Mechanistic studies of catalytic Stobbe condensation

We report here the results of a series of mechanistic investigations of the condensation reaction between formaldehyde and dimethyl succinate, performed under catalytic conditions. The objective of the project was to understand the reaction pathway towards the final product, citraconic anhydride. To investigate the reaction course we performed a series of experiments using deuterium-labeled compounds such as CH₃OD, CD₂O and CD₃OCOCH₂CH₂COOCD₃. The hydrogen-deuterium exchange was monitored using mass spectrometry techniques. The experiments were performed in the vapor phase, at atmospheric pressure and high temperatures, using γ-alumina as the catalyst. Our results indicated that the reaction is catalyzed by the acidic sites on the alumina surface. Also, unexpected hydrogen-deuterium exchange between the reacting species was detected. Mechanistic routes for the condensation reaction and for the hydrogen-deuterium exchange processes are proposed.