PURPOSE: To obtain the titled compound useful as an antioxidant, etc., quantitatively, at a low temperature, in high selectivity, by dissolving o-tert-butylphenol in a specific solvent to a specific low concentration, and oxidizing the compound with O2 in the presence of a catalyst such as cuprous chloride.

CONSTITUTION: o-ter-Butylphenol is dissolved in a nitrile such as acetonitrile, benzonitrile, etc. or in a mixture of the nitrile and a lower aliphatic alcohol such as methanol, ethanol, etc. or a lower aliphatic ester such as methyl acetate, ethyl acetate, etc., to a concentration of ≤20g/1, preferably ≤5g/1, and is made to react with O2 under the O2 partial pressure of 2W100kg/cm2 at -20W +20°C in the presence of CuCl or CuBr catalyst to obtain the objective compound. The solvent is preferably a mixture of a nitrile and an alcohol or an ester to achieve high selectivity.

USE: Intermediate for the production of tert-butylhydroquinone, etc.