COMPARISON OF DIBENZO-16-CROWN-5 COMPOUNDS WITH PENDENT AMIDE GROUPS AS SODIUM IONOPHORES IN ION-SELECTIVE ELECTRODES AND IN SOLVENT-EXTRACTION

Potentiometric selectivities for alkali metal, alkaline earth metal an d ammonium ions for a series of N,N-dialkyl sym-(R)dibenzo-16-crown-5- oxyacetamides in solvent polymeric membrane electrodes are determined. For N,N-dipentyl sym-(R)dibenzo-16-crown-5-oxyacetamides, the Na+/Kselectivity increases with variation of the R group in the order: hydr ogen much less than propyl (linear alkyl) < isopropyl, neopentyl (bran ched alkyl). Solvent extractions of sodium and potassium picrates from aqueous solutions into 1,2-dichloroethane were also performed. Ratios of the extraction constants for Na+ and K+ (log K-ex(Na)/K-ex(K)) are similar in magnitude and show the same trends for structural variatio n within the ionophore as do the potentiometric selectivities between Na+ and K+ (log K-Na,K(Pot)) in the polymeric membrane electrodes. Fro m the picrate extraction results, it is deduced that the enhancement i n potentiometric selectivity for Na+ over K+ when the R group is chang ed from hydrogen to propyl arises from increased binding of Na+ and di minished complexation of K+. On the other hand, the enhanced potentiom etric selectivity for Na+ over K+ when a linear alkyl R group is repla ced by a branched alkyl group appears to result from decreased complex ation of K+ only.