Acid–base bifunctional magnesium oxide catalyst prepared from a simple hydrogen peroxide treatment for highly selective synthesis of jasminaldehyde

Abstract

ABSTRACT The aldol reaction between benzaldehyde and heptanal for jasminaldehyde synthesis has been widely tested over various heterogeneous catalysts. The reaction is preferred to be conducted over acid-base bifunctional catalyst for high jasminaldehyde selectivity. Generally, Magnesium oxide (MgO) is not considered to be suitable for jasminaldehyde synthesis due to its monobasic property and low jasminaldehyde selectivity. In this work, the MgO sample was treated through a simple hydrogen peroxide reflux-calcination process to create acid-base bifunctional surface. The resulting catalyst afforded high selectivity to jasminaldehyde of 88–90% even at a benzaldehyde to heptanal molar ratio of 5. The mechanism of this high jasminaldehyde selectivity was investigated in this paper, and the results indicate that this novel acid-base bifunctional MgO catalyst is preferential adsorption of benzaldehyde over heptanal, which leads to a higher benzaldehyde: heptanal ratio on its surface. In addition, the presence of weak Lewis acid sites on catalyst’s surface induces a partial positive charge on carbonyl group of benzaldehyde, making it susceptible to a nucleophilic attack by the heptanal carbanion. The reusability of this novel acid-base bifunctional MgO catalyst was also studied.