Correlation between the standard Gibbs energies of an anion transfer from water to highly hydrophobic ionic liquids and to 1,2-dichloroethane

•We report the transfer of anions across a water/ionic liquid (IL) interface.•Standard Gibbs energy of anion transfer from water to IL is evaluated.•Thermodynamic correlations for the ion transfer to IL and 1,2-DCE are established.•Systematic effect of the cationic IL component is manifested.•Weak solvation effect discriminates hydrophilic cation against anion transfer.

Cyclic voltammetry is used to investigate the transfer of several semihydrophobic and hydrophilic anions (F−, Cl−, Br−, I−, NO3-, NO2-, SCN−, BF4-, ClO4-, PF6-) across the polarized interface between an aqueous electrolyte solution and a highly hydrophobic ionic liquid (IL) membrane. Three ILs are examined being composed of the trioctadecylmethylammonium (TOMA+), tridodecylmethylammonium (TDMA+) or tetradodecylammonium (TDA+) cation and the tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB−) anion. The standard Gibbs energies of the anion transfer from water to IL, ΔGtr,i0,w→IL, are evaluated from the voltammetric measurements by applying the classical tetraphenylarsonium-tetraphenylborate hypothesis. Comparison of data for various ILs points to a small systematic effect of the cationic IL component, which is manifested by somewhat lower values of ΔGtr,i0,w→IL for most anions in the presence of TDMA+ or TDA+, indicating their stronger association with the anions. The capillary electrophoresis measurements suggest that the degree of interaction of anions with the IL cations in water could follow the order TDMA+ >TOMA+ >TDA+. It is shown that a linear correlation with the nearly unity slope between ΔGtr,i0,w→IL and the standard Gibbs energy of anion transfer from water to 1,2-dichloroethane (DCE), ΔGtr,i0,w→DCE, can be established for all three ILs studied. An extended correlation including both the present and the literature values of ΔGtr,i0,w→IL for the ion transfer from water to TDMATFPB reveals the consistency of data for the semihydrophobic cations and anions, and the presence of a weak solvation effect favoring the transfer of hydrophilic anions (F−, Cl−, Br−, I−) and disfavoring the transfer of hydrophilic cations (H+, Li+, Na+, K+, Rb+, Cs+).