3-Hydroxybutanal

In organic chemistry, 3-hydroxybutanal (acetaldol, aldol) is an organic compound with the formula CH3CH(OH)CH2CHO and the structure H3C\sCH(OH)\sCH2\sCH\dO. It is classified as an aldol (R\sCH(OH)\sCHR'\sC(\dO)\sR") and the word "aldol" can refer specifically to 3-hydroxybutanal. It is formally the product of the dimerization of acetaldehyde (CH3CHO). A thick colorless or pale-yellow liquid, it is a versatile and valuable intermediate with diverse impacts. The compound is chiral although this aspect is not often exploited.

Production
Acetaldehyde dimerizes upon treatment with aqueous sodium hydroxide:
 * 2 CH3CHO -> CH3CH(OH)CH2CHO  +  H2O

This is the prototypical aldol reaction.

Reactions and uses
Dehydration of 3-hydroxybutanal gives crotonaldehyde. Distillation of 3-hydroxybutanal is sufficiently forcing to effect this conversion:
 * CH3CH(OH)CH2CHO -> CH3CH\dCHCHO  +  H2O

Hydrogenation of 3-hydroxybutanal gives 1,3-butanediol:
 * CH3CH(OH)CH2CHO + H2  ->  CH3CH(OH)CH2CH2OH

This diol is a precursor to 1,3-butadiene, precursor to diverse polymers.

Polymerization of 3-hydroxybutanal is also spontaneous, but can be stopped with the addition of water.

Aldol has been used in making perfumes and in ore flotation.

Former or niche uses
It was formerly used in medicine as a hypnotic and sedative.