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Ethylbenzene Oxidation to its Hydroperoxide in the presence of N Hydroxyimides and Minute Amounts of Sodium Hydroxide
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•
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.The authors acknowledge Repsol-YPF and Spain’s Ministry of Science and
Education (projects FIT-320100-2006-88 and PSE-310200-2006-2) for their financial
support.Peer reviewe