 10 °C gives telluric acid tetrahydrate Te(OH) 6 ·4H 2 O . [ 3 ] It is an oxidising agent, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations. [ 4 ]
Chlorine , by comparison, is +1.36 V and selenous acid is +0.74 V in oxidizing conditions.
The anhydrous acid is stable in air at 100 °C but above this it dehydrates to form polymetatelluric acid, a white hygroscopic powder (approximate composition (H 2 TeO 4 ) 10 ), and allotelluric acid, an acid syrup of unknown structure (approximate composition 3·H 2 TeO 4 ·4H 2 O ). [ 6 ] [ 3 ]
Typical salts of the acid contains the anions [Te(O)(OH) 5 ] − and [Te(O) 2 (OH) 4 ] 2− . The presence of the tellurate ion TeO 2− 4 has been confirmed in the solid state structure of Rb 6 [TeO 5 ][TeO 4 ] . [ 7 ] Strong heating at over 300 °C produces the α crystalline modification of tellurium trioxide , α- TeO 3 . [ 5 ] Reaction with diazomethane gives the hexamethyl ester, Te(OCH 3 ) 6 . [ 3 ]
Telluric acid and its salts mostly contain hexacoordinate tellurium . [ 4 ] This is true even for salts such as magnesium tellurate, MgTeO 4 , which is isostructural with magnesium molybdate and contains TeO 6 octahedra. [ 4 ]
Metatelluric acid, H 2 TeO 4 , the tellurium analogue of sulfuric acid , H 2 SO 4 , is unknown. Allotelluric acid of approximate composition 3·H 2 TeO 4 ·4H 2 O , is not well characterised and may be a mixture of Te(OH) 6 and (H 2 TeO 4 ) n . [ 3 ]
Tellurous acid H 2 TeO 3 , containing tellurium in its +4 oxidation state, is known but not well characterised. Hydrogen telluride is an unstable gas that forms hydrotelluric acid upon addition to water. | https://en.wikipedia.org/wiki/H6TeO6 |
Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English ); (NH 4 ) 2 SO 4 , is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen and 24% sulfur .
The primary use of ammonium sulfate is as a fertilizer for alkaline soils . In the soil, the ammonium ion is released and forms a small amount of acid, lowering the pH balance of the soil , while contributing essential nitrogen for plant growth. One disadvantage to the use of ammonium sulfate is its low nitrogen content relative to ammonium nitrate , which elevates transportation costs. [ 2 ]
It is also used as an agricultural spray adjuvant for water-soluble insecticides , herbicides , and fungicides . There, it functions to bind iron and calcium cations that are present in both well water and plant cells. It is particularly effective as an adjuvant for 2,4-D (amine), glyphosate , and glufosinate herbicides.
Ammonium sulfate precipitation is a common method for protein purification by precipitation. As the ionic strength of a solution increases, the solubility of proteins in that solution decreases. Being extremely soluble in water, ammonium sulfate can "salt out" (precipitate) proteins from aqueous solutions. [ 3 ] [ 4 ] Precipitation by ammonium sulfate is a result of a reduction in solubility rather than protein denaturation , thus the precipitated protein can be resolubilized through the use of standard buffers . [ 5 ] Ammonium sulfate precipitation provides a convenient and simple means to fractionate complex protein mixtures. [ 6 ]
In the analysis of rubber lattices, volatile fatty acids are analyzed by precipitating rubber with a 35% ammonium sulfate solution, which leaves a clear liquid from which volatile fatty acids are regenerated with sulfuric acid and then distilled with steam. Selective precipitation with ammonium sulfate, opposite to the usual precipitation technique which uses acetic acid, does not interfere with the determination of volatile fatty acids. [ 7 ]
As a food additive, ammonium sulfate is considered generally recognized as safe (GRAS) by the U.S. Food and Drug Administration , [ 8 ] and in the European Union it is designated by the E number E517. It is used as an acidity regulator in flours and breads. [ 9 ] [ 10 ] [ 11 ]
Ammonium sulfate is a precursor to other ammonium salts, especially ammonium persulfate .
Ammonium sulfate is listed as an ingredient for many United States vaccines per the Centers for Disease Control . [ 12 ]
Ammonium sulfate has also been used in flame retardant compositions acting much like diammonium phosphate . As a flame retardant, it increases the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char. [ 13 ]
Ammonium sulfate is made by treating ammonia with sulfuric acid :
A mixture of ammonia gas and water vapor is introduced into a reactor that contains a saturated solution of ammonium sulfate and about 2% to 4% of free sulfuric acid at 60 °C. Concentrated sulfuric acid is added to keep the solution acidic, and to retain its level of free acid. The heat of reaction keeps reactor temperature at 60 °C. Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, forming a powdery salt. Approximately 6,000 million tons were produced in 1981. [ 2 ]
Ammonium sulfate also is manufactured from gypsum (CaSO 4 ·2H 2 O). Finely divided gypsum is added to an ammonium carbonate solution. Calcium carbonate precipitates as a solid, leaving ammonium sulfate in the solution.
Ammonium sulfate occurs naturally as the rare mineral mascagnite in volcanic fumaroles and due to coal fires on some dumps. [ 14 ]
Ammonium sulfate is a byproduct in the production of methyl methacrylate . [ 15 ]
Ammonium sulfate becomes ferroelectric at temperatures below −49.5 °C. At room temperature it crystallises in the orthorhombic system, with cell sizes of a = 7.729 Å, b = 10.560 Å, c = 5.951 Å. When chilled into the ferrorelectric state, the symmetry of the crystal changes to space group Pna2 1 . [ 16 ]
Ammonium sulfate decomposes upon heating above 250 °C (482 °F), first forming ammonium bisulfate . Heating at higher temperatures results in decomposition into ammonia , nitrogen , sulfur dioxide , and water. [ 17 ]
As a salt of a strong acid (H 2 SO 4 ) and weak base (NH 3 ), its solution is acidic; the pH of 0.1 M solution is 5.5. In aqueous solution the reactions are those of NH + 4 and SO 2− 4 ions. For example, addition of barium chloride , precipitates out barium sulfate . The filtrate on evaporation yields ammonium chloride .
Ammonium sulfate forms many double salts (ammonium metal sulfates) when its solution is mixed with equimolar solutions of metal sulfates and the solution is slowly evaporated. With trivalent metal ions, alums such as ferric ammonium sulfate are formed. Double metal sulfates include ammonium cobaltous sulfate, ferrous diammonium sulfate , ammonium nickel sulfate which are known as Tutton's salts and ammonium ceric sulfate . [ 2 ] Anhydrous double sulfates of ammonium also occur in the Langbeinites family. The ammonia produced has a pungent smell and is toxic.
Airborne particles of evaporated ammonium sulfate comprise approximately 30% of fine particulate pollution worldwide. [ 18 ]
It reacts with additional sulfuric acid to give triammonium hydrogen disulphate,, (NH 4 ) 3 H(SO 4 ) 2 . [ 19 ]
In November 2009, a ban on ammonium sulfate, ammonium nitrate and calcium ammonium nitrate fertilizers was imposed in the former Malakand Division —comprising the Upper Dir , Lower Dir , Swat , Chitral and Malakand districts of the North West Frontier Province (NWFP) of Pakistan , by the NWFP government, following reports that they were used by militants to make explosives. In January 2010, these substances were also banned in Afghanistan for the same reason. [ 20 ] | https://en.wikipedia.org/wiki/H8N2O4S |
The HA-tag is a protein tag derived from the human influenza hemagglutinin (HA) protein, which allows the virus to target and enter host cells. An HA-tag is composed of a peptide derived from the HA-molecule corresponding to amino acids 98-106, which can be recognized and selectively bound by commercially available antibodies . This makes HA a powerful tool in molecular biology , commonly included in expression vectors and in the production of recombinant proteins . [ 1 ] Like other epitope tags, HA-tag is small and generally does not alter the traits of proteins it is attached to. [ 2 ] As a result HA-tags are often used to identify protein-protein interactions or to detect protein expression, using Co-Immunoprecipitation or Western blot respectively. [ 3 ] [ 4 ]
The HA-tag is not suitable for detection or purification of proteins from apoptotic cells since it is cleaved by Caspase-3 and / or Caspase-7 after its sequence DVPD, causing it to lose its immunoreactivity . [ 5 ] Labeling of endogenous proteins with HA-tag using CRISPR was recently accomplished in-vivo in differentiated neurons . [ 6 ]
The DNA sequences for the HA-tag include: 5'-TAC-CCA-TAC-GAT-GTT-CCA-GAT-TAC-GCT-3' or 5'-TAT-CCA-TAT-GAT-GTT-CCA-GAT-TAT-GCT-3'. The resulting amino acid sequence is YPYDVPDYA (Tyr-Pro-Tyr-Asp-Val-Pro-Asp-Tyr-Ala). [ 7 ] | https://en.wikipedia.org/wiki/HA-tag |
The HACEK organisms are a group of fastidious Gram-negative bacteria that are an unusual cause of infective endocarditis , which is an inflammation of the heart due to bacterial infection. [ 1 ] HACEK is an abbreviation of the initials of the genera of this group of bacteria: Haemophilus , Aggregatibacter (previously Actinobacillus ), Cardiobacterium , Eikenella , Kingella . [ 1 ] The HACEK organisms are a normal part of the human microbiota , living in the oral - pharyngeal region. [ 2 ]
The bacteria were originally grouped because they were thought to be a significant cause of infective endocarditis, but recent research has shown that they are rare and only responsible for 1.4–3.0% of all cases of this disease. [ 1 ]
HACEK originally referred to Haemophilus parainfluenzae , Haemophilus aphrophilus , Actinobacillus actinomycetemcomitans , Cardiobacterium hominis , Eikenella corrodens , and Kingella kingae . However, taxonomic rearrangements have changed the A to Aggregatibacter species and the H to Haemophilus species to reflect the recategorization and novel identification of many of the species in these genera . [ 1 ] Some reviews of medical literature on HACEK organisms use the older classification, [ 3 ] but recent papers are using the new classification. [ 4 ] [ 5 ] [ 6 ]
A list of HACEK organisms:
All of these organisms are part of the normal oropharyngeal flora, which grow slowly (up to 14 days), prefer a carbon dioxide–enriched atmosphere, and share an enhanced capacity to produce endocardial infections, especially in young children. Collectively, they account for 5–10% of cases of infective endocarditis involving native valves and are the most common Gram-negative cause of endocarditis among people who do not use drugs intravenously. They have been a frequent cause of culture-negative endocarditis. Culture-negative refers to an inability to produce a colony on regular agar plates because these bacteria are fastidious (require a specific nutrient).
In addition to valvular infections in the heart, they can also produce other infections, such as bacteremia , abscess , peritonitis , otitis media , conjunctivitis , pneumonia , arthritis , osteomyelitis , and periodontal infections .
The treatment of choice for HACEK organisms in endocarditis is the third-generation cephalosporin and β-Lactam antibiotic ceftriaxone . Ampicillin (a penicillin ), combined with low-dose gentamicin (an aminoglycoside ) is another therapeutic option. [ 7 ] | https://en.wikipedia.org/wiki/HACEK_organisms |
HALCA ( Highly Advanced Laboratory for Communications and Astronomy ), also known for its project name VSOP ( VLBI Space Observatory Programme ), the code name MUSES-B (for the second of the Mu Space Engineering Spacecraft series), or just Haruka ("far away, distant" ( はるか ) ) [ 2 ] was a Japanese 8 meter diameter radio telescope satellite which was used for Very Long Baseline Interferometry (VLBI) . It was the first such space-borne dedicated VLBI mission.
It was placed in a highly elliptical orbit with an apogee altitude of 21,400 km and a perigee altitude of 560 km, with an orbital period of approximately 6.3 hours. This orbit allowed imaging of celestial radio sources by the satellite in conjunction with an array of ground-based radio telescopes, such that both good (u,v) plane coverage and very high resolution were obtained.
Although designed to observe in three frequency bands: 1.6 GHz, 5.0 GHz, and 22 GHz, it was found that the sensitivity of the 22 GHz band had severely degraded after orbital deployment, probably caused by vibrational deformation of the dish shape at launch, thus limiting observations to the 1.6 GHz and 5.0 GHz bands.
HALCA was launched in February 1997 from Kagoshima Space Center , and made its final VSOP observations in October 2003, far exceeding its 3-year predicted lifespan, before the loss of attitude control. All operations were officially ended in November 2005. [ 3 ]
A follow-up mission ASTRO-G (VSOP-2) was planned, with a proposed launch date of 2012, but the project was eventually cancelled in 2011 due to increasing costs and the difficulties of achieving its science goals. It was expected to achieve resolutions up to ten times higher and up to ten times greater sensitivity than its predecessor HALCA.
The cancellation of ASTRO-G left the Russian Spektr-R mission as the only then operational space VLBI facility. Spektr-R stopped operating in 2019.
The large 8 meter antenna was designed to unfold in space as the unfolded configuration did not fit inside the rocket fairing. The antenna was a metal mesh of 6000 cables. To form an ideal shape the length of the cables were adjusted on the backside of the antenna. One concern was that the cables could entangle. [ 4 ] The deployment of the main reflector started on February 27, 1997. The deployment was done over three hours on the first day and was completed in 20 minutes during the next day. [ 5 ] | https://en.wikipedia.org/wiki/HALCA |
HARASSmap is a mobile and online technology non-profit that uses interactive mapping to try to reduce the social acceptability of sexual harassment throughout Egypt. [ 1 ]
As of 2005, HARASSmap co-founder Rebecca Chiao began investigating the prevalence of sexual harassment in the daily life of Egyptian women and eventually, with the help of friends and volunteers, launched a campaign that would eventually be adopted by the Egyptian Center for Women's Rights. [ 2 ] While these efforts were aimed towards changing sexual harassment legislation within the Egyptian government to better criminalize offences, there was a push for more urgent action. In a 2008 study conducted by the Egyptian Center for Women's Rights, researchers found that out of the 1,010 women they surveyed, 83% of Egyptian women and 98% of foreign women in Egypt said they had experienced sexual harassment. [ 3 ] Deciding it was time for some on-the-ground action, Chiao and HARASSmap co-founder Engy Ghozlan decided to harness the power of a mobile friendly population and linked FrontlineSMS and Ushahidi to create the technological basis for HARASSmap. [ 4 ] [ 5 ]
HARASSmap was co-founded in 2010 by Rebecca Chiao (Project Leader), Engy Ghozlan, Amel Fahmy (Principal investigator of Research Unit) and Sawsan Gad. [ 6 ]
As a volunteer-based initiative, HARASSmap aims to end the social acceptability of sexual harassment and assault in Egypt. [ 7 ] In addition to its interactive mapping service and community outreach service, HARASSmap offers self-defence classes and community education for both men and women. [ 8 ]
When someone experiences or is a witness to an incidence of sexual harassment, they can fill out an online report or send the report via SMS, e-mail, Twitter or Facebook [ 9 ] including the details of the incident as well as address, street name and public points of interest. [ 10 ] HARASSmap then verifies the reports and places them on a Google map of Egypt, which localises sexual harassment hotspots. [ 11 ] The map will show red dots where incidences of sexual harassment have taken place.
HARASSmap volunteers visit the areas where incidences have occurred to raise awareness about what constitutes sexual harassment and to work towards ending it. [ 12 ] [ 13 ] By meeting with local shop owners, police officers, doormen and other public venues, the HARASSmap team is working to mobilize them to make their neighbourhoods "harassment-free zones". [ 14 ]
HARASSmap won the 2011 World Summit Youth Award [ 15 ] and the 2012 Deutsche Welle Best of the Blogs Award for 'Best Use of Technology for Social Good' [ 16 ] and is now an incubated social enterprise at Nahdey El Mahrousa. [ 17 ] Since HARASSmap's inception, they have been approached by activists from 25 countries for help adopting similar initiatives. In 2012, the International Development Research Centre (IDRC) of Canada offered HARASSmap a grant to continue study sexual harassment in Egypt based on reports submitted by participants and gather information on the methodological issues in the collection and use of crowd sourced data. [ 18 ] | https://en.wikipedia.org/wiki/HARASSmap |
HARMST is an acronym for h igh a spect r atio m icrostructure t echnology, which describes fabrication technologies,
used to create high- aspect-ratio microstructures [ 1 ] with heights between tens of micrometers up to a centimeter, and aspect ratios greater than 10:1. Examples include the LIGA fabrication process, advanced silicon etch , and deep reactive ion etching .
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HARMST |
HARPS-N , the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere is a high-precision radial-velocity spectrograph , installed at the Italian Telescopio Nazionale Galileo , a 3.58-metre telescope located at the Roque de los Muchachos Observatory on the island of La Palma, Canary Islands , Spain.
HARPS-N is the counterpart for the Northern Hemisphere of the similar HARPS instrument installed on the ESO 3.6 m Telescope at La Silla Observatory in Chile. [ 1 ] It allows for planetary research in the northern sky which hosts the Cygnus and Lyra constellations. In particular it allows for detailed follow up research to Kepler mission planet candidates, which are located in the Cygnus constellation region.
The instrument's main scientific goals are the discovery and characterization of terrestrial super-Earths by combining the measurements using transit photometry and doppler spectroscopy which provide both, the size and mass of the exoplanet. Based on the resulting density, rocky (terrestrial) Super-Earths can be distinguished from gaseous exoplanets. [ 2 ]
The HARPS-N Project is a collaboration between the Geneva Observatory (lead), the Center for Astrophysics in Cambridge ( Massachusetts ), the Universities of St. Andrews and Edinburgh , the Queen's University Belfast , the UK Astronomy Technology Centre and the Italian Istituto Nazionale di Astrofisica .
First light on sky was obtained by HARPS-N on March 27, 2012, and official operations started on August 1, 2012. [ 3 ]
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This spectroscopy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HARPS-N |
HASTAC (/ˈhāˌstak/), also known as the Humanities, Arts, Science and Technology Alliance and Collaboratory, is a virtual organization and platform comprising over 18,000 individuals and more than 400 affiliate institutions. Members of the HASTAC network actively contribute to the community through an open-access website, [ 1 ] by organizing and participating in HASTAC conferences and workshops, and by collaborating with fellow network members.
Until 2016, HASTAC managed the annual $2 million MacArthur Foundation Digital Media and Learning Competition. [ 2 ] The 2011 competition, titled “Badges for Lifelong Learning,” was launched in collaboration with the Mozilla Foundation and focused on the use of digital badges to motivate learning, recognize achievement, and validate the acquisition of knowledge or skills.
HASTAC has received funding from various institutions. As of 2021, HASTAC is jointly administered and funded by The Graduate Center, CUNY and Dartmouth College .
HASTAC was founded in 2002 by Cathy N. Davidson , Ruth F. DeVarney Professor of English, John Hope Franklin Humanities Institute Professor of Interdisciplinary Studies and co-director of the PhD Lab in Digital Knowledge at Duke University and co-founder of the John Hope Franklin Humanities Institute at Duke University , [ 3 ] and David Theo Goldberg , Director of the University of California 's statewide Humanities Research Institute ( UCHRI ). [ 4 ]
At a meeting of humanities leaders held by the Mellon Foundation in 2002, it was noted that Davidson and Goldberg had each, independently, been working on a variety of projects with scientists and engineers dedicated to expanding the uses of technology in research, teaching, and electronic publishing. They resolved to contact others who were building and analyzing the social and ethical dimensions of new technologies and soon formed the HASTAC.
Currently, HASTAC is governed by a Steering Committee [ 5 ] of individuals from different institutions and disciplines.
In 2008, HASTAC initiated the HASTAC Scholars Program, an annual fellowship program that recognizes graduate and undergraduate students engaged in work across the areas of technology, the arts, the humanities, and the social sciences. As of 2021, over 1,800 people from 260 institutions have been named HASTAC Scholars. [ 6 ]
Created in 2007, the HASTAC/MacArthur Foundation Digital Media and Learning Competition is designed to find and inspire the most uses of new media in support of connected learning . [ 7 ] Awards have recognized individuals, for-profit companies, universities, and community organizations using new media to transform learning. Information about Digital Media and Learning Competition winners can be found on HASTAC.
Digital Publication Projects: Michigan Series in Digital Humanities@digitalculturebooks and the UM/HASTAC Digital Humanities Publication Prize
The University of Michigan Press and HASTAC launched The University of Michigan Series in Digital Humanities@digitalculturebooks and the UM/HASTAC Digital Humanities Publication Prize in December 2009. [ 8 ] Series editors include Julie Thompson Klein and Tara McPherson; advisory board includes Cathy N. Davidson, Daniel Herwitz, and Wendy Chun (Brown). [ 9 ] Initial 2012 winners were Jentery Sayers and Sheila Brennan. [ 10 ]
HASTAC member organizations organize international conferences.
HASTAC hosted the "Storming the Academy" tent, which discussed and workshopped open learning and peer-to-peer assessment strategies, ideas, and lessons, at the Mozilla Drumbeat Festival in Barcelona on Nov. 3–5, 2010.
On October 16, 2010, HASTAC hosted and helped to organize THATCamp RTP at Duke University's John Hope Franklin Humanities Institute. [ 25 ] It was the first area THATCamp [ 26 ] for the Research Triangle Park area of North Carolina. | https://en.wikipedia.org/wiki/HASTAC |
Hypermedia as the engine of application state ( HATEOAS ) is a constraint of the REST software architectural style that distinguishes it from other network architectural styles . [ 1 ]
With HATEOAS, a client interacts with a network application whose application servers provide information dynamically through hypermedia . A REST client needs little to no prior knowledge about how to interact with an application or server beyond a generic understanding of hypermedia.
By contrast, clients and servers in Common Object Request Broker Architecture (CORBA) interact through a fixed interface shared through documentation or an interface description language (IDL).
The restrictions imposed by HATEOAS decouple client and server. This enables server functionality to evolve independently.
The term was coined in 2000 by Roy Fielding in his doctoral dissertation. [ 2 ]
A user-agent makes an HTTP request to a REST API through an entry point URL . All subsequent requests the user-agent may make are discovered inside the response to each request. The media types used for these representations, and the link relations they may contain, are part of the API. The client transitions through application states by selecting from the links within a representation or by manipulating the representation in other ways afforded by its media type. In this way, RESTful interaction is driven by hypermedia, rather than out-of-band information. [ 3 ]
For example, this GET request fetches an account resource, requesting details in a JSON representation: [ 4 ]
The response is:
The response contains these possible follow-up links: POST a deposit, withdrawal, transfer, or close request (to close the account).
As an example, later, after the account has been overdrawn, there is a different set of available links, because the account is overdrawn.
Now only one link is available: to deposit more money (by POSTing to deposits). In its current state , the other links are not available. Hence the term Engine of Application State . What actions are possible varies as the state of the resource varies.
A client does not need to understand every media type and communication mechanism offered by the server. The ability to understand new media types may be acquired at run-time through " code-on-demand " provided to the client by the server. [ 2 ]
The HATEOAS constraint is an essential part of the "uniform interface" feature of REST, as defined in Roy Fielding 's doctoral dissertation. [ 2 ] Fielding has further described the concept on his blog. [ 3 ]
The purpose of some of the strictness of this and other REST constraints, Fielding explains, is "software design on the scale of decades: every detail is intended to promote software longevity and independent evolution. Many of the constraints are directly opposed to short-term efficiency. Unfortunately, people are fairly good at short-term design, and usually awful at long-term design". [ 3 ] | https://en.wikipedia.org/wiki/HATEOAS |
Hazmat Class 1 are explosive materials which are any substance or article, including a device, which is designed to function by explosion or which, by chemical reaction within itself is able to function in a similar manner even if not designed to function by explosion. [ a ]
Class 1 consists of six ' divisions ', that describes the potential hazard posed by the explosive. The division number is the second number after the decimal point on a placard. [ b ] The classification has an additional layer, of categorization, known as ' compatibility groups ', which breaks explosives in the same division into one of 13 groups, identified by a letter, which is used to separate incompatible explosives from each other. This letter also appears on the placard, following the number. [ c ]
The movement of class 1 materials is tightly regulated, especially for divisions 1.1 and 1.2, which represent some of the most dangerous explosives, with the greatest potential for destruction and loss of life. Regulations in the United States require drivers have and follow a pre-prepared route, not park the vehicle within 300 feet (91 m) of bridges, tunnels, a fire, or crowded places. [ 1 ] The vehicle must be attended to by its driver at all times while its parked. Drivers are also required to carry the following paperwork and keep it in an accessible and easy to locate location: written emergency instructions, written route plan, a copy of Federal Motor Carrier Safety Regulations, Part 397 - Transport of Hazardous Materials; driving and parking rules . [ 2 ] Some tunnels and bridges severely restrict or completely forbid vehicles carrying Class 1 cargoes. [ 3 ] [ 4 ]
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 7 ]
Except as provided in the following paragraph, explosives of the same compatibility group but of different divisions may be transported together provided that the whole shipment is transported as though its entire contents were of the lower numerical division (i.e., Division 1.1 being lower than 1.2). For example, a mixed shipment of Division 1.2 materials and Division 1.4 materials, both of compatibility group D, must be transported as Division 1.2 materials
When Division 1.5 materials, compatibility group D, are transported in the same freight container as Division 1.2 materials, compatibility group D, the shipment must be transported as Division 1.1 materials, compatibility group D.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 8 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_1_Explosives |
The HAZMAT Class 2 in United States law includes all gases which are compressed and stored for transportation. Class 2 has three divisions: Flammable (also called combustible ), Non-Flammable/Non-Poisonous, and Poisonous. This classification is based on the United Nations' Recommendations on the Transport of Dangerous Goods - Model Regulations. In Canada, the Transportation of Dangerous Goods Regulations , or TDGR, are also based on the UN Model Regulations and contain the same three divisions.
A gas is a substance which
Gases are assigned to one of three divisions
Aerosols also fall into Class 2 divisions where an aerosol is defined as an article consisting of any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, the sole purpose of which is to expel a nonpoisonous (other than a Division 6.1 Packing Group III material) liquid, paste, or powder and fitted with a self-closing release device allowing the contents to be ejected by the gas.
Division 2.1 : Flammable, Non-Toxic Gas
Flammable gas means any material that:
The following applies to aerosols:
Division 2.2 : Non-Flammable, Non-Toxic Gas
This division includes compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas. A non-flammable, nonpoisonous compressed gas (Division 2.2) means any material (or mixture) which:
A non-flammable gas means any material that:
The following applies to aerosols:
Division 2.3 : Toxic Gas
Gas poisonous by inhalation means a material which is a gas at 20 °C or less and a pressure of 101.3 kPa (a material which has a boiling point of 20 °C or less at 101.3kPa (14.7 psi)) and which:
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_2_Gases |
A flammable liquid is a liquid with flash point of not more than 60.5 °C (141 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging.
Class 3 : Flammable Liquids
A flammable liquid is a liquid having a flash point of not more than 60 °C (140 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging. The following exceptions apply:
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_3_Flammable_liquids |
Flammable solids are any materials in the solid phase of matter that can readily undergo combustion in the presence of a source of ignition under standard circumstances, i.e. without:
Division 4.1 : Flammable solid
Flammable solids are any of the following four types of materials:
Division 4.2 : Spontaneously combustible
Spontaneously combustible material is:
Division 4.3 : Dangerous when wet
Dangerous when wet material is material that, by contact with water, is liable to become spontaneously flammable or to give off flammable or toxic gas at a rate greater than 1 liter per kilogram of the material, per hour, when tested in accordance with the UN Manual of Tests and Criteria. Pure alkali metals are known examples of this.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_4_Flammable_solids |
An oxidizer is a chemical that readily yields oxygen in reactions, thereby causing or enhancing combustion.
An oxidizer is a material that may, generally by yielding oxygen, cause or enhance the combustion of other materials.
An organic peroxide is any organic compound containing oxygen (O) in the bivalent -O-O- structure and which may be considered a derivative of hydrogen peroxide, where one or more of the hydrogen atoms have been replaced by organic radicals, unless any of the following paragraphs applies:
Prior to 2007, the placard for 'Organic Peroxide' (5.2) was entirely yellow, like placard 5.1.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_5_Oxidizing_agents_and_organic_peroxides |
Poisonous material is a material, other than a gas, known to be so toxic to humans that it presents a health hazard during transportation.
Division 6.1 : Poisonous material is a material, other than a gas, which is known to be so toxic to humans as to afford a hazard to health during transportation, or which, in the absence of adequate data on human toxicity:
Division 6.2 : Biohazards .
where:
C {\displaystyle C} = the percent concentration of constituent A, B ... Z in the mixture; T {\displaystyle T} = the oral LD50 values of constituent A, B ... Z;
LC 50 for acute toxicity on inhalation means that concentration of vapor, mist, or dust which, administered by continuous inhalation for one hour to both male and female young adult albino rats, causes death within 14 days in half of the animals tested. If the material is administered to the animals as a dust or mist, more than 90% of the particles available for inhalation in the test must have a diameter of 10 μm or less if it is reasonably foreseeable that such concentrations could be encountered by a human during transport. The result is expressed in mg/L of air for dusts and mists or in mL/m 3 of air ( parts per million ) for vapors. See 49CFR 173.133(b) for LC50 determination for mixtures and for limit tests.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ]
1. The packing group assignment for routes of administration other than inhalation of vapors shall be in accordance with the following table:
2. The packing group and hazard zone assignments for liquids (see 49CFR 173.115(c) of this subpart for gases) based on inhalation of vapors shall be in accordance with the following Table:
The criteria for packing group I, hazard zone A are not met.
The criteria for packing group I, hazard zones A and B are not met.
The criteria for packing groups I and II, hazard zones A, B and C are not met.
Note 2 : A liquid in Division 6.1 meeting criteria for packing group I, hazard zones A or B stated in paragraph (a)(2) of this section is a material poisonous by inhalation subject to the additional hazard communication requirements in 49CFR 172.203(m)(3), 49CFR 172.313 and Table 1 of 49CFR 172.504(e) of this subchapter.
3. When the packing group determined by applying these criteria is different for two or more (oral, dermal or inhalation) routes of administration, the packing group assigned to the material shall be that indicated for the highest degree of toxicity for any of the routes of administration.
4. Notwithstanding the provisions of this paragraph, the packing group and hazard zone of a tear gas substance is as assigned in Column 5 of the 49CFR 172.101 Table.
L C 50 ( m i x t u r e ) = 1 ∑ i = 1 n f i L C 50 i {\displaystyle LC_{50}(mixture)={\cfrac {1}{\textstyle \sum _{i=1}^{n}{\cfrac {f_{i}}{LC_{50i}}}}}}
2. The volatility of each component substance is estimated using the formula:
V i = P i × 10 6 101.3 [ m L m 3 ] {\displaystyle V_{i}=P_{i}\times {\tfrac {10^{6}}{101.3}}[{\tfrac {mL}{m^{3}}}]}
3. The ratio of the volatility to the LC 50 is calculated using the formula:
The criteria for packing group I, hazard zone A are not met.
The criteria for packing group I, hazard zones A and B are not met.
The criteria for packing group I, hazard zones A, B and packing group II.
