Applicability of a fluorous solvent 1,1,1,2,3,4,4,5,5,5-decafluoropentane for the non-aqueous medium in liquid-liquid electrochemistry

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 (CH3(CH2)n-2COO- with n = 8-12 and CF3(CF2)n-2COO- with n = 3-9) were investigated at the polarized Cl-(CH2)m-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, Δ G tr,O → W 0 ' . The Δ G tr,O → W 0 ' values for CH3(CH2)n-2COO- and CF3(CF2)n-2COO- increased linearly with n, allowing the estimation of Δ G tr,O → W 0 ' for methylene and difluoromethylene groups, Δ G tr,O → W 0 ' (CH2) and Δ G tr,O → W 0 ' (CF2), and for their terminal groups, Δ G tr,O → W 0 ' (COO-  + CH3) and Δ G tr,O → W 0 ' (COO- + CF3). Whereas the Δ G tr,O → W 0 ' (CH2) and Δ G tr,O → W 0 ' (CF2) hardly changed with the variation in m, the Δ G tr,O → W 0 ' (COO- + CH3) and Δ G tr,O → W 0 ' (COO- + CF3) decreased noticeably. These results suggest that the solvation energy for ions in Cl-(CH2)m-Cl increases with m, regardless of hydrophilic or lipophilic nature of the ions. Based on these findings, the advantage of using Cl-(CH2)m-Cl with a large m as a non-aqueous solvent for ion-transfer voltammetry was discussed.

Separation of an ε-poly-L-lysine derivative by solvent extraction under a controlled interfacial potential difference

This paper describes the availability of a 1,2-dichloroethane (DCE)-water (W) interfacial system under a controlled interfacial potential difference for the separation of polycationic species. The system was applied to the production of polyethylene glycol-modified ε-poly-L-lysine (PEG-εPL). PEG-εPL is produced by a fermentation process, and the crude product contains a significant amount of non-modified εPL, which is hardly separated by conventional chromatographic techniques. Both εPL species exist in fully protonated forms under certain acidic conditions, and an extractant, dibenzo-18-crown-6 (DB18C6), associates with their ammonium groups to stabilize the polycations in DCE. Despite the polydispersity of the samples, the εPL and crude PEG-εPL give well-defined cyclic voltammetric waves due to the DB18C6-assisted transfer of the polycations at the polarizable DB18C6 (DCE) | (W, pH ~ 3) interface with midpoint potentials useful for a rough prediction of ion partition equilibria. Thus, the partition experiment was performed using the DB18C6, Bu4N[(CF3SO2)2N] (DCE) | crude PEG-εPL, Li[(CF3SO2)2N] (W, pH ~ 3) interfacial system, of which the potential difference was controlled to enable selective extraction of polycationic PEG-εPL by partition of the [(CF3SO2)2N]- ion. The extract could be collected from the DCE phase and was found to consist of highly purified PEG-εPL.

Tetraphenylantimony(V)-assisted transfer of hydroxide and fluoride anions across the 1,6-dichlorohexane | water interface

The ion-transfer reaction at the 1,6-dichlorohexane (DCH) | water (W) interface in the presence of an organometallic cation, tetraphenylantimony (TPhSb⁺), in DCH was studied voltammetrically. When TPhSb⁺ salt with [(C₄F₉SO₂)₂N]^- ion was added to the DCH-phase and the W-phase was buffered at pH < 6, a reversible cyclic voltammogram due to the simple transfer of TPhSb⁺ ion across the DCH | W interface was observed within the polarizable potential window. When the W-phase was buffered at pH > 7, the midpoint potential shifted to more positive potentials with increasing pH. The voltammogram could be attributed to the transfer of the OH^- ion assisted by the formation of TPhSbOH, which is stable in DCH. Also, a 7reversible voltammogram due to the TPhSb⁺-assisted transfer of F^- ion was observed at the TPhSb⁺ (DCH) | F^- (W, unbuffered) interfacial system. The same results were achieved when TPhSb[(C₄F₉SO₂)₂N] in DCH was replaced by TPhSbOH or TPhSbF, indicating the applicability of the TPhSb⁺ and TPhSbOH (DCH) | OH^- (W) interfacial system to a pH sensor for alkaline solution and that of the TPhSb⁺ and TPhSbF (DCH) | F^- (W) interface to a F^- ion sensor.