Ion-transfers of sodium and potassium cations facilitated by naphtho-15-crown-5 between water and nitrobenzene

The ion-transfers of sodium and potassium cations, facilitated by naptho-15-crown-5, N15C5, were studied at an interface between water and nitrobenzene using current-scan polarography. A polarographic wave caused by the facilitated transfer of sodium cation was observed under the condition that the concentration of sodium cation was much higher than that of N15C5, [Na+]>>[N15C5]. It is inferred from an analysis of the wave that a sodium cation trasfer is facilitated due to the formation of a 1:1 complex of metal-to-ligand ratio, Na(N15C5)(+). However, since no wave was observed under the condition [N15C5]>>[Na+], a 1:2 complex may not exist in this condition. On the other hand, since a clear facilitated wave of potassium cation was only obtained under the condition [N15C5]>>[K+], the transfer of a 1:2 complex, K(N15C5)(2)(+), is inferred. Since an indistinct wave overlapped by an anodic final current rise in [K+]>>[N15C5] appeared, a small stability of a 1:1 complex, K(N15C5)(+), is expected. Considering the EC mechanisms for those transfers, the stability constants of those complexes in the nitrobenzene phase were determined. The values are 5.0X10(6) M-1 for Na(N15C5)(+) and 6.0X10(8) M-2 for K(N15C5)(2)(+). These results are quite consistent with the results from a solvent extraction study of these complexes.