Ion-Transfer Voltammetry at Fluorous Ether | Water Interfaces

Fluorination Effect on the Gibbs Transfer Energy for Methylene Group from 1,2-Dichloroethane or 1,1,1,2,3,4,4,5,5,5-​Decafluoropentane to Water

The ion-transfer reactions of alkyl and perfluoroalkyl carboxylate ions (CH₃(CH₂)_n-2COO^- and CF₃(CF₂)_n-2COO^-) at 1,2-dichloroethane (DCE) | water (W) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (DFP) | W interfaces were investigated. These ions gave reversible or quasi-reversible voltammetric waves due to their ion transfer across the interfaces, and the formal potentials and the formal Gibbs transfer energies from a non-aqueous solvent to water, ΔG°^'_tr,α→W (α = DCE and DFP), were determined. The ΔG°^'_tr,α→W for CH₃(CH₂)_n-2COO^- and CF₃(CF₂)_n-2COO^- linearly increased with n, allowing for estimating ΔG°^'_tr,α→W for methylene groups. The estimated value of ΔG°^'_tr,DCE→W for the -CH₂- group was higher than that of ΔG°^'_tr,DCE→W for the -CH₂- group, whereas the ΔG°^'_tr,DCE→W for the -CF₂- group was lower than that of ΔG°^'_tr,DCE→W for the -CF₂- group, indicating that the -CH₂- (or -CF₂-) group is more favorably (or unfavorably) solvated in the DCE phase compared to the DFP phase. From the estimated values, the fluorination effect of alkyl chains on partitioning the alkyl group between the biphase media has also been discussed.

A Theoretical Approach to the Fluorophilicity of Ions via the Gibbs Energy of Ion Transfer at the Fluorous Solvent/Water Interface

The non-Bornian solvation model has been applied to a theoretical consideration of the Gibbs free energy for the transfer of fluorinated anions, non-fluorinated cations, and non-fluorinated anions at the 2H,3H-decafluoropentane (DFP)/water (W) and 1,2-dichloroethane (DCE)/W interfaces. According to our previous experimental results, the fluorinated anions are more stable in DFP than DCE, while the non-fluorinated cations and anions are less stable in DFP. To understand this characteristic feature of DFP, energy decomposition analyses have been performed for the hypothetical transfer of ions at the DFP/DCE interface. In conclusion, the characteristics of DFP as a fluorous solvent should be explained in terms of the higher repulsive interaction of the solvent molecule with ions, particularly with non-fluorinated ions.