PURPOSE: An alkylphenol or α-naphthol, which is unsubstituted in the para-position to the hydroxyl group and at least one more position, is used as a starting material to effect the oxidation with an oxygen-containing gas in the presence of a specific catalyst to achieve inexpensive production of the titled substance used as an intermediate of drugs in high yield.

CONSTITUTION: An alkylphenol or α-naphthol, which is unsubstituted in the para- position to the hydroxyl group and at least one more position, is used as a starting material to effect the oxidation with an oxygen-containing gas in an alcoholic solvent in the presence of a catalyst of a combination of a cupric halide with a tertiary alkylamine, preferably at a molar ratio of 0.1W10, preferably 1W 3 amine to the cupric compound, to form the objective compound. The alkylphenol used as a substrate preferably has a bulky alkyl group of 3 or more carbon atoms, especially in the 2-position such as o-t-butylphenol.