Rotating-disc electrode kinetic studies of the electron-transfer reactions of tetrathiofulvalene and its mono-and di-cations in aqueous/micellar media

Abstract

Electrochemical studies of tetrathiofulvalene (TTF) in aqueous/CTAC micellar solution, comprising cyclic voltammetry and rotating-disc kinetic studies, provide a variety of both thermodynamic and kinetic information concerning the system. In addition to the usual redox equilibria and electron-transfer kinetic data, obtained from electrochemical measurements, data regarding the phase distribution and kinetics of phase exchange is derived. It is found that TTF is predominantly solubilized in the micellar phase, with a micelle/solubilizate association equilibrium constant, K M ∼8×10 5 M −1, and undergoes rapid phase exchange with rate constants for micelle exit and entry, k out∼7×10 3 s −1 and k in∼5×10 9 M −1 s −1, respectively. On the other hand, the mono- and di-cations of TTF are solubilized predominantly in the aqueous phase. Oxidation of the micellar TTF species to its aqueous cation radical proceeds via the species in the aqueous phase and is preceeded by exit of TTF species in the reaction layer close to the electrode surface. No direct electron transfer between the electrode and micellar species is apparent. The homogeneous solution reaction of TTF with its electrochemically generated dication to form the monocation, TTF+TTF 2+ ag2TTF +, was also studied and, like the heterogeneous electron-transfer reaction of TTF, is found to proceed predominantly via species in the aqueous phase.