Aldol condensation of benzaldehyde with heptanal to jasminaldehyde over novel Mg–Al mixed oxide on hexagonal mesoporous silica

Abstract

A novel calcined hydrotalcite supported on hexagonal mesoporous silica (CHT/HMS) was synthesized and characterized by XRD, TG–DTA, pore size analysis, SEM–EDAX, and TEM. It possesses high thermal stability, high adsorption capacity and large surface area. 20% (w/w) CHT/HMS was highly active and selective in aldol-condensation of benzaldehyde with heptanal. A kinetic model was developed and validated against experimental data. Jasminaldehyde selectivity of 86% was obtained with heptanal to benzaldehyde mole ratio of 1:5 at 150 °C by using 20% (w/w) CHT/HMS. The results are explained on the basis of the bi-functional character of CHT/HMS, where the role of the weak acid sites is the activation of benzaldehyde by protonation of the carbonyl group which favors the attack of the enolate heptanal intermediate generated on basic sites. The catalyst is stable and reusable.