Cation fluxes from binary Ag+-Mn+ mixtures in a water-trichloromethane-water liquid membrane system containing a series of macrocyclic ligand carriers

Abstract

Cation fluxes were determined for Ag/sup +/-M/sup n+/ binary cation mixtures in a H/sub 2/O-CHCl/sub 3/-H/sub 2/O liquid membrane system, using macrocyclic ligands as carries. Alkali metal, alkaline earth metal, Pb/sup 2 +/, and Tl/sup +/ cations served as M/sup n+/ in these experiments while macrocyclic polyether ligands having varying ring cavity radii, donor atom types, and substituents served as carriers. Correlations were found between relative cation transport rates and these ligand structural features as well as the equilibrium constant (K) for the formation of the various cation-macrocycle complexes. Selection of macrocycles having proper carrier cavity radii and appropriate combinations of oxygen with either nitrogen or sulfur donor atoms led to selective transport of Ag/sup +/ in preference to any of the other cations studied. Transport was also enhanced by certain aliphatic substituents on the macrocycles. The most effective macrocycles in transporting large quantities of Ag/sup +/ in the presence of M/sup n+/ were diketopyridino-18-crown-6(DKP18C6), diketopyridino-21-crown-7 (DKP21C7), 4-octoxydiketopyridino-18-crown-6 (ODKP18C6), and dicyclohexano-18-crown-6 (DC18C6). Silver ion was transported selectively by these ligands over all M/sup n+/ cations studied except in the cases of Pb/sup 2 +/, which was transported in preference to Ag/sup +/ by DKP18C6, ODKP18C6, DC18C6; Tl/sup +/, which wasmore » transported preferentially by DKP21C7 and DC18C6; and Ba/sup 2 +/ and Sr/sup 2 +/, which were transported selectively by DC18C6.« less