N-hydroxyimides of the type N-hydroxyphthalimide (NHPI), N-hydroxysuccinimide (NHSI), N-hydroxymaleinimide (NHMI) and N-hydroxynaphthalimide (NHNI) were used in ethylbenzene oxidation with air under soft reaction conditions. The ethylbenzene conversion profile was found to increase almost linearly with time, and the rate of ethylbenzene conversion was the highest in the presence of NHNI. Nevertheless, the selectivity reached in all cases is still far from the values required for industrial application. On the other hand, the hydroperoxide yield increased dramatically with the addition of minute amounts of sodium hydroxide to the reaction mixture. It is worth noting that this increase can be associated to an enhancement in the selectivity to hydroperoxide because, in fact, ethylbenzene conversion slightly decreased with the addition of sodium. Indeed, this behavior is puzzling, because the amount of sodium is very small regarding ethylbenzene (0.005 mol%) and yet its effect is enormous. Finally, a tenfold increase in the concentration of N-hydroxyimide yielded only a slight increase in ethylbenzene conversion, but no improvement in hydroperoxide concentration. This behavior is related to the participation of NO center dot radicals in the formation of by-products (alcohols and ketones) from hydroperoxide. Up to date, the combination of NHPI and NaOH produces the highest hydroperoxide yield reported. (C) 2009 Elsevier B.V. All rights reserved.