Structure

Production

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 tonnes).[4] An
important production method for acetaldehyde is the Wacker process.
The hydration of acetylene, catalyzed by mercury
salts gives ethenol, which tautomerizes to acetaldehyde. This
process was conducted on an industrial scale prior to the Wacker
process.[5]

Reactions

Acetaldehyde is a common 2-carbon building block in organic
synthesis.[6] 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.[7]
Grignard reagents and organolithium compounds react with MeCHO to
give hydroxyethyl derivatives.[8] In one
of the more spectacular condensation reactions, three equivalents
of formaldehyde
add to MeCHO to give pentaerythritol,
C(CH2OH)4.[9]

In a Strecker reaction,
acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine.[10]
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.[11]

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”).[12]

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,"[13]
although acetal is used more
widely to describe other compounds with the formula
RCH(OR')2.

The drug disulfiram
(Antabuse) prevents the oxidation of acetaldehyde to acetic acid,
and it has the same unpleasant effect on drinkers. Antabuse is used
as a deterrent for alcoholics who wish to stay sober.

Tobacco
addiction

Acetaldehyde is a significant constituent of tobacco smoke. It
has been demonstrated to have a synergistic effect with nicotine,
increasing the onset and tenacity of addiction to cigarettesmoking,
particularly in adolescents.[19][20]

Alzheimer's disease

People who have a genetic deficiency for the conversion of
acetaldehyde into acetic
acid may have a greater risk of Alzheimer's disease. "These results
indicate that the ALDH2
deficiency is a risk factor for LOAD [late-onset Alzheimer's
disease] …"[21]

Organ
Disease

Acetaldehyde has the capability to bind to certain proteins.
After ethanol is consumed,
acetaldehyde binds to proteins to form adducts. These adducts are
linked to organ disease[22].

Neuronal
Damage

When acetaldehyde is present in the brain, it binds to proteins
in the brain to form adducts. Acetaldehyde adducts are found in
the frontal cortex and midbrain of alcoholics.
These adducts cause neuronal damage. They can cause neurons and
their related synaptic receptors to disappear[23].

Carcinogen

Acetaldehyde is a probable carcinogen in humans.[24] The
International
Agency for Research on Cancer states, "There is
sufficient evidence for the carcinogenicity of
acetaldehyde (the major metabolite of ethanol) in experimental
animals."[25] In
addition, acetaldehyde is damaging to DNA[26] and
causes abnormal muscle development as it binds to proteins.[27]

A study of 818 heavy drinkers found that those who are exposed
to more acetaldehyde than normal through a defect in the gene for
alcohol dehydrogenase are at
greater risk of developing cancers of the upper gastrointestinal
tract and liver.[28]

Safety

Acetaldehyde is toxic when applied externally for prolonged
periods, an irritant, and a probable carcinogen.[29]