In presence of dilute base NaOH, or KOH, two molecules of an aldehyde or ketone having α – hydrogen add together to give 3 – hydroxyl aldehyde (aldol) or – hydroxyl ketone (ketol). The reaction is called aldol condensation reaction.
Mechanism
The mechanism of aldol condensation of acetaldehyde takes place in three steps.
Step 1: The carbanion is formed as the α – hydrogen atom is removed as a proton by the base.
Step 2: The carbanion attacks the carbonyl carbon of another unionized aldehyde to form an alkoxide ion.
Step 3: The alkoxide ion formed is protonated by water to form aldol.
The aldol rapidly undergoes dehydration on heating with acid to form a, f3 unsaturated aldehyde.
