Oxidation of cyclohexane over copper phthalocyanines encapsulated in zeolites

Abstract

The oxidation of cyclohexane to cyclohexanol, cyclohexanone and adipic acid has been studied using phthalocyanines and substituted (chloro- and nitro-) phthalocyanines of copper, cobalt and iron encapsulated in zeolites X and Y, at ambient conditions and using molecular oxygen as well as alkyl (tertiary butyl, cyclohexyl and cumyl) hydroperoxides as the oxidants. The catalytic efficiencies of the encapsulated materials are much higher than those of the neat complexes. The rate of oxidation of cyclohexane using copper hexadecachloro phthalocyanine- encapsulated Y zeolite catalysts is quite high (TOF=400 h⁻¹) with TBHP efficiencies which can reach upto 90%. The isolated encapsulated metal complex is the active site. Solvents exert a major influence on product distribution (cyclohexanol, cyclohexanone and adipic acid are the major products). Byproducts like succinic and glutaric acids are not formed when using acetonitrile as the solvent. Rates of oxidation when using the alkyl hydroperoxides as oxidants decrease with an increase in their molecular cross-section (cyclohexyl > t-butyl > cumyl) confirming that the active site is indeed located inside the zeolitic cavities and not on the external surface.