Aerobic liquid-phase oxidation of metal loporphyrins p-xylene over

The five metalloporphyrins (T(p-Cl)PPM, M = Fe, Mn, Co, Cu, Zn) with different metal nuclei were synthesized, and their catalytic aerobic liquid-phase oxidations of p-xvicne into p-toluic acid, p-toluic aldehyde and terephthalic acid using a low concentration of acetic acid as solvent without any halide additives, were studied. The p-xylene conversions and the oxidation product distributions were found to be affected by the structures and concentration of the metalloporphyrins as well as the reaction parameters such as time, temperature and air pressure. The formation of some intermediate oxidation products in the oxidation process also influenced the reaction conversions and the product distribution. Among the metalloporphyrins used, tetrakis(p-chlorophenylporphinato)manganese chloride (T(p-Cl)PPMnCl) was, the most efficient catalyst for the oxidation of p-xylene. Under the conditions of 180 degrees C and 2.0 MPa, 44% conversion of p-xylene and 85% selectivity of p-toluic acid were obtained. Based on the results obtained, a preliminary mechanism of the oxidation of p-xylene over metalloporphyrins was proposed. Copyright (C) 2007 Society of Porphyrins & Phthalocyanines.