Electrocatalysis reaction shuttles halides from molecule to molecule

Vicinal dihalides—molecules that feature halogen atoms on adjacent carbons—are useful as flame retardants, as pesticides, and as intermediates en route to polymers and pharmaceuticals. But making these molecules typically requires hazardous chlorine or bromine. Now, chemists led by Bill Morandi at the Swiss Federal Institute of Technology (ETH), Zurich, and Siegfried R. Waldvogel at Johannes Gutenberg University report an electrocatalytic method for making vicinal dihalides from other vicinal dihalides (Science 2021, DOI: 10.1126/science.abf2974). The method zaps simple vicinal dihalides, including 1,2-dibromoethane, 1,1,1,2-tetrachloroethane, and 1,2-dichloroethane, between two graphite electrodes in the presence of an alkene, shuttling two halides from the simple molecule to the more complex one (example shown). Because the reaction also works in reverse, chemists could use it to recycle vicinal dihalide waste. For example, Morandi, Waldvogel, and coworkers take soil contaminated with the persistent pollutant lindane, a cyclohexane molecule with a chlorine on each carbon that was once used as a pesticide, and electrocatalytically transform it into benzene and simple vicinal dihalides. They perform the transformation directly on contaminated soil, showing that the shuttling reaction tolerates biological and mineral impurities that might be present in the soil.