Aldol condensation

Aldehydes containing alpha hydrogens undergoes self-addition in the presence of a base to form product called aldols. The reaction is called aldol condensation the term aldol is derived from the combination of the words aldehyde and alcohol, the two functional groups present in the product, For example two molecules of acetaldehyde combine with each other in the presence of dilute NaOH to form 3-Hydroxy butanol.

Mechanism:-

The reaction is reversible

Step 1:- The enolate ion is formed.

Step2 :- The enolate ion attacks the carbonyl carbon of another un ionised aldehyde molecule.

Step3 :-

Mixed aldol condensation :-

The reaction of two different carbonyl compounds ( one of which must have an alpha hydrogen) in the presence of a base is known as mixed aldol condensation. For example, acetaldehyde reacts with benzaldehyde (which has no alpha hydrogen) in the presence of a base to form cinnamaldehyde.