Perkin Condensation

About Perkin Condensation

C₆H₅CHO + (CH₃CO)₂O→ C₆H₅CH = CHCO₂H

The reaction between aromatic aldehydes and alkanoic anhydrides in presence of alkanoate is called Perkin reaction. The reaction is similar to aldol condensation.

In this reaction, the carbanion is obtained by the removal of an Alpha hydrogen atom from acid anhydride by carboxylate (anion of the corresponding acid of the acid anhydride). The carbanion then attacks the aromatic aldehyde to yield alkoxide anion. The transfer of acetyl group then takes place from the carboxyl oxygen to alkoxy oxygen via a cyclic intermediate to give a more stable anion. Removal of an Alpha hydrogen from this anion by carboxylate results in the loss of good leaving group from the position to give anion of the Alpha, beta unsaturated acid. This on acidification gives Alpha,-unsaturated acid. For example, PhCHO on reaction with excess acetic anhydride in presence of sodium acetate followed by acidification gives cinnamic acid (3-phenyl propenoic acid).

Perkin Condensation Mechanism:

It is observed that the acetate ion abstracts a proton from the α-carbon of the anhydride producing a carbanion which then attacks the carbonyl group of the aldehyde. The product then abstracts a proton from the acid to form – aldol type compound. The latter then undergoes dehydration in the presence of hot acetic anhydride.

Prolonged heating (about 5 hours) and high temperature is required, since a weak base (acetate ion) has to react with a weak acid (anhydride).

Related Reactions

• Benzoin Condensation
• Grignard Reagent

List of Name Reaction of Organic Chemistry consist of detail Reaction Mechanism of all name reactions of Organic Chemistry.