Attractive interactions of alkyl substituents with palladium catalyst in the hydrogenation of cyclohexanones

Abstract

Cyclohexanone and its 4-alkyl-substituted derivatives were hydrogenated over Pd catalyst in cyclohexane solvent both individually and competitively in pairs (cyclohexanone and one of the derivatives). Most of the derivatives were less reactive than cyclohexanone individually, but more reactive competitively. These findings were explained in terms of attractive interactions between Pd and the alkyl substituents. Similar results were obtained on 2- and 3-alkyl-substituted cyclohexanones. The rate of cyclohexanone hydrogenation was different in five different hexane isomers used individually as solvents. This solvent effect was also explicably based on the concept of Pd-alkyl interactions.