Mechanism of Ester Formation from Benzaldehyde over Solid Base Catalysts

The esterification of b6nzaldehyde has been studiedi over solid NaOH, NaOH-SiO2, A120s, SrO2, BaOz, SrO and CaO. The catalytic'activity was found not. only to closely relate with the basic properties, but also to relate, with the acidic proPerties (Fig., 6). lt was o. bserv. ed that two d-hYdrogens of benzyl groups of benzyl benzoate (major product) and benzyl alcohol (miner product) produced by the esterification of ibenzaldehyde-a-at were deuterat. ed. and t-hqt there The catalytic activity was was no hydrogen isotope effect(kH/kD=1, o, 2)(Figs, 1and 2), decreased by the addition of benzoic acid or phenol, but not by. the addition of benzene or cyclohexane' (Figs.3, 4 and 5). Thg amount of benzylE alcohol formed was increased by the addition of aliphatic alcohols (Fig.4). On the basi's of the observed results, it has been concluded that the aetive sites for the esterification are metal bezylates and those for the formation of metal benzylate consist of both basic sites (surface OZ) and Lewis acid sites (Ca2" etc. ). The mechanism of the esterification has been N@discussed in detail and 'c'ompared, with those of Cannizzaro and Tishchenko reaction in homogeneous system,