Effect of the alkyl chain length of α,ω-dichloroalkane on the Gibbs energy of transfer for functional groups.

Ion-transfer reactions of alkyl and perfluoroalkyl carboxylate ions (CH(CH)COO with n = 8-12 and CF(CF)COO with n = 3-9) were investigated at the polarized Cl-(CH)-Cl with m = 2, 4, 6, and 8 (O) | water (W) interface to evaluate the effects of n and m on the solvation energy of the ions, as well as on their methylene and terminal groups. These ions exhibited reversible or quasi-reversible voltammetric waves due to their transfer across the O | W interfaces, enabling the determination of formal potentials and formal Gibbs transfer energies from O to W, . The values for CH(CH)COO and CF(CF)COO increased linearly with n, allowing the estimation of for methylene and difluoromethylene groups, (CH) and (CF), and for their terminal groups, (COO  + CH) and (COO + CF). Whereas the (CH) and (CF) hardly changed with the variation in m, the (COO + CH) and (COO + CF) decreased noticeably. These results suggest that the solvation energy for ions in Cl-(CH)-Cl increases with m, regardless of hydrophilic or lipophilic nature of the ions. Based on these findings, the advantage of using Cl-(CH)-Cl with a large m as a non-aqueous solvent for ion-transfer voltammetry was discussed.