Quinones Electrochemistry in Room-Temperature Ionic Liquids

The two-step electrochemical reduction of tetrachloro-1,2-benzoquinone (chloranil), 2-methyl-1,2-benzoquinone (toluquinone), and 9,10-anthraquinone in two room-temperature ionic liquids is addressed by means of voltammetry on a platinum electrode. For the subsequent quinone/radical anion (Q/Q•−) and radical anion/dianion (Q•−/Q2−) redox reactions, the experimental data on formal potentials in 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and literature data for the same reactants in various aprotic molecular solvents are considered in the framework of a common potential sequence (Fc+/Fc scale) and compared with solvation energies computed at various levels. For the Q/Q•− couple, the agreement appeared to be satisfactory when solvation is described at the polarized continuum model (PCM) level. In contrast, for the Q•−/Q2− couple, the account for specific solvation at the molecular level is crucial.