In the absence of LC 50 data on the poisonous (toxic) constituent substances, the mixture may be assigned a packing group and hazard zone based on simplified threshold toxicity tests. When these threshold tests are used, the most restrictive packing group and hazard zone must be determined and used for the transportation of the mixture. | https://en.wikipedia.org/wiki/HAZMAT_Class_6_Toxic_and_infectious_substances |
Radioactive substances are materials that emit radiation .
Any quantity of packages bearing the RADIOACTIVE YELLOW III label (LSA-III).
Some radioactive materials in "exclusive use" with low specific activity radioactive materials will not bear the label, however, the RADIOACTIVE placard is required.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 2 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_7_Radioactive_substances |
A corrosive material is a liquid or solid that causes full thickness destruction of human skin at the site of contact within a specified period of time. A liquid that has a severe corrosion rate on steel or aluminum based on the criteria in 49CFR 173.137(c)(2) is also a corrosive material .
454 kg (1001 lbs) or more gross weight of a corrosive material. Although the corrosive class includes both acids and bases , the hazardous materials load and segregation chart does not make any reference to the separation of various incompatible corrosive materials from each other. In spite of this, however, when shipping corrosives, care should be taken to ensure that incompatible corrosive materials can not become mixed, as many corrosives react very violently if mixed. If responding to a transportation incident involving corrosive materials (especially a mixture of corrosives), caution should be exercised.
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ] | https://en.wikipedia.org/wiki/HAZMAT_Class_8_Corrosive_substances |
The miscellaneous hazardous materials category encompasses all hazardous materials that do not fit one of the definitions listed in Class 1 through Class 8.
The miscellaneous hazardous material is a material that presents a hazard during transportation but which does not meet the definition of any other hazard class . This class includes:
A new sub-class, class 9A, has been in effect since January 1, 2017. This is limited to the labeling of the transport of lithium batteries .
Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. [ 1 ]
The packing group of a Class 9 material is as indicated in Column 5 of the 49CFR 172.101 Table. | https://en.wikipedia.org/wiki/HAZMAT_Class_9_Miscellaneous |
Hazardous Waste Operations and Emergency Response ( HAZWOPER ; / ˈ h æ z w ɒ p ər / HAZ -waw-pər ) is a set of guidelines produced by a collaboration between National Institute of Occupational Safety and Health , Occupational Safety and Health Administration , United States Coast Guard , and Environmental Protection Agency and more which regulates hazardous waste operations and emergency services in the United States and its territories. [ 1 ] These regulations are recognized and implement throughout many government departments and need their cooperation to work effectively. With these guidelines, the U.S. government regulates hazardous wastes and dangerous goods from inception to disposal.
HAZWOPER applies to five groups of employers and their employees. This includes employees who are exposed (or potentially exposed) to hazardous substances (including hazardous waste) and who are engaged in one of the following operations as specified by OSHA regulations 1910.120(a)(1)(i-v) and 1926.65(a)(1)(i-v): [ 2 ]
The most commonly used manual for HAZWOPER activities is Department of Health and Human Services Publication 85–115, Occupational Safety and Health Guidance Manual for Hazardous Waste Site Activities . [ 1 ] Written for government contractors and first responders , the manual lists safety requirements for cleanups and emergency-response operations. Sources that should be used when determining the regulation of HAZWOPER are the Emergency Response Guidebook [ 3 ] This is a book that shows how hazardous materials should be labelled and what each visual indicator means, this can assist emergency responders when trying to figure out the cause of the fire or what kind of material they are dealing with. This guidebook is through the Department of Transportation (DOT) so it is catered towards transporting and storing materials. It is very important that these rules and regulation to be put into place because these hazardous materials can cause chronic and acute problems such as irritation, sanitation, and other toxic illnesses that could be fatal. Incorrect disposal of hazardous waste can also have bigger effects such as fires, explosions, or other emergency events. [ 2 ]
Although it is a multi-agency collaboration, HAZWOPER describes OSHA-required regulatory training. Its relevance dates to World War II, when waste accumulated during construction of the atomic bomb at the Hanford Site . Years later, high-profile environmental mishaps (such as Love Canal in 1978 and the attempted 1979 Valley of the Drums cleanup) spurred federal legislative action, [ 4 ] awakening the U.S. to the need to control and contain hazardous waste . Two programs— CERCLA , the Comprehensive Environmental Response, Compensation, and Liability Act and the Resource Conservation and Recovery Act (RCRA) of 1976—were implemented to deal with these wastes. CERCLA (the Superfund) was designed to deal with existing waste sites, and RCRA addressed newly generated waste. The acronym HAZWOPER originally derived from the Department of Defense 's Hazardous Waste Operations (HAZWOP), implemented on military bases slated for the disposal of hazardous waste left on-site after World War II . In 1989 production ended at the Hanford Site, and work shifted to the cleanup of portions of the site contaminated with hazardous substances including radionuclides and chemical waste. [ 5 ] These agencies used their knowledge together to create a manual on how to handle hazardous waste. These regulations are published through a joint effort between the federal agencies and are enforced in the states by each agency. In 1984, the combined-agency effort resulted in the Hazardous Waste Operations and Emergency Response Guidance Manual . [ 1 ] On March 6, 1990, OSHA published Hazardous Waste Operations and Emergency Response 1910.120, [ 6 ] the HAZWOPER standard codifying the health-and-safety requirements companies must meet to perform hazardous-waste cleanup or respond to emergencies. There are similar versions of these regulations throughout the federal agencies, the EPA and OSHA versions are the most followed. The EPA version is more focused on the environment and protecting nature, while OSHA focuses more on workers and how they should handle waste cleanup. [ 7 ] There are more versions such as the Department of Transportation [ 3 ] and Federal Emergency Management Association that implement the rules of hazardous waste cleanup and regulations.
Hazardous waste, as defined by the standard, is a waste (or combination of wastes) according to 40 CFR §261.3 [ 7 ] or substances defined as hazardous wastes in 49 CFR §171.8. [ 8 ] Hazardous waste is characterized if the substance is ignitable, toxic, corrosive, reactive, or toxic. There are four different categories of hazardous waste, they are listed as groups F, K, P, and U. F group wastes are common industries that do not fit into a specific category, and K group wastes include industries from a specific list. P and U materials are composed of pure hazards and commercial grade formulas. [ 9 ] It is important to make sure that these categories and groups are labelled correctly and workers have proper training on storing hazardous waste as incorrectly moving and places hazardous chemicals together may cause a fire hazard or another explosion hazard. The EPA made sure to check all the types of chemicals and waste and compiled this classification system under The Resource Conservation and Recovery Act (RCRA) which was a bill passed in 1976. [ 10 ]
OSHA recognizes several levels of training, based on the work the employee performs and the degree of hazard faced. Each level requires a training program, with OSHA-specified topics and minimum training time.
In some instances, training levels overlap; other levels are not authorized by OSHA because their training is not sufficiently specific. [ 7 ] A site safety supervisor (or officer) and a competent industrial hygienist or other technically qualified, HAZWOPER-trained person should be consulted.
An employer must ensure that the training provider covers the areas of knowledge required by the standard and provides certification to students that they have passed the training. Since the certification is for the student, not the employer, the trainer must cover all aspects of HAZWOPER operations and not only those at the current site. OSHA training requires cleanup workers to focus on personal protective equipment separately from emergency-response equipment. [ 5 ] There are 4 levels of PPE that range from A-D that HAZWOPER training will cover that vary in skin, respiratory and eye protection. [ 11 ] NIOSH created a handbook that explains the types of respiratory equipment that should be used in a hazardous material situation. This guidebook is named Chemical, Biological, Radiological, and Nuclear (CBRN) Respiratory Protection Handbook, [ 12 ] this book tells the reader about how to maintain their respirators, training for the equipment, and how to dispose of the respirators. NIOSH and OSHA also created a pyramid matrix on what types of protection is needed for each level of waste management. There are three different levels that correlate with different levels of coverage. Each layer of the pyramid correlates with the likeliness of CBRN contamination is known, according to those exposures is what OSHA and NIOSH decide what kind of equipment is needed. [ 13 ] | https://en.wikipedia.org/wiki/HAZWOPER |
Hydrogen chloride Hydrogen fluoride Hydrogen iodide
Hydrogen astatide , also known as astatine hydride , astatane , astatidohydrogen or hydroastatic acid , is a chemical compound with the chemical formula HAt, consisting of an astatine atom covalently bonded to a hydrogen atom. [ 4 ] It thus is a hydrogen halide .
This chemical compound can dissolve in water to form hydroastatic acid, which exhibits properties very similar to the other five binary acids , and is in fact the strongest among them. However, it is limited in use due to its ready decomposition into elemental hydrogen and astatine, [ 5 ] as well as the short half-life of the various isotopes of astatine . Because the atoms have a nearly equal electronegativity , and as the At + ion has been observed, [ 6 ] dissociation could easily result in the hydrogen carrying the negative charge. Thus, a hydrogen astatide sample can undergo the following reaction:
This results in elemental hydrogen gas and astatine precipitate . Furthermore, a trend for hydrogen halides, or HX, is that enthalpy of formation becomes less negative, i.e., decreases in magnitude but increases in absolute terms, as the halide becomes larger. Whereas hydroiodic acid solutions are stable, the hydronium-astatide solution is clearly less stable than the water-hydrogen-astatine system. Finally, radiolysis from astatine nuclei could sever the H–At bonds.
Additionally, astatine has no stable isotopes . The most stable is astatine-210, which has a half-life of approximately 8.1 hours, making its chemical compounds especially difficult to work with, [ 7 ] as the astatine will quickly decay into other elements.
Hydrogen astatide can be produced by reacting astatine with hydrocarbons (such as ethane ): [ 8 ]
This reaction also produces the corresponding alkyl astatide, in this case ethyl astatide (astatoethane). | https://en.wikipedia.org/wiki/HAt |
Chloroauric acid is an inorganic compound with the chemical formula H[AuCl 4 ] . It forms hydrates H[AuCl 4 ]· n H 2 O . Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl 4 ] − anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia . These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles .
The tetrahydrate crystallizes as [H 5 O 2 ] + [AuCl 4 ] − and two water molecules. [ 2 ] [ 3 ]
The oxidation state of gold in H[AuCl 4 ] and [AuCl 4 ] − anion is +3. The salts of H[AuCl 4 ] (tetrachloroauric(III) acid) are tetrachloroaurates(III), containing [AuCl 4 ] − anions (tetrachloroaurate(III) anions), which have square planar molecular geometry . The Au–Cl distances are around 2.28 Å. Other d 8 complexes adopt similar structures, e.g. tetrachloroplatinate(II) [PtCl 4 ] 2− .
Solid chloroauric acid is a hydrophilic ( ionic ) protic solute . It is soluble in water and other oxygen-containing solvents, such as alcohols, esters, ethers, and ketones. For example, in dry dibutyl ether or diethylene glycol , the solubility exceeds 1 M. [ 4 ] [ 5 ] [ 6 ] Saturated solutions in the organic solvents often are the liquid solvates of specific stoichiometry. Chloroauric acid is a strong monoprotic acid.
When heated in air, solid H[AuCl 4 ]· n H 2 O melts in the water of crystallization, quickly darkens and becomes dark brown.
Since [AuCl 4 ] − is prone to hydrolyze, [ 7 ] upon treatment with an alkali metal base, chloroauric acid converts to gold(III) hydroxide . [ 8 ] The related thallium salt( Tl + [AuCl 4 ] − ) is poorly soluble in all nonreacting solvents. Salts of quaternary ammonium cations are known. [ 9 ] Other complex salts include [Au( bipy )Cl 2 ] + [AuCl 4 ] − [ 10 ] and [Co(NH 3 ) 6 ] 3+ [AuCl 4 ] − (Cl − ) 2 .
Partial reduction of chloroauric acid gives oxonium dichloridoaurate(1−). [ 11 ] Reduction may also yield other gold(I) complexes, especially with organic ligands. Often the ligand serves as reducing agent as illustrated with thiourea , CS(NH 2 ) 2 :
Chloroauric acid is the precursor to gold nanoparticles by precipitation onto mineral supports. [ 12 ] Heating of H[AuCl 4 ]· n H 2 O in a stream of chlorine gives gold(III) chloride ( Au 2 Cl 6 ). [ 13 ] Gold nanostructures can be made from chloroauric acid in a two-phase redox reaction whereby metallic clusters are amassed through the simultaneous attachment of self-assembled thiol monolayers on the growing nuclei. [AuCl 4 ] − is transferred from aqueous solution to toluene using tetraoctylammonium bromide where it is then reduced with aqueous sodium borohydride in the presence of a thiol. [ 14 ]
Chloroauric acid is produced by dissolving gold in aqua regia (a mixture of concentrated nitric and hydrochloric acids) followed by careful evaporation of the solution: [ 15 ] [ 16 ]
Under some conditions, oxygen can be used as an oxidant. [ 17 ] For higher efficiency, these processes are conducted in autoclaves , which allows greater control of temperature and pressure. Alternatively, a solution of H[AuCl 4 ] can be produced by electrolysis of gold metal in hydrochloric acid :
To prevent the deposition of gold on the cathode, the electrolysis is carried out in a cell equipped with a membrane. This method is used for refining gold. Some gold remains in solution in the form of [AuCl 2 ] − . [ 18 ]
Chloroauric acid is the precursor used in the purification of gold by electrolysis .
Liquid–liquid extraction of chloroauric acid is used for the recovery, concentrating, purification, and analytical determinations of gold. Of great importance is the extraction of H[AuCl 4 ] from hydrochloric medium by oxygen-containing extractants, such as alcohols, ketones, ethers and esters. The concentration of gold(III) in the extracts may exceed 1 mol/L. [ 4 ] [ 5 ] [ 6 ] Frequently used extractants for this purpose are dibutyl glycol, methyl isobutyl ketone , tributyl phosphate , dichlorodiethyl ether (chlorex). [ 19 ]
In histology , chlorauric acid is known as "brown gold chloride", and its sodium salt Na[AuCl 4 ] ( sodium tetrachloroaurate(III) ) as "gold chloride", "sodium gold chloride" or "yellow gold chloride". The sodium salt is used in a process called "toning" to improve the optical definition of tissue sections stained with silver . [ 20 ]
In photography , chlorauric acid can be used as a gold toner . [ 21 ]
Chloroauric acid is a strong eye, skin, and mucous membrane irritant. Prolonged skin contact with chloroauric acid may result in tissue destruction. Concentrated chloroauric acid is corrosive to skin and must, therefore, be handled with appropriate care, since it can cause skin burns, permanent eye damage, and irritation to mucous membranes. Gloves are worn when handling the compound. [ citation needed ] | https://en.wikipedia.org/wiki/HAuCl4 |
The trispyrazolylborate ligand , abbreviated Tp − , is an anionic tridentate and tripodal ligand . Trispyrazolylborate refers specifically to the anion [HB(C 3 N 2 H 3 ) 3 ] − . However, the term can also be used to refer to derivatives having substituents on the pyrazolyl rings. This class of compounds belongs to the family of ligands called scorpionate ligands . [ 1 ] [ 2 ]
As suggested by the resonance structures, the nitrogen centers that are not bonded to boron are basic. These centers bind to three adjacent sites of a metal such that the simple adducts have C 3v symmetry . The facial bonding mode is reminiscent of cyclopentadienyl ligands, although the ligand field stabilization energy of Tp − is weaker as indicated by the fact that Fe(Tp) 2 is a spin-crossover complex whereas ferrocene is low-spin.
The Tp ligands are usually prepared from the reaction of pyrazole with potassium borohydride : [ 3 ]
Intermediates include the monopyrazolylborate ([H 3 B(C 3 N 2 H 3 )] − ) and the bispyrazolylborate ([H 2 B(C 3 N 2 H 3 ) 2 ] − ). KTp (m.p. 188-189 °C) is a colourless solid that soluble in polar solvents.
Condensation of 3-substituted pyrazoles with borohydride affords the corresponding substituted Tp derivatives. The substituent forces boron to the less hindered nitrogen center. Thus 3-phenylpyrazole gives HB(C 3 N 2 H 2 Ph) 3 ] − , abbreviated [Tp Ph ] − , wherein the phenyl substituents project away from the metal. Analogously 3-isopropylpyrazole gives HB(C3N2H2iPr)3]-, abbreviated [Tp iPr ] − . 3,5-Dimethylpyrazole gives the hexamethylated ligand [HB(C 3 N 2 HMe 2 ) 3 ] − , sometimes called Tp* − . Because pyrazoles are readily prepared from 1,3-diketones, a large number of substituted Tp complexes are possible. Derivatives are known with perfluorinated, chiral, and functional substituents.
Illustrative of the synthetic routes to Tp R− complexes, MnBr(CO) 5 and KTp react as follows:
Electronically related compounds are known, such as CpMn(CO) 3 and [( 9-ane-S3 )Mn(CO) 3 ] + . The labile acetonitrile complex Mo(CO) 3 (MeCN) 3 reacts with KTp to give the anion [MoTp(CO) 3 ] − , which can be crystallised as its tetraethylammonium salt (see figure):
Protonation, allylation, and nitrosylation of this salt gives the corresponding neutral hydride , allyl , and nitrosyl (see figure) derivatives.
The inductive effect of substituents on the pyrazolyl groups is illustrated by the values of ν CO for Tp CF 3 CuCO (2201 cm −1 ) vs Tp Me CuCO (2137 cm −1 ). [ 4 ]
Although of no practical value, trispyrazolylborate compounds have been applied to a variety of themes. In bioinorganic chemistry , some of the first crystallizable copper dioxygen complexes were obtained using this ligand platform, including examples of the Cu 2 (μ-η2,η2-O 2 ) bonding mode. Models for hemerythrin , an enzyme with a diiron active site, and xanthine oxidase , a molybdoenzyme, have been examined. In such model complexes, the Tp − simulates the coordination environment provided by three imidazole ligands in proteins .
In organometallic chemistry , Tp*Rh(CO) 2 and related complexes participate in C-H activation reactions.
Derivatives of Grignard reagents can be generated, such as Tp iBu MgCH 3 . | https://en.wikipedia.org/wiki/HB(C3N2H3)3 |
Fluoroboric acid or tetrafluoroboric acid (archaically, fluoboric acid ) is an inorganic compound with the simplified chemical formula H + [ B F 4 ] − . Solvent-free tetrafluoroboric acid ( H[BF 4 ] ) has not been reported. The term "fluoroboric acid" usually refers to a range of compounds including hydronium tetrafluoroborate ( [H 3 O] + [BF 4 ] − ), which are available as solutions. The ethyl ether solvate is also commercially available, where the fluoroboric acid can be represented by the formula [H((CH 3 CH 2 ) 2 O) n ] + [BF 4 ] − , where n is 2.
It is mainly produced as a precursor to other fluoroborate salts. [ 3 ] It is a strong acid . Fluoroboric acid is corrosive and attacks the skin. It is available commercially as a solution in water and other solvents such as diethyl ether . It is a strong acid with a weakly coordinating , non-oxidizing conjugate base. [ 2 ] It is structurally similar to perchloric acid , but lacks the hazards associated with oxidants .
Pure H[BF 4 ] has not been described. The same holds true for the superacids that are known by the simplified formulas H[PF 6 ] and H[SbF 6 ] . [ 4 ] [ 5 ] However, a solution of BF 3 in HF is highly acidic, having an approximate speciation of [H 2 F] + [BF 4 ] − (fluoronium tetrafluoroborate) and a Hammett acidity function of −16.6 at 7 mol % BF 3 , easily qualifying as a superacid. [ 6 ] Although the solvent-free H[BF 4 ] has not been isolated, its solvates are well characterized. These salts consist of protonated solvent as a cation, e.g., H 3 O + and H 5 O + 2 , and the tetrahedral BF − 4 anion. The anion and cations are strongly hydrogen-bonded. [ 7 ]
Aqueous solutions of H[BF 4 ] are produced by dissolving boric acid in aqueous hydrofluoric acid . [ 8 ] [ 9 ] Three equivalents of HF react to give the intermediate boron trifluoride and the fourth gives fluoroboric acid:
An anhydrous fluoroboric acid solution can be prepared by adding aqueous fluoroboric acid to an excess of acetic anhydride at 0°C, which produces a solution of fluoroboric acid, acetic acid , and residual acetic anhydride. [ 10 ]
The acidity of fluoroboric acid is complicated by the fact that its name refers to a range of different compounds, e.g. [H(CH 3 CH 2 ) 2 O] + [BF 4 ] − (dimethyloxonium tetrafluoroborate), [H 3 O] + [BF 4 ] − (oxonium tetrafluoroborate), and HF·BF 3 ( hydrogen fluoride - boron trifluoride 1:1 adduct) – each with a different acidity. The aqueous p K a is quoted as −0.44. [ 3 ] Titration of [N((CH 2 ) 3 CH 3 ) 4 ] + [BF 4 ] − (tetrabutylammonium tetrafluoroborate) in acetonitrile solution indicates that H[BF 4 ] , i.e., HF·BF 3 , has a p K a of 1.6 in that solvent. Its acidity is thus comparable to that of fluorosulfonic acid . [ 2 ]
Fluoroboric acid is the principal precursor to fluoroborate salts, which are typically prepared by treating the metal oxides with fluoroboric acid. The inorganic salts are intermediates in the manufacture of flame-retardant materials and glazing frits , and in electrolytic generation of boron . H[BF 4 ] is also used in aluminum etching and acid pickling.
H[BF 4 ] is used as a catalyst for alkylations and polymerizations . In carbohydrate protection reactions, ethereal fluoroboric acid is an efficient and cost-effective catalyst for transacetalation and isopropylidenation reactions. Acetonitrile solutions cleave acetals and some ethers . Many reactive cations have been obtained using fluoroboric acid, e.g. tropylium tetrafluoroborate ( C 7 H 7 + [BF 4 ] − ), triphenylcarbenium tetrafluoroborate ( Ph 3 C] + [BF 4 ] − ), triethyloxonium tetrafluoroborate ( Et 3 O] + [BF 4 ] − ), and benzenediazonium tetrafluoroborate ( [PhN 2 ] + [BF 4 ] − ).
Solutions of H[BF 4 ] are used in the electroplating of tin and tin alloys. In this application, methanesulfonic acid is displacing the use of H[BF 4 ] . [ 11 ] Fluoroboric acid is also used for high-speed electroplating of copper in fluoroborate baths. [ 12 ]
Fluoroboric acid is toxic and attacks skin and eyes. It attacks glass. [ 3 ] It hydrolyzes, releasing corrosive, volatile hydrogen fluoride . [ 11 ]
A series of fluoroboric acids is known in aqueous solutions. The series can be presented as follows: [ 13 ] | https://en.wikipedia.org/wiki/HBF4 |
5,5'-Hydrazinebistetrazole
HBT is a bistetrazole . [ 1 ] It is an explosive approximately as powerful as HMX or CL-20 , but it releases less toxic reaction products when detonated: ammonia and hydrogen cyanide . When combined with ADN or AN oxidizers, the amount of hydrogen cyanide produced by a deflagration may be reduced. The compound is thus considered by its advocates to be a more environmentally friendly explosive than traditional nitroamine -based explosives.
This article about a heterocyclic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HBT_(explosive) |
Bromous acid is the inorganic compound with the formula of HBrO 2 . It is an unstable compound, although salts of its conjugate base – bromites – have been isolated. In acidic solution, bromites decompose to bromine. [ 1 ]
In 1905, Richards A. H. proved the existence of bromous acid through a series of experiments involving silver nitrate (AgNO 3 ) and bromine. [ 2 ] The reaction of excess cold aqueous to form hypobromous acid (HBrO), silver bromide (AgBr) and nitric acid (HNO 3 ):
Richards discovered that the effect of adding excess liquid bromine in a concentrated silver nitrate (AgNO 3 ) resulted in a different reaction mechanism. From numbers of equivalent portions of acid bromine formed from the previous reaction, the ratio between oxygen and bromine was calculated, with the exact value of O:Br (0.149975:0.3745), suggesting the acid compound contains two oxygen atom to one bromine atom. Thus, the chemical structure of the acid compound was deducted as HBrO 2 . [ 2 ]
According to Richards, hypobromous acid (HBrO) arises by the reaction of bromine and silver nitrate solution: [ 2 ]
The molecule HBrO 2 has a bent structure with ∠(H−O−Br) angles of 106.1°. HOBrO also adopts a non-planar conformation with one isomer structure (2a) adopting a dihedral angle ∠(H−O−Br−O) of 74.2°. Moreover, the planar structures of two other isomers (2b- cis and 2c- trans ) are transition state for fast enantiomerization. [ 3 ]
Another study identified three isomers: HOOBr, HOBrO, and HBr(O)O. [ 4 ]
A oxidation reaction between hypobromous acid (HBrO) and hypochlorous acid (HClO) can be used to produce bromous acid (HBrO 2 ) and hydrochloric acid (HCl). [ citation needed ]
A redox reaction of hypobromous acid (HBrO) can form bromous acid (HBrO 2 ) as its product: [ citation needed ]
The disproportionation reaction of two equivalents hypobromous acid (HBrO) results in the formation of both bromous acid (HBrO 2 ) and hydrobromic acid (HBr): [ citation needed ]
A rearrangement reaction, which results from the syn-proportion of bromic acid (HBrO 3 ) and hydrobromic acid (HBr) gives bromous acid (HBrO 2 ): [ citation needed ]
The salts NaBrO 2 ·3H 2 O and Ba(BrO 2 ) 2 ·H 2 O have been crystallized. Upon treatment of these aqueous solutions with salts of Pb 2+ , Hg 2+ , and Ag + , the corresponding heavy metal bromites precipitate as solids. [ 1 ]
Bromous acid is a product of the Belousov–Zhabotinsky reaction resulting from the combination of potassium bromate, cerium(IV) sulfate, propanedioic acid and citric acid in dilute sulfuric acid. Bromous acid is an intermediate stage of the reaction between bromate ion ( BrO − 3 ) and bromine (Br − ): [ 5 ] [ 6 ]
Other relevant reactions in such oscillating reactions are:
Bromites reduce permanganates to manganates (VI): [ 1 ]
The acid dissociation constant of bromous acid, K a = [H + ][ BrO − 2 ] / [HBrO 2 ] , was determined using different methods.
The value of the p K a for bromous acid was estimated in research studying the decomposition of bromites. The research measured the rate of bromite decomposition as a function of hydrogen and bromite ion concentrations. The experimental data of the log of the initial velocity were plotted against pH. Using this method, the estimated p K a value for bromous acid was 6.25. [ 7 ]
Using another method, the pK a for bromous acid was measured based on the initial velocity of the reaction between sodium bromites and potassium iodine in a pH range of 2.9–8.0, at 25 °C and ionic strength of 0.06 M. The first order dependence of the initial velocity of this disproportionation reaction on [H + ] in a pH range of 4.5–8.0. The value of acid dissociation constant measured by this method is K a = (3.7 ± 0.9) × 10 −4 M and p K a = 3.43 ± 0.05 . [ 8 ]
In comparison to other oxygen-centered oxidants (hypohalites, anions of peroxides) and in line with its low basicity, bromite is a rather weak nucleophile. [ 9 ] Rate constants of bromite towards carbocations and acceptor-substituted olefins are by 1–3 orders of magnitude lower than the ones measured with hypobromite. | https://en.wikipedia.org/wiki/HBrO2 |
Bromic acid , also known as hydrogen bromate, is an oxoacid with the molecular formula HBrO 3 . It only exists in aqueous solution . [ 1 ] [ 2 ] It is a colorless solution that turns yellow at room temperature as it decomposes to bromine . [ 1 ] [ 3 ] Bromic acid and bromates are powerful oxidizing agents and are common ingredients in Belousov–Zhabotinsky reactions . [ 3 ] [ 4 ] Belousov-Zhabotinsky reactions are a classic example of non-equilibrium thermodynamics .
Low concentrations dissociate completely to hydronium and bromate while high concentrations decompose to form bromine. Bromic acid's high instability can be explained because the positively charged hypervalent bromine is connected to the electronegative OH group. [ 5 ]
There are several isomers of HBrO 3 . [ 5 ] [ 6 ] The calculated bond lengths are listed below based on three high level theories G2MP2, CCSD(T), and QCISD(T). [ 5 ]
The large energy barriers between these structures do not make isomerization possible. HOBrO 2 is the most stable isomer and is the one pictured above. [ 6 ]
Bromic acid is the product of a reaction of barium bromate and sulfuric acid. [ 1 ]
Barium sulfate is insoluble in water and forms a precipitate. The aqueous bromic acid can be decanted removing the barium sulfate. | https://en.wikipedia.org/wiki/HBrO3 |
Perbromic acid is the inorganic compound with the formula H Br O 4 . Perbromic acid is characterized as a colorless liquid which has no characteristic scent. It is an oxoacid of bromine , with an oxidation state of +7. Perbromic acid is a strong acid and strongly oxidizing , though dilute perbromic acid solutions are slow oxidizing agents. It is the most unstable of the halogen(VII) oxoacids. It decomposes rapidly on standing to bromic acid and oxygen , which releases toxic brown bromine vapors. It can be used in the synthesis of perbromate salts, by reacting with a base .
Perbromic acid is unstable and cannot be formed by displacement of chlorine from perchloric acid , as periodic acid is prepared; it can only be made by protonation of the perbromate ion. Perbromic acid is stable in aqueous solutions no greater than 6M. Perbromic acid solutions greater than 6M are unstable in air, where an autocatalytic decomposition of the compound will occur. Metals such as Ce 4+ and Ag + can also catalyze the compound.
Perbromic acid was discovered through the decay of a radioactive selenate sample, SeO 2− 4 , where bromine crystals were exposed to gamma radiation.
Perbromic acid is corrosive and an irritant, therefore it is extremely dangerous to the skin, eyes, airways, and digestive tract. Overexposure can lead to various effects such as suffocation of the lungs, loss of consciousness, and death. Due to its toxicity, prolonged or repeated exposure could also lead to organ damage via the lungs, kidneys, and intestines.
| https://en.wikipedia.org/wiki/HBrO4 |
Cyanoacetylene is an organic compound with the formula C 3 H N or H−C≡C−C≡N . It is the simplest cyanopolyyne . Cyanoacetylene has been detected by spectroscopic methods in interstellar clouds , [ 2 ] in the coma of comet Hale–Bopp and in the atmosphere of Saturn 's moon Titan , [ 3 ] where it sometimes forms expansive fog-like clouds. [ 4 ]
Cyanoacetylene is one of the molecules that was produced in the Miller–Urey experiment . [ 5 ]
Nickel carbonyl catalyzes cyanoacetylene carboalkoxylation to cyanoacrylate esters. [ 6 ] | https://en.wikipedia.org/wiki/HC3N |
In organic chemistry , cyanopolyynes are a family of organic compounds with the chemical formula HC n N ( n = 3,5,7,…) and the structural formula H−[C≡C−] n C≡N ( n = 1,2,3,…). Structurally, they are polyynes with a cyano group ( −C≡N ) covalently bonded to one of the terminal acetylene units ( H−C≡C ).
