Voltammetric investigation of the dissociative electron transfer to polychloromethanes at catalytic and non-catalytic electrodes

• Published in: Electrochimica acta Vol. 54; no. 12; pp. 3235 - 3243
• Main Authors: Isse, Abdirisak Ahmed, Sandonà, Giancarlo, Durante, Christian, Gennaro, Armando
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 30.04.2009; Elsevier
• Subjects: Carbene; Carbon–halogen bond; Chemistry; Electrocatalysis; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions; Polychloromethanes; Silver cathode; Electrocatalysis; Carbene; Silver cathode; Carbon–halogen bond; Polychloromethanes; Carbon tetrachloride; Electron transfer; Voltammetry; Electrode material; Electrodes; Chemical reduction; Dehydrochlorination; Chlorocarbon; Electrochemical reaction; Chloroform; Cathode; Organic perhalocompound; Transition metal; Carbon; Carbon-halogen bond; Silver; Organic solvent; N,N-Dimethylformamide; Organic free biradical; Dichloromethane; Glassy state
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2008.12.034

The electrochemical behavior of CCl 4, CHCl 3 and CH 2Cl 2 has been investigated by cyclic voltammetry at glassy carbon and silver electrodes in DMF + 0.1 M Et 4NClO 4 in the absence and presence of a good proton donor. At both electrodes, each compound exhibits a series of reduction peaks which represent sequential hydrodechlorination steps up to methane. The nature of the electrode material and the proton availability of the medium affect drastically the voltammetric pattern of the compounds. Silver exhibits extraordinary electrocatalytic properties toward the reduction process, with positive shifts of the peak potentials of about 0.57–0.95 V as compared to glassy carbon. Reduction of any polychloromethane, CH n Cl (4− n) ( n = 0–2), yields the carbanion CH n Cl (3− n) − which partitions into two reaction channels: (i) protonation and (ii) Cl − elimination to give a carbene :CH n Cl (2− n) . If a strong proton donor is added into the solution, sequential hydrodechlorination becomes the principal reaction route at both electrodes. When, instead, purposely added acid is not present in solution, both reaction pathways ought to be considered. In these conditions, when possible, self-protonation reactions play an important role in the overall reduction process.