On the Facilitation Effect of Neutral Macrocyclic Ligands on the Ion Transfer across the Interface between Aqueous and Organic Solutions. I. Theoretical Equation of Ion-Transfer-Polarographic Current-Potential Curves and Its Experimental Verification

Abstract

A theoretical equation of the reversible polarographic current-potential curves for the ion transfer across the aqueous/organic interface facilitated by the neutral macrocyclic ligand present in the o-phase is derived without any limitation on the magnitude of distribution constant of the ligand. In two limiting cases, which have been employed in common experimental practice, i.e., (A) the bulk concentration of cation, c*M, in the aqueous phase >> that of ligand, c*L, in the organic phase and (B) the reverse condition, c*M<<c*L, the equation of current-potential curves becomes the same in form as that of reversible D. C. polarographic waves. It is shown that the limiting current is controlled by diffusion of ligand in the organic phase for (A) and of cation in the aqueous phase for (B) and, on the other hand, the half-wave potential depends on c*M for (A) and on c*L for (B). Furthermore, an analysis method to determine the complex formation constants in the organic phase (and in the aqueous phase for favorable cases) from the concentration dependence of the half-wave potential is presented. The theoretical predictions are verified experimentally using dibenzo-18-crown-6 and 18-crown-6 as macrocyclic ligands and sodium, cesium, barium, and oxonium ions as transferred cations.

Complex Formation of Oxonium Ion with 18-Crown-6 and 24-Crown-8 Derivatives in a Nitrobenzene Solution Saturated with Water

“…(1) and (2). 8 We use here the value, 0.33, which was previously obtained by considering the diffusion of H30+ in the w-phases Figure 1 shows the plots of Z/1/2 vs. log CH and log CDB18c6. For all the cases, straight lines were obtained with slopes of -57 mV/decade for L=DCH24C8, -56 for DCH18C6 and -62 for DB24C8, DB18C6 and This result suggests that, in spite of variation in the ring flexibility of 18C6 derivatives, the H30+ complexes are stabilized mainly by increasing the basicity of ethereal oxygen atoms.…”

Charge Transfer across Liquid—Liquid Interfaces

“…Matsuda et al 111 have published a general theoretical equation for reversible polarographtc current-potential curves, for ion transfer facilitated by a neutral ligand distributed between the two phases. Even in 1: 1 stoichiometry, the equations obtained are too complicated to be reproduced or used directly.…”

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

“…Girault et al [63] proposed general thermodynamic equations for 1:m ion-to-ligand stoichiometries for the four listed FIT mechanisms, following from Matsuda's model [64] of half-wave potential values for FIT reactions. These expressions are established for two limiting cases: (i) an excess of the ligand in the organic phase relative to the ion of interest in the aqueous phase (cLinit >> cMinit) and (ii) an excess of the ion in the aqueous phase relative to the ligand in the organic phase (cMinit >> cLinit).…”