A rarely seen group of molecules both due to the difficulty in production and the unstable nature of the paired groups, the cyanopolyynes have been observed as a major organic component in interstellar clouds . [ 1 ] This is believed to be due to the hydrogen scarcity of some of these clouds. Interference with hydrogen is one of the reason for the molecule's instability due to the energetically favorable dissociation back into hydrogen cyanide and acetylene. [ 2 ]
Cyanopolyynes were first discovered in interstellar molecular clouds in 1971 using millimeter wave and microwave telescopes . [ 1 ] Since then many higher weight cyanopolyynes such as HC 7 N and HC 11 N have been discovered, although some of these identifications have been disputed. Other derivatives such as methylcyanoacetylene CH 3 C 3 N and ethylcyanoacetylene CH 3 CH 2 C 3 N have been observed as well. [ 3 ] The simplest example is cyanoacetylene , H−C≡C−C≡N. Cyanoacetylene is more common on Earth and it is believed to be the initial reagent for most of the photocatalyzed formation of the interstellar cyanopolyynes. Cyanoacetylene is one of the molecules that was produced in the Miller–Urey experiment and is expected to be found in carbon-rich environments. [ 4 ]
Identification is made through comparison of experimental spectrum with spectrum gathered from the telescope. This is commonly done with measurement of the rotational constant , the energy of the rotational transitions, or a measurement of the dissociation energy. These spectra can either be generated ab initio from a computational chemistry program or, such as with the more stable cyanoacetylene , by direct measurement of the spectra in an experiment. Once the spectra are generated, the telescope can scan within certain frequencies for the desired molecules. Quantification can be accomplished as well to determine the density of the compounds in the cloud.
The formation of cyanopolyynes in interstellar clouds is time-dependent. The formation of cyanopolyyne was studied and the abundances calculated in the dark cloud TMC-1 . In the early days of the TMC-1, the governing reactions were ion–molecule reactions. During this time cyanoacetylene, HC 3 N , formed through a series of ion-neutral reactions, with the final chemical reaction being:
However, for time after 10,000 years the dominant reactions were neutral–neutral reactions and two reaction mechanisms for the formation of cyanopolyynes became possible.
The reaction mechanism that occurs in the present day depends on the environment of the cloud. For the first reaction mechanism to take place, the cloud must contain an abundance of C 2 H . The second reaction mechanism occurs if there is an abundance of C 2 H 2 . C 2 H and C 2 H 2 exist in different conditions, so the formation of cyanopolyynes relies on high accessibility to either molecule. The calculations by Winstanley show that photoionization and dissociation reactions play a profound role in the abundances of cyanopolyynes after about 1 million years. However, the fractional abundances of cyanopolyyne are less affected by changes in radiation field intensity past time 1 million years because the prevailing neutral-neutral reactions surpass the effects of photoreactions. [ 5 ]
Cyanopolyynes are relatively common in interstellar clouds , where they were first detected in 1971. As with many other molecules the cyanopolyynes are detected with a spectrometer which records the quantum energy levels of the electrons within the atoms. [ 6 ] This measurement is done with a source of light which passes through the desired molecule. The light interacts with the molecule and can either absorb the light or reflect it, as not all light behaves the same way. This separates the light into a spectrum with alterations due to the molecule in question. This spectrum is recorded by a computer which is able to determine which wavelengths of the spectrum have been altered in some way. With the wide range of light affected the wavelengths can be determined by looking for spikes in the spectrum. The detection process usually happens within the outer ranges of the electromagnetic spectrum , usually in infrared or radio waves . [ 7 ]
The spectrum is able to show the energy of the rotational state due to the wavelengths that are absorbed by the molecule; using these rotational transitions the energy level of each electron can be shown to determine the identity of the molecule. Rotational transitions can be determined by this equation: [ 8 ]
where
This shows that the rotational distortion of an atom is related to the vibrational frequency of the molecule in question. With this ability to detect the cyanopolyynes these molecules have been recorded in several places around the galaxy. Such places include the atmosphere on Titan and the gas clouds that are within nebulae and the confines of dying stars. [ 9 ]
Species as large as HC 9 N were detected in Taurus Molecular Cloud 1 , where they are believed to be formed by reaction of atomic nitrogen with hydrocarbons . [ 10 ] For a while, HC 11 N held the record as the largest molecule detected in interstellar space, but its identification was challenged. [ 11 ] [ 12 ] | https://en.wikipedia.org/wiki/HC5N |
Cyanoacetylene is an organic compound with the formula C 3 H N or H−C≡C−C≡N . It is the simplest cyanopolyyne . Cyanoacetylene has been detected by spectroscopic methods in interstellar clouds , [ 2 ] in the coma of comet Hale–Bopp and in the atmosphere of Saturn 's moon Titan , [ 3 ] where it sometimes forms expansive fog-like clouds. [ 4 ]
Cyanoacetylene is one of the molecules that was produced in the Miller–Urey experiment . [ 5 ]
Nickel carbonyl catalyzes cyanoacetylene carboalkoxylation to cyanoacrylate esters. [ 6 ] | https://en.wikipedia.org/wiki/HCCCN |
Chloroform , [ 9 ] or trichloromethane (often abbreviated as TCM ), is an organochloride with the formula C H Cl 3 and a common solvent . It is a volatile , colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and PTFE . [ 10 ] Chloroform was once used as an inhalational anesthetic between the 19th century and the first half of the 20th century. [ 11 ] [ 12 ] It is miscible with many solvents but it is only very slightly soluble in water (only 8 g/L at 20°C).
The molecule adopts a tetrahedral molecular geometry with C 3v symmetry . [ 13 ] The chloroform molecule can be viewed as a methane molecule with three hydrogen atoms replaced with three chlorine atoms, leaving a single hydrogen atom.
The name "chloroform" is a portmanteau of terchloride (tertiary chloride, a trichloride) and formyle , an obsolete name for the methylylidene radical (CH) derived from formic acid . [ citation needed ]
Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil. [ 14 ] Abiotic processes are also believed to contribute to natural chloroform productions in soils, although the mechanism is still unclear. [ 15 ]
Chloroform is a volatile organic compound. [ 16 ]
Chloroform was synthesized independently by several investigators c. 1831 :
In 1834, French chemist Jean-Baptiste Dumas determined chloroform's empirical formula and named it: [ 25 ] " Es scheint mir also erweisen, dass die von mir analysirte Substanz, … zur Formel hat: C 2 H 2 Cl 6 . " (Thus it seems to me to show that the substance I analyzed … has as [its empirical] formula: C 2 H 2 Cl 6 .). [Note: The coefficients of his empirical formula should be halved.] ... " Diess hat mich veranlasst diese Substanz mit dem Namen 'Chloroform' zu belegen. " (This had caused me to impose the name "chloroform" upon this substance [i.e., formyl chloride or chloride of formic acid].)
In 1835, Dumas prepared the substance by alkaline cleavage of trichloroacetic acid .
In 1842, Robert Mortimer Glover in London discovered the anaesthetic qualities of chloroform on laboratory animals. [ 26 ]
In 1847, Scottish obstetrician James Y. Simpson was the first to demonstrate the anaesthetic properties of chloroform (provided by local pharmacist William Flockhart of Duncan, Flockhart and company, [ 27 ] ) in humans, and helped to popularize the drug for use in medicine. [ 28 ]
By the 1850s, chloroform was being produced on a commercial basis. In Britain, about 750,000 doses a week were being produced by 1895, [ 29 ] using the Liebig procedure, which retained its importance until the 1960s. Today, chloroform – along with dichloromethane – is prepared exclusively and on a massive scale by the chlorination of methane and chloromethane. [ 10 ]
Industrially, chloroform is produced by heating a mixture of chlorine and either methyl chloride ( CH 3 Cl ) or methane ( CH 4 ). [ 10 ] At 400–500 °C, free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds:
Chloroform undergoes further chlorination to yield carbon tetrachloride ( CCl 4 ):
The output of this process is a mixture of the four chloromethanes: chloromethane , methylene chloride (dichloromethane), trichloromethane (chloroform), and tetrachloromethane (carbon tetrachloride). These can then be separated by distillation . [ 10 ]
Chloroform may also be produced on a small scale via the haloform reaction between acetone and sodium hypochlorite :
Deuterated chloroform is an isotopologue of chloroform with a single deuterium atom. CDCl 3 is a common solvent used in NMR spectroscopy . Deuterochloroform is produced by the reaction of hexachloroacetone with heavy water . [ 30 ] The haloform process is now obsolete for production of ordinary chloroform. Deuterochloroform can also be prepared by reacting sodium deuteroxide with chloral hydrate . [ 31 ] [ 32 ]
The haloform reaction can also occur inadvertently in domestic settings. Sodium hypochlorite solution ( chlorine bleach ) mixed with common household liquids such as acetone , methyl ethyl ketone , ethanol , or isopropyl alcohol can produce some chloroform, in addition to other compounds, such as chloroacetone or dichloroacetone . [ citation needed ]
In terms of scale, the most important reaction of chloroform is with hydrogen fluoride to give monochlorodifluoromethane (HCFC-22), a precursor in the production of polytetrafluoroethylene ( Teflon ) and other fluoropolymers: [ 10 ]
The reaction is conducted in the presence of a catalytic amount of mixed antimony halides . Chlorodifluoromethane is then converted to tetrafluoroethylene , the main precursor of Teflon . [ 33 ]
The hydrogen attached to carbon in chloroform participates in hydrogen bonding, [ 34 ] [ 35 ] making it a good solvent for many materials.
Worldwide, chloroform is also used in pesticide formulations, as a solvent for lipids , rubber , alkaloids , waxes , gutta-percha , and resins , as a cleaning agent, as a grain fumigant , in fire extinguishers , and in the rubber industry. [ 36 ] [ 37 ] CDCl 3 is a common solvent used in NMR spectroscopy . [ 38 ]
Chloroform is used as a precursor to make R-22 (chlorodifluoromethane). This is done by reacting it with a solution of hydrofluoric acid (HF) which fluorinates the CHCl 3 molecule and releases hydrochloric acid as a byproduct. [ 39 ] Before the Montreal Protocol was enforced, most of the chloroform produced in the United States was used in the production of chlorodifluoromethane . However, its production remains high, as it is a key precursor of PTFE. [ 40 ]
Although chloroform has properties such as a low boiling point, and a low global warming potential of only 31 (compared to the 1760 of R-22), which are appealing properties for a refrigerant, there is little information to suggest that it has seen widespread use as a refrigerant in any consumer products. [ 41 ]
In solvents such as CCl 4 and alkanes, chloroform hydrogen bonds to a variety of Lewis bases. HCCl 3 is classified as a hard acid , and the ECW model lists its acid parameters as E A = 1.56 and C A = 0.44.
As a reagent , chloroform serves as a source of the dichlorocarbene intermediate CCl 2 . [ 42 ] It reacts with aqueous sodium hydroxide , usually in the presence of a phase transfer catalyst , to produce dichlorocarbene , CCl 2 . [ 43 ] [ 44 ] This reagent effects ortho-formylation of activated aromatic rings , such as phenols , producing aryl aldehydes in a reaction known as the Reimer–Tiemann reaction . Alternatively, the carbene can be trapped by an alkene to form a cyclopropane derivative. In the Kharasch addition , chloroform forms the •CHCl 2 free radical which adds to alkenes. [ citation needed ]
Chloroform is a powerful general anesthetic , euphoriant , anxiolytic , and sedative when inhaled or ingested. The anaesthetic qualities of chloroform were first described in 1842 in a thesis by Robert Mortimer Glover , which won the Gold Medal of the Harveian Society for that year. [ 45 ] [ 46 ] Glover also undertook practical experiments on dogs to prove his theories, refined his theories, and presented them in his doctoral thesis at the University of Edinburgh in the summer of 1847, identifying anaesthetizing halogenous compounds as a "new order of poisonous substances". [ 45 ]
The Scottish obstetrician James Young Simpson was one of those examiners required to read the thesis, but later claimed to have never read it and to have come to his own conclusions independently. [ 45 ] Perkins-McVey, among others, have raised doubts about the credibility of Simpson's claim, noting that Simpson's publications on the subject in 1847 explicitly echo Glover's and, being one of the thesis examiners, Simpson was likely aware of the content of Glover's study, even if he skirted his duties as an examiner. [ 45 ] In 1847 and 1848, Glover would pen a series of heated letters accusing Simpson of stealing his discovery, which had already earned Simpson considerable notoriety. [ 45 ] Whatever the source of his inspiration, on 4 November 1847, Simpson argued that he had discovered the anaesthetic qualities of chloroform in humans. He and two colleagues entertained themselves by trying the effects of various substances, and thus revealed the potential for chloroform in medical procedures. [ 27 ]
A few days later, during the course of a dental procedure in Edinburgh , Francis Brodie Imlach became the first person to use chloroform on a patient in a clinical context. [ 47 ]
In May 1848, Robert Halliday Gunning made a presentation to the Medico-Chirurgical Society of Edinburgh following a series of laboratory experiments on rabbits that confirmed Glover's findings and also refuted Simpson's claims of originality. The laboratory experiments that proved the dangers of chloroform were largely ignored. [ 48 ]
The use of chloroform during surgery expanded rapidly in Europe; for instance in the 1850s chloroform was used by the physician John Snow during the births of Queen Victoria 's last two children Leopold and Beatrice . [ 49 ] In the United States, chloroform began to replace ether as an anesthetic at the beginning of the 20th century; [ 50 ] it was abandoned in favor of ether on discovery of its toxicity, especially its tendency to cause fatal cardiac arrhythmias analogous to what is now termed " sudden sniffer's death ". Some people used chloroform as a recreational drug or to attempt suicide. [ 51 ] One possible mechanism of action of chloroform is that it increases the movement of potassium ions through certain types of potassium channels in nerve cells . [ 52 ] Chloroform could also be mixed with other anesthetic agents such as ether to make C.E. mixture, [ 53 ] or ether and alcohol to make A.C.E. mixture . [ 54 ] [ 55 ]
In 1848, Hannah Greener, a 15-year-old girl who was having an infected toenail removed, died after being given the anaesthetic. [ 56 ] Her autopsy establishing the cause of death was undertaken by John Fife assisted by Robert Mortimer Glover . [ 26 ] A number of physically fit patients died after inhaling it. In 1848, however, John Snow developed an inhaler that regulated the dosage and so successfully reduced the number of deaths. [ 57 ]
The opponents and supporters of chloroform disagreed on the question of whether the medical complications were due to respiratory disturbance or whether chloroform had a specific effect on the heart. Between 1864 and 1910, numerous commissions in Britain studied chloroform but failed to come to any clear conclusions. It was only in 1911 that Levy proved in experiments with animals that chloroform can cause ventricular fibrillation. [ 58 ] Despite this, between 1865 and 1920, chloroform was used in 80 to 95% of all narcoses performed in the UK and German-speaking countries. In Germany, comprehensive surveys of the fatality rate during anaesthesia were made by Gurlt between 1890 and 1897. [ 50 ] At the same time in the UK the medical journal The Lancet carried out a questionnaire survey [ 59 ] and compiled a report detailing numerous adverse reactions to anesthetics, including chloroform. [ 60 ] In 1934, Killian gathered all the statistics compiled until then and found that the chances of suffering fatal complications under ether were between 1:14,000 and 1:28,000, whereas with chloroform the chances were between 1:3,000 and 1:6,000. [ 50 ] The rise of gas anaesthesia using nitrous oxide , improved equipment for administering anesthetics, and the discovery of hexobarbital in 1932 led to the gradual decline of chloroform narcosis. [ 61 ]
The latest reported anaesthetic use of chloroform in the Western world dates to 1987, when the last doctor who used it retired, about 140 years after its first use. [ 62 ]
Chloroform has been used by criminals to knock out, daze, or murder victims. Joseph Harris was charged in 1894 with using chloroform to rob people. [ 63 ] Serial killer H. H. Holmes used chloroform overdoses to kill his female victims. In September 1900, chloroform was implicated in the murder of the U.S. businessman William Marsh Rice . Chloroform was deemed a factor in the alleged murder of a woman in 1991, when she was asphyxiated while asleep. [ 64 ] In 2002, 13-year-old Kacie Woody was sedated with chloroform when she was abducted by David Fuller and during the time that he had her, before he shot and killed her. [ 65 ] In a 2007 plea bargain, a man confessed to using stun guns and chloroform to sexually assault minors. [ 66 ]
The use of chloroform as an incapacitating agent has become widely recognized, bordering on cliché , through the adoption by crime fiction authors of plots involving criminals' use of chloroform-soaked rags to render victims unconscious. However, it is nearly impossible to incapacitate someone using chloroform in this way. [ 67 ] It takes at least five minutes of inhalation of chloroform to render a person unconscious. Most criminal cases involving chloroform involve co-administration of another drug, such as alcohol or diazepam , or the victim being complicit in its administration. After a person has lost consciousness owing to chloroform inhalation, a continuous volume must be administered, and the chin must be supported to keep the tongue from obstructing the airway, a difficult procedure, typically requiring the skills of an anesthesiologist . In 1865, as a direct result of the criminal reputation chloroform had gained, the medical journal The Lancet offered a "permanent scientific reputation" to anyone who could demonstrate "instantaneous insensibility", i.e. loss of consciousness, using chloroform. [ 68 ]
Chloroform is formed as a by-product of water chlorination , along with a range of other disinfection by-products , and it is therefore often present in municipal tap water and swimming pools. Reported ranges vary considerably, but are generally below the current health standard for total trihalomethanes (THMs) of 100 μg/L. [ 69 ] However, when considered in combination with other trihalomethanes often present in drinking water, the concentration of THMs often exceeds the recommended limit of exposure. [ 70 ]
Historically, chloroform exposure may well have been higher, owing to its common use as an anesthetic, as an ingredient in cough syrups, and as a constituent of tobacco smoke , where DDT had previously been used as a fumigant . [ 71 ]
Chloroform is well absorbed, metabolized, and eliminated rapidly by mammals after oral, inhalation, or dermal exposure. Accidental splashing into the eyes has caused irritation. [ 36 ] Prolonged dermal exposure can result in the development of sores as a result of defatting . Elimination is primarily through the lungs as chloroform and carbon dioxide; less than 1% is excreted in the urine. [ 37 ]
Chloroform is metabolized in the liver by the cytochrome P-450 enzymes, by oxidation to trichloromethanol and by reduction to the dichloromethyl free radical . Other metabolites of chloroform include hydrochloric acid and diglutathionyl dithiocarbonate, with carbon dioxide as the predominant end-product of metabolism. [ 72 ]
Like most other general anesthetics and sedative-hypnotic drugs, chloroform is a positive allosteric modulator at GABA A receptors . [ 73 ] Chloroform causes depression of the central nervous system (CNS), ultimately producing deep coma and respiratory center depression. [ 72 ] When ingested, chloroform causes symptoms similar to those seen after inhalation. Serious illness has followed ingestion of 7.5 g (0.26 oz). The mean lethal oral dose in an adult is estimated at 45 g (1.6 oz). [ 36 ]
The anesthetic use of chloroform has been discontinued, because it caused deaths from respiratory failure and cardiac arrhythmias. Following chloroform-induced anesthesia, some patients suffered nausea , vomiting , hyperthermia , jaundice , and coma owing to hepatic dysfunction . At autopsy, liver necrosis and degeneration have been observed. [ 36 ] The hepatotoxicity and nephrotoxicity of chloroform is thought to be due largely to phosgene , one of its metabolites. [ 72 ]
Chloroform converts slowly in the presence of UV light and air to the extremely poisonous gas phosgene ( COCl 2 ), releasing HCl in the process. [ 74 ]
To prevent accidents, commercial chloroform is stabilized with ethanol or amylene , but samples that have been recovered or dried no longer contain any stabilizer. Amylene has been found to be ineffective, and the phosgene can affect analytes in samples, lipids, and nucleic acids dissolved in or extracted with chloroform. [ 75 ] When ethanol is used as a stabiliser for chloroform, it reacts with phosgene (which is soluble in chloroform) to form the relatively harmless diethyl carbonate ester:
Phosgene and HCl can be removed from chloroform by washing with saturated aqueous carbonate solutions, such as sodium bicarbonate . This procedure is simple and results in harmless products. Phosgene reacts with water to form carbon dioxide and HCl, [ 76 ] and the carbonate salt neutralizes the resulting acid. [ 77 ]
Suspected samples can be tested for phosgene using filter paper which when treated with 5% diphenylamine , 5% dimethylaminobenzaldehyde in ethanol , and then dried, turns yellow in the presence of phosgene vapour. [ 78 ] There are several colorimetric and fluorometric reagents for phosgene, and it can also be quantified using mass spectrometry . [ 79 ]
Chloroform is suspected of causing cancer (i.e. it is possibly carcinogenic , IARC Group 2B ) as per the International Agency for Research on Cancer (IARC) Monograph. There is no convincing evidence that chloroform causes cancer in humans. [ 80 ]
It is classified as an extremely hazardous substance in the United States, as defined in Section 302 of the US Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities that produce, store, or use it in significant quantities. [ 81 ]
Some anaerobic bacteria use chloroform for respiration, termed organohalide respiration , converting it to dichloromethane . [ 82 ] [ 83 ] | https://en.wikipedia.org/wiki/HCCl3 |
Formaldehyde ( / f ɔːr ˈ m æ l d ɪ h aɪ d / ⓘ for- MAL -di-hide , US also / f ə r -/ ⓘ fər- ) ( systematic name methanal ) is an organic compound with the chemical formula CH 2 O and structure H−CHO , more precisely H 2 C=O . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde . It is stored as aqueous solutions ( formalin ), which consists mainly of the hydrate CH 2 (OH) 2 . It is the simplest of the aldehydes ( R−CHO ). As a precursor to many other materials and chemical compounds, in 2006 the global production of formaldehyde was estimated at 12 million tons per year. [ 14 ] It is mainly used in the production of industrial resins , e.g., for particle board and coatings .
Formaldehyde also occurs naturally. It is derived from the degradation of serine , dimethylglycine , and lipids . Demethylases act by converting N-methyl groups to formaldehyde. [ 15 ]
Formaldehyde is classified as a group 1 carcinogen [ note 1 ] [ 17 ] and can cause respiratory and skin irritation upon exposure. [ 16 ]
Formaldehyde is more complicated than many simple carbon compounds in that it adopts several diverse forms. These compounds can often be used interchangeably and can be interconverted. [ citation needed ]
A small amount of stabilizer , such as methanol , is usually added to suppress oxidation and polymerization . A typical commercial-grade formalin may contain 10–12% methanol in addition to various metallic impurities.
"Formaldehyde" was first used as a generic trademark in 1893 following a previous trade name, "formalin". [ 18 ]
Molecular formaldehyde contains a central carbon atom with a double bond to the oxygen atom and a single bond to each hydrogen atom . This structure is summarised by the condensed formula H 2 C=O. [ 19 ] The molecule is planar, Y-shaped and its molecular symmetry belongs to the C 2v point group . [ 20 ] The precise molecular geometry of gaseous formaldehyde has been determined by gas electron diffraction [ 19 ] [ 21 ] and microwave spectroscopy . [ 22 ] [ 23 ] The bond lengths are 1.21 Å for the carbon–oxygen bond [ 19 ] [ 21 ] [ 22 ] [ 23 ] [ 24 ] and around 1.11 Å for the carbon–hydrogen bond , [ 19 ] [ 21 ] [ 22 ] [ 23 ] while the H–C–H bond angle is 117°, [ 22 ] [ 23 ] close to the 120° angle found in an ideal trigonal planar molecule . [ 19 ] Some excited electronic states of formaldehyde are pyramidal rather than planar as in the ground state . [ 24 ]
Processes in the upper atmosphere contribute more than 80% of the total formaldehyde in the environment. [ 25 ] Formaldehyde is an intermediate in the oxidation (or combustion ) of methane , as well as of other carbon compounds, e.g. in forest fires , automobile exhaust, and tobacco smoke . When produced in the atmosphere by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons , it becomes part of smog . Formaldehyde has also been detected in outer space.
Formaldehyde and its adducts are ubiquitous in nature. Food may contain formaldehyde at levels 1–100 mg/kg. [ 26 ] Formaldehyde, formed in the metabolism of the amino acids serine and threonine , is found in the bloodstream of humans and other primates at concentrations of approximately 50 micromolar . [ 27 ] Experiments in which animals are exposed to an atmosphere containing isotopically labeled formaldehyde have demonstrated that even in deliberately exposed animals, the majority of formaldehyde-DNA adducts found in non-respiratory tissues are derived from endogenously produced formaldehyde. [ 28 ]
Formaldehyde does not accumulate in the environment, because it is broken down within a few hours by sunlight or by bacteria present in soil or water. Humans metabolize formaldehyde quickly, converting it to formic acid . [ 29 ] [ 30 ] It nonetheless presents significant health concerns , as a contaminant .
Formaldehyde appears to be a useful probe in astrochemistry due to prominence of the 1 10 ←1 11 and 2 11 ←2 12 K -doublet transitions. It was the first polyatomic organic molecule detected in the interstellar medium . [ 31 ] Since its initial detection in 1969, it has been observed in many regions of the galaxy . Because of the widespread interest in interstellar formaldehyde, it has been extensively studied, yielding new extragalactic sources. [ 32 ] A proposed mechanism for the formation is the hydrogenation of CO ice: [ 33 ]
HCN , HNC , H 2 CO, and dust have also been observed inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) . [ 34 ] [ 35 ]
Formaldehyde was discovered in 1859 by the Russian chemist Aleksandr Butlerov (1828–1886) when he attempted to synthesize methanediol ("methylene glycol") from iodomethane and silver oxalate . [ 36 ] In his paper, Butlerov referred to formaldehyde as "dioxymethylen" (methylene dioxide) because his empirical formula for it was incorrect, as atomic weights were not precisely determined until the Karlsruhe Congress .
The compound was identified as an aldehyde by August Wilhelm von Hofmann , who first announced its production by passing methanol vapor in air over hot platinum wire. [ 37 ] [ 38 ] With modifications, Hofmann's method remains the basis of the present day industrial route.
Solution routes to formaldehyde also entail oxidation of methanol or iodomethane . [ 39 ]
Formaldehyde is produced industrially by the catalytic oxidation of methanol . The most common catalysts are silver metal (i.e. the FASIL process ), iron(III) oxide , [ 40 ] iron molybdenum oxides (e.g. iron(III) molybdate ) with a molybdenum -enriched surface, [ 41 ] or vanadium oxides . In the commonly used formox process , methanol and oxygen react at c. 250–400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation : [ 42 ]
The silver-based catalyst usually operates at a higher temperature, about 650 °C. Two chemical reactions on it simultaneously produce formaldehyde: that shown above and the dehydrogenation reaction:
In principle, formaldehyde could be generated by oxidation of methane , but this route is not industrially viable because the methanol is more easily oxidized than methane. [ 42 ]
Formaldehyde is produced via several enzyme-catalyzed routes. [ 43 ] Living beings, including humans, produce formaldehyde as part of their metabolism. Formaldehyde is key to several bodily functions (e.g. epigenetics [ 27 ] ), but its amount must also be tightly controlled to avoid self-poisoning. [ 44 ]
Formaldehyde is catabolized by alcohol dehydrogenase ADH5 and aldehyde dehydrogenase ALDH2 . [ 45 ]
Formaldehyde is a building block in the synthesis of many other compounds of specialised and industrial significance. It exhibits most of the chemical properties of other aldehydes but is more reactive. [ 46 ]
Monomeric CH 2 O is a gas and is rarely encountered in the laboratory. Aqueous formaldehyde, unlike some other small aldehydes (which need specific conditions to oligomerize through aldol condensation ) oligomerizes spontaneously at a common state. The trimer 1,3,5-trioxane, (CH 2 O) 3 , is a typical oligomer. Many cyclic oligomers of other sizes have been isolated. Similarly, formaldehyde hydrates to give the geminal diol methanediol , which condenses further to form hydroxy-terminated oligomers HO(CH 2 O) n H. The polymer is called paraformaldehyde . The higher concentration of formaldehyde—the more equilibrium shifts towards polymerization. Diluting with water or increasing the solution temperature, as well as adding alcohols (such as methanol or ethanol) lowers that tendency.
Gaseous formaldehyde polymerizes at active sites on vessel walls, but the mechanism of the reaction is unknown. [ 47 ] Small amounts of hydrogen chloride , boron trifluoride , or stannic chloride present in gaseous formaldehyde provide the catalytic effect and make the polymerization rapid. [ 48 ]
Formaldehyde forms cross-links by first combining with a protein to form methylol , which loses a water molecule to form a Schiff base . [ 49 ] The Schiff base can then react with DNA or protein to create a cross-linked product. [ 49 ] This reaction is the basis for the most common process of chemical fixation .
Formaldehyde is readily oxidized by atmospheric oxygen into formic acid . For this reason, commercial formaldehyde is typically contaminated with formic acid. Formaldehyde can be hydrogenated into methanol .
In the Cannizzaro reaction , formaldehyde and base react to produce formic acid and methanol, a disproportionation reaction .
Formaldehyde reacts with many compounds, resulting in hydroxymethylation :
The resulting hydroxymethyl derivatives typically react further. Thus, amines give hexahydro-1,3,5-triazines :
Similarly, when combined with hydrogen sulfide , it forms trithiane : [ 50 ]
In the presence of acids, it participates in electrophilic aromatic substitution reactions with aromatic compounds resulting in hydroxymethylated derivatives:
When conducted in the presence of hydrogen chloride, the product is the chloromethyl compound, as described in the Blanc chloromethylation . If the arene is electron-rich, as in phenols, elaborate condensations ensue. With 4-substituted phenols one obtains calixarenes . [ 51 ] Phenol results in polymers.
Many amino acids react with formaldehyde. [ 43 ] Cysteine converts to thioproline .
Formaldehyde is a common precursor to more complex compounds and materials. In approximate order of decreasing consumption, products generated from formaldehyde include urea formaldehyde resin , melamine resin , phenol formaldehyde resin , polyoxymethylene plastics , 1,4-butanediol , and methylene diphenyl diisocyanate . [ 42 ] The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant. [ 52 ]
When condensed with phenol , urea , or melamine , formaldehyde produces, respectively, hard thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin. These polymers are permanent adhesives used in plywood and carpeting . They are also foamed to make insulation , or cast into moulded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.
Formaldehyde is also a precursor to polyfunctional alcohols such as pentaerythritol , which is used to make paints and explosives . Other formaldehyde derivatives include methylene diphenyl diisocyanate, an important component in polyurethane paints and foams, and hexamine , which is used in phenol-formaldehyde resins as well as the explosive RDX .
