Kinetics and mechanism of the redox reaction of N,N′-phenylenebis-(salicylideneiminato)iron(III) with oxalic acid in mixed aqueous medium

The kinetics of electron transfer between N,N′-phenylenebis-(salicylideneiminato)iron(III), hereafter referred to as [Fe(Salphen)]+, and oxalic acid was studied in mixed aqueous medium (DMSO:H2O; 1:4 v/v) under pseudo-first-order conditions at 26 ± 1 °C, I = 0.2 coulomb2 mol dm−3 (NaCl) and λmax = 435 nm. The reaction was found to be second order overall and acid independent, and displayed zero Brønsted–Debye salt effect. There was no evidence for the formation of an intermediate complex or free radicals during the reaction. Overall, the kinetic data suggest an inner-sphere mechanism for the reaction, which is first order in both reactants. A plausible reaction mechanism is proposed.