Acetaldehyde
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| Acetaldehyde | |
|---|---|
 |  |
| |
| IUPAC name | acetaldehyde |
| Systematic name | ethanal |
| Other names | acetaldehyde |
| Identifiers | |
| CAS number | |
| RTECS number | AB1925000 |
| SMILES | CC=O |
| Properties | |
| Molecular formula | C2H4O |
| Molar mass | 44.05 g mol−1 |
| Appearance | Colorless liquid Pungent, fruity odor |
| Density | 0.788 g cm−3 |
| Melting point |
−123.5 °C |
| Boiling point |
20.2 °C |
| Solubility in water | soluble in all proportions |
| Viscosity | ~0.215 at 20 °C |
| Structure | |
| Molecular shape | trigonal planar (sp²) at C1 tetrahedral (sp³) at C2 |
| Dipole moment | 2.7 D |
| Hazards | |
| EU classification | Very flammable (F+) Harmful (Xn) Carc. Cat. 3 |
| NFPA 704 |
|
| R-phrases | R12, R36/37, R40 |
| S-phrases | (S2), S16, S33, S36/37 |
| Flash point | −39 °C |
| Autoignition temperature | 185 °C |
| Related Compounds | |
| Related aldehydes | Formaldehyde Propionaldehyde Ethylene oxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
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Acetaldehyde, sometimes known as ethanal, is an organic chemical compound with the formula CH3CHO or MeCHO. It is a flammable liquid with a fruity smell. Acetaldehyde occurs naturally in ripe fruit, coffee, and fresh bread and is produced by plants as part of their normal metabolism. It is popularly known as the chemical that causes hangovers.
In the chemical industry, acetaldehyde is used as an intermediate in the production of acetic acid, certain esters, and a number of other chemicals. In 1989, US production stood at 740 million pounds (336,000 t). An important production method for acetaldehyde is the Wacker process.
Ethenol
Only a trace of acetaldehyde exists as the enol form, ethenol, with Keq = 6 x 10-5.[1] Ethenol has been detected in the interstellar medium, specifically in between our Milky Way Galaxy and the Galaxy N-ID9[1]
Applications in organic synthesis
Acetaldehyde is a common 2-carbon building block in organic synthesis.[1] Because of its small size and its availability as the anhydrous monomer (unlike formaldehyde), it is a common electrophile. With respect to its condensation reactions, acetaldehyde is prochiral. It is mainly used as a source of the CH3C+H(OH) synthon in aldol and related condensation reactions.[1] Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives.[1] In one of the more spectacular condensation reactions, three equivalents of formaldehyde add to MeCHO to give pentaerythritol, C(CH2OH)4.[1]
In a Strecker reaction, acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine.[1] Acetaldehyde can condense with amines to yield imines, such as the condensation with cyclohexylamine to give N-ethylidenecyclohexylamine. These imines can be used to direct subsequent reactions like an aldol condensation.[1]
It is also an important building block for the synthesis of heterocyclic compounds. A remarkable example is its conversion upon treatment with ammonia to 5-ethyl-2-methylpyridine ("aldehyde-collidine”).[1]
Acetal derivatives
Three molecules of acetaldehyde condense to form “paraldehyde,” a cyclic trimer containing C-O single bonds; four condense to form the cyclic molecule called metaldehyde.
Acetaldehyde forms a stable acetal upon reaction with ethanol under conditions that favor dehydration. The product, CH3CH(OCH2CH3)2, is in fact called "acetal,"[1] although acetal is used more widely to describe other compounds with the formula RCH(OR')2.
Biological aspects
In the liver, the enzyme alcohol dehydrogenase converts ethanol into acetaldehyde, which is then further converted into harmless acetic acid by acetaldehyde dehydrogenase. The last steps of alcoholic fermentation in bacteria, plants and yeast involve the conversion of pyruvate into acetaldehyde 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.
Acetaldehyde and hangovers
Most people of East Asian descent have a mutation in their alcohol dehydrogenase gene that makes this enzyme unusually effective at converting ethanol to acetaldehyde, and about half of such people also have a form of acetaldehyde dehydrogenase which is less effective at converting acetaldehyde to acetic acid[1]. This combination causes them to suffer from the alcohol flush reaction, in which acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become alcoholics. The drug Antabuse (disulfiram) also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It has been used in the treatment of alcoholism.
Other occurrences
Acetaldehyde is an air pollutant resulting from combustion, such as automotive exhaust and tobacco smoke, contributing to the addictive properties of tobacco.[1]
Safety
Acetaldehyde is toxic, an irritant, and a probable carcinogen.[1]
References
See also
External links
- International Chemical Safety Card 0009
- National Pollutant Inventory - Acetaldehde
- NIOSH Pocket Guide to Chemical Hazards
- IARC Monograph: "Acetaldehyde"
- EPA factsheet about acetaldehyde
- Hal Kibbey, Genetic Influences on Alcohol Drinking and Alcoholism, Indiana University Research and Creative Activity, Vol. 17 no. 3.
- United States Food and Drug Administration (FDA) information for acetaldehyde
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
