In organic chemistry, 3-hydroxybutanal (acetaldol, aldol) is an organic compound with the formula CH3CH(OH)CH2CHO and the structure H3C−CH(OH)−CH2−CH=O. It is classified as an aldol (R−CH(OH)−CHR'−C(=O)−R") 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.[2] The compound is chiral although this aspect is not often exploited.
Acetaldehyde dimerizes upon treatment with aqueous sodium hydroxide:[2]
This is the prototypical aldol reaction.
Dehydration of 3-hydroxybutanal gives crotonaldehyde. Distillation of 3-hydroxybutanal is sufficiently forcing to effect this conversion:[2]
Hydrogenation of 3-hydroxybutanal gives 1,3-butanediol:
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.[3]
It was formerly used in medicine as a hypnotic and sedative.[4]