DIRECT HYDROXYLATION OF AROMATICS TO THEIR CORRESPONDING PHENOLS CATALYZED BY H-[AL]ZSM-5 ZEOLITE

The direct hydroxylation of benzene and its derivatives with N2O is st udied using H-[Al]ZSM-5 zeolite as catalyst. The activity of the H-[Al ]ZSM-5 zeolite is increased by hydrothermal treatment. This treatment dealuminates the zeolitic framework and creates Lewis acidic extra fra mework alumina (EFA) which controls the catalytic activity. It is show n by Al-27 MAS NMR and IR measurements that the degree of dealuminatio n correlates with the amount of EFA species formed and the yield of ph enol obtained. Simple calcination of the H-[Al]ZSM-5 zeolite for a lon ger time (18 h/550 degrees C) increases the selectivity whereas conver sion remains unchanged. Furthermore, benzene derivatives, naphthalene and biphenyl were used as substrates in the direct hydroxylation with N2O. The selectivity to the corresponding phenols is lower than in the case of benzene because the functional groups participate in the reac tion mechanism. No correlation is found between the activation or deac tivation of the aromatic ring by the functional group and the yield of the corresponding hydroxylated product. In case of naphthalene and bi phenyl the yield is limited by substrate decomposition. (C) 1998 Elsev ier Science B.V. All rights reserved.