Metal ion-sulfur(IV) chemistry. 3. Thermodynamics and kinetics of transient iron(III)-sulfur(IV) complexes

Abstract

Stability constants for the formation of Fe(III)-S(IV) complexes at µ = 0.4 M were determined spectroscopically. Values of K_1 = 10^(6.6) M^(-1) for Fe^(3+) + SO_3^(2-) ⇌ FeSO_3^+ and K_4 = 10^(7.3) M^(-1) for FeOH^(2+) + SO_3^(2-) ⇌ HOFeSO_3 were obtained. Raman measurements indicate that sulfite binds to the metal through oxygen. The kinetics of electron transfer between Fe(III) and S(IV) have been studied, and a mechanism is proposed. Kinetic and mechanistic aspects of the Fe(III)-catalyzed autoxidation of S(IV) are discussed in light of these results.