The conversion of benzaldehyde into benzyl benzoate with alkaline earth metal oxide catalysts

Abstract

Abstract When benzaldehyde was treated at 120–200 °C over alkaline earth metal oxides, a large amount of benzyl benzoate and a very small amount of benzyl alcohol were found as the reaction products. The time variation of the ester formation gave a S-shaped curve including an induction period. After the induction period, the reaction obeyed the first order rate equation with respect to the concentration of benzaldehyde. The catalytic activity increased in the order of MgO It was observed in the experiment using deuterated benzaldehyde that the two α-hydrogens of benzyl groups of benzyl benzoate and benzyl alcohol formed were deuterated and that there was no kinetic isotope effect for the ester formation ( k H k D = 1.0 ± 0.2 ), whereas the induction period was prolonged. Infrared spectra of the adsorbed benzaldehyde showed the existence of the metal benzylate and benzoate on the surface. It has been concluded that the active species of MgO and CaO for the ester formation are the metal benzylates whose formation is facilitated by both the basic sites (O2−) and acidic sites (Me2+) on the surface. The reaction mechanism was discussed in comparison with the homogeneous base-catalyzed reaction.