. What is Perkin Reaction
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 beta-position to give anion of the alpha,beta-unsaturated acid. This on acidification gives alpha, beta-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).