PURPOSE: To obtain the title compound useful as an intermediate raw material for pharmaceuticals, agricultural chemicals, etc., or raw material for perfume, with simple operation at a low cost, by using inexpensive diphenylethanes as a raw material and oxidizing the material with oxygen in the presence of an alkali metal hydroxide, etc.

CONSTITUTION: A compound of formula II is produced by oxidizing a compound of formula I (R1WR5 are H or 1W5C alkyl) with oxygen or an oxygen-containing gas in the presence of an alkali metal hydroxide or an alkali metal alkoxide at 100W160°C, preferably in a solvent such as dimethyl sulfoxide. The oxygen partial pressure of the oxygen or the oxygen-containing gas is preferably 1kg/ cm2W20kg/cm2 at room temperature. The reaction is carried out preferably keeping the oxygen partial pressure by replenishing the consumed oxygen during the reaction. The amount of the above basic catalyst is preferably 0.5W4pts.wt. per 1pt.wt. of the compound of formula I.