Development of oxidation system with molecular oxygen catalyzed by N-hydroxyphthalimide (NHPI)

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N-Hydroxyphthalimide (NHPI) was found to be an efficient catalyst for the aerobic oxidation of various alkanes to the corresponding oxygen-containing products such as alcohols, ketones, and carboxylic acids. The oxidation of cyclohexane catalyzed by NHPI combined with a trace amount of transion metal salt such as Mn (acaca)_2 produced adipic acid in good yield. Isobutane was also oxidized by the use of NHPI and Co (acac)_2 as catalyst to give t-butyl alcohol.Furthermore, the selective oxidation of alkylbenzenes such as toluene and xylene were successfully achieved under normal pressure and temperature. For instance, the oxidation of toluene with dioxygen in the presence of catalytic amount of NHPI and Co (OAc)_2 in acetic acid at room temperature for 20 h formed benzoic acid in 81% selectivity at 84% conversion. Although the oxidation of alkylbenzenes has been so far operated under relatively severe reaction conditions, higher temperature (150ﾟC) and oxygen (or air) pressure (5-10 atm), the NHPI-catalyzed oxidation system is expected to provide a new methodology in the oxidation processes and promises to enhance commercial potentialities by the achievement of oxidation under ambient conditions.