Reduction by hydrogen transfer processes, II. Reduction of substituted derivatives of benzaldehyde

Abstract

In the present paper, date are reported on transfer hydrogenation of aromatic aldehydes with commercial and synthetic Pd catalysts, based on SiO2−AlPO4 (20∶80 mass). Cyclohexenes and α,β-unsaturated alcohols have been tested as hydrogen donors. The reaction products obtained upon reduction of benzaldehyde were benzyl alcohol and toluene (hydrogenation) and benzene and formaldehyde (hydrogenolysis), while methyl, ethoxycarbonyl and hydroxyl groups also present are not affected by the reaction. The selectivity towards each product depends on both the hydrogen donor and the catalyst used. When electron-donor substituents exist on the substrate, a decrease of the reaction rate towards the hydrogenolysis products is observed.