Analytical Sciences

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

Kohei UEMATSU,* Junpei YAMAGATA,* Hiroki SAKAE,* Hajime KATANO,* and Toshiyuki OSAKAI**

*Department of Bioscience and Biotechnology, Fukui Prefectural University, Eiheiji, Fukui 910-1195, Japan
**Department of Chemistry, Kobe University, Nada, Kobe 657-8501, Japan

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.

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