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Determination of the kinetic and activation parameters for the electro-oxidation of N,N,N', N'-tetramethyl-p-phenylenediamine (TMPD) in acetonitrile (ACN) by chronocoulometry and other electrochemical techniques

1990; Elsevier BV; Volume: 283; Issue: 1-2 Linguagem: Inglês

10.1016/0022-0728(90)87394-y

2590-2954

Héctor Fernández, Marı́a Alicia Zón,

Electrochemical sensors and biosensors

The heterogeneous electron exchange between N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and its mono-cation radical (TMPD.+) has been studied at platinum and glassy carbon electrodes in acetonitrile solutions containing supporting electrolytes of different natures and concentrations. Formal potentials, diffusion coefficients and formal rate constants were evaluated at different temperatures mainly by chronocoulometry, but also by semi-integration of voltammograms, by the classical Nicholson Ψ-ΔEp method and by a new method recently developed by us. Entropies of solvation of the mono-cation radical as well as activation parameters for the electron-transfer reaction were obtained. The experimental activation Gibbs energy for electron transfer was found to agree satisfactorily with the theoretical value calculated considering that the image interaction of the reactant with the electrode can be neglected and that the reacting particle can be approximated by an ellipsoid with semi-axes a >b >c. The inner reorganization energy has to be considered for the best fit between experimental and theoretical activation Gibbs energies. Values of the pre-exponential and exponential factors lower than those predicted by theory were found when the temperature-dependent longitudinal relaxation time expression in the “encounter pre-equilibrium” model was used.