Conversion of Syringaldehyde to Sinapinic Acid through Knoevenagel-Doebner Condensation

Sinapinic acid is a widespread compound in vegetable material and is as such common in the human diet. Recently it has drawn attention because of its biological activities. Sinapinic acid can be synthesized from syringaldehyde via the Knoevenagel-Doebner condensation. However this reaction is limited by the formation of 4-vinylsyringol after a second decarboxylation. To gain more detailed information about this reaction and to improve control over the formation of sinapinic acid, the concentration time history of syringaldehyde and the reaction products of this reaction have been monitored over time at different reaction temperatures. The formation of 4-vinylsyringol was found to be inhibited by performing the reaction at temperature below 80°C. This allows the reaction to be optimized for the production of sinapinic acid, with an optimal yield of 78% after 2.5 hours at 70°C.