Homogeneous Copper(I) Electrocatalyzed Degradation of Ultra-Short and Long-Chain Perfluoroalkyl Substances

While the defluorination of environmentally persistent poly- and perfluoroalkyl substances (PFASs) requires the development of energy-efficient methodologies for complete mineralization, electrochemical CF bond activation remains a fundamental research challenge. Although CF activation chemistry is commonly studied using fluoromethylarenes as substrates, the stronger CF bonds in short-chain perfluoroalkyl carboxylic acids (PFCAs), fluorinated aliphatic alcohols, and fluorotelomers are yet to be explored. Herein, we report a molecular copper(I) complex that activates the CF bonds in trifluoroacetic acid (TFA), 2,2,2-trifluoroethanol (TFE), 2,2-difluoroethanol (DFE), and 2-fluoroethanol (MFE) when a constant reductive current of 6 mA is applied. 99% free fluoride was recovered from MFE after 12 h of electrolysis, which is comparatively higher than that of TFE (∼15%), DFE (19.2%), or TFA (∼14%), and is attributable to the strengths of the CF bonds in these molecules. We also defluorinated four selected PFCAs bearing short-chain CF backbones and terminal trifluoromethyl groups, which are common end products formed by the degradation of toxic perfluoroalkyl substances. In addition, we investigated the defluorination and degradation of two fluorotelomers under ambient conditions. Density functional theory calculations revealed a correlation between the %fluoride recovery and the CF bond dissociation energy of each substrate. Accordingly, we report a rare example of a molecular electrocatalytic system that activates the strong CF bonds in fluoromethylalkyls, including short-chain PFASs, which are typical end products of common PFAS degradation processes.