KINETICS AND MECHANISM OF THE REDOX BEHAVIOR OF THE ETHYLENEDIAMINETETRAACETATOFERRATE(III) SULFITE SYSTEM IN AQUEOUS-SOLUTION

The decomposition reaction of [Fe(III)(edta)(SO3)]3- has been studied as a function of total sulfite, [Fe(III)(edta)-], oxygen concentration, pH and temperature using spectrophotometric, potentiometric and ion-chromatographic techniques. The catalysed autoxidation of sulfite is significantly slower for [Fe(III)(edta)]- than for aquated iron(III) ions. The reaction exhibits a strong oxygen dependence, and the participation of oxygenated complexes is suggested to account for this effect. The major redox products are sulfate and [Fe(II)(edta)]2-, which is rapidly reoxidized to [Fe(III)(edta)]- in the presence of oxygen. Various possible redox mechanisms are discussed, and the results are compared to corresponding data for the non-chelated iron(III) system.