The preparation of methacrolein by Mannich reaction using a bifunctional heterogeneous catalyst

Methacrolein is an important intermediate in the fine chemical industry, and its synthesis has garnered significant attention from researchers. In this study, sixteen bifunctional heterogeneous catalysts (designated as PILCN-x) were synthesized. The activity of the catalyst was evaluated based on the synthesis of methacrolein from formaldehyde and propionaldehyde, with PILCN-II identified as the most effective catalyst. The optimal catalyst PILCN-II was characterized by FT-IR, SEM, BET, 1 H NMR, 13 C NMR, XPS and TGA. The effects of various reaction conditions, including solvent, acid, and reaction temperature, on catalytic performance were investigated in detail. The results showed that the optimum reaction conditions were as follows: DMF was used as the solvent; the catalyst dosage was 0.85 g; the formaldehyde/propionaldehyde molar ratio was maintained at 1:1; the reaction temperature was 70 °C; and the reaction time was 50 min. Under the optimal reaction conditions, the conversion rate of propionaldehyde was up to 99.09 %, and the yield of methacrolein was 98.70 %. Notably, after 5 reaction cycles, the catalytic activity of PILCN-II did not decrease significantly. In order to determine the reaction conditions more accurately, the response surface methodology was used, and the fitting results were in good agreement with the experimental results. Finally, kinetic studies showed that the reaction catalyzed by PILCN-II followed quasi-first-order kinetics.