Ion transfer from water to mixtures of formamide and water studied by polarography at the electrolyte | solution dropping electrode

Abstract

Voltammetry for ion transfer at the interface of two immiscible electrolyte solutions was demonstrated to be feasible at the interface between various mixtures of formamide (FA) and water (W) and 2,6-dimethylnitrobenze. Standard Gibbs transfer energies ΔG0tr of ions from W to FA + W were evaluated from the differences in the half-wave potentials of the voltammograms. Values of ΔG0tr for ions of moderately small volumes, such as (CH3)4N+, BF−4 and ClO−4, were almost independent of the FA content, which was explained by the electrostatic and non-electrostatic interactions between the ion and solvents. Values of ΔG0tr for alkali metal ions decreased and those for halide ions increased with the increasing FA content, and the changes were remarkable in the range below 30% FA, which was explained in terms of short-range interactions between the ions and FA or W. The decrease in ΔG0tr for an uncharged moiety such as CH2 on addition of FA to W was interpreted in terms of the decrease in the cavity formation energy.