Condensation with acetaldehyde affords pentaerythritol , a chemical necessary in synthesizing PETN , a high explosive: [ 53 ]
An aqueous solution of formaldehyde can be useful as a disinfectant as it kills most bacteria and fungi (including their spores). It is used as an additive in vaccine manufacturing to inactivate toxins and pathogens. [ 54 ] Formaldehyde releasers are used as biocides in personal care products such as cosmetics. Although present at levels not normally considered harmful, they are known to cause allergic contact dermatitis in certain sensitised individuals. [ 55 ]
Aquarists use formaldehyde as a treatment for the parasites Ichthyophthirius multifiliis and Cryptocaryon irritans . [ 56 ] Formaldehyde is one of the main disinfectants recommended for destroying anthrax . [ 57 ]
Formaldehyde is also approved for use in the manufacture of animal feeds in the US. It is an antimicrobial agent used to maintain complete animal feeds or feed ingredients Salmonella negative for up to 21 days. [ 58 ]
Formaldehyde preserves or fixes tissue or cells. The process involves cross-linking of primary amino groups . The European Union has banned the use of formaldehyde as a biocide (including embalming ) under the Biocidal Products Directive (98/8/EC) due to its carcinogenic properties. [ 59 ] [ 60 ] Countries with a strong tradition of embalming corpses, such as Ireland and other colder-weather countries, have raised concerns. Despite reports to the contrary, [ 61 ] no decision on the inclusion of formaldehyde on Annex I of the Biocidal Products Directive for product-type 22 (embalming and taxidermist fluids) had been made as of September 2009 [update] . [ 62 ]
Formaldehyde-based crosslinking is exploited in ChIP-on-chip or ChIP-sequencing genomics experiments, where DNA-binding proteins are cross-linked to their cognate binding sites on the chromosome and analyzed to determine what genes are regulated by the proteins. Formaldehyde is also used as a denaturing agent in RNA gel electrophoresis , preventing RNA from forming secondary structures. A solution of 4% formaldehyde fixes pathology tissue specimens at about one mm per hour at room temperature.
Formaldehyde and 18 M (concentrated) sulfuric acid makes Marquis reagent —which can identify alkaloids and other compounds.
In photography, formaldehyde is used in low concentrations for the process C-41 (color negative film) stabilizer in the final wash step, [ 63 ] as well as in the process E-6 pre-bleach step, to make it unnecessary in the final wash. Due to improvements in dye coupler chemistry, more modern (2006 or later) E-6 and C-41 films do not need formaldehyde, as their dyes are already stable.
In view of its widespread use, toxicity, and volatility, formaldehyde poses a significant danger to human health. [ 64 ] [ 65 ] In 2011, the US National Toxicology Program described formaldehyde as "known to be a human carcinogen". [ 66 ] [ 67 ] [ 68 ]
Concerns are associated with chronic (long-term) exposure by inhalation as may happen from thermal or chemical decomposition of formaldehyde-based resins and the production of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust gases). As formaldehyde resins are used in many construction materials , it is one of the more common indoor air pollutants . [ 69 ] [ 70 ] At concentrations above 0.1 ppm in air, formaldehyde can irritate the eyes and mucous membranes . [ 71 ] Formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, and can trigger or aggravate asthma symptoms. [ 72 ] [ 73 ]
The CDC considers formaldehyde as a systemic poison. Formaldehyde poisoning can cause permanent changes in the nervous system 's functions. [ 74 ]
A 1988 Canadian study of houses with urea-formaldehyde foam insulation found that formaldehyde levels as low as 0.046 ppm were positively correlated with eye and nasal irritation. [ 75 ] A 2009 review of studies has shown a strong association between exposure to formaldehyde and the development of childhood asthma . [ 76 ]
A theory was proposed for the carcinogenesis of formaldehyde in 1978. [ 77 ] In 1987 the United States Environmental Protection Agency (EPA) classified it as a probable human carcinogen , and after more studies the WHO International Agency for Research on Cancer (IARC) in 1995 also classified it as a probable human carcinogen . Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a known human carcinogen [ 78 ] associated with nasal sinus cancer and nasopharyngeal cancer . [ 79 ] Studies in 2009 and 2010 have also shown a positive correlation between exposure to formaldehyde and the development of leukemia , particularly myeloid leukemia . [ 80 ] [ 81 ] Nasopharyngeal and sinonasal cancers are relatively rare, with a combined annual incidence in the United States of < 4,000 cases. [ 82 ] [ 83 ] About 30,000 cases of myeloid leukemia occur in the United States each year. [ 84 ] [ 85 ] Some evidence suggests that workplace exposure to formaldehyde contributes to sinonasal cancers. [ 86 ] Professionals exposed to formaldehyde in their occupation, such as funeral industry workers and embalmers , showed an increased risk of leukemia and brain cancer compared with the general population. [ 87 ] Other factors are important in determining individual risk for the development of leukemia or nasopharyngeal cancer. [ 86 ] [ 88 ] [ 89 ] In yeast, formaldehyde is found to perturb pathways for DNA repair and cell cycle. [ 90 ]
In the residential environment, formaldehyde exposure comes from a number of routes; formaldehyde can be emitted by treated wood products, such as plywood or particle board , but it is produced by paints, varnishes , floor finishes, and cigarette smoking as well. [ 91 ] In July 2016, the U.S. EPA released a prepublication version of its final rule on Formaldehyde Emission Standards for Composite Wood Products. [ 92 ] These new rules impact manufacturers, importers, distributors, and retailers of products containing composite wood, including fiberboard, particleboard, and various laminated products, who must comply with more stringent record-keeping and labeling requirements. [ 93 ]
The U.S. EPA allows no more than 0.016 ppm formaldehyde in the air in new buildings constructed for that agency. [ 94 ] [ failed verification ] A U.S. EPA study found a new home measured 0.076 ppm when brand new and 0.045 ppm after 30 days. [ 95 ] The Federal Emergency Management Agency (FEMA) has also announced limits on the formaldehyde levels in trailers purchased by that agency. [ 96 ] The EPA recommends the use of "exterior-grade" pressed-wood products with phenol instead of urea resin to limit formaldehyde exposure, since pressed-wood products containing formaldehyde resins are often a significant source of formaldehyde in homes. [ 79 ]
The eyes are most sensitive to formaldehyde exposure: The lowest level at which many people can begin to smell formaldehyde ranges between 0.05 and 1 ppm. The maximum concentration value at the workplace is 0.3 ppm. [ 97 ] [ need quotation to verify ] In controlled chamber studies, individuals begin to sense eye irritation at about 0.5 ppm; 5 to 20 percent report eye irritation at 0.5 to 1 ppm; and greater certainty for sensory irritation occurred at 1 ppm and above. While some agencies have used a level as low as 0.1 ppm as a threshold for irritation, the expert panel found that a level of 0.3 ppm would protect against nearly all irritation. In fact, the expert panel found that a level of 1.0 ppm would avoid eye irritation—the most sensitive endpoint—in 75–95% of all people exposed. [ 98 ]
Formaldehyde levels in building environments are affected by a number of factors. These include the potency of formaldehyde-emitting products present, the ratio of the surface area of emitting materials to volume of space, environmental factors, product age, interactions with other materials, and ventilation conditions. Formaldehyde emits from a variety of construction materials, furnishings, and consumer products. The three products that emit the highest concentrations are medium density fiberboard , hardwood plywood, and particle board. Environmental factors such as temperature and relative humidity can elevate levels because formaldehyde has a high vapor pressure . Formaldehyde levels from building materials are the highest when a building first opens because materials would have less time to off-gas. Formaldehyde levels decrease over time as the sources suppress.
In operating rooms , formaldehyde is produced as a byproduct of electrosurgery and is present in surgical smoke, exposing surgeons and healthcare workers to potentially unsafe concentrations. [ 99 ]
Formaldehyde levels in air can be sampled and tested in several ways, including impinger, treated sorbent, and passive monitors. [ 100 ] The National Institute for Occupational Safety and Health (NIOSH) has measurement methods numbered 2016, 2541, 3500, and 3800. [ 101 ]
In June 2011, the twelfth edition of the National Toxicology Program (NTP) Report on Carcinogens (RoC) changed the listing status of formaldehyde from "reasonably anticipated to be a human carcinogen" to "known to be a human carcinogen." [ 66 ] [ 67 ] [ 68 ] Concurrently, a National Academy of Sciences (NAS) committee was convened and issued an independent review of the draft U.S. EPA IRIS assessment of formaldehyde, providing a comprehensive health effects assessment and quantitative estimates of human risks of adverse effects. [ 102 ]
For most people, irritation from formaldehyde is temporary and reversible, although formaldehyde can cause allergies and is part of the standard patch test series. In 2005–06, it was the seventh-most-prevalent allergen in patch tests (9.0%). [ 103 ] People with formaldehyde allergy are advised to avoid formaldehyde releasers as well (e.g., Quaternium-15 , imidazolidinyl urea , and diazolidinyl urea ). [ 104 ] People who suffer allergic reactions to formaldehyde tend to display lesions on the skin in the areas that have had direct contact with the substance, such as the neck or thighs (often due to formaldehyde released from permanent press finished clothing) or dermatitis on the face (typically from cosmetics). [ 55 ] Formaldehyde has been banned in cosmetics in both Sweden [ 105 ] and Japan . [ 106 ]
In humans, ingestion of as little as 30 millilitres (1.0 US fl oz) of 37% formaldehyde solution can cause death. Other symptoms associated with ingesting such a solution include gastrointestinal damage (vomiting, abdominal pain), and systematic damage (dizziness). [ 74 ] Testing for formaldehyde is by blood and/or urine by gas chromatography–mass spectrometry . Other methods to detect formaldehyde include infrared detection, gas detector tubes, gas detectors using electrochemical sensors, and high-performance liquid chromatography (HPLC). HPLC is the most sensitive. [ 107 ]
The fifteenth edition (2021) of the U.S. National Toxicology Program Report on Carcinogens notes that currently in the U.S. “The general population can be exposed to formaldehyde primarily from breathing indoor or outdoor air, from tobacco smoke, from use of cosmetic products containing formaldehyde, and, to a more limited extent, from ingestion of food and water.” Affected water includes groundwater, surface water, and bottled water. It also notes that occupational exposure can be significant. [ 108 ]
Formaldehyde in food can be present naturally, added as an inadvertent contaminant, or intentionally added as a preservative, disinfectant, or bacteriostatic agent . Cooking and smoking food can also result in formaldehyde being produced in food. Foods that the U.S. National Toxicology Program has reported to have higher levels compared to other foods are fish, seafood, and smoked ham. It also notes formaldehyde in food generally occurs in a bound form and that formaldehyde is unstable in an aqueous solution . [ 109 ]
Scandals have broken in both the 2005 Indonesia food scare and 2007 Vietnam food scare regarding the addition of formaldehyde to foods to extend shelf life. In 2011, after a four-year absence, Indonesian authorities found foods with formaldehyde being sold in markets in a number of regions across the country. [ 110 ] In August 2011, at least at two Carrefour supermarkets, the Central Jakarta Livestock and Fishery Sub-Department found cendol containing 10 parts per million of formaldehyde. [ 111 ] In 2014, the owner of two noodle factories in Bogor , Indonesia, was arrested for using formaldehyde in noodles. [ 112 ] Foods known to be contaminated included noodles, salted fish, and tofu. Chicken and beer were also rumored to be contaminated. In some places, such as China, manufacturers still use formaldehyde illegally as a preservative in foods, which exposes people to formaldehyde ingestion. [ 113 ]
In 2011 in Nakhon Ratchasima , Thailand, truckloads of rotten chicken were treated with formaldehyde for sale in which "a large network", including 11 slaughterhouses run by a criminal gang, were implicated. [ 114 ] In 2012, 1 billion rupiah (almost US$100,000) of fish imported from Pakistan to Batam , Indonesia, were found laced with formaldehyde. [ 115 ]
Formalin contamination of foods has been reported in Bangladesh , with stores and supermarkets selling fruits, fishes, and vegetables that have been treated with formalin to keep them fresh. [ 116 ] However, in 2015, a Formalin Control Bill was passed in the Parliament of Bangladesh with a provision of life-term imprisonment as the maximum punishment as well as a maximum fine of 2,000,000 BDT but not less than 500,000 BDT for importing, producing, or hoarding formalin without a license. [ 117 ]
In the early 1900s, formaldehyde was frequently added by US milk plants to milk bottles as a method of pasteurization due to the lack of knowledge and concern [ 118 ] regarding formaldehyde's toxicity. [ 119 ] [ 120 ]
Formaldehyde was one of the chemicals used in 19th century industrialised food production that was investigated by Dr. Harvey W. Wiley with his famous 'Poison Squad' as part of the US Department of Agriculture . This led to the 1906 Pure Food and Drug Act , a landmark event in the early history of food regulation in the United States . [ 121 ]
Formaldehyde is banned from use in certain applications (preservatives for liquid-cooling and processing systems, slimicides , metalworking-fluid preservatives, and antifouling products) under the Biocidal Products Directive. [ 122 ] [ 123 ] In the EU, the maximum allowed concentration of formaldehyde in finished products is 0.2%, and any product that exceeds 0.05% has to include a warning that the product contains formaldehyde. [ 55 ]
In the United States, Congress passed a bill July 7, 2010, regarding the use of formaldehyde in hardwood plywood , particle board , and medium density fiberboard . The bill limited the allowable amount of formaldehyde emissions from these wood products to 0.09 ppm, and required companies to meet this standard by January 2013. [ 124 ] The final U.S. EPA rule specified maximum emissions of "0.05 ppm formaldehyde for hardwood plywood, 0.09 ppm formaldehyde for particleboard, 0.11 ppm formaldehyde for medium-density fiberboard, and 0.13 ppm formaldehyde for thin medium-density fiberboard." [ 125 ]
Formaldehyde was declared a toxic substance by the 1999 Canadian Environmental Protection Act . [ 126 ]
The FDA is proposing a ban on hair relaxers with formaldehyde due to cancer concerns. [ 127 ] | https://en.wikipedia.org/wiki/HCHO |
Perchloric acid is a mineral acid with the formula H Cl O 4 . It is an oxoacid of chlorine . Usually found as an aqueous solution , this colorless compound is a stronger acid than sulfuric acid , nitric acid and hydrochloric acid . It is a powerful oxidizer when hot, but aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate , an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures. [ 4 ]
Perchloric acid was first synthesized (together with potassium perchlorate ) by Austrian chemist Friedrich von Stadion [ de ] and called "oxygenated chloric acid " in mid-1810s. French pharmacist Georges-Simon Serullas introduced the modern designation along with discovering its solid monohydrate, which he mistook for an anhydride . [ 5 ] Berzelius produced dilute perchloric acid by electrolysis of chloric acid. In the late 1800's German and Swedish workers commercialized the electrolysis. [ 6 ]
Perchloric acid is produced industrially by two routes. The traditional method exploits the high aqueous solubility of sodium perchlorate (209 g/100 ml of water at room temperature). Treatment of such solutions with hydrochloric acid gives perchloric acid, precipitating solid sodium chloride:
The concentrated acid can be purified by distillation . The alternative route, which is more direct and avoids salts, entails anodic oxidation of aqueous chlorine at a platinum electrode. [ 6 ] [ 7 ]
It can be distilled from a solution of potassium perchlorate in sulfuric acid. [ 8 ] Treatment of barium perchlorate with sulfuric acid precipitates barium sulfate , leaving perchloric acid. It can also be made by mixing nitric acid with ammonium perchlorate and boiling while adding hydrochloric acid. The reaction gives nitrous oxide and perchloric acid due to a concurrent reaction involving the ammonium ion and can be concentrated and purified significantly by boiling off the remaining nitric and hydrochloric acids.
Anhydrous perchloric acid is an unstable oily liquid at room temperature. It forms at least five hydrates , several of which have been characterized crystallographically . These solids consist of the perchlorate anion linked via hydrogen bonds to H 2 O and H 3 O + centers. [ 9 ] An example is hydronium perchlorate . Perchloric acid forms an azeotrope with water, consisting of about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are hygroscopic . Thus, if left open to the air, concentrated perchloric acid dilutes itself by absorbing water from the air.
Dehydration of perchloric acid gives the anhydride dichlorine heptoxide : [ 10 ]
Perchloric acid is mainly produced as a precursor to ammonium perchlorate , which is used in rocket propellant. The growth in rocketry has led to increased production of perchloric acid. Several million kilograms are produced annually. [ 6 ] Perchloric acid is one of the most proven materials for etching of liquid crystal displays and critical electronics applications as well as ore extraction and has unique properties in analytical chemistry. [ 11 ] Additionally it is a useful component in etching of chrome. [ 12 ]
Perchloric acid, a superacid , is one of the strongest Brønsted–Lowry acids . That its p K a is lower than −9 is evidenced by the fact that its monohydrate contains discrete hydronium ions and can be isolated as a stable, crystalline solid, formulated as [H 3 O + ][ ClO – 4 ]. [ 13 ] The most recent estimate of its aqueous p K a is −15.2 ± 2.0 . [ 3 ] It provides strong acidity with minimal interference because perchlorate is weakly nucleophilic (explaining the high acidity of HClO 4 ). Other acids of noncoordinating anions , such as fluoroboric acid and hexafluorophosphoric acid are susceptible to hydrolysis, whereas perchloric acid is not. Despite hazards associated with the explosiveness of its salts, the acid is often preferred in certain syntheses. [ 14 ] For similar reasons, it is a useful eluent in ion-exchange chromatography . It is also used in electropolishing or the etching of aluminium, molybdenum, and other metals.
In geochemistry, perchloric acid aids in the digestion of silicate mineral samples for analysis, and also for complete digestion of organic matter. [ 15 ]
Given its strong oxidizing properties, perchloric acid is subject to extensive regulations as it can react violently with metals and flammable substances such as wood, plastics, and oils. [ 16 ] Work conducted with perchloric acid must be conducted in fume hoods with a wash-down capability to prevent accumulation of oxidisers in the ductwork .
On February 20, 1947 in Los Angeles, California, 17 people were killed and 150 injured in the O'Connor Plating Works disaster . A bath, consisting of over 1000 litres of 75% perchloric acid and 35% acetic anhydride by volume which was being used to electro-polish aluminium furniture, exploded. Organic compounds were added to the overheating bath when an iron rack was replaced with one coated with cellulose acetobutyrate ( Tenit-2 plastic). A few minutes later the bath exploded. [ 17 ] [ 18 ] The O'Connor Electro-Plating plant, 25 other buildings, and 40 automobiles were destroyed, and 250 nearby homes were damaged. | https://en.wikipedia.org/wiki/HCIO4 |
Hyperpolarization-activated cyclic nucleotide–gated (HCN) channels are integral membrane proteins that serve as nonselective voltage-gated cation channels in the plasma membranes of heart and brain cells. [ 1 ] HCN channels are sometimes referred to as pacemaker channels because they help to generate rhythmic activity within groups of heart and brain cells. HCN channels are activated by membrane hyperpolarization, are permeable to Na + and K + , and are constitutively open at voltages near the resting membrane potential. [ 2 ] HCN channels are encoded by four genes ( HCN1 , 2 , 3 , 4 ) and are widely expressed throughout the heart and the central nervous system . [ 3 ] [ 4 ]
The current through HCN channels, designated I f or I h , plays a key role in the control of cardiac and neuronal rhythmicity and is called the pacemaker current or "funny" current. Expression of single isoforms in heterologous systems such as human embryonic kidney ( HEK ) cells, Chinese hamster ovary ( CHO ) cells and Xenopus oocytes yield homotetrameric channels able to generate ion currents with properties similar to those of the native I f / I h current, but with quantitative differences in the voltage-dependence, activation/deactivation kinetics and sensitivity to the nucleotide cyclic AMP (cAMP): HCN1 channels have a more positive threshold for activation, faster activation kinetics, and a lower sensitivity to cAMP, while HCN4 channels are slowly gating and strongly sensitive to cAMP. HCN2 and HCN3 have intermediate properties. [ 5 ] [ 6 ] [ 7 ]
Hyperpolarization -activated and cyclic nucleotide–gated (HCN) channels belong to the superfamily of voltage-gated K + (Kv) and cyclic nucleotide–gated (CNG) channels. HCN channels are thought to consist of four either identical or non-identical subunits that are integrally embedded in the cell membrane to create an ion-conducting pore. [ 8 ] Each subunit comprises six membrane-spanning (S1–6) domains which include a putative voltage sensor (S4) and a pore region between S5 and S6 carrying the GYG triplet signature of K + -permeable channels, and a cyclic nucleotide-binding domain (CNBD) in the C-terminus. HCN isoforms are highly conserved in their core transmembrane regions and cyclic nucleotide binding domain (80–90% identical), but diverge in their amino- and carboxy-terminal cytoplasmic regions. [ 6 ]
HCN channels are regulated by both intracellular and extracellular molecules [ clarification needed ] , but most importantly, by cyclic nucleotides (cAMP, cGMP, cCMP). [ 9 ] [ 10 ] [ 11 ] Binding of cyclic nucleotides lowers the threshold potential of HCN channels, thus activating them. cAMP is a primary agonist of HCN2 while cGMP and cCMP may also bind to it. All three, however, are potent agonists. [ 12 ]
HCN4 is the main isoform expressed in the sinoatrial node , but low levels of HCN1 and HCN2 have also been reported.
The current through HCN channels, called the pacemaker current ( I f ), plays a key role in the generation and modulation of cardiac rhythmicity , [ 13 ] as they are responsible for the spontaneous depolarization in pacemaker action potentials in the heart. HCN4 isoforms are regulated by cCMP and cAMP and these molecules are agonists at I f . [ 14 ] [ 15 ]
All four HCN subunits are expressed in the brain. [ 4 ] In addition to their proposed roles in pacemaking rhythmic or oscillatory activity, HCN channels may control the way that neurons respond to synaptic input. Initial studies suggest roles for HCN channels in sour taste, coordinated motor behavior and aspects of learning and memory. Clinically, there is evidence that HCN channels play roles in epilepsy and neuropathic pain . HCN channels have been shown to be important for activity-dependent mechanisms for olfactory sensory neuron growth. [ 16 ]
HCN1 and 2 channels have been found in dorsal root ganglia , basal ganglia , and the dendrites of neurons in the hippocampus . It has been found that human cortical neurons have particularly high amount of HCN1 channel expression in all layers. [ 17 ] HCN channel trafficking along dendrites in the hippocampus of rats has shown that HCN channels are quickly shuttled to the surface in response to neural activity. [ 18 ] HCN channels have also been observed in the retrotrapezoid nucleus (RTN), a respiratory control center that responds to chemical signals such as CO 2 . [ citation needed ] When HCN is inhibited, serotonin fails to stimulate chemoreceptors in the RTN. This illustrates a connection between HCN channels and respiratory regulation . [ 19 ] Due to the complex nature of HCN channel regulation, as well as the complex interactions between multiple ion channels, HCN channels are fine-tuned to respond to certain thresholds and agonists. This complexity is believed to affect neural plasticity . [ 18 ]
HCN channel was first identified in 1976 in the heart by Noma and Irisawa and characterized by Brown, Difrancesco and Weiss [ 20 ] | https://en.wikipedia.org/wiki/HCN_channel |
Formic acid (from Latin formica ' ant ' ), systematically named methanoic acid , is the simplest carboxylic acid . It has the chemical formula HCOOH and structure H−C(=O)−O−H . This acid is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Esters , salts , and the anion derived from formic acid are called formates . Industrially, formic acid is produced from methanol . [ 5 ]
Formic acid, which has a pungent, penetrating odor, is found naturally in insects, weeds, fruits and vegetables, and forest emissions. It appears in most ants and in stingless bees of the genus Oxytrigona . [ 6 ] [ 7 ] Wood ants from the genus Formica can spray formic acid on their prey or to defend the nest. The puss moth caterpillar ( Cerura vinula ) will spray it as well when threatened by predators. It is also found in the trichomes of stinging nettle ( Urtica dioica ). Apart from that, this acid is incorporated in many fruits such as pineapple (0.21 mg per 100 g), apple (2 mg per 100 g) and kiwi (1 mg per 100 g), as well as in many vegetables, namely onion (45 mg per 100 g), eggplant (1.34 mg per 100 g) and, in extremely low concentrations, cucumber (0.11 mg per 100 g). [ 8 ] Formic acid is a naturally occurring component of the atmosphere primarily due to forest emissions. [ 9 ]
As early as the 15th century, some alchemists and naturalists were aware that ant hills give off an acidic vapor. The first person to describe the isolation of this substance (by the distillation of large numbers of ants) was the English naturalist John Ray , in 1671. [ 10 ] [ 11 ] Ants secrete the formic acid for attack and defense purposes. Formic acid was first synthesized from hydrocyanic acid by the French chemist Joseph Gay-Lussac . In 1855, another French chemist, Marcellin Berthelot , developed a synthesis from carbon monoxide similar to the process used today. [ 12 ]
Formic acid was long considered a chemical compound of only minor interest in the chemical industry. In the late 1960s, significant quantities became available as a byproduct of acetic acid production. It now finds increasing use as a preservative and antibacterial in livestock feed. [ 12 ]
Formic acid is a colorless liquid having a pungent, penetrating odor [ 13 ] at room temperature, comparable to the related acetic acid . Formic acid is about ten times stronger than acetic acid having a (logarithmic) dissociation constant of 3.745 compared to 4.756 for acetic acid. [ 3 ]
It is miscible with water and most polar organic solvents , and is somewhat soluble in hydrocarbons . In hydrocarbons and in the vapor phase, it consists of hydrogen-bonded dimers rather than individual molecules. [ 14 ] [ 15 ] Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law . [ 15 ] Solid formic acid, which can exist in either of two polymorphs , consists of an effectively endless network of hydrogen-bonded formic acid molecules. Formic acid forms a high-boiling azeotrope with water (107.3 °C; 77.5% formic acid). Liquid formic acid tends to supercool .
Formic acid readily decomposes by dehydration in the presence of concentrated sulfuric acid to form carbon monoxide and water:
Treatment of formic acid with sulfuric acid is a convenient laboratory source of CO. [ 16 ] [ 17 ]
In the presence of platinum , it decomposes with a release of hydrogen and carbon dioxide .
Soluble ruthenium catalysts are also effective for producing carbon monoxide-free hydrogen. [ 18 ]
Formic acid shares most of the chemical properties of other carboxylic acids . Because of its high acidity, solutions in alcohols form esters spontaneously; in Fischer esterifications of formic acid, it self-catalyzes the reaction and no additional acid catalyst is needed. [ 19 ] Formic acid shares some of the reducing properties of aldehydes , reducing solutions of metal oxides to their respective metal. [ 20 ]
Formic acid is a source for a formyl group for example in the formylation of N -methylaniline to N -methylformanilide in toluene . [ 21 ]
In synthetic organic chemistry , formic acid is often used as a source of hydride ion, as in the Eschweiler–Clarke reaction :
It is used as a source of hydrogen in transfer hydrogenation , as in the Leuckart reaction to make amines , and (in aqueous solution or in its azeotrope with triethylamine ) for hydrogenation of ketones . [ 22 ]
Formic acid is unique among the carboxylic acids in its ability to participate in addition reactions with alkenes . Formic acids and alkenes readily react to form formate esters . In the presence of certain acids, including sulfuric and hydrofluoric acids , however, a variant of the Koch reaction occurs instead, and formic acid adds to the alkene to produce a larger carboxylic acid. [ 23 ]
An unstable formic anhydride , H(C=O)−O−(C=O)H, can be obtained by dehydration of formic acid with N , N ′ -dicyclohexylcarbodiimide in ether at low temperature. [ 24 ]
In 2009, the worldwide capacity for producing formic acid was 720 thousand tonnes (1.6 billion pounds) per year, roughly equally divided between Europe (350 thousand tonnes or 770 million pounds, mainly in Germany) and Asia (370 thousand tonnes or 820 million pounds, mainly in China) while production was below 1 thousand tonnes or 2.2 million pounds per year in all other continents. [ 25 ] It is commercially available in solutions of various concentrations between 85 and 99 w/w %. [ 14 ] As of 2009 [update] , the largest producers are BASF , Eastman Chemical Company , LC Industrial , and Feicheng Acid Chemicals , with the largest production facilities in Ludwigshafen (200 thousand tonnes or 440 million pounds per year, BASF, Germany), Oulu (105 thousand tonnes or 230 million pounds, Eastman, Finland), Nakhon Pathom (n/a, LC Industrial), and Feicheng (100 thousand tonnes or 220 million pounds, Feicheng, China). 2010 prices ranged from around €650/tonne (equivalent to around $800/tonne) in Western Europe to $1250/tonne in the United States. [ 25 ]
Regenerating CO 2 to make useful products, that displace incumbent fossil fuel based pathways is a more impactful process than CO 2 sequestration.
Both formic acid and CO (carbon monoxide) are C1 (one carbon molecules). Formic is a hydrogen-rich liquid which can be transported and easily donates its hydrogen to enable a variety of condensation and esterification reactions to make a wide variety of derivative molecules. CO, while more difficult to transport as a gas, is also one of the primary constituents of syngas useful in synthesizing a wide variety of molecules.
CO 2 electrolysis is distinct from photosynthesis and offers a promising alternative to accelerate decarbonization. By converting CO 2 into products using clean electricity, we reduce CO 2 emissions in two ways: first and most simply by the amount of CO 2 that is regenerated, but the second way is less obvious but even more consequential by avoiding the CO 2 emissions otherwise generated by making these same products from fossil fuels. This is known as carbon displacement or abatement.
CO 2 electrolysis holds promise for reducing atmospheric CO 2 levels and providing a sustainable method for producing chemicals, materials, and fuels. Its efficiency and scalability are active areas of research, but now also commercialization, aiming to make it a viable commercial technology for both carbon management and molecule production. [ 26 ]
When methanol and carbon monoxide are combined in the presence of a strong base , the result is methyl formate , according to the chemical equation : [ 14 ]
In industry, this reaction is performed in the liquid phase at elevated pressure. Typical reaction conditions are 80 °C and 40 atm. The most widely used base is sodium methoxide . Hydrolysis of the methyl formate produces formic acid:
Efficient hydrolysis of methyl formate requires a large excess of water. Some routes proceed indirectly by first treating the methyl formate with ammonia to give formamide , which is then hydrolyzed with sulfuric acid :
A disadvantage of this approach is the need to dispose of the ammonium sulfate byproduct. This problem has led some manufacturers to develop energy-efficient methods of separating formic acid from the excess water used in direct hydrolysis. In one of these processes, used by BASF , the formic acid is removed from the water by liquid-liquid extraction with an organic base. [ citation needed ]
A significant amount of formic acid is produced as a byproduct in the manufacture of other chemicals. At one time, acetic acid was produced on a large scale by oxidation of alkanes , by a process that cogenerates significant formic acid. [ 14 ] This oxidative route to acetic acid has declined in importance so that the aforementioned dedicated routes to formic acid have become more important. [ citation needed ]
The catalytic hydrogenation of CO 2 to formic acid has long been studied. This reaction can be conducted homogeneously. [ 27 ] [ 28 ] [ 29 ]
Formic acid can also be obtained by aqueous catalytic partial oxidation of wet biomass by the OxFA process . [ 30 ] [ 31 ] A Keggin-type polyoxometalate (H 5 PV 2 Mo 10 O 40 ) is used as the homogeneous catalyst to convert sugars, wood, waste paper, or cyanobacteria to formic acid and CO 2 as the sole byproduct. Yields of up to 53% formic acid can be achieved. [ citation needed ]
In the laboratory, formic acid can be obtained by heating oxalic acid in glycerol followed by steam distillation. [ 32 ] Glycerol acts as a catalyst, as the reaction proceeds through a glyceryl oxalate intermediate. If the reaction mixture is heated to higher temperatures, allyl alcohol results. The net reaction is thus:
Another illustrative method involves the reaction between lead formate and hydrogen sulfide , driven by the formation of lead sulfide . [ 33 ]
Formate is formed by the electrochemical reduction of CO 2 (in the form of bicarbonate ) at a lead cathode at pH 8.6: [ 34 ]
or
If the feed is CO 2 and oxygen is evolved at the anode, the total reaction is:
Formic acid is named after ants which have high concentrations of the compound in their venom, derived from serine through a 5,10-methenyltetrahydrofolate intermediate. [ 35 ] The conjugate base of formic acid, formate, also occurs widely in nature. An assay for formic acid in body fluids, designed for determination of formate after methanol poisoning, is based on the reaction of formate with bacterial formate dehydrogenase . [ 36 ]
A major use of formic acid is as a preservative and antibacterial agent in livestock feed. It arrests certain decay processes and causes the feed to retain its nutritive value longer,
In Europe, it is applied on silage , including fresh hay, to promote the fermentation of lactic acid and to suppress the formation of butyric acid ; it also allows fermentation to occur quickly, and at a lower temperature, reducing the loss of nutritional value. [ 14 ] It is widely used to preserve winter feed for cattle , [ 37 ] and is sometimes added to poultry feed to kill E. coli bacteria. [ 38 ] [ 39 ] Use as a preservative for silage and other animal feed constituted 30% of the global consumption in 2009. [ 25 ]
Beekeepers use formic acid as a miticide against the tracheal mite ( Acarapis woodi ) and the Varroa destructor mite and Varroa jacobsoni mite . [ 40 ]
Formic acid can be used directly in formic acid fuel cells or indirectly in hydrogen fuel cells . [ 41 ] [ 42 ]
Electrolytic conversion of electrical energy to chemical fuel has been proposed as a large-scale source of formate by various groups. [ 43 ] The formate could be used as feed to modified E. coli bacteria for producing biomass . [ 44 ] [ 45 ] Natural methylotroph microbes can feed on formic acid or formate.
