Sensitized photooxygenation of 2,6-, 2,4-, and 3,4-xylenols was studied using hypocrellin A as a sensitizer with a high-pressure sodium lamp in methanol and benzene. Dialkylated phenols react with singlet oxygen via 1,4-cycloaddn., followed by a rearrangement to give hydroperoxide or epoxide. The relative and absolute rate constants were determine by competitive inhibition.

Key words: PHENOL, CYCLOADDITION REACTION, REACTION RATE CONSTANT, ANTIOXIDANTS, SINGLET, PHOTOSENSITIZATION OXIDATION, DIMETHYLBENZENE P