Oxidation of para-xylene over zeolite-encapsulated copper and manganese complexes

Salen, saltin and salcyhexen complexes of copper and manganese, encapsulate d in the cavities of zeolite NaX have been investigated as catalysts for th e aerobic oxidation of para-xylene in the absence of added halogen promoter s and using tertiary-butyl hydroperoxide as the initiator at low temperatur es. Significant conversion levels (upto 50-60%) are attained. The major pro ducts include toluic acid, toluyl aldehyde and toluyl alcohol. The zeolite- encapsulated complexes did not undergo any colour change during the reactio n and could be easily separated and reused many times. In contrast, the nea t complexes, while they were active in the first cycle, were completely des troyed during the run and changed colour. They, however, gave lower convers ions compared to the encapsulated catalysts. Conversion increases when elec tron-withdrawing substituents (like Cl, Br and NO2) are substituted in the aromatic ring. (C) 1999 Elsevier Science B.V. All rights reserved.