Everything about Acetaldehyde totally explained
| Section2 =
| Section3 =
| Section7 =,,
| SPhrases =,,,
| FlashPt = −39 °C
| Autoignition = 185 °C
}}
| Section8 =
}}
Acetaldehyde, sometimes known as
ethanal, is an
organic chemical compound with the
formula CH3CH
O 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 Mg). An important production method for acetaldehyde is the
Wacker process.
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 that's less effective at converting acetaldehyde to acetic acid. 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
disulfiram (Antabuse) also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It is used in the treatment of alcoholism.
Applications in organic synthesis
Acetaldehyde is a common 2-carbon building block in
organic synthesis. Because of its small size and its availability as the anhydrous monomer (unlike formaldehyde), it's a common electrophile. With respect to its condensation reactions, acetaldehyde is
prochiral. It is mainly used as a source of the CH
3C
+H(OH)
synthon in
aldol and related condensation reactions. Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives. In one of the more spectacular condensation reactions, three equivalents of
formaldehyde add to MeCHO to give
pentaerythritol, C(CH
2OH)
4.
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, such as the condensation with cyclohexylamine to give N-ethylidenecyclohexylamine. These imines can be used to direct subsequent reactions like an aldol condensation.
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”).
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, CH
3CH(OCH
2CH
3)
2, is in fact called "acetal," although
acetal is used more widely to describe other compounds with the formula RCH(OR')
2.
Ethenol
Only a trace of acetaldehyde exists as the
enol form,
ethenol, with K
eq = 6 x 10
-5.
Environmental occurrence
Acetaldehyde is an
air pollutant resulting from combustion, such as automotive exhaust and
tobacco smoke. It is also created by
thermal degradation of polymers in the
plastics processing industry.
Safety
Acetaldehyde is toxic, an irritant, and a probable
carcinogen.
Further Information
Get more info on 'Acetaldehyde'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://acetaldehyde.totallyexplained.com">Acetaldehyde Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
