In this paper a preliminary report is presented on studies of the reaction of several commercially important hydroxyphenyl-benzotriazole light stabilizers during AIBN initiated oxidation of cumene in chlorobenzene at 65°C. Each of the compounds studied reacted readily, the rate of reaction depending on the substitution pattern of the phenolic ring. In the case of 5-chloro-2-(3′-tert-butyl-2′-hydroxy-5′-methyl)phenylbenzotriazole, the major product was characterized as the corresponding cumyl-peroxycyclohexa-2,5-dienone. Thermal decomposition of tert-butylperoxycyclohexa-2,5-dienones derived from 2,6-di-tert-butyl-4-methylphenol, 2,4,6-tri-tert-butylphenol, and several hydroxyphenylbenzotriazole light stabilizers is reported. Decomposition by both O-O and C-O bond scission is observed, the CO bond scission mechanism being the major pathway for thermal decomposition of the benzotriazolyl substituted tert-butylperoxycyclohexa-2,5-dienones.