Acetaldehyde
Acetaldehyde, systematically known as ethanal, is an
organic chemical compound. It is an
aldehyde with the
formula CH3CH
O. It is a highly reactive flammable liquid with a strong fruity smell. 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.
Encyclopedia
| Acetaldehyde |
|---|
| |
| IUPAC recommended name | Acetaldehyde |
| Systematic name | Ethanal |
| Chemical formula | CH3CHO |
| SMILES | CC=O |
| Molecular mass | 44.05 g mol-1 |
| Appearance | Colorless liquid
Pungent, fruity odor |
| CAS number | [75-07-0] |
| Properties |
|---|
| Density | 0.788 g cm-3 |
| Solubility in water | soluble in all proportions |
| Melting point | -123.5 °C |
| Boiling point | 20.2 °C |
| crit. temp. / crit. press. | 188 °C / 6.4 MPa |
| Viscosity | ~0.215 at 20 °C |
| Structure |
|---|
| Molecular shape | trigonal planar at C1
tetrahedral at C2 |
| Dipole moment | 2.7 D |
| Hazards |
|---|
| MSDS | External MSDS |
| EU classification | Very flammable
Harmful
Carc. Cat. 3 |
| NFPA 704 | |
| R-phrases | , , |
| S-phrases | , , , |
| Flash point | -39 °C |
| Autoignition temperature | 185 °C |
| RTECS number | AB1925000 |
| Supplementary data page |
|---|
Structure and
properties | n, er, etc. |
Thermodynamic
data | Phase behaviour
Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds |
|---|
| Related aldehydes | Formaldehyde
Propionaldehyde |
| |
|
Acetaldehyde, systematically known as
ethanal, is an
organic chemical compound. It is an
aldehyde with the
formula CH3CH
O. It is a highly reactive flammable liquid with a strong fruity smell. 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 is known to assist in processing acetaldehyde in the body and therefore can help to relieve hangover symptoms.
Cysteine, which contains 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. Known as the
alcohol flush reaction, acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become alcoholics. The drug
Antabuse 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 .
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
metaldehyde.
Cancer link
After some experiments with animals, acetaldehyde is classified as a probable carcinogen.
See also
External links
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- Hal Kibbey: , Indiana University Research and Creative Activity, Vol. 17 no. 3.
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