Dynamic behavior of basic sites of MgO in Tishchenko reaction

Tishchenko reaction of benzaldehyde was carried out over the MgO whose surface O atoms were enriched with 18O to examine whether the surface O atoms of MgO are incorporated into the product and reactant. The surface lattice 18O atoms were incorporated in both the product and reactant. The 18O concentration was significantly higher for the product than for the reactant. In addition, the 18O in the product ester was located not only in the carbonyl group (Cdouble bond; length as m-dashO) but also in the bridging position (Csingle bondOsingle bondC); 18O exchange between benzaldehyde and MgO surface occurred not only in the adsorption–desorption of benzaldehyde, but also in the dimerization process. The oxygen exchange results in the migration of active sites of coordinative unsaturated site (CUS) over the surface of MgO catalyst during the reaction.