Immobilized zinc acetate complex on the surface of silica-alumina gel modified by succinic acid: an efficient catalyst for the esterification of DMT

The immobilization of a zinc acetate complex on the surface of silica-alumina gel, chemically modified with succinic acid, and its catalytic activity in the reaction of esterification of dimethyl terephthalate with ethylene glycol, are presented in this study. A unidentate bonding mode is observed between the succinic acid and the hydroxyl groups of the silica-alumina sol. The immobilization of the zinc acetate on the treated silica-alumina sol surface was accomplished via unidentate bonding between the free succinic acid hydroxyl group and the acetate group of the zinc acetate complex, giving rise to a surface compound very close in structure to that of the pure complex. The catalytic activity of the silica-alumina gel-succinic acid zinc acetate catalyst is slightly higher than that of the homogeneous zinc acetate catalyst. The mixed gel catalyst can be easily separated from the reaction product and reutilized during various catalytic cycles.