Characteristic mechanisms of the homogeneous and heterogeneous oxidation of aromatic amines with transition metal-oxalate complexes

The oxidation-reduction reactions of aromatic amines {o-aminophenol (o-AP), o-phenylenediamine (o-PDA) and p-phenylenediamine (p-PDA)} with Co(III)-, Mn(III)-, and Cu(II)-oxalate complexes have been investigated in homogeneou s and heterogeneous systems. The kinetics of the redox reaction of both sys tems have been studied spectrophotometrically. The redox products were iden tified and characterised by diffuse reflectance spectroscopy (DRS), and mas s spectrometry. The redox reactions follow first-order kinetics with respec t to each of the reactants and first order in [amines] in homogeneous and h eterogeneous (supported complexes on Amberlite IRA 904 anion-exchange resin ) phases, respectively. However, the specific oxidation rate of the amines is found to follow the order, p-PDA > o-AP > o-PDA. The effect of the oxala te anion on the reaction rate of both systems was examined. There is a sign ificant difference in the behaviour of the oxidation of o-AP and o-, p-PDA with all the metal complexes in both systems. Moreover, the oxidation of o- AP and o-, p-PDA appears to follow the outer- and inner-sphere mechanistic classification, respectively. (C) 2000 Elsevier Science Ltd. All rights res erved.