Selective transfer dehydrogenation of aromatic alcohols on supported palladium

Abstract

Transfer dehydrogenation of various alcohols has been investigated over heterogeneous palladium catalysts using olefins as hydrogen acceptors. Pd/Al₂O₃ together with cyclohexene is the most active and selective system, affording a simple and convenient laboratory synthesis of aromatic ketones in refluxing cyclohexane. Hydrogenolysis-type side reactions can be suppressed by minute amounts of a tertiary amine (selective poisoning of Pd). Aliphatic and cycloaliphatic alcohols are barely reactive under these conditions, a difference which offers the possibility of the selective transformation of aromatic alcohols even in the presence of an aliphatic OH group.