Study of the reaction 1-methoxy-4-(methylthio)benzene + IO4−: importance of micellar medium effects

Abstract

The oxidation of 1-methoxy-4-(methylthio)benzene by IO₄⁻, rendering the corresponding sulfoxide and IO₃⁻, was studied in zwitterionic (SB3-16) and nonionic (Brij₃₅ , Tween 20, Tween 40, Tween 60 and Tween 80) aqueous micellar solutions. The association equilibrium constants of the sulfide molecules to the micellar aggregates present in the different media were obtained by spectroscopic measurements. In the case of the sulfobetaine micellar solutions, the equilibrium constant for the incorporation of periodate anions in the zwitterionic micellar aggregates was obtained through conductivity measurements. Taking into account literature data on this reaction in cationic and anionic micellar solutions, a comparison of the second order rate constants in the micellar pseudophases of nonionic, anionic, cationic and zwitterionic micellar solutions was undertaken. This comparison, together with kinetic data obtained in water–cosolvent mixtures, as well as in aqueous electrolyte solutions, shows that charge–charge interactions and the low polarity of the micellar pseudophases account for the large differences between the second order rate constants in pure water and those in micellar solutions.