Formic acid has been considered as a means of hydrogen storage . [ 46 ] The co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. Formic acid contains 53 g/L hydrogen at room temperature and atmospheric pressure, which is three and a half times as much as compressed hydrogen gas can attain at 350 bar pressure (14.7 g/L). Pure formic acid is a liquid with a flash point of 69 °C, much higher than that of gasoline (−40 °C) or ethanol (13 °C). [ citation needed ]
It is possible to use formic acid as an intermediary to produce isobutanol from CO 2 using microbes. [ 47 ] [ 48 ]
Formic acid has a potential application in soldering . Due to its capacity to reduce oxide layers, formic acid gas can be blasted at an oxide surface to increase solder wettability . [ citation needed ]
Formic acid is used as a volatile pH modifier in HPLC and capillary electrophoresis . Formic acid is often used as a component of mobile phase in reversed-phase high-performance liquid chromatography (RP-HPLC) analysis and separation techniques for the separation of hydrophobic macromolecules, such as peptides, proteins and more complex structures including intact viruses. Especially when paired with mass spectrometry detection, formic acid offers several advantages over the more traditionally used phosphoric acid . [ 49 ] [ 50 ]
Formic acid is also significantly used in the production of leather, including tanning (23% of the global consumption in 2009 [ 25 ] ), and in dyeing and finishing textiles (9% of the global consumption in 2009 [ 25 ] ) because of its acidic nature. Use as a coagulant in the production of rubber [ 14 ] consumed 6% of the global production in 2009. [ 25 ]
Formic acid is also used in place of mineral acids for various cleaning products, [ 14 ] such as limescale remover and toilet bowl cleaner . Some formate esters are artificial flavorings and perfumes.
Formic acid application has been reported to be an effective treatment for warts . [ 51 ]
Formic acid has low toxicity (hence its use as a food additive), with an LD 50 of 1.8 g/kg (tested orally on mice). The concentrated acid is corrosive to the skin. [ 14 ]
Formic acid is readily metabolized and eliminated by the body. Nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness, seen in methanol poisoning . [ 52 ] Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen . [ 53 ] Chronic exposure in humans may cause kidney damage. [ 53 ] Another possible effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.
Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the containing vessel. For this reason, 98% formic acid is shipped in plastic bottles with self-venting caps. [ citation needed ]
The hazards of solutions of formic acid depend on the concentration. The following table lists the Globally Harmonized System of Classification and Labelling of Chemicals for formic acid solutions: [ citation needed ]
Formic acid in 85% concentration is flammable, and diluted formic acid is on the U.S. Food and Drug Administration list of food additives. [ 54 ] The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. The U.S. OSHA Permissible Exposure Level ( PEL ) of formic acid vapor in the work environment is 5 parts per million (ppm) of air. [ 55 ] | https://en.wikipedia.org/wiki/HCO2H |
Performic acid (PFA) is an organic compound with the formula CH 2 O 3 . It is an unstable colorless liquid which can be produced by mixing formic acid with hydrogen peroxide . Owing to its oxidizing and disinfecting action, it is used in the chemical, medical and food industries.
Performic acid is a colorless liquid soluble in water, alcohols, ether , benzene , chloroform and other organic solvents. [ 4 ] [ 5 ] Its strong oxidizing properties are used for cleaving disulfide bonds in protein mapping, [ 6 ] as well as for epoxidation, hydroxylation [ 7 ] and oxidation reactions in organic synthesis. [ 5 ] In the medical and food industries, performic acid is commonly used to disinfect equipment. It is effective against viruses, bacterial spores, algae , microscopic fungi and mycobacteria , as well as other microorganisms such as zooplankton .
The popularity of performic acid as a sterilizer originates from the safe nature of its degradation products, mostly carbon dioxide , oxygen and water. [ 4 ] [ 8 ] The disinfecting action of performic acid is also faster than that of the related compounds peracetic acid and hydrogen peroxide. [ 9 ] The major drawbacks of performic acid are handling dangers related to its high reactivity, as well as instability, especially upon heating, which means that the acid must be used within about 12 hours of it being synthesised. [ 9 ] [ 10 ] [ 11 ]
Performic acid is synthesized by the reaction of formic acid and hydrogen peroxide by the following equilibrium reaction :
Synthesis of pure performic acid has not been reported, but aqueous solutions up to about 48% can be formed by simply mixing equimolar amounts of concentrated aqueous reactant solutions. [ 4 ] Using an excess of either reactant shifts the equilibrium towards the product side. The aqueous product solution can be distilled to increase the concentration of performic acid to about 90%. [ 4 ]
This reaction is reversible and can be used for large scale industrial production if accelerated with a catalyst ; however, its temperature must be kept below 80–85 °C to avoid an explosion. [ 12 ] The catalyst can be nitric , hydrofluoric , phosphoric or sulfuric acid or their salts; [ 4 ] [ 13 ] it can also be an organic compound containing at least one ester group, such as carboxylic acid ester [ 14 ] or peracetic acid. [ 9 ]
Performic acid is non-toxic; it does irritate the skin, but less so than peracetic acid. Concentrated acid (above 50%) is highly reactive; it readily decomposes upon heating, and explodes upon rapid heating to 80–85 °C. It may ignite or explode at room temperature when combined with flammable substances, such as formaldehyde , benzaldehyde , or aniline , and explodes violently upon addition of metal powders. [ 4 ] For this reason, spilled performic acid is diluted with cold water and collected with neutral, non-flammable inorganic absorbents, such as vermiculite . [ 5 ] | https://en.wikipedia.org/wiki/HCO3H |
Formyl fluoride is the organic compound with the formula HC(O)F.
HC(O)F was first reported in 1934. [ 2 ] Among the many preparations, a typical one involves the reaction of sodium formate with benzoyl fluoride (generated in situ from KHF 2 and benzoyl chloride ): [ 3 ]
The molecule is planar; C-O and C-F distances are 1.18 and 1.34 A, respectively. [ 1 ]
HC(O)F decomposes autocatalytically near room temperature to carbon monoxide and hydrogen fluoride :
Because of the compound's sensitivity, reactions are conducted at low temperatures and samples are often stored over anhydrous alkali metal fluorides, e.g. potassium fluoride which absorbs HF.
Benzene (and other arenes ) react with formyl fluoride in the presence of boron trifluoride to give benzaldehyde . In a related reaction, formyl chloride is implicated in Gattermann-Koch formylation reaction. The reaction of formyl fluoride/BF 3 with perdeuteriobenzene (C 6 D 6 ) exhibits a kinetic isotope effect of 2.68, similar to the isotope effect observed in Friedel-Crafts acetylation of benzene. Formylation of benzene with a mixture of CO and hexafluoroantimonic acid however, exhibits no isotope effect (C 6 H 6 and C 6 D 6 react at the same rate), indicating that this reaction involves a more reactive formylating agent, possibly CHO + . [ 3 ]
Formyl fluoride undergoes the reactions expected of an acyl halide: alcohols and carboxylic acids are converted to formate esters and mixed acid anhydrides , respectively. [ 4 ] | https://en.wikipedia.org/wiki/HCOF |
Formamide is an amide derived from formic acid . It is a colorless liquid which is miscible with water and has an ammonia -like odor. It is chemical feedstock for the manufacture of sulfa drugs and other pharmaceuticals , herbicides and pesticides , and in the manufacture of hydrocyanic acid . It has been used as a softener for paper and fiber. It is a solvent for many ionic compounds . It has also been used as a solvent for resins and plasticizers . [ 4 ] Some astrobiologists suggest that it may be an alternative to water as the main solvent in other forms of life. [ 5 ]
Formamides are compounds of the type RR′NCHO. One important formamide is dimethylformamide , (CH 3 ) 2 NCHO.
In the past, formamide was produced by treating formic acid with ammonia , which produces ammonium formate , which in turn yields formamide upon heating: [ 6 ]
Formamide is also generated by aminolysis of ethyl formate : [ 7 ]
The current industrial process for the manufacture of formamide involves the carbonylation of ammonia: [ 4 ]
An alternative two-stage process involves the ammonolysis of methyl formate , which is formed from carbon monoxide and methanol :
Formamide is used in the industrial production of hydrogen cyanide . It is also used as a solvent for processing various polymers such as polyacrylonitrile . [ 8 ]
Formamide decomposes into carbon monoxide and ammonia when heated above 100 °C.
The reaction is slow below 160 °C, but accelerates thereafter. At very high temperatures, the reaction products shift to hydrogen cyanide (HCN) and water instead:
The same effect occurs in the presence of solid acid catalysts. [ 8 ]
Formamide is a constituent of cryoprotectant vitrification mixtures used for cryopreservation of tissues and organs .
Formamide is also used as an RNA stabiliser in gel electrophoresis by deionizing RNA. In capillary electrophoresis, it is used for stabilizing (single) strands of denatured DNA.
Another use is to add it in sol-gel solutions in order to avoid cracking during sintering .
Formamide, in its pure state, has been used as an alternative solvent for the electrostatic self-assembly of polymer nanofilms. [ 9 ]
Formamide is used to prepare primary amines directly from ketones via their N-formyl derivatives, using the Leuckart reaction .
Formamides are intermediates in the methanogenesis cycle.
Formamide has been proposed as an alternative solvent to water, perhaps with the ability to support life with alternative biochemistries to that currently found on Earth. It forms by the hydrolysis of hydrogen cyanide. With a large dipole moment, its solvation properties are similar to those of water. [ 11 ]
Formamide has been shown to convert to traces of guanine upon heating in the presence of ultraviolet light. [ 12 ]
Several prebiotic chemical reactions producing amino acid derivatives have been shown to take place in formamide. [ 13 ]
Contact with skin and eyes is not recommended. With an LD50 of grams per kg, formamide is of low acute toxicity. It also has low mutagenicity. [ 8 ]
Formamide is classified as toxic to reproductive health. [ 14 ] | https://en.wikipedia.org/wiki/HCONH2 |
Ethyl formate is an ester formed when ethanol (an alcohol ) reacts with formic acid (a carboxylic acid ). Ethyl formate has the characteristic smell of rum and is partially responsible for the flavor of raspberries , [ 3 ] occurring naturally in some plant oils, fruits, and juices.
Ethyl formate is generally recognized as safe by the U.S. Food and Drug Administration . [ 4 ]
According to the U.S Occupational Safety and Health Administration (OSHA), ethyl formate can irritate eyes, skin, mucous membranes , and the respiratory system of humans and other animals; it is also a central nervous system depressant . [ 5 ] In industry, it is used as a solvent for cellulose nitrate , cellulose acetate , oils, and greases. It can be used as a substitute for acetone ; workers may also be exposed to it under the following circumstances: [ 5 ]
OSHA considers a time-weighted average of 100 parts per million (300 milligrams per cubic meter) over an eight-hour period as the permissible exposure limit . The U.S. National Institute for Occupational Safety and Health (NIOSH) also considers a time-weighted average of 100 ppm over an eight-hour period as the recommended exposure limit . [ 6 ]
Ethyl formate has been identified in dust clouds in an area of the Milky Way galaxy called Sagittarius B2 . It is among 50 molecular species identified using the 30 metre IRAM radiotelescope . [ 3 ] | https://en.wikipedia.org/wiki/HCOOCH2CH3 |
Methyl formate , also called methyl methanoate , is the methyl ester of formic acid . The simplest example of a carboxylate ester, it is a colorless liquid with an ethereal odour, high vapor pressure , and low surface tension . It is a precursor to many other compounds of commercial interest. [ 4 ]
In the laboratory, methyl formate can be produced by the condensation reaction of methanol and formic acid , as follows:
Industrial methyl formate, however, is usually produced by the combination of methanol and carbon monoxide ( carbonylation ) in the presence of a strong base, such as sodium methoxide : [ 4 ]
This process, practiced commercially by BASF among other companies gives 96% selectivity toward methyl formate. The catalyst for this process is sensitive to water, which can be present in the carbon monoxide feedstock, which is commonly derived from synthesis gas . Very dry carbon monoxide is, therefore, essential. [ 5 ]
Methyl formate is used primarily to manufacture formamide , dimethylformamide , and formic acid . These compounds are precursors or building blocks for many useful derivatives.
Because of its high vapor pressure , it is used for quick-drying finishes and as a blowing agent for some polyurethane foam applications (for example Ecomate ® manufactured by Foam Supplies Inc.) [ 6 ] and as a replacement for CFCs , HCFCs , and HFCs . Methyl formate has near zero ozone depletion potential and zero global warming potential and a short atmospheric life of 3 days. [ 7 ]
It is also used as an insecticide . [ citation needed ]
A historical use of methyl formate, which sometimes brings it attention, was in refrigeration. Before the introduction of less-toxic refrigerants, methyl formate was used as an alternative to sulfur dioxide in domestic refrigerators, such as some models of the famous GE Monitor Top. | https://en.wikipedia.org/wiki/HCOOCH3 |
Formic acid (from Latin formica ' ant ' ), systematically named methanoic acid , is the simplest carboxylic acid . It has the chemical formula HCOOH and structure H−C(=O)−O−H . This acid is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Esters , salts , and the anion derived from formic acid are called formates . Industrially, formic acid is produced from methanol . [ 5 ]
Formic acid, which has a pungent, penetrating odor, is found naturally in insects, weeds, fruits and vegetables, and forest emissions. It appears in most ants and in stingless bees of the genus Oxytrigona . [ 6 ] [ 7 ] Wood ants from the genus Formica can spray formic acid on their prey or to defend the nest. The puss moth caterpillar ( Cerura vinula ) will spray it as well when threatened by predators. It is also found in the trichomes of stinging nettle ( Urtica dioica ). Apart from that, this acid is incorporated in many fruits such as pineapple (0.21 mg per 100 g), apple (2 mg per 100 g) and kiwi (1 mg per 100 g), as well as in many vegetables, namely onion (45 mg per 100 g), eggplant (1.34 mg per 100 g) and, in extremely low concentrations, cucumber (0.11 mg per 100 g). [ 8 ] Formic acid is a naturally occurring component of the atmosphere primarily due to forest emissions. [ 9 ]
As early as the 15th century, some alchemists and naturalists were aware that ant hills give off an acidic vapor. The first person to describe the isolation of this substance (by the distillation of large numbers of ants) was the English naturalist John Ray , in 1671. [ 10 ] [ 11 ] Ants secrete the formic acid for attack and defense purposes. Formic acid was first synthesized from hydrocyanic acid by the French chemist Joseph Gay-Lussac . In 1855, another French chemist, Marcellin Berthelot , developed a synthesis from carbon monoxide similar to the process used today. [ 12 ]
Formic acid was long considered a chemical compound of only minor interest in the chemical industry. In the late 1960s, significant quantities became available as a byproduct of acetic acid production. It now finds increasing use as a preservative and antibacterial in livestock feed. [ 12 ]
Formic acid is a colorless liquid having a pungent, penetrating odor [ 13 ] at room temperature, comparable to the related acetic acid . Formic acid is about ten times stronger than acetic acid having a (logarithmic) dissociation constant of 3.745 compared to 4.756 for acetic acid. [ 3 ]
It is miscible with water and most polar organic solvents , and is somewhat soluble in hydrocarbons . In hydrocarbons and in the vapor phase, it consists of hydrogen-bonded dimers rather than individual molecules. [ 14 ] [ 15 ] Owing to its tendency to hydrogen-bond, gaseous formic acid does not obey the ideal gas law . [ 15 ] Solid formic acid, which can exist in either of two polymorphs , consists of an effectively endless network of hydrogen-bonded formic acid molecules. Formic acid forms a high-boiling azeotrope with water (107.3 °C; 77.5% formic acid). Liquid formic acid tends to supercool .
Formic acid readily decomposes by dehydration in the presence of concentrated sulfuric acid to form carbon monoxide and water:
Treatment of formic acid with sulfuric acid is a convenient laboratory source of CO. [ 16 ] [ 17 ]
In the presence of platinum , it decomposes with a release of hydrogen and carbon dioxide .
Soluble ruthenium catalysts are also effective for producing carbon monoxide-free hydrogen. [ 18 ]
Formic acid shares most of the chemical properties of other carboxylic acids . Because of its high acidity, solutions in alcohols form esters spontaneously; in Fischer esterifications of formic acid, it self-catalyzes the reaction and no additional acid catalyst is needed. [ 19 ] Formic acid shares some of the reducing properties of aldehydes , reducing solutions of metal oxides to their respective metal. [ 20 ]
Formic acid is a source for a formyl group for example in the formylation of N -methylaniline to N -methylformanilide in toluene . [ 21 ]
In synthetic organic chemistry , formic acid is often used as a source of hydride ion, as in the Eschweiler–Clarke reaction :
It is used as a source of hydrogen in transfer hydrogenation , as in the Leuckart reaction to make amines , and (in aqueous solution or in its azeotrope with triethylamine ) for hydrogenation of ketones . [ 22 ]
Formic acid is unique among the carboxylic acids in its ability to participate in addition reactions with alkenes . Formic acids and alkenes readily react to form formate esters . In the presence of certain acids, including sulfuric and hydrofluoric acids , however, a variant of the Koch reaction occurs instead, and formic acid adds to the alkene to produce a larger carboxylic acid. [ 23 ]
An unstable formic anhydride , H(C=O)−O−(C=O)H, can be obtained by dehydration of formic acid with N , N ′ -dicyclohexylcarbodiimide in ether at low temperature. [ 24 ]
In 2009, the worldwide capacity for producing formic acid was 720 thousand tonnes (1.6 billion pounds) per year, roughly equally divided between Europe (350 thousand tonnes or 770 million pounds, mainly in Germany) and Asia (370 thousand tonnes or 820 million pounds, mainly in China) while production was below 1 thousand tonnes or 2.2 million pounds per year in all other continents. [ 25 ] It is commercially available in solutions of various concentrations between 85 and 99 w/w %. [ 14 ] As of 2009 [update] , the largest producers are BASF , Eastman Chemical Company , LC Industrial , and Feicheng Acid Chemicals , with the largest production facilities in Ludwigshafen (200 thousand tonnes or 440 million pounds per year, BASF, Germany), Oulu (105 thousand tonnes or 230 million pounds, Eastman, Finland), Nakhon Pathom (n/a, LC Industrial), and Feicheng (100 thousand tonnes or 220 million pounds, Feicheng, China). 2010 prices ranged from around €650/tonne (equivalent to around $800/tonne) in Western Europe to $1250/tonne in the United States. [ 25 ]
Regenerating CO 2 to make useful products, that displace incumbent fossil fuel based pathways is a more impactful process than CO 2 sequestration.
Both formic acid and CO (carbon monoxide) are C1 (one carbon molecules). Formic is a hydrogen-rich liquid which can be transported and easily donates its hydrogen to enable a variety of condensation and esterification reactions to make a wide variety of derivative molecules. CO, while more difficult to transport as a gas, is also one of the primary constituents of syngas useful in synthesizing a wide variety of molecules.
CO 2 electrolysis is distinct from photosynthesis and offers a promising alternative to accelerate decarbonization. By converting CO 2 into products using clean electricity, we reduce CO 2 emissions in two ways: first and most simply by the amount of CO 2 that is regenerated, but the second way is less obvious but even more consequential by avoiding the CO 2 emissions otherwise generated by making these same products from fossil fuels. This is known as carbon displacement or abatement.
CO 2 electrolysis holds promise for reducing atmospheric CO 2 levels and providing a sustainable method for producing chemicals, materials, and fuels. Its efficiency and scalability are active areas of research, but now also commercialization, aiming to make it a viable commercial technology for both carbon management and molecule production. [ 26 ]
When methanol and carbon monoxide are combined in the presence of a strong base , the result is methyl formate , according to the chemical equation : [ 14 ]
In industry, this reaction is performed in the liquid phase at elevated pressure. Typical reaction conditions are 80 °C and 40 atm. The most widely used base is sodium methoxide . Hydrolysis of the methyl formate produces formic acid:
Efficient hydrolysis of methyl formate requires a large excess of water. Some routes proceed indirectly by first treating the methyl formate with ammonia to give formamide , which is then hydrolyzed with sulfuric acid :
A disadvantage of this approach is the need to dispose of the ammonium sulfate byproduct. This problem has led some manufacturers to develop energy-efficient methods of separating formic acid from the excess water used in direct hydrolysis. In one of these processes, used by BASF , the formic acid is removed from the water by liquid-liquid extraction with an organic base. [ citation needed ]
A significant amount of formic acid is produced as a byproduct in the manufacture of other chemicals. At one time, acetic acid was produced on a large scale by oxidation of alkanes , by a process that cogenerates significant formic acid. [ 14 ] This oxidative route to acetic acid has declined in importance so that the aforementioned dedicated routes to formic acid have become more important. [ citation needed ]
The catalytic hydrogenation of CO 2 to formic acid has long been studied. This reaction can be conducted homogeneously. [ 27 ] [ 28 ] [ 29 ]
Formic acid can also be obtained by aqueous catalytic partial oxidation of wet biomass by the OxFA process . [ 30 ] [ 31 ] A Keggin-type polyoxometalate (H 5 PV 2 Mo 10 O 40 ) is used as the homogeneous catalyst to convert sugars, wood, waste paper, or cyanobacteria to formic acid and CO 2 as the sole byproduct. Yields of up to 53% formic acid can be achieved. [ citation needed ]
In the laboratory, formic acid can be obtained by heating oxalic acid in glycerol followed by steam distillation. [ 32 ] Glycerol acts as a catalyst, as the reaction proceeds through a glyceryl oxalate intermediate. If the reaction mixture is heated to higher temperatures, allyl alcohol results. The net reaction is thus:
Another illustrative method involves the reaction between lead formate and hydrogen sulfide , driven by the formation of lead sulfide . [ 33 ]
Formate is formed by the electrochemical reduction of CO 2 (in the form of bicarbonate ) at a lead cathode at pH 8.6: [ 34 ]
or
If the feed is CO 2 and oxygen is evolved at the anode, the total reaction is:
Formic acid is named after ants which have high concentrations of the compound in their venom, derived from serine through a 5,10-methenyltetrahydrofolate intermediate. [ 35 ] The conjugate base of formic acid, formate, also occurs widely in nature. An assay for formic acid in body fluids, designed for determination of formate after methanol poisoning, is based on the reaction of formate with bacterial formate dehydrogenase . [ 36 ]
A major use of formic acid is as a preservative and antibacterial agent in livestock feed. It arrests certain decay processes and causes the feed to retain its nutritive value longer,
In Europe, it is applied on silage , including fresh hay, to promote the fermentation of lactic acid and to suppress the formation of butyric acid ; it also allows fermentation to occur quickly, and at a lower temperature, reducing the loss of nutritional value. [ 14 ] It is widely used to preserve winter feed for cattle , [ 37 ] and is sometimes added to poultry feed to kill E. coli bacteria. [ 38 ] [ 39 ] Use as a preservative for silage and other animal feed constituted 30% of the global consumption in 2009. [ 25 ]
Beekeepers use formic acid as a miticide against the tracheal mite ( Acarapis woodi ) and the Varroa destructor mite and Varroa jacobsoni mite . [ 40 ]
Formic acid can be used directly in formic acid fuel cells or indirectly in hydrogen fuel cells . [ 41 ] [ 42 ]
Electrolytic conversion of electrical energy to chemical fuel has been proposed as a large-scale source of formate by various groups. [ 43 ] The formate could be used as feed to modified E. coli bacteria for producing biomass . [ 44 ] [ 45 ] Natural methylotroph microbes can feed on formic acid or formate.
Formic acid has been considered as a means of hydrogen storage . [ 46 ] The co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. Formic acid contains 53 g/L hydrogen at room temperature and atmospheric pressure, which is three and a half times as much as compressed hydrogen gas can attain at 350 bar pressure (14.7 g/L). Pure formic acid is a liquid with a flash point of 69 °C, much higher than that of gasoline (−40 °C) or ethanol (13 °C). [ citation needed ]
It is possible to use formic acid as an intermediary to produce isobutanol from CO 2 using microbes. [ 47 ] [ 48 ]
Formic acid has a potential application in soldering . Due to its capacity to reduce oxide layers, formic acid gas can be blasted at an oxide surface to increase solder wettability . [ citation needed ]
Formic acid is used as a volatile pH modifier in HPLC and capillary electrophoresis . Formic acid is often used as a component of mobile phase in reversed-phase high-performance liquid chromatography (RP-HPLC) analysis and separation techniques for the separation of hydrophobic macromolecules, such as peptides, proteins and more complex structures including intact viruses. Especially when paired with mass spectrometry detection, formic acid offers several advantages over the more traditionally used phosphoric acid . [ 49 ] [ 50 ]
Formic acid is also significantly used in the production of leather, including tanning (23% of the global consumption in 2009 [ 25 ] ), and in dyeing and finishing textiles (9% of the global consumption in 2009 [ 25 ] ) because of its acidic nature. Use as a coagulant in the production of rubber [ 14 ] consumed 6% of the global production in 2009. [ 25 ]
Formic acid is also used in place of mineral acids for various cleaning products, [ 14 ] such as limescale remover and toilet bowl cleaner . Some formate esters are artificial flavorings and perfumes.
Formic acid application has been reported to be an effective treatment for warts . [ 51 ]
Formic acid has low toxicity (hence its use as a food additive), with an LD 50 of 1.8 g/kg (tested orally on mice). The concentrated acid is corrosive to the skin. [ 14 ]
Formic acid is readily metabolized and eliminated by the body. Nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness, seen in methanol poisoning . [ 52 ] Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen . [ 53 ] Chronic exposure in humans may cause kidney damage. [ 53 ] Another possible effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.
Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the containing vessel. For this reason, 98% formic acid is shipped in plastic bottles with self-venting caps. [ citation needed ]
The hazards of solutions of formic acid depend on the concentration. The following table lists the Globally Harmonized System of Classification and Labelling of Chemicals for formic acid solutions: [ citation needed ]
Formic acid in 85% concentration is flammable, and diluted formic acid is on the U.S. Food and Drug Administration list of food additives. [ 54 ] The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. The U.S. OSHA Permissible Exposure Level ( PEL ) of formic acid vapor in the work environment is 5 parts per million (ppm) of air. [ 55 ] | https://en.wikipedia.org/wiki/HCOOH |
Potassium formate , HCO 2 K, HCOOK, or KHCO 2 , is the potassium salt of formic acid . This strongly hygroscopic white solid [ 2 ] is an intermediate in the formate potash process for the production of potassium. [ 3 ] Potassium formate has also been studied as a potential environmentally friendly deicing salt for use on roads. [ 4 ] [ 5 ] It has also been suggested for use in a less corrosive liquid desiccant . [ 6 ] A 52% solution of potassium formate has a freezing point of −60 °C (−76 °F). [ 7 ] Potassium formate brines are sometimes used for heat transfer, despite being much more corrosive than many other liquid coolants, especially to zinc and aluminum but even to many steels, [ 8 ] though some formulations are compatible with aluminum and steels. [ 9 ]
Since 1995, potassium formate has been increasingly used in aqueous drilling fluids to increase density, stabilize the hole, and improve drilling performance. [ 10 ] [ 11 ] [ 12 ]
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HCOOK |
Sodium formate , HCOONa, is the sodium salt of formic acid , HCOOH. It usually appears as a white deliquescent powder.
For commercial use, sodium formate is produced by absorbing carbon monoxide under pressure in solid sodium hydroxide at 130 °C and 6-8 bar pressure: [ 1 ]
Because of the low-cost and large-scale availability of formic acid by carbonylation of methanol and hydrolysis of the resulting methyl formate, sodium formate is usually prepared by neutralizing formic acid with sodium hydroxide . Sodium formate is also unavoidably formed as a by-product in the final step of the pentaerythritol synthesis and in the crossed Cannizzaro reaction of formaldehyde with the aldol reaction product trimethylol acetaldehyde [3-hydroxy-2,2-bis(hydroxymethyl)propanal]. [ 2 ]
In the laboratory, sodium formate can be prepared by neutralizing formic acid with sodium carbonate . It can also be obtained by reacting chloroform with an alcoholic solution of sodium hydroxide .
or by reacting sodium hydroxide with chloral hydrate .
The latter method is, in general, preferred to the former because the low aqueous solubility of CHCl 3 makes it easier to separate out from the sodium formate solution, by fractional crystallization , than the soluble NaCl would be.
Sodium formate crystallizes in a monoclinic crystal system with the lattice parameters a = 6,19 Å, b = 6,72 Å, c = 6,49 Å and β = 121,7°. [ 3 ]
On heating, sodium formate decomposes to form sodium oxalate and hydrogen. [ 4 ] The resulting sodium oxalate can be converted by further heating to sodium carbonate upon release of carbon monoxide: [ 5 ] [ 4 ]
As a salt of a weak acid ( formic acid ) and a strong base ( sodium hydroxide ) sodium formate reacts in aqueous solutions basic:
A solution of formic acid and sodium formate can thus be used as a buffer solution.
Sodium formate is slightly water-hazardous and inhibits some species of bacteria but is degraded by others.
Sodium formate is used in several fabric dyeing and printing processes. It is also used as a buffering agent for strong mineral acids to increase their pH , as a food additive (E237), and as a de-icing agent.
In structural biology , sodium formate can be used as a cryoprotectant for X-ray diffraction experiments on protein crystals, [ 6 ] which are typically conducted at a temperature of 100 K to reduce the effects of radiation damage .
Sodium formate plays a role in the synthesis of formic acid , it is converted by sulfuric acid via the following reaction equation:
The urticating hair of stinging nettles contain sodium formate as well as formic acid.
