Selective oxidation of aromatic hydrocarbons over copper complexes encapsulated in molecular sieves

Abstract

The selective, low temperature oxidation of benzene, toluene, ethyl benzene and naphthalene over chloro-and nitro substituted phthalocyanine complexes of copper encapsulated in zeolites X and Y, using molecular oxygen, as well as aqueous H2O2 as the oxidants, has been studied. The integrity of the copper complexes in the supercage of the faujasite zeolites was confirmed by IR, UV-Vis, ESCA and ESR spectroscopic techniques. Computer modelling and quantum chemical energy calculations indicate that the symmetry environment around the copper ions is distorted, from the square planarity in the encapsulated state due to the geometric constraints within the supercage. The copper atom is at the bottom of a “hydrophobic bowl” formed by the phthalocyanine complex. The catalytic efficiency (turnover numbers) of the copper atoms are higher in the encapsulated state compared to that in the “neat” copper phthalocyanines. While benzene was oxidised to phenol, both ring hydroxylation as well as side chain oxidation were observed in the case of alkyl aromatics. Chloro-and nitro substituted complexes of copper, cobalt and iron encapsulated in molecular sieves are promising, selective oxidation catalysts.