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

Abstract

Salen, saltin and salcyhexen complexes of copper and manganese, encapsulated in the cavities of zeolite NaX have been investigated as catalysts for the aerobic oxidation of para-xylene in the absence of added halogen promoters and using tertiary-butyl hydroperoxide as the initiator at low temperatures. Significant conversion levels (upto 50-60%) are attained. The major products include toluic acid, toluyl aldehyde and toluyl alcohol. The zeolite-encapsulated complexes did not undergo any colour change during the reaction and could be easily separated and reused many times. In contrast, the neat complexes, while they were active in the first cycle, were completely destroyed during the run and changed colour. They, however, gave lower conversions compared to the encapsulated catalysts. Conversion increases when electron-withdrawing substituents (like Cl, Br and NO) are substituted in the aromatic ring.