Solid sodium formate is used as a non-corrosive agent at airports for de-icing of runways in mix with corrosion inhibitors and other additives, which rapidly penetrate solid snow and ice layers, detach them from the asphalt or concrete and melt the ice rapidly. Sodium formate was also used as a road deicer in the city of Ottawa from 1987 to 1988. [ 7 ]
The high freezing point depression e.g. in comparison to the still frequently used urea (which is effective but problematic due to eutrophication ) effectively prevents the re-icing, even at temperatures below −15 °C. The thawing effect of the solid sodium formate can even be increased by moistening with aqueous potassium formate or potassium acetate solutions. The degradability of sodium formate is particularly advantageous with a chemical oxygen demand (COD) of 211 mg O 2 /g compared with the de-icing agents sodium acetate (740 mg O 2 /g) and urea with (> 2,000 mg O 2 /g). [ 8 ]
Saturated sodium formate solutions (as well as mixtures of other alkali metal formates such as potassium and cesium formate) are used as important drilling and stabilizing aids in gas and oil exploration because of their relatively high density. By mixing the corresponding saturated alkali metal formate solutions any densities between 1,0 and 2,3 g/cm 3 can be set. The saturated solutions are biocidal and long-term stable against microbial degradation. Diluted, on the other hand, they are fast and completely biodegradable. As alkali metal formates as drilling aids make it unnecessary to add solid fillers to increase the density (such as barytes ) and the formate solutions can be recovered and recycled at the drilling site, formates represent an important advance in exploration technology. [ 9 ] | https://en.wikipedia.org/wiki/HCOONa |
The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide . At room temperature , it is a colorless gas , which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor . Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.
Hydrogen chloride is a diatomic molecule , consisting of a hydrogen atom H and a chlorine atom Cl connected by a polar covalent bond . The chlorine atom is much more electronegative than the hydrogen atom, which makes this bond polar. Consequently, the molecule has a large dipole moment with a negative partial charge (δ−) at the chlorine atom and a positive partial charge (δ+) at the hydrogen atom. [ 9 ] In part because of its high polarity, HCl is very soluble in water (and in other polar solvents ).
Upon contact, H 2 O and HCl combine to form hydronium cations [H 3 O] + and chloride anions Cl − through a reversible chemical reaction :
The resulting solution is called hydrochloric acid and is a strong acid . The acid dissociation or ionization constant, K a , is large, which means HCl dissociates or ionizes practically completely in water. Even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol :
Hydrogen chloride can protonate molecules or ions and can also serve as an acid- catalyst for chemical reactions where anhydrous (water-free) conditions are desired.
Because of its acidic nature, hydrogen chloride is a corrosive substance , particularly in the presence of moisture.
Frozen HCl undergoes a phase transition at 98.4 K (−174.8 °C; −282.5 °F). X-ray powder diffraction of the frozen material shows that the material changes from an orthorhombic structure to a cubic one during this transition. In both structures the chlorine atoms are in a face-centered array . However, the hydrogen atoms could not be located. [ 10 ] Analysis of spectroscopic and dielectric data, and determination of the structure of DCl (deuterium chloride) indicates that HCl forms zigzag chains in the solid, as does HF (see figure on right). [ 11 ]
The infrared spectrum of gaseous hydrogen chloride, shown on the left, consists of a number of sharp absorption lines grouped around 2886 cm −1 (wavelength ~3.47 μm). At room temperature, almost all molecules are in the ground vibrational state v = 0. Including anharmonicity the vibrational energy can be written as:
To promote an HCl molecule from the v = 0 to the v = 1 state, we would expect to see an infrared absorption about ν o = ν e + 2 x e ν e = 2880 cm −1 . However, this absorption corresponding to the Q-branch is not observed due to it being forbidden by symmetry. Instead, two sets of signals (P- and R-branches) are seen owing to a simultaneous change in the rotational state of the molecules. Because of quantum mechanical selection rules, only certain rotational transitions are permitted. The states are characterized by the rotational quantum number J = 0, 1, 2, 3, ... selection rules state that Δ J is only able to take values of ±1.
The value of the rotational constant B is much smaller than the vibrational one ν o , such that a much smaller amount of energy is required to rotate the molecule; for a typical molecule, this lies within the microwave region. However, the vibrational energy of HCl molecule places its absorptions within the infrared region, allowing a spectrum showing the rovibrational transitions of this molecule to be easily collected using an infrared spectrometer with a gas cell. The latter can even be made of quartz as the HCl absorption lies in a window of transparency for this material.
Naturally abundant chlorine consists of two isotopes, 35 Cl and 37 Cl, in a ratio of approximately 3:1. While the spring constants are nearly identical, the disparate reduced masses of H 35 Cl and H 37 Cl cause measurable differences in the rotational energy, thus doublets are observed on close inspection of each absorption line, weighted in the same ratio of 3:1.
Most hydrogen chloride produced on an industrial scale is used for hydrochloric acid production. [ 13 ]
In the 17th century, Johann Rudolf Glauber from Karlstadt am Main, Germany used sodium chloride salt and sulfuric acid for the preparation of sodium sulfate in the Mannheim process , releasing hydrogen chloride. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, [ 14 ] and by 1808 Humphry Davy of Penzance , England had proved that the chemical composition included hydrogen and chlorine . [ 15 ]
Hydrogen chloride is produced by combining chlorine and hydrogen :
As the reaction is exothermic , the installation is called an HCl oven or HCl burner. The resulting hydrogen chloride gas is absorbed in deionized water , resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.
The reaction can also be triggered by blue light. [ 16 ]
The industrial production of hydrogen chloride is often integrated with the formation of chlorinated and fluorinated organic compounds, e.g., Teflon , Freon , and other CFCs , as well as chloroacetic acid and PVC . Often this production of hydrochloric acid is integrated with captive use of it on-site. In the chemical reactions , hydrogen atoms on the hydrocarbon are replaced by chlorine atoms, whereupon the released hydrogen atom recombines with the spare atom from the chlorine molecule, forming hydrogen chloride. Fluorination is a subsequent chlorine-replacement reaction, producing again hydrogen chloride:
The resulting hydrogen chloride is either reused directly or absorbed in water, resulting in hydrochloric acid of technical or industrial grade.
Small amounts of hydrogen chloride for laboratory use can be generated in an HCl generator by dehydrating hydrochloric acid with either sulfuric acid or anhydrous calcium chloride . Alternatively, HCl can be generated by the reaction of sulfuric acid with sodium chloride: [ 17 ]
This reaction occurs at room temperature. Provided there is NaCl remaining in the generator and it is heated above 200 °C, the reaction proceeds further:
For such generators to function, the reagents should be dry.
Hydrogen chloride can also be prepared by the hydrolysis of certain reactive chloride compounds such as phosphorus chlorides , thionyl chloride ( SOCl 2 ), and acyl chlorides . For example, cold water can be gradually dripped onto phosphorus pentachloride ( PCl 5 ) to give HCl:
Most hydrogen chloride is consumed in the production of hydrochloric acid. It is also used in the production of vinyl chloride and many alkyl chlorides . [ 13 ] Trichlorosilane , a precursor to ultrapure silicon, is produced by the reaction of hydrogen chloride and silicon at around 300 °C. [ 18 ]
Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi (c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac ( ammonium chloride ), which when it was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride. [ 19 ] It is possible that in one of his experiments, al-Razi stumbled upon a primitive method to produce hydrochloric acid . [ 20 ] However, it appears that in most of these early experiments with chloride salts , the gaseous products were discarded, and hydrogen chloride may have been produced many times before it was discovered that it can be put to chemical use. [ 21 ]
One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts"), an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin by Gerard of Cremona (1144–1187). [ 22 ]
Another important development was the discovery by pseudo-Geber (in the De inventione veritatis , "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid , a strong solvent capable of dissolving gold (i.e., aqua regia ) could be produced. [ 23 ]
After the discovery in the late sixteenth century of the process by which unmixed hydrochloric acid can be prepared, [ 24 ] it was recognized that this new acid (then known as spirit of salt or acidum salis ) released vaporous hydrogen chloride, which was called marine acid air . In the 17th century, Johann Rudolf Glauber used salt ( sodium chloride ) and sulfuric acid for the preparation of sodium sulfate , releasing hydrogen chloride gas (see production, above). In 1772, Carl Wilhelm Scheele also reported this reaction and is sometimes credited with its discovery. Joseph Priestley prepared hydrogen chloride in 1772, and in 1810 Humphry Davy established that it is composed of hydrogen and chlorine . [ 25 ]
During the Industrial Revolution , demand for alkaline substances such as soda ash increased, and Nicolas Leblanc developed a new industrial-scale process for producing the soda ash. In the Leblanc process , salt was converted to soda ash, using sulfuric acid, limestone, and coal, giving hydrogen chloride as by-product. Initially, this gas was vented to air, but the Alkali Act 1863 prohibited such release, so then soda ash producers absorbed the HCl waste gas in water, producing hydrochloric acid on an industrial scale. Later, the Hargreaves process was developed, which is similar to the Leblanc process except sulfur dioxide , water, and air are used instead of sulfuric acid in a reaction which is exothermic overall. In the early 20th century the Leblanc process was effectively replaced by the Solvay process , which did not produce HCl. However, hydrogen chloride production continued as a step in hydrochloric acid production.
Historical uses of hydrogen chloride in the 20th century include hydrochlorinations of alkynes in producing the chlorinated monomers chloroprene and vinyl chloride , which are subsequently polymerized to make polychloroprene ( Neoprene ) and polyvinyl chloride (PVC), respectively. In the production of vinyl chloride, acetylene ( C 2 H 2 ) is hydrochlorinated by adding the HCl across the triple bond of the C 2 H 2 molecule, turning the triple into a double bond , yielding vinyl chloride.
The "acetylene process", used until the 1960s for making chloroprene , starts out by joining two acetylene molecules, and then adds HCl to the joined intermediate across the triple bond to convert it to chloroprene as shown here:
This "acetylene process" has been replaced by a process which adds Cl 2 to the double bond of ethylene instead, and subsequent elimination produces HCl instead, as well as chloroprene.
Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing , choking , inflammation of the nose, throat, and upper respiratory tract , and in severe cases, pulmonary edema , circulatory system failure, and death. [ 26 ] Skin contact can cause redness, pain , and severe chemical burns . Hydrogen chloride may cause severe burns to the eye and permanent eye damage.
The U.S. Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have established occupational exposure limits for hydrogen chloride at a ceiling of 5 ppm (7 mg/m 3 ), [ 27 ] and compiled extensive information on hydrogen chloride workplace safety concerns. [ 28 ] | https://en.wikipedia.org/wiki/HCl |
Chlorous acid is an inorganic compound with the formula HClO 2 . It is a weak acid . Chlorine has oxidation state +3 in this acid. The pure substance is unstable, disproportionating to hypochlorous acid (Cl oxidation state +1) and chloric acid (Cl oxidation state +5):
Although the acid is difficult to obtain in pure substance, the conjugate base, chlorite , derived from this acid is stable. One example of a salt of this anion is the well-known sodium chlorite . This and related salts are sometimes used in the production of chlorine dioxide .
HClO 2 can be prepared through reaction of barium or lead chlorite and dilute sulfuric acid :
Chlorous acid is a powerful oxidizing agent, although its tendency to undergo disproportionation counteracts its oxidizing potential. [ citation needed ]
Chlorine is the only halogen to form an isolable acid of formula HXO 2 . [ 1 ] Fluorine is resistant to oxidation, having a −1 oxidation state even in hypofluorous acid , and is thus unable to form any higher oxoacids; despite the name, fluorite minerals are chemically fluoride compounds. Neither bromous acid nor iodous acid has ever been isolated. A few salts of bromous acid , bromites, are known, but no iodites . [ 1 ]
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This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HClO2 |
Chloric acid , H Cl O 3 , is an oxoacid of chlorine , and the formal precursor of chlorate salts. It is a strong acid ( p K a ≈ −2.7) and an oxidizing agent .
Chloric acid is thermodynamically unstable with respect to disproportionation .
Chloric acid is stable in cold aqueous solution up to a concentration of approximately 30%, and solution of up to 40% can be prepared by careful evaporation under reduced pressure. Above these concentrations, chloric acid solutions decompose to give a variety of products, for example:
Chloric acid is a powerful oxidizing agent. Most organics and flammables will deflagrate on contact. [ citation needed ]
It may be produced from barium chlorate through its reaction with sulfuric acid , which results in a solution of chloric acid and insoluble barium sulfate precipitate: [ 2 ]
The chlorate must be dissolved in boiling water and the acid should be somewhat diluted in water and heated before mixing.
Another method which can be used to produce solutions up to 10% concentration is by the use of cation exchange resins and a soluble salt such as NaClO 3 , where the Na+ cation will exchange with H+. [ 2 ]
Another method is the heating of hypochlorous acid , producing chloric acid and hydrogen chloride : [ citation needed ]
Any way it is produced, the acid may be concentrated up to 40% in a vacuum dessicator over H 2 SO 4 . [ 2 ] | https://en.wikipedia.org/wiki/HClO3 |
Perchloric acid is a mineral acid with the formula H Cl O 4 . It is an oxoacid of chlorine . Usually found as an aqueous solution , this colorless compound is a stronger acid than sulfuric acid , nitric acid and hydrochloric acid . It is a powerful oxidizer when hot, but aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate , an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures. [ 4 ]
Perchloric acid was first synthesized (together with potassium perchlorate ) by Austrian chemist Friedrich von Stadion [ de ] and called "oxygenated chloric acid " in mid-1810s. French pharmacist Georges-Simon Serullas introduced the modern designation along with discovering its solid monohydrate, which he mistook for an anhydride . [ 5 ] Berzelius produced dilute perchloric acid by electrolysis of chloric acid. In the late 1800's German and Swedish workers commercialized the electrolysis. [ 6 ]
Perchloric acid is produced industrially by two routes. The traditional method exploits the high aqueous solubility of sodium perchlorate (209 g/100 ml of water at room temperature). Treatment of such solutions with hydrochloric acid gives perchloric acid, precipitating solid sodium chloride:
The concentrated acid can be purified by distillation . The alternative route, which is more direct and avoids salts, entails anodic oxidation of aqueous chlorine at a platinum electrode. [ 6 ] [ 7 ]
It can be distilled from a solution of potassium perchlorate in sulfuric acid. [ 8 ] Treatment of barium perchlorate with sulfuric acid precipitates barium sulfate , leaving perchloric acid. It can also be made by mixing nitric acid with ammonium perchlorate and boiling while adding hydrochloric acid. The reaction gives nitrous oxide and perchloric acid due to a concurrent reaction involving the ammonium ion and can be concentrated and purified significantly by boiling off the remaining nitric and hydrochloric acids.
Anhydrous perchloric acid is an unstable oily liquid at room temperature. It forms at least five hydrates , several of which have been characterized crystallographically . These solids consist of the perchlorate anion linked via hydrogen bonds to H 2 O and H 3 O + centers. [ 9 ] An example is hydronium perchlorate . Perchloric acid forms an azeotrope with water, consisting of about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are hygroscopic . Thus, if left open to the air, concentrated perchloric acid dilutes itself by absorbing water from the air.
Dehydration of perchloric acid gives the anhydride dichlorine heptoxide : [ 10 ]
Perchloric acid is mainly produced as a precursor to ammonium perchlorate , which is used in rocket propellant. The growth in rocketry has led to increased production of perchloric acid. Several million kilograms are produced annually. [ 6 ] Perchloric acid is one of the most proven materials for etching of liquid crystal displays and critical electronics applications as well as ore extraction and has unique properties in analytical chemistry. [ 11 ] Additionally it is a useful component in etching of chrome. [ 12 ]
Perchloric acid, a superacid , is one of the strongest Brønsted–Lowry acids . That its p K a is lower than −9 is evidenced by the fact that its monohydrate contains discrete hydronium ions and can be isolated as a stable, crystalline solid, formulated as [H 3 O + ][ ClO – 4 ]. [ 13 ] The most recent estimate of its aqueous p K a is −15.2 ± 2.0 . [ 3 ] It provides strong acidity with minimal interference because perchlorate is weakly nucleophilic (explaining the high acidity of HClO 4 ). Other acids of noncoordinating anions , such as fluoroboric acid and hexafluorophosphoric acid are susceptible to hydrolysis, whereas perchloric acid is not. Despite hazards associated with the explosiveness of its salts, the acid is often preferred in certain syntheses. [ 14 ] For similar reasons, it is a useful eluent in ion-exchange chromatography . It is also used in electropolishing or the etching of aluminium, molybdenum, and other metals.
In geochemistry, perchloric acid aids in the digestion of silicate mineral samples for analysis, and also for complete digestion of organic matter. [ 15 ]
Given its strong oxidizing properties, perchloric acid is subject to extensive regulations as it can react violently with metals and flammable substances such as wood, plastics, and oils. [ 16 ] Work conducted with perchloric acid must be conducted in fume hoods with a wash-down capability to prevent accumulation of oxidisers in the ductwork .
On February 20, 1947 in Los Angeles, California, 17 people were killed and 150 injured in the O'Connor Plating Works disaster . A bath, consisting of over 1000 litres of 75% perchloric acid and 35% acetic anhydride by volume which was being used to electro-polish aluminium furniture, exploded. Organic compounds were added to the overheating bath when an iron rack was replaced with one coated with cellulose acetobutyrate ( Tenit-2 plastic). A few minutes later the bath exploded. [ 17 ] [ 18 ] The O'Connor Electro-Plating plant, 25 other buildings, and 40 automobiles were destroyed, and 250 nearby homes were damaged. | https://en.wikipedia.org/wiki/HClO4 |
Chromium(II) hydride , systematically named chromium dihydride and poly(dihydridochromium) is pale brown solid inorganic compound with the chemical formula (CrH 2 ) n (also written ([CrH 2 ]) n or CrH 2 ). Although it is thermodynamically unstable toward decomposition at ambient temperatures, it is kinetically metastable.
Chromium(II) hydride is the second simplest polymeric chromium hydride (after chromium(I) hydride ). In metallurgical chemistry, chromium(II) hydride is fundamental to certain forms of chromium-hydrogen alloys .
The most common name for chromium(II) hydride is chromium dihydride , following the IUPAC compositional nomenclature . Because the compositional name does not distinguish between different compounds with stoichiometry CrH 2 , "chromium dihydride" is ambiguous between an unstable molecular species (see § Monomer ) and the metastable (but common) polymeric form.
The chromium(II) hydride monomer, is both thermodynamically and kinetically unstable towards autopolymerization at ambient temperature, and so cannot be concentrated. Nevertheless, molecules of CrH 2 and Cr 2 H 4 have been isolated in solid gas matrices. [ 1 ]
Cr is the second simplest molecular chromium hydride (after Chromium(I) hydride ). In the presence of pure hydrogen, dihydridochromium readily converts to bis(dihydrogen)dihydridochromium, CrH 2 (H 2 ) 2 in an exothermic reaction . [ 1 ]
In diluted CrH 2 , the molecules are known to oligomerise forming at least Cr 2 H 4 ( dimers ), being connected by covalent bonds . The dissociation enthalpy of the dimer is estimated to be 121 kJ mol −1 . [ 1 ] CrH 2 is bent, and is weakly repulsive to one hydrogen molecule, but attractive to two molecules of hydrogen. The bond angle is 118±5°. [ 2 ] The stretching force constant is 1.64 mdyn / Å. [ 2 ] The dimer has a distorted rhombus structure with C 2 h symmetry.
The dimer is produced synthetically by hydrogenation . In this process, chromium and hydrogen react according to the reaction:
This process involves atomic chromium as an intermediate, and occurs in two steps. The hydrogenation (step 2) is a spontaneous process.
In an inert gas matrix atomic Cr reacts with H 2 to make the dihydride when it is irradiated with ultraviolet light between 320 and 380 nm. [ 2 ] The reaction of chromium with molecular hydrogen is endothermic . 380 nm or greater wavelength radiation is required to procure photochemically generated CrH 2 .
In 1979 the simplest molecular chromium(II) hydride with the chemical formula CrH 2 (systematically named dihydridochromium) was synthesised and identified for the first time. It was synthesised directly from the elements, in a reaction sequence which consisted of simultaneous sublimation of chromium to atomic chromium and thermolysis of hydrogen , and concluded with co-deposition in a cryogenic argon matrix to form dihydridochromium. [ 3 ]
In 2003 the dimer with the chemical formula HCr(μ-H) 2 CrH (systematically named di-μ-hydrido-bis(hydridochromium)) was synthesised and identified for the first time. It was also synthesised directly from the elements, in a reaction sequence which consisted of laser ablation of chromium to atomic chromium, followed by co-deposition with hydrogen in a cryogenic matrix to produce dihydridochromium, and concluded with annealing to form didi-μ-hydrido-bis(hydridochromium). [ 1 ] | https://en.wikipedia.org/wiki/HCr(μ-H)2CrH |
Acetylene ( systematic name : ethyne ) is a chemical compound with the formula C 2 H 2 and structure HC≡CH . It is a hydrocarbon and the simplest alkyne . [ 8 ] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. [ 9 ] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine . [ 9 ] [ 10 ]
As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond . The carbon–carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. [ 11 ] The triple bond in acetylene results in a high energy content that is released when acetylene is burned. [ 12 ]
Acetylene was discovered in 1836 by Edmund Davy , who identified it as a "new carburet of hydrogen". [ 13 ] [ 14 ] It was an accidental discovery while attempting to isolate potassium metal. By heating potassium carbonate with carbon at very high temperatures, he produced a residue of what is now known as potassium carbide , (K 2 C 2 ), which reacted with water to release the new gas. [ 12 ] It was rediscovered in 1860 by French chemist Marcellin Berthelot , who coined the name acétylène . [ 15 ] Berthelot's empirical formula for acetylene (C 4 H 2 ), as well as the alternative name " quadricarbure d'hydrogène " (hydrogen quadricarbide), were incorrect because many chemists at that time used the wrong atomic mass for carbon (6 instead of 12). [ 16 ] Berthelot was able to prepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red hot tube and collecting the effluent . He also found that acetylene was formed by sparking electricity through mixed cyanogen and hydrogen gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbon arc . [ 17 ] [ 18 ]
Since the 1950s, acetylene has mainly been manufactured by the partial combustion of methane in the US, much of the EU, and many other countries: [ 9 ] [ 19 ] [ 20 ]
It is a recovered side product in production of ethylene by cracking of hydrocarbons . Approximately 400,000 tonnes were produced by this method in 1983. [ 9 ] Its presence in ethylene is usually undesirable because of its explosive character and its ability to poison Ziegler–Natta catalysts . It is selectively hydrogenated into ethylene, usually using Pd – Ag catalysts. [ 21 ]
The heaviest alkanes in petroleum and natural gas are cracked into lighter molecules which are dehydrogenated at high temperature:
This last reaction is implemented in the process of anaerobic decomposition of methane by microwave plasma. [ 22 ]
The first acetylene produced was by Edmund Davy in 1836, via potassium carbide. [ 23 ] Acetylene was historically produced by hydrolysis (reaction with water) of calcium carbide: [ 12 ]
This reaction was discovered by Friedrich Wöhler in 1862, [ 24 ] but a suitable commercial scale production method which allowed acetylene to be put into wider scale use was not found until 1892 by the Canadian inventor Thomas Willson while searching for a viable commercial production method for aluminum. [ 25 ]
As late as the early 21st century, China, Japan, and Eastern Europe produced acetylene primarily by this method. [ 26 ]
The use of this technology has since declined worldwide with the notable exception of China, with its emphasis on coal-based chemical industry, as of 2013. Otherwise oil has increasingly supplanted coal as the chief source of reduced carbon. [ 27 ]
Calcium carbide production requires high temperatures, ~2000 °C, necessitating the use of an electric arc furnace . In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls . [ 28 ]
In terms of valence bond theory , in each carbon atom the 2s orbital hybridizes with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap to form a strong σ valence bond between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π bonds . [ 29 ]
Since acetylene is a linear symmetrical molecule , it possesses the D ∞h point group . [ 30 ]
At atmospheric pressure, acetylene cannot exist as a liquid and does not have a melting point. The triple point on the phase diagram corresponds to the melting point (−80.8 °C) at the minimal pressure at which liquid acetylene can exist (1.27 atm). At temperatures below the triple point, solid acetylene can change directly to the vapour (gas) by sublimation . The sublimation point at atmospheric pressure is −84.0 °C. [ 31 ]
At room temperature, the solubility of acetylene in acetone is 27.9 g per kg. For the same amount of dimethylformamide (DMF), the solubility is 51 g. At
20.26 bar, the solubility increases to 689.0 and 628.0 g for acetone and DMF, respectively. These solvents are used in pressurized gas cylinders. [ 32 ]
Approximately 20% of acetylene is supplied by the industrial gases industry for oxyacetylene gas welding and cutting due to the high temperature of the flame. Combustion of acetylene with oxygen produces a flame of over 3,600 K (3,330 °C; 6,020 °F), releasing 11.8 kJ /g. Oxygen with acetylene is the hottest burning common gas mixture. [ 33 ] Acetylene is the third-hottest natural chemical flame after dicyanoacetylene 's 5,260 K (4,990 °C; 9,010 °F) and cyanogen at 4,798 K (4,525 °C; 8,177 °F). Oxy-acetylene welding was a popular welding process in previous decades. The development and advantages of arc-based welding processes have made oxy-fuel welding nearly extinct for many applications. Acetylene usage for welding has dropped significantly. On the other hand, oxy-acetylene welding equipment is quite versatile – not only because the torch is preferred for some sorts of iron or steel welding (as in certain artistic applications), but also because it lends itself easily to brazing, braze-welding, metal heating (for annealing or tempering, bending or forming), the loosening of corroded nuts and bolts, and other applications. Bell Canada cable-repair technicians still use portable acetylene-fuelled torch kits as a soldering tool for sealing lead sleeve splices in manholes and in some aerial locations. Oxyacetylene welding may also be used in areas where electricity is not readily accessible. Oxyacetylene cutting is used in many metal fabrication shops. For use in welding and cutting, the working pressures must be controlled by a regulator, since above 15 psi (100 kPa), if subjected to a shockwave (caused, for example, by a flashback ), acetylene decomposes explosively into hydrogen and carbon . [ 34 ]
Acetylene is useful for many processes, but few are conducted on a commercial scale. [ 35 ]
One of the major chemical applications is ethynylation of formaldehyde. [ 9 ] Acetylene adds to aldehydes and ketones to form α-ethynyl alcohols:
The reaction gives butynediol , with propargyl alcohol as the by-product. Copper acetylide is used as the catalyst. [ 36 ] [ 37 ]
In addition to ethynylation, acetylene reacts with carbon monoxide , acetylene reacts to give acrylic acid , or acrylic esters. Metal catalysts are required. These derivatives form products such as acrylic fibers , glasses , paints , resins , and polymers . Except in China, use of acetylene as a chemical feedstock has declined by 70% from 1965 to 2007 owing to cost and environmental considerations. [ 38 ] In China, acetylene is a major precursor to vinyl chloride . [ 35 ]
Prior to the widespread use of petrochemicals, coal-derived acetylene was a building block for several industrial chemicals. Thus acetylene can be hydrated to give acetaldehyde , which in turn can be oxidized to acetic acid. Processes leading to acrylates were also commercialized. Almost all of these processes became obsolete with the availability of petroleum-derived ethylene and propylene. [ 39 ]
In 1881, the Russian chemist Mikhail Kucherov [ 40 ] described the hydration of acetylene to acetaldehyde using catalysts such as mercury(II) bromide . Before the advent of the Wacker process , this reaction was conducted on an industrial scale. [ 41 ]
The polymerization of acetylene with Ziegler–Natta catalysts produces polyacetylene films. Polyacetylene, a chain of CH centres with alternating single and double bonds, was one of the first discovered organic semiconductors . Its reaction with iodine produces a highly electrically conducting material. Although such materials are not useful, these discoveries led to the developments of organic semiconductors , as recognized by the Nobel Prize in Chemistry in 2000 to Alan J. Heeger , Alan G MacDiarmid , and Hideki Shirakawa . [ 9 ]
In the 1920s, pure acetylene was experimentally used as an inhalation anesthetic . [ 42 ]
Acetylene is sometimes used for carburization (that is, hardening) of steel when the object is too large to fit into a furnace. [ 43 ]
Acetylene is used to volatilize carbon in radiocarbon dating . The carbonaceous material in an archeological sample is treated with lithium metal in a small specialized research furnace to form lithium carbide (also known as lithium acetylide). The carbide can then be reacted with water, as usual, to form acetylene gas to feed into a mass spectrometer to measure the isotopic ratio of carbon-14 to carbon-12. [ 44 ]
Acetylene combustion produces a strong, bright light and the ubiquity of carbide lamps drove much acetylene commercialization in the early 20th century. Common applications included coastal lighthouses , [ 45 ] street lights , [ 12 ] and automobile [ 46 ] and mining headlamps . [ 47 ] In most of these applications, direct combustion is a fire hazard , and so acetylene has been replaced, first by incandescent lighting and many years later by low-power/high-lumen LEDs. Nevertheless, acetylene lamps remain in limited use in remote or otherwise inaccessible areas and in countries with a weak or unreliable central electric grid . [ 47 ]
The energy richness of the C≡C triple bond and the rather high solubility of acetylene in water make it a suitable substrate for bacteria, provided an adequate source is available. [ 48 ] A number of bacteria living on acetylene have been identified. The enzyme acetylene hydratase catalyzes the hydration of acetylene to give acetaldehyde : [ 49 ]
Acetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giants . [ 50 ] One curious discovery of acetylene is on Enceladus , a moon of Saturn . Natural acetylene is believed to form from catalytic decomposition of long-chain hydrocarbons at temperatures of 1,700 K (1,430 °C; 2,600 °F) and above. Since such temperatures are highly unlikely on such a small distant body, this discovery is potentially suggestive of catalytic reactions within that moon, making it a promising site to search for prebiotic chemistry. [ 51 ] [ 52 ]
In vinylation reactions, H−X compounds add across the triple bond. Alcohols and phenols add to acetylene to give vinyl ethers . Thiols give vinyl thioethers. Similarly, vinylpyrrolidone and vinylcarbazole are produced industrially by vinylation of 2-pyrrolidone and carbazole . [ 32 ] [ 9 ]
The hydration of acetylene is a vinylation reaction, but the resulting vinyl alcohol isomerizes to acetaldehyde . The reaction is catalyzed by mercury salts. This reaction once was the dominant technology for acetaldehyde production, but it has been displaced by the Wacker process , which affords acetaldehyde by oxidation of ethylene , a cheaper feedstock. A similar situation applies to the conversion of acetylene to the valuable vinyl chloride by hydrochlorination vs the oxychlorination of ethylene.
Vinyl acetate is used instead of acetylene for some vinylations, which are more accurately described as transvinylations . [ 53 ] Higher esters of vinyl acetate have been used in the synthesis of vinyl formate .
Acetylene and its derivatives (2-butyne, diphenylacetylene, etc.) form complexes with transition metals . Its bonding to the metal is somewhat similar to that of ethylene complexes. These complexes are intermediates in many catalytic reactions such as alkyne trimerisation to benzene, tetramerization to cyclooctatetraene , [ 9 ] and carbonylation to hydroquinone : [ 54 ]
Metal acetylides , species of the formula L n M−C 2 R , are also common. Copper(I) acetylide and silver acetylide can be formed in aqueous solutions with ease due to a favorable solubility equilibrium . [ 55 ]
Acetylene has a p K a of 25, acetylene can be deprotonated by a superbase to form an acetylide : [ 55 ]
Various organometallic [ 56 ] and inorganic [ 57 ] reagents are effective.
