Organic electron-transfer reactions: complex kinetics in the thermal back reaction of 2,6- and 4,6-disulfonated leucothionine with ferric ion

Abstract

The kinetics of the oxidation with ferric ion of 2,6-and 4,6-disulfonated leucothionines has been examined by stopped-flow techniques. Ortho-sulfonation of the dye form of thionine (D) has led to complex kinetics that can be interpreted in terms of association or ion-pair formation between ferric ion and the fully reduced leuco form (L) of the dye. The resulting effect is that association of the reagents, instead of facilitating the oxidation of L, becomes a trap since the final stages of the oxidation are a relatively slow process. Return to the colored form D is viewed to take place mostly by electron exchange between nonassociated species. The behavior of