Reduction by oxidation: reduction of electron-deficient aryl halides by the electrochemically mediated oxidation of oxalate Joshua Beeler, Henry S. White, Seyyedamirhossein Hosseini University of Utah, USA Hydrodehalogenation reactions are quintessential in the remediation of harmful environmental pollutants and have also been found to be useful as an intermediate step in organic synthesis. 1,2 However, hydrodehalogenation requires harsh reaction conditions owing to the large bond dissociation energies associated with the cleavage of C–X (X = Cl, Br) bonds (200–450 kJ/mol). 3 Electrochemical hydrodehalogenation, therefore, requires the application of large negative potentials or the use of transition-metal-based electrocatalysis. 4,5 In this work we introduce a new electrochemical method where the redox-mediated oxidation of oxalate is used to reduce aryl halides. Oxidizing oxalate by one-electron results in the liberation of the strongly reducing carbon dioxide radical anion (CO 2 ·– ), which can subsequently reduce electron-deficient aryl halides. 6 Known as “oxidative reduction”, this method represents the case where electrochemical oxidation gives rise to the reduction of a molecule in solution. Mechanistic aspects of hydrodehalogenation by oxidative reduction were examined using cyclic voltammetry, finite difference simulations, and the products obtained from bulk electrolysis. It is assumed that two equivalents of CO 2 ·– participate in the homogeneous reduction of the aryl halide to form the corresponding aryl anion, which is protonated by water to give a hydrogenated product. Thus far, the efficient and selective hydrodehalogenation of electron-deficient aryl halides (chlorides and bromides) has been carried out with high yield and selectivity. References 1. Kametani, T.; Noguchi, I.; Saito, K. Kaneda, S. Chem. Soc. C. 1969 , 2036–2038. 2. Mitoma, Y.; Nagashima, S.; Simon, C.; Simion, A.M.; Yamada, T.; Mimura, K.; Ishimoto, K.; Tashiro, M. Sci. Technol. 2001 , 35 , 4145–4148. 3. Guo, Y.; Yang, L.; Wang, Z. Water Research 2023 , 324 , 119810.Cheng, H.; Scott, K.; Christensen, P.A. Electrochem. Soc. 2003 , 150 , D17–D24.
4. Ke, J.; Wang, H.; Zhou, L.; Mou, C.; Zhang, J.; Pan, L.; Chi, Y.R. Eur. J. 2019 , 25 , 6911–6914. 5. Hendy, C.M.; Smith, G.C.; Xu, Z.; Lian, T. Jui, N.T. Am. Chem. Soc. 2021 , 143 , 8987–8992.
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