In an attempt to gain a better understanding of the reduction mechanism of polyhalogenated organic compounds, we have explored in this study the electrochemical reductions of 1-bromo-6-chlorohexane and 1-bromo-6-chlorohexane. Cyclic voltammograms for reduction of 1-bromo-6-chlorohexane in dimethylformamide (DMF) containing 0.050 M tetra-n-butylammonium tetrafluoroborate (TBABF4) show a single cathodic peak at –1.45 V vs. a cadmium amalgam reference electrode.4 In comparison, voltammograms for the reduction of 1-chloro-6-iodohexane in DMF–0.050 M TBABF4 display two cathodic peaks at –0.83 and –1.53 V vs. a cadmium amalgam reference electrode. Controlled-potential (bulk) electrolyses were conducted to reduce 1-bromo-6-chlorohexane in DMF–0.050 M TBABF4 at a silver gauze cathode; calculated n values indicate that the mechanism includes a two-electron cleavage of the carbon–bromine bond to afford 1-chlorohexane as the major product, along with cyclohexane, n-hexane, 1‑hexene, and 1,6-hexadiene as minor species. In contrast, bulk electrolyses of 1-chloro-6-iodohexane indicate that reduction at a potential (–0.95 V) corresponding to the first voltammetric peak is a one-electron process that leads to significant production of a dimer (1,12-dichlorododecane) together with smaller amounts of 1-chlorohexane. On the other hand, electrolysis at a potential (–1.60 V) corresponding to the second voltammetric peak yields completely dehalogenated products in addition to 1,12-dichlorododecane and 1-chlorohexane, via a combination of one- and two-electron processes.
References:
- Peters, D. G.; McGuire, C. M.; Pasciak, E. M.; Peverly, A. A.; Strawsine, L. M.; Wagoner E. R.; Barnes, J. T. J. Mex. Chem. Soc. 2014, 58, 287–302.
- Strawsine, L. M.; Sengupta, A.; Raghavachari, K.; Peters, D. G. ChemElectroChem 2015, 2, 726–736.
- Martin, E. T.; Strawsine, L. M; Mubarak, M. S; Peters, D. G. Electrochim. Acta 2015, 186, 369–376.
- This reference electrode consists of a saturated cadmium–mercury amalgam in contact with DMF saturated with both sodium chloride and cadmium chloride; its potential is –0.76 V vs. SCE at 25°C.