Question
Explain the mechanism of aldol condensation.
✓
Answer
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.
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.
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