Reduction of polyfluorinated compounds

Reduction of perfluoroalkylphenylcyanides and perfluorodecalin was investigated by cyclic voltammetry and interpreted by intramolecular dissociative electron-transfer models, taking into account the dependence of the diffusion coefficient on the molecular volume of the substrate. In both cases, reduction is governed by the first electron transfer and the following chemical reaction corresponding to F- expulsion. In the case of perfluoroalkylphenylcyanides, at the first reduction stage, one electron is exchanged for each fluorinated carbon atom. For perfluorodecalin, the first stage involves a transfer of four electrons, leading to the formation of a diene, in agreement with literature data on the electrochemical behavior of fluorinated olefins. Comparison of the different parameters obtained (standard reduction potentials and cleavage rate constants) with existing thermodynamic values allows us to observe the effect of lowering the C-F bond dissociation energy on the cleavage rate constant when going from primary to tertiary fluorinated carbon atoms. Moreover, deviations from the existing model become more important when the number of electron-withdrawing groups increases, indicating interactions between the radical and fluoride ion fragments. In the special case of perfluorodecalin, the slowness of the electron transfer could be attributed to the nature of the sigma* orbital that receives the extra electron.