Preparation of substituted phenols

摘要

Substituted phenols of the general formula I I where R1, R2, R3, R4 and R5 are each hydrogen or an aliphatic or aromatic hydrocarbon radical, are prepared by dehydrogenating a cyclic alcohol of the general formula II II or a cyclic ketone of the general formula III III where one of the broken lines can be an additional C-C bond, in the gas phase at from 150 DEG to 380 DEG C. over a supported noble metal catalyst, by a process in which the dehydrogenation catalyst used is palladium or platinum on an aluminum spinel carrier, in particular an aluminum spinel which has a BET specific surface area of from 5 to 150 m2/g or, for the dehydrogenation of cyclohexenones, preferably from 10 to 50 m2/g. Particularly suitable aluminum spinels are those which, in addition to aluminum, contain magnesium, zinc, cobalt or nickel. In the novel process, substituted phenols are obtained in high yields and selectivities, and the catalyst has an extremely long life without a significant decrease in activity.