The electrochemical reduction of 1,4-benzoquinone in 1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)-imide, [C2mim][NTf2]: A voltammetric study of the comproportionation between benzoquinone and the benzoquinone dianion

The two-step electrochemical reduction of 1,4-benzoquinone, BQ was investigated on a microdisk electrode (10 mu m diameter Au) in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)-imide, [C(2)mim][Tf-2], over a wide range of scan-rates. Two reduction peaks were observed, corresponding to the reduction of BQ to the radical anion, BQ(center dot-), at a peak potential, E-p, of approximately -0.50 V. followed by reduction to the dianion, BQ(2-) at more negative potentials (E-p approximate to -0.89 V): BQ + e(-) reversible arrow BQ(center dot-) BQ(center dot-) + e(-) reversible arrow BQ(2-) The technique of potential step chronoamperometry was used to measure the diffusion coefficients of each of the three reaction species, BQ BQ(center dot-) and BQ(2-), and values of 4.73 (+/- 0.10) x 10(-11), 1.73 (+/- 0.08) x 10(-11) and 1.55 (+/- 0.15) x 10(-11) m(2) s(-1) were determined, respectively, at 298 K. This technique, together with cyclic voltammetric simulations, allows elucidation of the kinetic and thermodynamic parameters for both reduction processes and the following homogeneous comproportionation process: BQ(2-) + BQ reversible arrow 2BQ(center dot-) including the Gibbs energy, Delta G degrees(comp), for the reaction, where a value of -38.3 kJ mol(-1) suggests that the comproportionation of BQ(2-) and BQ to form BQ(center dot-) is thermodynamically downhill. (C) 2010 Elsevier B.V. All rights reserved.