Catalytic Oxidation of Alkylbenzenes with Molecular Oxygen under Normal Pressure and Temperature by N-Hydroxyphthalimide Combined with Co(OAc)2

Abstract

A practical catalytic method to convert alkylbenzenes into the corresponding carboxylic acids under atmospheric dioxygen at ambient temperature using a combined catalytic system consisting of N-hydroxyphthalimide (NHPI) and Co(OAc)2 was developed. For instance, the oxidation of toluene was completed by NHPI combined with Co(OAc)2 under an oxygen atmosphere at room temperature to give benzoic acid in 81% yield. Under these conditions, o- and p-xylenes were selectively converted into the corresponding monocarboxylic acids without the formation of the dicarboxylic acids. ESR measurements showed that Co(II) species assists in the formation of phthalimide-N-oxyl (PINO), which is a key species in this oxidation, from NHPI.