Reaction of benzaldehyde with acetic anhydride in presence of potassium acetate results in formation of cinnamic acid. Cinnamic acid contains cis and trans forms; hence, two types of acids are generated. This is called Perkin reaction.

Mechanism of Perkin reaction is as follows :

(i) The potassium acetate is a strong base and abstracts acidic $\alpha$-proton from acetic anhydride.


(ii) The negatively charged carbanion attacks the carbon of carbonyl group of benzaldehyde.



(iii) The intermediate formed undergoes rearrangement


(iv) Loss of proton from $\alpha$-carbon gives cinnamic acid



(v) Depending upon the orientation of carboxylic functional group cis and trans cinnamic acid are formed.