Green synthesis of α-methylcinnamaldehyde via Claisen-Schmidt condensation of benzaldehyde with propanal over Mg–Zr mixed oxide supported on HMS

Abstract

α-Methylcinnamaldehyde (2-methyl-3-phenyl-propen-2-al) is used in a variety of products such as balsamic compounds, cosmetics, flavors, perfumes, chewing gums, spice blends, soaps, mouth wash, detergents, shampoos and also as an intermediate for making the drug epalrestat. In this work, it was synthesized by Claisen-Schmidt condensation of benzaldehyde with propanal using supported solid bases as catalysts. Different mole ratios of magnesium to zirconium (1:1, 2:1 and 3:1) were used for Mg-Zr mixed oxide and loaded on hexagonal mesoporous silica (HMS). The catalysts were thoroughly characterized using FT-IR, TG–DSC, TPD, XRD, SEM-EDX, TEM and pore size analysis. 20% (w/w) Mg-Zr (2:1)/HMS catalyst was the best among all studied materials. The catalyst was thermally stable, active and selective. Benzaldehyde to propanal mole ratio of 1:1.5 at 443 K leads to 71% of benzaldehyde conversion and 92% selectivity of α-methylcinnamaldehyde on 20% (w/w) Mg-Zr (2:1)/HMS which exhibits bi-functional character. A mechanism was proposed and kinetics derived using experimental data. The reaction obeys second order kinetics with apparent activation energy of 9.54 kcal/mol.