Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarboxylate

The MOF Co-BTC (BTC = benzenetricarboxylate) has been synthesized by a hydrothermal method, and characterized by means of N-2 physical adsorption, X-ray diffraction, scanning electron microscope, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The material has multiple crevices, as opposed to a pore structure, and shows high thermal stability, with Co in the divalent state. It has been used in conjunction with N,N-dihydroxypyromellitimide to catalyze the oxidation of p-xylene to terephthalic acid, the reaction conditions for which have been investigated and optimized. At 150 degrees C, with acetonitrile as solvent instead of acetic acid and in the absence of corrosive bromine, the conversion of p-xylene reached 100 % and the selectivity for terephthalic acid exceeded 97 %. Under the optimized conditions, Co-BTC exhibits stronger catalytic activity than cobalt(II) acetate, and maintains excellent stability during the reaction. The reaction mechanism has been deduced, and the roles of N,N-dihydroxypyromellitimide and Co-BTC as synergistic catalysts in the reaction have been clarified.