Hydrogenation of alkyl-substituted phenols over nickel and palladium catalysts

The hydrogenation of alkyl-substituted phenols in the liquid phase was studied using supported nickel and palladium catalysts (< 0.02 mm) in stirred reactor. The distribution of hydrogenation products in the final mixture depends not only on the catalyst used, but also on the reactant structure. The palladium catalyst shows higher selectivity with respect to alkylcyclohexanone, formation. Also, the number of alkyl-substituents on the aromatic ring and the steric hindrance of hydroxyl group increases the selectivity of alkylcyclohexanone formation. Products of the hydrogenolytic cleavage were observed during hydrogenations on a nickel catalyst. With the help of molecular modelling (PM3 method) the global energy minima of alkylcyclohexanol isomers were determined. The findings were confirmed by GC-MS, high-energy collision induced decomposition (CID method) and by NMR spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.