aldol condensation

aldol condensation

Aldol condensation is a carbon-carbon bond formation reaction that involves two carbonyl groups. There must exist minimum one alpha hydrogen with at least one of these carbonyl groups. Aldol condensation is catalyzed by either acid or base that generates enol or enolate from the corresponding carbonyl group with the alpha hydrogen. If promoted by base, the enolate acts as nucleophile and attacks at the carbon of the other carbonyl group. On treatment with dilute acid, it produces beta-hydroxy carbonyl compound which undergoes elimination of water under heating condition. Hence,  alpha-beta unsaturated carbonyl compound is produced.

aldol condensation

Basically, there are three types of aldol condensations namely,
a.  self-aldol condensation
b.  crossed/ mixed aldol condensation
c.  intramolecular aldol condensation

 

aldol condensation of acetaldehyde

Aldol condensation of acetaldehyde is an example of self-aldol condensation.

aldol condensation

aldol condensation of acetaldehyde

Following is the mechanism for the aldol condensation of acetaldehyde.

aldol condensation of acetaldehyde

aldol condensation of acetaldehyde

Aldol condensation of acetaldehyde is catalyzed by base that generates enolate. The enolate acts as nucleophile and attacks at the carbon of the other carbonyl group from another acetaldehyde. On treatment with dilute acid, it produces beta-hydroxy carbonyl compound which undergoes elimination of water under heating condition. Hence, alpha-beta unsaturated carbonyl compound, crotonaldehyde  is produced.