Reductive cleavage of carbon–chlorine bonds at catalytic and non-catalytic electrodes in 1-butyl-3-methylimidazolium tetrafluoroborate

Abstract

Dissociative electron transfer (DET) to a series of organic chlorides at glassy carbon (GC), silver and copper electrodes has been studied in 1-butyl-3-methylimidazolium tetrafluoroborate. The overall results of this study show that the ionic liquid behaves like molecular solvents such as acetonitrile and dimethylfomamide. It is found that aromatic chlorides follow a stepwise mechanism, whereas concerted electron transfer/bond cleavage is the preferred reaction mechanism for alkyl and benzyl chlorides. Ag and Cu show catalytic effects only when the DET follows a concerted mechanism, but Ag proves to be a much better electrocatalyst than Cu. A series of substituted benzyl chlorides (Z-C₆H₄CH₂Cl, Z = H, 3-OCH₃, 3-F, 4-Cl, and 3-CF₃) show interesting results providing some insight into the reaction dynamics. The process occurs by a concerted mechanism and, albeit a constant standard potential for the whole series, E_p on GC and Cu, which does not show catalytic activity, is significantly affected by the substituents. In contrast, Ag shows good catalytic activity and, as expected, E_p does not change with the substituent. This difference in behavior may be rationalized by considering ion–dipole interactions between R˙ and Cl⁻ as opposed to adsorption of the fragments on the electrode surface.