Ion-pair formation in aqueous solutions of pyruvate anions: Polarographic study

Abstract

In alkaline solutions reduction of pyruvic acid occurs in two waves ( I A1 and I A2) separated by 0.2–0.3 V. The more positive wave ( I A1) corresponds to the reduction of an ion pair {CH 3COCOO − Me +}, the more negative wave ( I A2) to that of the anion CH 3COCOO −. The height of I A1 depends on the equilibrium concentration of the ion pair and on the rate of its formation. From the dependence of I A1 on [Me +] it is possible to obtain the product k f K (where k f is the rate constant of ion-pair formation, K = [ion pair]/[Me −][CH 3COCOO −]). The reactivity of the cation increases in the sequence Li + < Na + < K + < Cs +. Tetra- n-butylammonium ion acts as a surfactant; tetramethylammonium ion forms the ion pair but also shows surface activity.