Acetaldehyde

Acetaldehyde
Systematic name	Acetaldehyde
Other IUPAC name	Ethanal
Chemical formula	CH_{3_CHO}
SMILES	CC=O
Molecular mass	44.05 g/mol
Appearance	Colorless liquid Pungent, fruity odor
CAS number	^*
Properties
Density	0.788 g/cm³
Solubility in water	? g/100 ml (? °C)
Melting point	−124 °C
Boiling point	26 °C
Viscosity	? cP at ? °C
Structure
Molecular shape	?
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	Very flammable (F+) Harmful (Xn) Carc. Cat. 3
R-phrases	, ,
S-phrases	, , ,
Flash point	−39 °C
Autoignition temperature	185 °C
RTECS number	AB1925000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related aldehydes	Formaldehyde Propionaldehyde
Chemical infobox

Acetaldehyde, also known as ethanal, is an organic chemical compound. It is an aldehyde with the formula C H₃CHO. It is a highly reactive flammable liquid with a strong fruity smell. It melts at -123.5° C and boils at 21 °C. Acetaldehyde occurs naturally in ripe fruit, coffee, and fresh bread and is produced by plants as part of their normal metabolism.

In the liver, the enzyme alcohol dehydrogenase converts ethanol into acetaldehyde, which is then further converted into harmless acetic acid by acetaldehyde dehydrogenase. Acetaldehyde is more toxic than ethanol and is responsible for many hangover symptoms. N-Acetylcysteine (NAC) is known to assist in processing acetaldehyde in the body and therefore can help to relieve hangover symptoms. L-Cysteine and L-glutamine, which each contain a thiol group, can force conversion back into ethanol, to similar effect.

Some people of East Asian descent have a mutation in their acetaldehyde dehydrogenase gene, making this enzyme less effective. In these people, 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 is used in the treatment of certain alcoholics.

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 alcohol dehydrogenase, now operating in the opposite direction.

In the chemical industry, acetaldehyde is mainly 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).

When exposed to acetaldehyde vapors, humans develop irritation of the eyes, skin and the respiratory tract. Acetaldehyde is an air pollutant, emitted by cars and certain production facilities. It is also contained in tobacco smoke, contributing to the smoke's addictive properties.

Three molecules of acetaldehyde can form the cyclic paraldehyde, and four can form the cyclic acetaldehyde tetramer.

Cancer link

After some experiments with animals, acetaldehyde is classified as a probable carcinogen.

External links

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

Aldehydes | IARC Group 2B carcinogens

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Cancer link

See also

External links