REDUCTION OF ACETOPHENONES OVER PD ALPO4 CATALYSTS - LINEAR FREE-ENERGY RELATIONSHIP (LFER)

We studied the reduction of variously substituted acetophenones over Pd/AlPO4, Pd/AlPO4-SiO2, and Pd/SiO2 catalysts containing 3% Pd by weight. After the catalysts were characterized texturally and kinetically, they were used to reduce the different acetophenones at various temperatures under the same reaction conditions. The results correlate with the Hammett equation quite well, and the reaction was found to feature different sensitivity to electron-withdrawing (0.05 < ρ < 0.20) and electron-releasing substituents (0.76 < ρ < 1.37). On the other hand, a compensating effect was also found to occur, so the reaction mechanism can be assumed to be the same for every substrate. The reductions probably do nat take place via enol forms of the acetophenone. The reaction rate decreases with increasing solvent polarity. © 1993 Academic Press, Inc.