Ацетальдегид: свойства, применение и опасность

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|ImageFileR1 = Acetaldehyde tall 2D skeletal. png
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|ImageNameR1 = Skeletal structure of acetaldehyde
|ImageFileL2 = Acetaldehyde 3D balls. png
|ImageNameL2 = Ball and stick model
|ImageFileL1 = Acetaldehyde 2D flat. svg
|ImageNameL1 = Lewis structure of acetaldehyde
|ImageFileR2 = Acetaldehyde 3D vdW. png
|ImageNameR2 = Space filling model
|PIN = Acetaldehyde
|SystematicName = EthanalAcetylaldehyde
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|ExternalSDS = HMDB
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|LC50 = 13,000 ppm (rat), 17,000 ppm (hamster), 20,000 ppm (rat) 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. Pathways of exposure include air, water, land, or groundwater, as well as drink and smoke. 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. Acetaldehyde is "one of the most frequently found air toxins with cancer risk greater than one in a million".

Acetaldehyde was first observed by the Swedish pharmacist/chemist Carl Wilhelm Scheele (1774); it was then investigated by the French chemists Antoine François, comte de Fourcroy and Louis Nicolas Vauquelin (1800), and the German chemists Johann Wolfgang Döbereiner (1821, 1822, 1832) and Justus von Liebig (1835). In 1835, Liebig named it "aldehyde"; the name was later altered to "acetaldehyde".

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. At room temperature, acetaldehyde (CH3CH=O) is more stable than vinyl alcohol (CH2=CHOH) by 42.7 kJ/mol: 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.

Acetaldehyde is a common electrophile in organic synthesis. In addition reactions acetaldehyde is prochiral. It is used primarily as a source of the "CH3C+H(OH)" synthon in aldol reactions and related condensation reactions. Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives. In one of the more spectacular addition reactions, formaldehyde in the presence of calcium hydroxide adds to MeCHO to give pentaerythritol, C(CH2OH)4 and formate. In a Strecker reaction, acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine. 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. 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").

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 H2SO4 as the catalyst. At −40 °C in the presence of acid catalysts, polyacetaldehyde is produced. Although vinyl alcohol is a polymeric form of acetaldehyde , polyvinyl alcohol cannot be produced from acetaldehyde.

Acetaldehyde forms a stable acetal upon reaction with ethanol under conditions that favor dehydration. The product, CH3CH(OCH2CH3)2, is formally named 1,1 diethoxyethane but is commonly referred to as "acetal". 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.

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.

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. 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." 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. In addition, acetaldehyde is damaging to DNA and causes abnormal muscle development as it binds to proteins.

Acetaldehyde induces DNA interstrand crosslinks, a form of DNA damage. These can be repaired by either of two replication coupled DNA repair pathways. 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.

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.

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.

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. 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. 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.

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. Acetaldehyde is also present in automobile and diesel exhaust. As a result, acetaldehyde is "one of the most frequently found air toxics with cancer risk greater than one in a million". It has been demonstrated to have a synergistic effect with nicotine in rodent studies of addiction. 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.

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. 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.

Acetaldehyde can be produced by the photo oxidation of polyethylene terephthalate (PET), via a Type II Norrish reaction. 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. The level at which an average consumer could detect acetaldehyde is still considerably lower than any toxicity.

Candida albicans in patients with potentially carcinogenic oral diseases has been shown to produce acetaldehyde in quantities sufficient to cause problems.