Acetylene can be semihydrogenated to ethylene , providing a feedstock for a variety of polyethylene plastics. Halogens add to the triple bond.
Acetylene is not especially toxic, but when generated from calcium carbide , or CaC 2 , it can contain toxic impurities such as traces of phosphine and arsine , which gives it a distinct garlic -like smell. It is also highly flammable, as are most light hydrocarbons, hence its use in welding. Its most singular hazard is associated with its intrinsic instability, especially when it is pressurized: under certain conditions acetylene can react in an exothermic addition-type reaction to form a number of products, typically benzene and/or vinylacetylene , possibly in addition to carbon and hydrogen . [ citation needed ] Although it is stable at normal pressures and temperatures, if it is subjected to pressures as low as 15 psig it can explode. [ 12 ] The safe limit for acetylene therefore is 101 kPa gage , or 15 psig. [ 58 ] [ 59 ] Additionally, if acetylene is initiated by intense heat or a shockwave, it can decompose explosively if the absolute pressure of the gas exceeds about 200 kilopascals (29 psi). It is therefore supplied and stored dissolved in acetone or dimethylformamide (DMF), [ 59 ] [ 60 ] [ 61 ] contained in a gas cylinder with a porous filling , which renders it safe to transport and use, given proper handling. Acetylene cylinders should be used in the upright position to avoid withdrawing acetone during use. [ 62 ]
Information on safe storage of acetylene in upright cylinders is provided by the OSHA, [ 63 ] [ 64 ] Compressed Gas Association, [ 59 ] United States Mine Safety and Health Administration (MSHA), [ 65 ] EIGA, [ 62 ] and other agencies.
Copper catalyses the decomposition of acetylene, and as a result acetylene should not be transported in copper pipes. [ 66 ]
Cylinders should be stored in an area segregated from oxidizers to avoid exacerbated reaction in case of fire/leakage. [ 59 ] [ 64 ] Acetylene cylinders should not be stored in confined spaces, enclosed vehicles, garages, and buildings, to avoid unintended leakage leading to explosive atmosphere. [ 59 ] [ 64 ] In the US, National Electric Code (NEC) requires consideration for hazardous areas including those where acetylene may be released during accidents or leaks. [ 67 ] Consideration may include electrical classification and use of listed Group A electrical components in US. [ 67 ] Further information on determining the areas requiring special consideration is in NFPA 497. [ 68 ] In Europe, ATEX also requires consideration for hazardous areas where flammable gases may be released during accidents or leaks. [ 62 ] | https://en.wikipedia.org/wiki/HC☰CH |
HDPE pipe ( high-density polyethylene pipe ) is a type of flexible plastic pipe used to transfer fluids and gases . It is often employed for replacing aging concrete or steel main pipelines . Constructed from the thermoplastic HDPE (high-density polyethylene ), it has low permeability and robust molecular bonding, making it suitable for high-pressure pipelines . HDPE pipe is often used for water mains , gas mains , [ 1 ] sewer mains, slurry transfer lines, rural irrigation , fire-suppression system supply lines, electrical and communication conduits, and stormwater and drainage pipes. [ 2 ] [ 3 ]
It is frequently used in pipe bursting .
HDPE is resistant to many environmental factors and has applications where cheap but durable fluid piping systems are required.
HDPE pipe can be joined by butt welding , electrofusion welding , socket welding, or extrusion welding . These joints heat the pipe during the joining process to create a completely homogeneous joint without the need for additional seals or jointing compounds, reducing the likelihood of failure or negative environmental effects. HDPE is less likely than PVC pipe to have problems with root intrusion and provides integrity for the pipeline, even when installed in unstable soils. [ citation needed ]
Due to the fusion welding system, HDPE pipe does not need any additional supports around joints. This also allows for safer excavation close to the pipeline in the future, which is particularly important for high-pressure gas pipelines. HDPE pipe is highly durable and flexible even at lower ambient temperatures, enabling bends in the pipe system to be created with relative ease. Due to its high impact resistance and flexibility, HDPE pipe is well-suited for installation in dynamic soils, including those in earthquake-prone areas. HDPE has been considered to be cost-effective due to its versatility in installation and reduced need for maintenance. [ citation needed ]
Because food-grade polyethylene virgin material is used to fabricate HDPE pipes, they are safe for the transfer of drinking water . HDPE is resistant to many chemicals, facilitating its use in process plants or in corrosive or acidic environments without use of protective coatings or galvanization . As HDPE has a lower thermal conductivity than many metals it can maintain more uniform temperatures than metal pipes when carrying fluids, which reduces the need for insulation around a pipeline. [ 4 ]
To make lengths of HDPE pipe, polyethylene raw material is dried, heated to ~180 °C (356 °F), and extruded through a die .
Polyethylene pipe is usually black due to the addition of 3-5% of carbon black to the clear polyethylene material, which adds UV light resistance to the finished pipe. To create striped HDPE pipe a different die is used, containing small channels that the colored material runs through just before it is pushed through the die. Co-extruded, or co-ex HDPE pipe has an extra 'skin' of color around the black HDPE pipe, allowing the pipe to be colored on the outside for the identification of thermal cooling requirements.
After coming through the die the pipe is cooled by submerging in or spraying with water. The rate of cooling is carefully controlled to avoid deformation of the extruded pipe. Once cooled, a laser or powder printer prints the size, type, date, and manufacturer's name on the side of the pipe. It is then cut by a saw cutter or coiled into longer lengths on a coiler.
HDPE piping is estimated to last 50 years. However, technical white papers written by the Plastics Industry Pipe Association assert that HDPE pipe systems can be reasonably expected to last up to, or over 100 years. [ 5 ] | https://en.wikipedia.org/wiki/HDPE_pipe |
The High Energy Astronomy Observatory Program was a NASA program of the late 1970s and early 1980s that included a series of three large low-Earth-orbiting spacecraft for X-ray and Gamma-Ray astronomy and Cosmic-Ray investigations. After launch, they were denoted HEAO 1 , HEAO 2 (also known as The Einstein Observatory ), and HEAO 3 , respectively. The large (~3000 kg) satellites were 3-axis stabilized to arc-minute accuracy, with fixed solar panels. All three observatories were launched from Cape Canaveral, Florida on Atlas-Centaur SLV-3D launch vehicles into near-circular orbits with initial altitudes slightly above 500 km.
HEAO 1 , launched August 12, 1977, was a sky survey mission that included four large X-ray and gamma-ray astronomy instruments, known as A1, A2, A3, and A4, respectively. Inclination was about 22.7 degrees. It re-entered the Earth's atmosphere and burned up on March 15, 1979.
HEAO 2, more commonly known as the Einstein Observatory , launched 13 November 1978 into a 23.5 deg inclination orbit. It carried a single large grazing-incidence focusing X-ray telescope, providing unprecedented levels of sensitivity (hundreds of times better than previously achieved) and arc-second angular resolution for pointed observations of known objects, and operated over the 0.2 to 3.5 keV energy range. HEAO 2 differed from HEAO 1 and HEAO 3 in that it was used for pointed, deep, small-field-of-view observations rather than sky-survey studies.
A suite of four focal plane instruments were provided:
as well as a 1-20 keV Monitor Proportional Counter (MPC), a Broad Band Filter Spectrometer (BBFS), and an objective grating spectrometer (OGS). The observatory re-entered the Earth's atmosphere and burned up on March 25, 1982.
HEAO 3 , launched on 20 September 1979 into a 43.6-degree inclination orbit, carried three experiments, known as C1, C2, and C3. The first was a cryogenically cooled germanium (Ge) high-resolution gamma-ray spectrometer , while the C2 and C3 experiments were large cosmic-ray instruments. The satellite re-entered the Earth's atmosphere and burned up on December 7, 1981.
The experiment designations A1, A2, A3, A4, for HEAO A , thru C1, C2, C3 for HEAO C , were most common before launch, but also often appear in the later scientific literature. The overall HEAO program was managed out of NASA's Marshall Space Flight Center in Huntsville, AL. NASA Program Manager was Mr. Richard E. Halpern; NASA Program Scientist was Dr. Albert G. Opp. All three satellites were built by TRW Systems of Redondo Beach, California, who won the Nelson P. Jackson Aerospace Award for their work. [ 1 ] The total program cost was roughly $250 million. [ 2 ] | https://en.wikipedia.org/wiki/HEAO_Program |
For the purpose of DNA replication , the H paII tiny fragment E nrichment by L igation-mediated P CR Assay (HELP Assay) [ 1 ] is one of several techniques used for determining whether DNA has been methylated . The technique can be adapted to examine DNA methylation within and around individual genes , or it can be expanded to examine methylation in an entire genome .
The technique relies upon the properties of two restriction enzymes : Hpa II and Msp I. The HELP assay [ 1 ] compares representations generated by Hpa II and by Msp I digestion of the genome followed by ligation-mediated PCR. Hpa II only digests 5'-C CG G-3' sites when the cytosine in the central CG dinucleotide is unmethylated, the Hpa II representation is enriched for the hypomethylated fraction of the genome. The Msp I representation is a control for copy number changes and PCR amplification difficulties.
It was recently shown that cytosine methylation patterns tend to be concordant over short (~1 kb) regions. [ 2 ] The patterns represented by the Hpa II sites therefore tend to be representative of other CG dinucleotides locally.
The analysis of HELP data involves quality analysis and normalization. An analytical pipeline written in the R programming language was recently published to allow HELP data processing. [ 3 ] | https://en.wikipedia.org/wiki/HELP_assay |
HEPA ( / ˈ h ɛ p ə / , high efficiency particulate air ) filter, [ 1 ] also known as a high efficiency particulate arresting filter, [ 2 ] is an efficiency standard of air filters . [ 3 ]
Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% ( ISO , European Standard) [ 4 ] [ 5 ] or 99.97% ( ASME , U.S. DOE ) [ 6 ] [ 7 ] of particles whose diameter is equal to 0.3 μm , with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm. [ 8 ] HEPA filters capture pollen , dirt , dust , moisture , bacteria (0.2–2.0 μm), viruses (0.02–0.3 μm), and submicron liquid aerosol (0.02–0.5 μm). [ 9 ] [ 10 ] [ 11 ] Some microorganisms , for example, Aspergillus niger , Penicillium citrinum , Staphylococcus epidermidis , and Bacillus subtilis are captured by HEPA filters with photocatalytic oxidation (PCO). A HEPA filter is also able to capture some viruses and bacteria which are ≤0.3 μm. [ 12 ] A HEPA filter is also able to capture floor dust which contains bacteroidia , clostridia , and bacilli . [ 13 ] HEPA was commercialized in the 1950s, and the original term became a registered trademark and later a generic trademark for highly efficient filters. [ 14 ] HEPA filters are used in applications that require contamination control , such as the manufacturing of hard disk drives, medical devices, semiconductors, nuclear, food and pharmaceutical products, as well as in hospitals, [ 15 ] homes, and vehicles.
HEPA filters are composed of a mat of randomly arranged fibers . [ 16 ] The fibers are typically composed of polypropylene or fiberglass with diameters between 0.5 and 2.0 micrometers. Most of the time, these filters are composed of tangled bundles of fine fibers . These fibers create a narrow convoluted pathway through which air passes. When the largest particles are passing through this pathway, the bundles of fibers behave like a kitchen sieve which physically blocks the particles from passing through. However, when smaller particles pass with the air, as the air twists and turns, the smaller particles cannot keep up with the motion of the air and thus they collide with the fibers. The smallest particles have very little inertia and move randomly as a result of collisions with individual air molecules ( Brownian motion ). Because of their movement, they end up crashing into the fibers. [ 17 ] Key factors affecting its functions are fiber diameter, filter thickness, and face velocity, which is the measured air speed at an inlet or outlet of a heating ventilation and air conditioning (HVAC) system. Face velocity is measured in m/s and can be calculated as the volume flow rate (m 3 /s) divided by the face area (m 2 ). The air space between HEPA filter fibers is typically much greater than 0.3 μm. HEPA filters in very high level for smallest particulate matter. Unlike sieves or membrane filters , where particles smaller than openings or pores can pass through, HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to a fiber) through a combination of the following three mechanisms:
Diffusion predominates below the 0.1 μm diameter particle size, whilst impaction and interception predominate above 0.4 μm. [ 18 ] In between, near the most penetrating particle size (MPPS) 0.21 μm, both diffusion and interception are comparatively inefficient. [ 19 ] Because this is the weakest point in the filter's performance, the HEPA specifications use the retention of particles near this size (0.3 μm) to classify the filter. [ 18 ] However it is possible for particles smaller than the MPPS to not have filtering efficiency greater than that of the MPPS. This is due to the fact that these particles can act as nucleation sites for mostly condensation and form particles near the MPPS. [ 19 ]
HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds , chemical vapors, or cigarette , pet or flatulence odors call for the use of an activated carbon (charcoal) or other type of filter instead of or in addition to a HEPA filter. [ 20 ] Carbon cloth filters, claimed to be many times more efficient than the granular activated carbon form at adsorption of gaseous pollutants , are known as high efficiency gas adsorption filters (HEGA) and were originally developed by the British Armed Forces as a defense against chemical warfare . [ 21 ] [ 22 ]
A HEPA bag filter can be used in conjunction with a pre-filter (usually carbon-activated) to extend the usage life of the more expensive HEPA filter. [ 23 ] In such setup, the first stage in the filtration process is made up of a pre-filter which removes most of the larger dust, hair , PM10 and pollen particles from the air. The second stage high-quality HEPA filter removes the finer particles that escape from the pre-filter. This is common in air handling units . [ citation needed ]
HEPA filters, as defined by the United States Department of Energy (DOE) standard adopted by most American industries, remove at least 99.97% of aerosols 0.3 micrometers (μm) in diameter. [ 24 ] The filter's minimal resistance to airflow, or pressure drop , is usually specified around 300 pascals (0.044 psi) at its nominal volumetric flow rate . [ 7 ]
The specification used in the European Union : European Standard EN 1822-1:2019, from which ISO 29463 is derived, [ 4 ] defines several classes of filters by their retention at the given most penetrating particle size (MPPS): Efficient Particulate Air filters (EPA), High Efficiency Particulate Air filters (HEPA), and Ultra Low Particulate Air filters (ULPA). The averaged efficiency of the filter is called "overall", and the efficiency at a specific point is called "local": [ 4 ]
See also the different classes for air filters for comparison.
For respirators , MSHA and NIOSH define HEPA as filters blocking ≥ 99.97% of 0.3 micron DOP particles, under 30 CFR 11 and 42 CFR 84. Since the transition to 42 CFR 84 in 1995, use of the term HEPA has been deprecated except for powered air-purifying respirators . [ 25 ] However, by definition, ANSI Z88.2-2015 considers N100, R100, P100, and HE as HEPA filters. [ 26 ]
Some companies use the marketing term "True HEPA" to give consumers assurance that their air filters meet the HEPA standard, although this term has no legal or scientific meaning. [ 27 ] Products that are marketed to be "HEPA-type," "HEPA-like," "HEPA-style" or "99% HEPA" do not satisfy the HEPA standard and may not have been tested in independent laboratories. Although such filters may come reasonably close to HEPA standards, others fall significantly short. [ 28 ]
In general terms (and allowing for some variation depending on factors such as the air-flow rate, the physical properties of the particles being filtered, as well as engineering details of the entire filtration-system design and not just the filter-media properties), HEPA filters experience the most difficulty in capturing particles in the size range of 0.15 to 0.2 μm. [ 29 ] HEPA filtration works by mechanical means, unlike ionic and ozone treatment technologies, which use negative ions and ozone gas respectively. So, the likelihood of potential triggering of pulmonary side-effects such as asthma [ 30 ] and allergies is much lower with HEPA purifiers. [ 31 ]
To ensure that a HEPA filter is working efficiently, the filters should be inspected and changed at least every six months in commercial settings. In residential settings, and depending on the general ambient air quality, these filters can be changed every two to three years. Failing to change a HEPA filter in a timely fashion will result in it putting stress on the machine or system and not removing particles from the air properly. Additionally, depending on the gasketing materials chosen in the design of the system, a clogged HEPA filter can result in extensive bypassing of airflow around the filter. [ 32 ]
Medical filtration system use extreme ultraviolet light units effectively kill bacteria, mold and viruses panels with anti-microbial coating to kill off the live bacteria and viruses trapped by the HEPA filter media. [ citation needed ]
Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission . [ citation needed ]
HEPA filters are capable of removing viruses including COVID-19 (particles of 60-140 nanometer diameter) from the air harboring the live virus in the filter.
Extreme ultraviolet must be incorporated into the air purifier in order to kill Airborne pathogens such as viruses like COVID-19, mold & bacteria. As such saw a surge in adoption during the pandemic in order to mitigate infection risks.
To combat supply chain and cost issues hindering adoption of HEPA filters during the COVID-19 pandemic, a professor at University of California, Davis , created a simple do-it-yourself air purifier design called crbox( Corsi–Rosenthal Box ). It involves arranging 4 HEPA filters in a cubic shape, the bottom being made out of cardboard, sealing the filter sides with tape and adding a fan on top.
In addition, the COVID-19 Pandemic resulted in a surge of new air purifier products from new and established brands such as Dyson or Xiaomi hitting the markets.
Many vacuum cleaners also use HEPA filters as part of their filtration systems. This is beneficial for asthma and allergy sufferers, because the HEPA filter traps the fine particles (such as pollen and house dust mite feces ) which trigger allergy and asthma symptoms. For a HEPA filter in a vacuum cleaner to be effective, the vacuum cleaner must be designed so that all the air drawn into the machine is expelled through the filter, with none of the air leaking past it. This is often referred to as "Sealed HEPA" or sometimes the more vague "True HEPA". Vacuum cleaners simply labeled "HEPA" may have a HEPA filter, but not all air necessarily passes through it. Finally, vacuum cleaner filters marketed as "HEPA-like" will typically use a filter of a similar construction to HEPA, but without the filtering efficiency. Because of the extra density of a true HEPA filter, HEPA vacuum cleaners require more powerful motors to provide adequate cleaning power. [ citation needed ]
Washable filters or reusable filters have proven to be very effective in trapping and keeping Airborne contaminants for millennia. Many washable reusable filters today are cleverly designed
& engineered a substrate that electronically draw material to the substrate & attaching to that substrate, lock into place until washed away. Washable reusable filters meet air quality standards, are cost effective, environmentally friendly, no replacement required & little maintenance VS. true HEPA filters are expensive, with regular replacement damaging to the environment and can Harbor contagions which can breed and multiply within the filter substrate.
A high-quality HEPA filter can trap 99.97% of dust particles that are 0.3 microns in diameter. For comparison, a human hair is about 50 to 150 microns in diameter. So, a true HEPA filter is effectively trapping particles several hundred times smaller than the width of a human hair. [ 33 ] Some manufacturers claim filter standards such as "HEPA 4," without explaining the meaning behind them. [ citation needed ] This refers to their Minimum Efficiency Reporting Value (MERV) rating. [ citation needed ] These ratings are used to rate the ability of an air cleaner filter to remove dust from the air as it passes through the filter. MERV is a standard used to measure the overall efficiency of a filter. The MERV scale ranges from 1 to 16, and measures a filter's ability to remove particles from 10 to 0.3 micrometer in size. Filters with higher ratings not only remove more particles from the air, but they also remove smaller particles.
Heating, ventilation, and air conditioning (HVAC) [ 34 ] is technology that uses air filters, such as HEPA filters, to remove pollutants from the air either indoors or in vehicles. Pollutants include smoke, viruses, powders , etc., and can originate either outside or inside. HVAC is used to provide environmental comfort and in polluted cities to maintain health. [ citation needed ]
Modern airliners use HEPA filters to reduce the spread of airborne pathogens in recirculated air. Critics have expressed concern about the effectiveness and state of repair of air filtering systems, since they think that much of the air in an airplane cabin is recirculated. Almost all of the air in a pressurized aircraft is, in fact, brought in from the outside, circulated through the cabin and then exhausted through outflow valves in the rear of the aircraft. [ 35 ] About 40 percent of the cabin's air goes through a HEPA filter and the other 60 percent comes from outside the plane. Certified air filters block and capture 99.97 percent of airborne particles. [ 36 ]
In 2016, it was announced that the Tesla Model X would have the world's first HEPA-grade filter in a Tesla car. [ 37 ] Following the release of the Model X, Tesla has updated the Model S to also have an optional HEPA air filter. [ 38 ]
The idea behind the development of the HEPA filter was born from gas masks worn by soldiers fighting in World War II. A piece of paper found inserted into a German gas mask had a remarkably high capture efficiency for chemical smoke. The British Army Chemical Corps duplicated this and began to manufacture it in large quantities for their own service gas masks. They needed another solution for operational headquarters, where individual gas masks were impractical. The Army Chemical Corps developed a combination mechanical blower and air purifier unit, which incorporated cellulose-asbestos paper in a deeply-pleated form with spacers between the pleats. It was referred to as an "absolute" air filter and laid the groundwork for further research to come in developing the HEPA filter. [ 39 ]
The next phase of the HEPA filter was designed in the 1940s and was used in the Manhattan Project to prevent the spread of airborne radioactive contaminants. [ 40 ] The US Army Chemical Corps and National Defense Research Committee needed to develop a filter suitable for removing radioactive materials from the air. The Army Chemical Corps asked Nobel Laureate Irving Langmuir to recommend filter test methods and other general recommendations for creating the material to filter out these radioactive particles. He identified 0.3 micron size particles to be the "most penetrating size"—the most difficult and concerning. [ 41 ]
It was commercialized in the 1950s, and the original term became a registered trademark and later a generic trademark for highly efficient filters. [ 14 ]
Over the decades filters have evolved to satisfy the higher and higher demands for air quality in various high technology industries, such as aerospace, pharmaceutical industry, hospitals, health care, nuclear fuels, nuclear power, and integrated circuit fabrication. [ citation needed ] | https://en.wikipedia.org/wiki/HEPA |
HEPPS ( EPPS ) is a buffering agent used in biology and biochemistry . The pKa of HEPPS is 8.00. It is ones of Good's buffers . [ 1 ]
Research on mice with Alzheimer's disease -like amyloid beta plaques has shown that HEPPS can cause the plaques to break up, reversing some of the symptoms in the mice. [ 2 ] [ 3 ] [ 4 ] HEPPS was reported to dissociate amyloid beta oligomers in patients' plasma samples enabling blood diagnosis of Alzheimer's disease . [ 5 ] [ 6 ] [ 7 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HEPPS_(buffer) |
Trifluorosilane is the chemical compound with the formula F 3 H Si . At standard temperature and pressure, trifluorosilane is a colorless gas. [ 1 ] Note that the free radical F 3 Si is often also referred to as trifluorosilane, although more properly referred to as trifluorosilyl.
Trifluorosilane has been purified and separated by low-temperature high-vacuum distillation. One preparation method involves products of the reaction between SbF 3 and HSiCl 3 . [ 2 ] HSiCl 3 is obtained by copper catalyzed reaction between HCl and Silicon at 200-400 °C.
Formation has also been reported in certain etching operations of silicon. [ 3 ]
The electric dipole moment of trifluorosilane is 1.26 debye . [ 4 ] The length of the silicon to fluorine bond is 1.555 Å, Si-H length is 1.55 Å, and ∠FSiF is 110°. [ 5 ] | https://en.wikipedia.org/wiki/HF3Si |
Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride , containing various cations and anions (the simplest being H 2 F + and SbF − 6 ). This mixture is a superacid stronger than pure sulfuric acid , by many orders of magnitude, according to its Hammett acidity function . It even protonates some hydrocarbons to afford pentacoordinate carbocations ( carbonium ions ). [ 1 ] Like its precursor hydrogen fluoride , it attacks glass, but can be stored in containers lined with PTFE (Teflon) or PFA .
Fluoroantimonic acid is formed by combining hydrogen fluoride and antimony pentafluoride :
The speciation (i.e., the inventory of components) of fluoroantimonic acid is complex. Spectroscopic measurements show that fluoroantimonic acid consists of a mixture of HF-solvated protons, [ (HF) n H] + (such as H 3 F + 2 ), and SbF 5 -adducts of fluoride, [(SbF 5 ) n F] – (such as Sb 4 F − 21 ). Thus, the formula " [H 2 F] + [SbF 6 ] − " is a convenient but oversimplified approximation of the true composition. [ 2 ] Nevertheless, the extreme acidity of this mixture is evident from the inferior proton-accepting ability of the species present in the solution. Hydrogen fluoride, a weak acid in aqueous solution that is normally not thought to have any appreciable Brønsted basicity at all, is in fact the strongest Brønsted base in the mixture, protonating to H 2 F + in the same way water protonates to H 3 O + in aqueous acid. It is the fluoronium ion that accounts for fluoroantimonic acid's extreme acidity. The protons easily migrate through the solution, moving from H 2 F + to HF, when present, by the Grotthuss mechanism . [ 3 ]
Two related products have been crystallized from HF-SbF 5 mixtures, and both have been analyzed by single crystal X-ray crystallography . These salts have the formulas [H 2 F + ] [Sb 2 F − 11 ] and [H 3 F + 2 ] [Sb 2 F − 11 ] . In both salts, the anion is Sb 2 F − 11 . [ 4 ] As mentioned above, SbF − 6 is weakly basic; the larger anion Sb 2 F − 11 is expected to be a still weaker base.
Fluoroantimonic acid is the strongest superacid based on the measured value of its Hammett acidity function ( H 0 ), which has been determined for various ratios of HF:SbF 5 . The H 0 of HF is −15. [ 5 ] A solution of HF containing 1 mol % of SbF 5 is −20. The H 0 is −21 for 10 mol%. For > 50 mol % SbF 5 , the H 0 is between −21 and −23. The lowest attained H 0 is about −28 (although some sources have reported to reach below −31.) [ 6 ] [ 7 ] [ 8 ] The following H 0 values show that fluoroantimonic acid is stronger than other superacids. [ 9 ] Increased acidity is indicated by lower (in this case, more negative) values of H 0 .
Of the above, only the carborane acids , whose H 0 could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid. [ 9 ] [ 10 ]
The H 0 value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The p K a on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its p K a value is not well-defined. [ citation needed ]
The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods. [ 2 ] (Solution-phase p K a s of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [H 2 F] + · SbF – 6 was estimated to have a GPA of 254 kcal/mol. For comparison, the commonly encountered superacid triflic acid , TfOH, is a substantially weaker acid by this measure, with a GPA of 299 kcal/mol. [ 11 ] However, certain carborane superacids have GPAs lower than that of [H 2 F] + · SbF – 6 . For example, H(CHB 11 Cl 11 ) has an experimentally determined GPA of 241 kcal/mol. [ 12 ]
Fluoroantimonic acid solution is so reactive that it is challenging to identify media with which it is unreactive. Materials compatible with fluoroantimonic acid as a solvent include SO 2 ClF , and sulfur dioxide ; some chlorofluorocarbons have also been used. Containers for HF/SbF 5 are made of PTFE . [ citation needed ]
Fluoroantimonic acid solutions decompose when heated, generating free hydrogen fluoride gas and liquid antimony pentafluoride at a temperature of 40 °C. [ 13 ]
As a superacid , fluoroantimonic acid solutions protonate nearly all organic compounds , often causing dehydrogenation, or dehydration. In 1967, Bickel and Hogeveen showed that 2HF·SbF 5 reacts with isobutane and neopentane to form carbenium ions: [ 14 ] [ 15 ]
It is also used in the synthesis of tetraxenonogold complexes. [ 16 ]
HF/SbF 5 is a highly corrosive substance that reacts violently with water. Heating it is dangerous as well, as it decomposes into toxic hydrogen fluoride . With superacids that are fuming and toxic, proper personal protective equipment should be used. In addition to the obligatory gloves and goggles , the use of a face shield and respirator are also required. Regular lab gloves are not recommended, as this acid can react with the gloves. [ 10 ] Safety gear must be worn at all times when handling or going anywhere near the substance, as fluoroantimonic acid can protonate every compound in the human body. [ 17 ] | https://en.wikipedia.org/wiki/HF6Sb |
Fluorosulfuric acid ( IUPAC name: sulfurofluoridic acid ) is the inorganic compound with the chemical formula HSO 3 F . It is one of the strongest acids commercially available. It is a tetrahedral molecule and is closely related to sulfuric acid , H 2 SO 4 , substituting a fluorine atom for one of the hydroxyl groups. It is a colourless liquid, although commercial samples are often yellow. [ 2 ]
Fluorosulfuric acid is a free-flowing colorless liquid. It is soluble in polar organic solvents (e.g. nitrobenzene , acetic acid , and ethyl acetate ), but poorly soluble in nonpolar solvents such as alkanes.
HSO 3 F is one of the strongest known simple Brønsted acids . [ 3 ] It has an H 0 value of −15.1 compared to −12 for sulfuric acid. The combination of HSO 3 F and the Lewis acid antimony pentafluoride produces " Magic acid ", which is a far stronger protonating agent. These acids are categorized as " superacids ", acids stronger than 100% sulfuric acid.
Reflecting its strong acidity, HSO 3 F dissolves almost all organic compounds that are even weak proton acceptors. [ 4 ] HSO 3 F hydrolyzes slowly to hydrogen fluoride (HF) and sulfuric acid . The related triflic acid ( CF 3 SO 3 H ) retains the high acidity of HSO 3 F but is more hydrolytically stable. The self-ionization of fluorosulfonic acid also occurs:
HSO 3 F isomerizes alkanes and catalyzes the alkylation of hydrocarbons with alkenes, [ 5 ] although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent. [ 6 ]
Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide : [ 2 ]
Alternatively, KHF 2 or CaF 2 can be treated with oleum at 250 °C. Once freed from HF by sweeping with an inert gas, HSO 3 F can be distilled in a glass apparatus. [ 6 ]
Fluorosulfuric acid is considered to be highly toxic and extremely corrosive. It hydrolyzes to release HF. Addition of water to HSO 3 F is similar to, and even more violent than, the addition of water to sulfuric acid . | https://en.wikipedia.org/wiki/HFSO3 |
Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride , containing various cations and anions (the simplest being H 2 F + and SbF − 6 ). This mixture is a superacid stronger than pure sulfuric acid , by many orders of magnitude, according to its Hammett acidity function . It even protonates some hydrocarbons to afford pentacoordinate carbocations ( carbonium ions ). [ 1 ] Like its precursor hydrogen fluoride , it attacks glass, but can be stored in containers lined with PTFE (Teflon) or PFA .
