Influence of mixed sulfur–nitrogen oxides on the redox kinetics of iron ions in aqueous solution

The influence of mixed sulfur–nitrogen oxides on the redox chemistry of iron-(III) and -(II) species in aqueous solution was studied kinetically as a function of various concentrations. Two oxides, viz. HONH(SO3)– and HON(SO3)22–, were found to reduce FeIII to FeII, whereby these oxides undergo an iron(III)-induced hydrolysis reaction. The hydrolysis products were analysed by ion chromatography. These redox reactions can in principle account for the inhibiting effect of sulfur–nitrogen oxides on the metal-catalysed autoxidation of sulfur(IV) oxides. Possible reaction mechanisms are suggested.