Aldol condensation of benzaldehyde with heptanal using solid-supported caesium and potassium catalysts

Abstract

In this work, the possibility of using different heterogeneous basic catalysts in the aldol condensation of benzaldehyde and heptanal was tested. The solid basic catalysts were magnesium and calcium oxide, and different zeolites (HY, NaY, USY). Other catalysts were prepared – caesium-modified zeolites and MCM-41 and potassium-modified alumina. The basic properties of the used catalysts were studied using acid–base titration and temperature programmed desorption of carbon dioxide. Several techniques (UV-Vis and infrared spectroscopy, X-ray diffraction, nitrogen physisorption) were used to characterise the catalysts. These catalysts were used in the aldol condensation of benzaldehyde and heptanal, to test the influence of catalyst type, solvent, ratio of reactants and temperature on the course of reaction. Caesium and potassium leaching from catalysts was also monitored using atomic absorption spectroscopy. The best results were obtained using magnesium oxide (96% heptanal conversion, 68% selectivity to jasmine aldehyde), but all caesium- or potassium-modified catalysts showed reasonable results as well (caesium-MCM-41 40% heptanal conversion, 31% selectivity to jasmine aldehyde; potassium-alumina 62% heptanal conversion, 34% selectivity to jasmine aldehyde).