Hydrogenation of Alkyl-Substituted Phenols

Abstract

The review deals with catalytic hydrogenation of alkyl-substituted phenols. Its aim was to summarize general findings from this field of heterogeneous catalysis and to try to formulate general rules describing the effects of various factors on stereoselectivity of the hydrogenation. Nickel and platinum metals rank among the most frequently used catalysts, the palladium catalysts affording the highest yields of alkylcyclohexanones, hydrogenation by-products. Their formation affects the final ratio of cis/trans isomers of alkylcyclohexanols but acids and bases exert the greatest influence. The influence of alkyl substituents, which, in dependence on their bulkiness, promote either the formation of a substituted cyclohexanone or cyclohexanol, cannot be neglected either. The influence of pressure and temperature on the stereoselectivity of hydrogenation of alkyl-substituted phenols is not so pronounced as the influence of the other factors. Although mechanistic studies of hydrogenation of alkyl-substituted phenols are not simple due to consecutive reaction steps, they deserve more attention. The importance of the problem is due to its theoretical and practical aspects.