Condensation of an aromatic aldehyde with acid anhydride in presence of sodium salt of the acid from which anhydride is derived to form α, β-unsaturated acid is known as Perkin reaction.
(a) \(\underset {Benzaldehyde}{C_6H_5CHO\\}\,+\,\underset {Acetic\,anhydride}{(CH_3CO)_2O\\}\,\xrightarrow [180°C]{CH_3COONa}\)
\(\underset{Cinnamic\,acid}{C_6H_5CH=CHCOOH\\}\)
Note that in the second example it is the α-carbon atom of the propionic anhydride that reacts with the aldehydic group.