Fluoroantimonic acid is formed by combining hydrogen fluoride and antimony pentafluoride :
The speciation (i.e., the inventory of components) of fluoroantimonic acid is complex. Spectroscopic measurements show that fluoroantimonic acid consists of a mixture of HF-solvated protons, [ (HF) n H] + (such as H 3 F + 2 ), and SbF 5 -adducts of fluoride, [(SbF 5 ) n F] – (such as Sb 4 F − 21 ). Thus, the formula " [H 2 F] + [SbF 6 ] − " is a convenient but oversimplified approximation of the true composition. [ 2 ] Nevertheless, the extreme acidity of this mixture is evident from the inferior proton-accepting ability of the species present in the solution. Hydrogen fluoride, a weak acid in aqueous solution that is normally not thought to have any appreciable Brønsted basicity at all, is in fact the strongest Brønsted base in the mixture, protonating to H 2 F + in the same way water protonates to H 3 O + in aqueous acid. It is the fluoronium ion that accounts for fluoroantimonic acid's extreme acidity. The protons easily migrate through the solution, moving from H 2 F + to HF, when present, by the Grotthuss mechanism . [ 3 ]
Two related products have been crystallized from HF-SbF 5 mixtures, and both have been analyzed by single crystal X-ray crystallography . These salts have the formulas [H 2 F + ] [Sb 2 F − 11 ] and [H 3 F + 2 ] [Sb 2 F − 11 ] . In both salts, the anion is Sb 2 F − 11 . [ 4 ] As mentioned above, SbF − 6 is weakly basic; the larger anion Sb 2 F − 11 is expected to be a still weaker base.
Fluoroantimonic acid is the strongest superacid based on the measured value of its Hammett acidity function ( H 0 ), which has been determined for various ratios of HF:SbF 5 . The H 0 of HF is −15. [ 5 ] A solution of HF containing 1 mol % of SbF 5 is −20. The H 0 is −21 for 10 mol%. For > 50 mol % SbF 5 , the H 0 is between −21 and −23. The lowest attained H 0 is about −28 (although some sources have reported to reach below −31.) [ 6 ] [ 7 ] [ 8 ] The following H 0 values show that fluoroantimonic acid is stronger than other superacids. [ 9 ] Increased acidity is indicated by lower (in this case, more negative) values of H 0 .
Of the above, only the carborane acids , whose H 0 could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid. [ 9 ] [ 10 ]
The H 0 value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The p K a on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its p K a value is not well-defined. [ citation needed ]
The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods. [ 2 ] (Solution-phase p K a s of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [H 2 F] + · SbF – 6 was estimated to have a GPA of 254 kcal/mol. For comparison, the commonly encountered superacid triflic acid , TfOH, is a substantially weaker acid by this measure, with a GPA of 299 kcal/mol. [ 11 ] However, certain carborane superacids have GPAs lower than that of [H 2 F] + · SbF – 6 . For example, H(CHB 11 Cl 11 ) has an experimentally determined GPA of 241 kcal/mol. [ 12 ]
Fluoroantimonic acid solution is so reactive that it is challenging to identify media with which it is unreactive. Materials compatible with fluoroantimonic acid as a solvent include SO 2 ClF , and sulfur dioxide ; some chlorofluorocarbons have also been used. Containers for HF/SbF 5 are made of PTFE . [ citation needed ]
Fluoroantimonic acid solutions decompose when heated, generating free hydrogen fluoride gas and liquid antimony pentafluoride at a temperature of 40 °C. [ 13 ]
As a superacid , fluoroantimonic acid solutions protonate nearly all organic compounds , often causing dehydrogenation, or dehydration. In 1967, Bickel and Hogeveen showed that 2HF·SbF 5 reacts with isobutane and neopentane to form carbenium ions: [ 14 ] [ 15 ]
It is also used in the synthesis of tetraxenonogold complexes. [ 16 ]
HF/SbF 5 is a highly corrosive substance that reacts violently with water. Heating it is dangerous as well, as it decomposes into toxic hydrogen fluoride . With superacids that are fuming and toxic, proper personal protective equipment should be used. In addition to the obligatory gloves and goggles , the use of a face shield and respirator are also required. Regular lab gloves are not recommended, as this acid can react with the gloves. [ 10 ] Safety gear must be worn at all times when handling or going anywhere near the substance, as fluoroantimonic acid can protonate every compound in the human body. [ 17 ] | https://en.wikipedia.org/wiki/HFSbF5 |
The Harrow–Hassidim–Lloyd ( HHL ) algorithm is a quantum algorithm for numerically solving a system of linear equations , designed by Aram Harrow , Avinatan Hassidim, and Seth Lloyd . The algorithm estimates the result of a scalar measurement on the solution vector to a given linear system of equations. [ 1 ]
The algorithm is one of the main fundamental algorithms expected to provide a speedup over their classical counterparts, along with Shor's factoring algorithm and Grover's search algorithm . Provided the linear system is sparse [ 2 ] and has a low condition number κ {\displaystyle \kappa } , and that the user is interested in the result of a scalar measurement on the solution vector, instead of the values of the solution vector itself, then the algorithm has a runtime of O ( log ( N ) κ 2 ) {\displaystyle O(\log(N)\kappa ^{2})} , where N {\displaystyle N} is the number of variables in the linear system. This offers an exponential speedup over the fastest classical algorithm, which runs in O ( N κ ) {\displaystyle O(N\kappa )} (or O ( N κ ) {\displaystyle O(N{\sqrt {\kappa }})} for positive semidefinite matrices).
An implementation of the quantum algorithm for linear systems of equations was first demonstrated in 2013 by three independent publications. [ 3 ] [ 4 ] [ 5 ] The demonstrations consisted of simple linear equations on specially designed quantum devices. [ 3 ] [ 4 ] [ 5 ] The first demonstration of a general-purpose version of the algorithm appeared in 2018. [ 6 ]
Due to the prevalence of linear systems in virtually all areas of science and engineering, the quantum algorithm for linear systems of equations has the potential for widespread applicability. [ 7 ]
The HHL algorithm tackles the following problem: given a N × N {\displaystyle N\times N} Hermitian matrix A {\displaystyle A} and a unit vector b → ∈ R N {\displaystyle {\vec {b}}\in \mathbb {R} ^{N}} , prepare the quantum state | x ⟩ {\displaystyle |x\rangle } corresponding to the vector x → ∈ R N {\displaystyle {\vec {x}}\in \mathbb {R} ^{N}} that solves the linear system A x → = b → {\displaystyle A{\vec {x}}={\vec {b}}} . More precisely, the goal is to prepare a state | x ⟩ {\displaystyle |x\rangle } whose amplitudes equal the elements of x → {\displaystyle {\vec {x}}} . This means, in particular, that the algorithm cannot be used to efficiently retrieve the vector x → {\displaystyle {\vec {x}}} itself. It does, however, allow to efficiently compute expectation values of the form ⟨ x | M | x ⟩ {\displaystyle \langle x|M|x\rangle } for some observable M {\displaystyle M} .
First, the algorithm represents the vector b → {\displaystyle {\vec {b}}} as a quantum state of the form:
Next, Hamiltonian simulation techniques are used to apply the unitary operator e i A t {\displaystyle e^{iAt}} to | b ⟩ {\displaystyle |b\rangle } for a superposition of different times t {\displaystyle t} . The ability to decompose | b ⟩ {\displaystyle |b\rangle } into the eigenbasis of A {\displaystyle A} and to find the corresponding eigenvalues λ j {\displaystyle \lambda _{j}} is facilitated by the use of quantum phase estimation .
The state of the system after this decomposition is approximately:
where u j {\displaystyle u_{j}} is the eigenvector basis of A {\displaystyle A} , and | b ⟩ = ∑ j = 1 N β j | u j ⟩ {\displaystyle |b\rangle =\sum _{j\mathop {=} 1}^{N}\beta _{j}|u_{j}\rangle } .
We would then like to perform the linear map taking | λ j ⟩ {\displaystyle |\lambda _{j}\rangle } to C λ j − 1 | λ j ⟩ {\displaystyle C\lambda _{j}^{-1}|\lambda _{j}\rangle } , where C {\displaystyle C} is a normalizing constant. The linear mapping operation is not unitary and thus will require a number of repetitions as it has some probability of failing. After it succeeds, we uncomputed the | λ j ⟩ {\displaystyle |\lambda _{j}\rangle } register and are left with a state proportional to:
where | x ⟩ {\displaystyle |x\rangle } is a quantum-mechanical representation of the desired solution vector x . To read out all components of x would require the procedure be repeated at least N times. However, it is often the case that one is not interested in x {\displaystyle x} itself, but rather some expectation value of a linear operator M acting on x . By mapping M to a quantum-mechanical operator and performing the quantum measurement corresponding to M , we obtain an estimate of the expectation value ⟨ x | M | x ⟩ {\displaystyle \langle x|M|x\rangle } . This allows for a wide variety of features of the vector x to be extracted including normalization, weights in different parts of the state space, and moments without actually computing all the values of the solution vector x .
Firstly, the algorithm requires that the matrix A {\displaystyle A} be Hermitian so that it can be converted into a unitary operator . In the case where A {\displaystyle A} is not Hermitian, define
As C {\displaystyle C} is Hermitian, the algorithm can now be used to solve C y = [ b 0 ] {\displaystyle Cy={\begin{bmatrix}b\\0\end{bmatrix}}} to obtain y = [ 0 x ] {\displaystyle y={\begin{bmatrix}0\\x\end{bmatrix}}} .
Secondly, the algorithm requires an efficient procedure to prepare | b ⟩ {\displaystyle |b\rangle } , the quantum representation of b. It is assumed that there exists some linear operator B {\displaystyle B} that can take some arbitrary quantum state | i n i t i a l ⟩ {\displaystyle |\mathrm {initial} \rangle } to | b ⟩ {\displaystyle |b\rangle } efficiently or that this algorithm is a subroutine in a larger algorithm and is given | b ⟩ {\displaystyle |b\rangle } as input. Any error in the preparation of state | b ⟩ {\displaystyle |b\rangle } is ignored.
Finally, the algorithm assumes that the state | ψ 0 ⟩ {\displaystyle |\psi _{0}\rangle } can be prepared efficiently, where
for some large T {\displaystyle T} . The coefficients of | ψ 0 ⟩ {\displaystyle |\psi _{0}\rangle } are chosen to minimize a certain quadratic loss function which induces error in the U i n v e r t {\displaystyle U_{\mathrm {invert} }} subroutine described below.
Hamiltonian simulation is used to transform the Hermitian matrix A {\displaystyle A} into a unitary operator, which can then be applied at will. This is possible if A is s -sparse and efficiently row computable, meaning it has at most s nonzero entries per row and given a row index these entries can be computed in time O( s ). Under these assumptions, quantum Hamiltonian simulation allows e i A t {\displaystyle e^{iAt}} to be simulated in time O ( log ( N ) s 2 t ) {\displaystyle O(\log(N)s^{2}t)} .
The key subroutine to the algorithm, denoted U i n v e r t {\displaystyle U_{\mathrm {invert} }} , is defined as follows and incorporates a phase estimation subroutine:
1. Prepare | ψ 0 ⟩ C {\displaystyle |\psi _{0}\rangle ^{C}} on register C
2. Apply the conditional Hamiltonian evolution (sum)
3. Apply the Fourier transform to the register C . Denote the resulting basis states with | k ⟩ {\displaystyle |k\rangle } for k = 0, ..., T − 1. Define λ k := 2 π k / t 0 {\displaystyle \lambda _{k}:=2\pi k/t_{0}} .
4. Adjoin a three-dimensional register S in the state
5. Reverse steps 1–3, uncomputing any garbage produced along the way.
The phase estimation procedure in steps 1-3 allows for the estimation of eigenvalues of A up to error ϵ {\displaystyle \epsilon } .
The ancilla register in step 4 is necessary to construct a final state with inverted eigenvalues corresponding to the diagonalized inverse of A . In this register, the functions f , g , are called filter functions. The states 'nothing', 'well' and 'ill' are used to instruct the loop body on how to proceed; 'nothing' indicates that the desired matrix inversion has not yet taken place, 'well' indicates that the inversion has taken place and the loop should halt, and 'ill' indicates that part of | b ⟩ {\displaystyle |b\rangle } is in the ill-conditioned subspace of A and the algorithm will not be able to produce the desired inversion. Producing a state proportional to the inverse of A requires 'well' to be measured, after which the overall state of the system collapses to the desired state by the extended Born rule .
The body of the algorithm follows the amplitude amplification procedure: starting with U i n v e r t B | i n i t i a l ⟩ {\displaystyle U_{\mathrm {invert} }B|\mathrm {initial} \rangle } , the following operation is repeatedly applied:
where
and
After each repetition, S {\displaystyle S} is measured and will produce a value of 'nothing', 'well', or 'ill' as described above. This loop is repeated until | w e l l ⟩ {\displaystyle |\mathrm {well} \rangle } is measured, which occurs with a probability p {\displaystyle p} . Rather than repeating 1 p {\displaystyle {\frac {1}{p}}} times to minimize error, amplitude amplification is used to achieve the same error resilience using only O ( 1 p ) {\displaystyle O\left({\frac {1}{\sqrt {p}}}\right)} repetitions.
After successfully measuring 'well' on S {\displaystyle S} the system will be in a state proportional to:
Finally, we perform the quantum-mechanical operator corresponding to M and obtain an estimate of the value of ⟨ x | M | x ⟩ {\displaystyle \langle x|M|x\rangle } .
The best classical algorithm which produces the actual solution vector x → {\displaystyle {\vec {x}}} is Gaussian elimination , which runs in O ( N 3 ) {\displaystyle O(N^{3})} time.
If A is s -sparse and positive semi-definite, then the Conjugate Gradient method can be used to find the solution vector x → {\displaystyle {\vec {x}}} , which can be found in O ( N s κ ) {\displaystyle O(Ns\kappa )} time by minimizing the quadratic function | A x → − b → | 2 {\displaystyle |A{\vec {x}}-{\vec {b}}|^{2}} .
When only a summary statistic of the solution vector x → {\displaystyle {\vec {x}}} is needed, as is the case for the quantum algorithm for linear systems of equations, a classical computer can find an estimate of x → † M x → {\displaystyle {\vec {x}}^{\dagger }M{\vec {x}}} in O ( N κ ) {\displaystyle O(N{\sqrt {\kappa }})} .
The runtime of the quantum algorithm for solving systems of linear equations originally proposed by Harrow et al. was shown to be O ( κ 2 log N / ε ) {\displaystyle O(\kappa ^{2}\log N/\varepsilon )} , where ε > 0 {\displaystyle \varepsilon >0} is the error parameter and κ {\displaystyle \kappa } is the condition number of A {\displaystyle A} . This was subsequently improved to O ( κ log 3 κ log N / ε 3 ) {\displaystyle O(\kappa \log ^{3}\kappa \log N/\varepsilon ^{3})} by Andris Ambainis [ 8 ] and a quantum algorithm with runtime polynomial in log ( 1 / ε ) {\displaystyle \log(1/\varepsilon )} was developed by Childs et al. [ 9 ] Since the HHL algorithm maintains its logarithmic scaling in N {\displaystyle N} only for sparse or low rank matrices, Wossnig et al. [ 10 ] extended the HHL algorithm based on a quantum singular value estimation technique and provided a linear system algorithm for dense matrices which runs in O ( N log N κ 2 ) {\displaystyle O({\sqrt {N}}\log N\kappa ^{2})} time compared to the O ( N log N κ 2 ) {\displaystyle O(N\log N\kappa ^{2})} of the standard HHL algorithm.
An important factor in the performance of the matrix inversion algorithm is the condition number κ {\displaystyle \kappa } , which represents the ratio of A {\displaystyle A} 's largest and smallest eigenvalues. As the condition number increases, the ease with which the solution vector can be found using gradient descent methods such as the conjugate gradient method decreases, as A {\displaystyle A} becomes closer to a matrix which cannot be inverted and the solution vector becomes less stable. This algorithm assumes that all singular values of the matrix A {\displaystyle A} lie between 1 κ {\displaystyle {\frac {1}{\kappa }}} and 1, in which case the claimed run-time proportional to κ 2 {\displaystyle \kappa ^{2}} will be achieved. Therefore, the speedup over classical algorithms is increased further when κ {\displaystyle \kappa } is a p o l y ( log ( N ) ) {\displaystyle \mathrm {poly} (\log(N))} . [ 1 ]
If the run-time of the algorithm were made poly-logarithmic in κ {\displaystyle \kappa } then problems solvable on n qubits could be solved in poly( n ) time, causing the complexity class BQP to be equal to PSPACE . [ 1 ]
Performing the Hamiltonian simulation, which is the dominant source of error, is done by simulating e i A t {\displaystyle e^{iAt}} . Assuming that A {\displaystyle A} is s-sparse, this can be done with an error bounded by a constant ε {\displaystyle \varepsilon } , which will translate to the additive error achieved in the output state | x ⟩ {\displaystyle |x\rangle } .
The phase estimation step errs by O ( 1 t 0 ) {\displaystyle O\left({\frac {1}{t_{0}}}\right)} in estimating λ {\displaystyle \lambda } , which translates into a relative error of O ( 1 λ t 0 ) {\displaystyle O\left({\frac {1}{\lambda t_{0}}}\right)} in λ − 1 {\displaystyle \lambda ^{-1}} . If λ ≥ 1 / κ {\displaystyle \lambda \geq 1/\kappa } , taking t 0 = O ( κ ε ) {\displaystyle t_{0}=O(\kappa \varepsilon )} induces a final error of ε {\displaystyle \varepsilon } . This requires that the overall run-time efficiency be increased proportional to O ( 1 ε ) {\displaystyle O\left({\frac {1}{\varepsilon }}\right)} to minimize error.
While there does not yet exist a quantum computer that can truly offer a speedup over a classical computer, implementation of a "proof of concept" remains an important milestone in the development of a new quantum algorithm. Demonstrating the quantum algorithm for linear systems of equations remained a challenge for years after its proposal until 2013 when it was demonstrated by Cai et al., Barz et al. and Pan et al. in parallel.
Published in Physical Review Letters 110, 230501 (2013), Cai et al. reported an experimental demonstration of the simplest meaningful instance of this algorithm, that is, solving 2 × 2 {\displaystyle 2\times 2} linear equations for various input vectors. The quantum circuit is optimized and compiled into a linear optical network with four photonic quantum bits (qubits) and four controlled logic gates, which is used to coherently implement every subroutine for this algorithm. For various input vectors, the quantum computer gives solutions for the linear equations with reasonably high precision, ranging from fidelities of 0.825 to 0.993. [ 11 ]
On February 5, 2013, Stefanie Barz and co-workers demonstrated the quantum algorithm for linear systems of equations on a photonic quantum computing architecture. This implementation used two consecutive entangling gates on the same pair of polarization-encoded qubits. Two separately controlled NOT gates were realized where the successful operation of the first was heralded by a measurement of two ancillary photons. Barz et al. found that the fidelity in the obtained output state ranged from 64.7% to 98.1% due to the influence of higher-order emissions from spontaneous parametric down-conversion. [ 4 ]
On February 8, 2013, Pan et al. reported a proof-of-concept experimental demonstration of the quantum algorithm using a 4-qubit nuclear magnetic resonance quantum information processor. The implementation was tested using simple linear systems of only 2 variables. Across three experiments they obtain the solution vector with over 96% fidelity. [ 5 ]
Another experimental demonstration using NMR for solving an 8*8 system was reported by Wen et al. [ 12 ] in 2018 using the algorithm developed by Subaşı et al. [ 13 ]
Quantum computers are devices that harness quantum mechanics to perform computations in ways that classical computers cannot. For certain problems, quantum algorithms supply exponential speedups over their classical counterparts, the most famous example being Shor's factoring algorithm. Few such exponential speedups are known, and those that are (such as the use of quantum computers to simulate other quantum systems) have so far found limited practical use due to the current small size of quantum computers. This algorithm provides an exponentially faster method of estimating features of the solution of a set of linear equations, which is a problem ubiquitous in science and engineering, both on its own and as a subroutine in more complex problems.
Clader et al. provided a preconditioned version of the linear systems algorithm that provided two advances. First, they demonstrated how a preconditioner could be included within the quantum algorithm. This expands the class of problems that can achieve the promised exponential speedup, since the scaling of HHL and the best classical algorithms are both polynomial in the condition number . The second advance was the demonstration of how to use HHL to solve for the radar cross-section of a complex shape. This was one of the first end to end examples of how to use HHL to solve a concrete problem exponentially faster than the best known classical algorithm. [ 14 ]
Dominic Berry proposed a new algorithm for solving linear time dependent differential equations as an extension of the quantum algorithm for solving linear systems of equations. Berry provides an efficient algorithm for solving the full-time evolution under sparse linear differential equations on a quantum computer. [ 15 ]
Two groups proposed [ 16 ] efficient algorithms for numerically integrating dissipative nonlinear ordinary differential equations. Liu et al. [ 17 ] utilized Carleman linearization technique for second order equations and Lloyd et al. [ 18 ] employed a mean field linearization method inspired by nonlinear Schrödinger equation for general order nonlinearities. The resulting linear equations are solved using quantum algorithms for linear differential equations.
The Finite Element Method uses large systems of linear equations to find approximate solutions to various physical and mathematical models. Montanaro and Pallister demonstrate that the HHL algorithm, when applied to certain FEM problems, can achieve a polynomial quantum speedup. They suggest that an exponential speedup is not possible in problems with fixed dimensions, and for which the solution meets certain smoothness conditions.
Quantum speedups for the finite element method are higher for problems which include solutions with higher-order derivatives and large spatial dimensions. For example, problems in many-body dynamics require the solution of equations containing derivatives on orders scaling with the number of bodies, and some problems in computational finance , such as Black-Scholes models, require large spatial dimensions. [ 19 ]
Wiebe et al. provide a new quantum algorithm to determine the quality of a least-squares fit in which a continuous function is used to approximate a set of discrete points by extending the quantum algorithm for linear systems of equations. As the number of discrete points increases, the time required to produce a least-squares fit using even a quantum computer running a quantum state tomography algorithm becomes very large. Wiebe et al. find that in many cases, their algorithm can efficiently find a concise approximation of the data points, eliminating the need for the higher-complexity tomography algorithm. [ 20 ]
Machine learning is the study of systems that can identify trends in data. Tasks in machine learning frequently involve manipulating and classifying a large volume of data in high-dimensional vector spaces. The runtime of classical machine learning algorithms is limited by a polynomial dependence on both the volume of data and the dimensions of the space. Quantum computers are capable of manipulating high-dimensional vectors using tensor product spaces and thus are well-suited platforms for machine learning algorithms. [ 21 ]
The quantum algorithm for linear systems of equations has been applied to a support vector machine, which is an optimized linear or non-linear binary classifier. A support vector machine can be used for supervised machine learning, in which training set of already classified data is available, or unsupervised machine learning, in which all data given to the system is unclassified. Rebentrost et al. show that a quantum support vector machine can be used for big data classification and achieve an exponential speedup over classical computers. [ 22 ]
In June 2018, Zhao et al. developed an algorithm for performing Bayesian training of deep neural networks in quantum computers with an exponential speedup over classical training due to the use of the quantum algorithm for linear systems of equations, [ 6 ] providing also the first general-purpose implementation of the algorithm to be run in cloud-based quantum computers . [ 23 ]
Proposals for using HHL in finance include solving partial differential equations for the Black–Scholes equation and determining portfolio optimization via a Markowitz solution . [ 24 ]
In 2023, Baskaran et al. proposed the use of HHL algorithm to quantum chemistry calculations, via the linearized coupled cluster method (LCC). [ 25 ] The connection between the HHL algorithm and the LCC method is due to the fact that the latter can be recast in the form of system of linear equations. A key factor that makes this approach useful for quantum chemistry is that the number of state register qubits is the natural logarithm of the number of excitations, thus offering an exponential suppression in the number of required qubits when compared to variational quantum eigensolver or the quantum phase estimation algorithms. This leads to a 'coexistence across scales', where in a given quantum computing era, HHL-LCC could be applied to much larger systems whereas QPE- CASCI could be employed for smaller molecular systems but with better accuracy in predicting molecular properties. On the algorithmic side, the authors introduce the 'AdaptHHL' approach, which circumvents the need to expend an ~Ο(N 3 ) classical overhead associated with fixing a value for the parameter 'c' in the controlled-rotation module of the algorithm.
Recognizing the importance of the HHL algorithm in the field of quantum machine learning , Scott Aaronson [ 26 ] analyzes the caveats and factors that could limit the actual quantum advantage of the algorithm. | https://en.wikipedia.org/wiki/HHL_algorithm |
HHTDD ( hexanitrohexaazatricyclododecanedione ) is a powerful but moisture sensitive explosive compound. It is essentially an open analogue of the cyclic nitroamine cage compounds such as CL-20 . While it is highly explosive, with a velocity of detonation even higher than that of CL-20, HHTDD readily decomposes in the presence of even trace amounts of water, making it unsuitable for any practical applications. [ 1 ]
This explosives -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/HHTDD |
HIBARI is a space mission by Japan for a microsatellite that would test a new attitude control (orientation) method to achieve high accuracy pointing for its small telescope, and was launched on 9 November 2021 by an Epsilon launch vehicle as part of the Innovative Satellite Technology Demonstration Program -2 mission. [ 1 ] The key technology to be tested on HIBARI is called "Variable Shape Attitude Control" (VSAC), and it is based on reaction torque by rotating its four solar array paddles.
HIBARI is a space mission by the Japanese scientists from the Tokyo Institute of Technology to develop high pointing stability and agile maneuvering of a small satellite by using reaction torque of the satellite's structure. [ 2 ] [ 3 ] This technology, first presented in 2016, [ 4 ] is hoped to substitute the use of reaction wheels and control moment gyroscopes (CMG), which arguably have difficulty achieving both agility and stability simultaneously. [ 2 ] This capability would be useful for a very fast response to observe in the direction of gravitational waves or other transient astrophysical phenomena. [ 3 ]
The spacecraft is a 55 kg (121 lb) microsatellite configured in a 50 cm (20 in) cube, [ 3 ] where half of it would carry a small ultraviolet telescope to verify the pointing stability (< 10 𝑎𝑟𝑐𝑠𝑒𝑐 2 ) and accuracy of the VSAC system. The orientation high accuracy would be achieved by rotating the arms of its four solar arrays in an orthogonal axis. [ 2 ] Solar cells would be mounted on both sides of each of four solar array paddles. [ 3 ] | https://en.wikipedia.org/wiki/HIBARI_(satellite) |
Iodic acid is a white water-soluble solid with the chemical formula HIO 3 . Its robustness contrasts with the instability of chloric acid and bromic acid . Iodic acid features iodine in the oxidation state +5 and is one of the most stable oxo-acids of the halogens . When heated, samples dehydrate to give iodine pentoxide . On further heating, the iodine pentoxide further decomposes, giving a mix of iodine, oxygen and lower oxides of iodine.
Iodic acid can be produced by oxidizing iodine with strong oxidizers such as nitric acid , chlorine, chloric acid or hydrogen peroxide, [ 3 ] for example:
Iodic acid is also produced by the reaction of iodine monochloride with water:
Iodic acid crystallises from acidic solution as orthorhombic α- HIO 3 in space group P 2 1 2 1 2 1 . The structure consists of pyramidal molecules linked by hydrogen bonding and intermolecular iodine-oxygen interactions. The I=O bond lengths are 1.81 Å while the I–OH distance is 1.89 Å. [ 4 ] [ 5 ] [ 6 ] Several other polymorphs have been reported, including an orthorhombic γ form in space group Pbca [ 7 ] and an orthorhombic δ form in space group P 2 1 2 1 2 1 . [ 8 ] All of the polymorphs contain pyramidal molecules, hydrogen bonding and I···O interactions, but differ in packing arrangement.
Iodic acid is a relatively strong acid with a p K a of 0.75. It is strongly oxidizing in acidic solution, less so in basic solution. When iodic acid acts as oxidizer, then the product of the reaction is either iodine, or iodide ion. Under some special conditions (very low pH and high concentration of chloride ions, such as in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride , a golden yellow compound in solution and no further reduction occurs. In the absence of chloride ions, when there is an excess amount of reductant, then all iodate is converted to iodide ion. When there is an excess amount of iodate, then part of the iodate is converted to iodine. [ citation needed ]
Iodic acid is used as a strong acid (though it is not truly a strong acid, but a weak acid that is very close to being a strong acid) in analytical chemistry . It may be used to standardize solutions of both weak and strong bases , using methyl red or methyl orange as the indicator .
Iodic acid can be used to synthesize sodium or potassium iodate for increasing iodine content of salt. [ citation needed ]
Iodic acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known. | https://en.wikipedia.org/wiki/HIO3 |
Periodic acid ( / ˌ p ɜːr aɪ ˈ ɒ d ɪ k / per-eye- OD -ik ) is an oxoacid of iodine . It can exist in two forms: orthoperiodic acid, with the chemical formula H 5 IO 6 , and metaperiodic acid, which has the formula HIO 4 . Periodic acids are colourless crystals. Periodic acid features iodine in the highest oxidation state of +7.
Periodic acid was discovered by Heinrich Gustav Magnus and C. F. Ammermüller in 1833. [ 3 ]
Modern industrial scale production involves the oxidation of a solution of sodium iodate under alkaline conditions , either electrochemically on a PbO 2 anode , or by treatment with chlorine : [ 4 ]
A standard laboratory preparation involves treating a mixture of tribarium dihydrogen orthoperiodate with nitric acid . Upon concentrating the mixture, the barium nitrate , which is less soluble, is separated from periodic acid: [ 6 ]
Orthoperiodic acid has a number of acid dissociation constants . [ 7 ] [ 8 ] The p K a of metaperiodic acid has not been determined.
There being two forms of periodic acid, it follows that two types of periodate salts are formed. For example, sodium metaperiodate , NaIO 4 , can be synthesised from HIO 4 while sodium orthoperiodate , Na 5 IO 6 can be synthesised from H 5 IO 6 .
Orthoperiodic acid forms monoclinic crystals ( space group P2 1 / n ) consisting of a slightly deformed IO 6 octahedron interlinked via bridging hydrogens. Five I–O bond distances are in the range 1.87–1.91 Å and one I–O bond is 1.78 Å. [ 9 ] [ 10 ] The structure of metaperiodic acid also includes IO 6 octahedra, however these are connected via cis -edge-sharing with bridging oxygens to form one-dimensional infinite chains. [ 11 ]
Orthoperiodic acid can be dehydrated to give metaperiodic acid by heating to 100 °C under reduced pressure.
Further heating to around 150 °C gives iodine pentoxide ( I 2 O 5 ) rather than the expected anhydride diiodine heptoxide ( I 2 O 7 ). Metaperiodic acid can also be prepared from various orthoperiodates by treatment with dilute nitric acid . [ 12 ]
Like all periodates periodic acid can be used to cleave various 1,2-difunctional compounds. Most notably periodic acid will cleave vicinal diols into two aldehyde or ketone fragments ( Malaprade reaction ).
This can be useful in determining the structure of carbohydrates as periodic acid can be used to open saccharide rings. This process is often used in labeling saccharides with fluorescent molecules or other tags such as biotin . Because the process requires vicinal diols, periodate oxidation is often used to selectively label the 3′-termini of RNA ( ribose has vicinal diols) instead of DNA as deoxyribose does not have vicinal diols.
Periodic acid is also used as an oxidising agent of moderate strength, as exemplified in the Babler oxidation of secondary allyl alcohols which are oxidised to enones by stoichiometric amounts of orthoperiodic acid with catalyst PCC . [ 13 ]
Periodic acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.
Compounds with a similar structure:
Compounds with similar chemistry: | https://en.wikipedia.org/wiki/HIO4 |
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