Chemistry of the oxidation of acetic acid during the homogeneous metal-catalyzed aerobic oxidation of alkylaromatic compounds

Acetic acid is the solvent used for the commercial production of five aromatic acids from polyallcylbenzenes using homogeneous aerobic oxidation. The most important catalysts are mixtures of cobalt(II) and manganese(II) acetates. The co-oxidation of the acetic acid to carbon dioxide and carbon monoxide, denoted COx, is one of the economic disadvantages of the processes. Understanding the chemistry of the oxidation of acetic acid can led to reduction in these greenhouse gases. This paper assembles and summarizes the organic, free-radical and coordination chemistry detailing how the various products from the oxidation of acetic acid form. It is suggested that the initiation of the acetic acid occurs primarily through the thermal decomposition of cobalt(III) acetate. This leads to three families of by-products starting from the oxidation of methanol, succinic acid and glycolic acid. Carbon monoxide forms by decarbonylation of many of these intermediates. Concerted reactions via polynuclear cobalt and manganese complexes provides efficient mechanistic pathways to these intermediates and by-products. The chemistry presented for the oxidation of the acetic acid is consistent with known optimization methods which are used to reduce acetic acid loss. (C) 2011 Elsevier B.V. All rights reserved.