Hydrogenation of alkyl-substituted phenols

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 plati num metals rank among the most frequently used catalysts, the palladium cat alysts affording the highest yields of alkylcyclohexanones, hydrogenation b y-products. Their formation affects the final ratio of cis/trans isomers of alkylcyclohexanols but acids and bases exert the greatest influence. The i nfluence of alkyl substituents, which, in dependence on their bulkiness, pr omote either the formation of a substituted cyclohexanone or cyclohexanol, cannot be neglected either. The influence of pressure and temperature on th e stereoselectivity of hydrogenation of alkyl-substituted phenols is not so pronounced as the influence of the other factors. Although mechanistic stu dies of hydrogenation of alkyl-substituted phenols are not simple due to co nsecutive reaction steps, they deserve more attention. The importance of th e problem is due to its theoretical and practical aspects.