Selective catalytic aerobic oxidation of substituted ethylbenzenes under mild conditions

Ethylbenzene is oxidized to the corresponding hydroperoxide (PEHP) with high selectivity, under mild conditions, by means of a metal-free catalytic system consisting of an aldehyde and N-hydroxyphthalimide (NHPI). The process occurs via a free radical mechanism by in situ generation of the phthalimido-N-oxyl (PINO) radical. The protocol is applied with success on a wide range of substituted ethylbenzenes (ETBs). The competitive experiments carried out on few couples of ETBs revealed a marked polar effect, this proving the key role that PINO plays as real hydrogen abstracting species, at least at low conversion. At higher conversion, the formation of highly reactive OH radicals from PEHP reduces the differences in the reactivity of selected couples of ETBs. The study of the reaction mechanism, including the investigation on aldehyde and catalyst percentage amounts, and temperature and concentration effects, allows to achieve the final PEHPs products with good yields.

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► We have developed a metal-free catalytic system consisting of an aldehyde and NHPI.
► We have employed the catalytic system for the oxidation of substituted ethylbenzenes.
► We have shown the high selectivity in the hydroperoxide products.
► We have shown the marked polar effect in the presence of the catalytic system.
► We have studied the effect of temperature and catalyst and substrate concentration.