The Perkin reaction is an organic reaction developed by English chemist William Henry Perkin in 1868 that is used to make cinnamic acids.

It gives an α,β-unsaturated aromatic acid or α-substituted β-aryl acrylic acid by the aldol condensation of an aromatic aldehyde and an acid anhydride, in the presence of an alkali salt of the acid.

[1][2] The alkali salt acts as a base catalyst, and other bases can be used instead.

[4][5][6] Clear from the reaction mechanism, the anhydride of aliphatic acid must contain at least 2 α-H for the reaction to occur.

The above mechanism is not universally accepted, as several other versions exist, including decarboxylation without acetic group transfer.