Comparison of dibenzo‐16‐crown‐5 compounds with pendent amide groups as sodium ionophores in ion‐selective electrodes and in solvent extraction

Abstract

Potentiometric selectivities for alkali metal, alkaline earth metal and ammonium ions for a series of N,N‐dialkylsym‐( R)dibenzo‐ 16‐crown‐5‐oxyacetamides in solvent polymeric membrane electrodes are determined. For N, N‐dipentyl sym‐(R)dibenzo‐ 16‐crown‐5‐oxyacetdamides, the Na⁺/K⁺selectivity increases with variation of the R group in the order: hydrogen « propyl (linear alkyl) < isopropyl, neopentyl (branched 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⁺(logK/K) are similar in magnitude and show the same trends for structural variation within the ionophore as do the potentiometric selectivities between Na⁺and K⁺(logK) in the polymeric membrane electrodes. From the picrate extraction results. it is deduced that the enhancement in potentiometric selectivity for Na⁺over K⁺when the R group is changed from hydrogen to propyl arises from increased binding of Na⁺and diminished complexation of K⁺. On the other hand, the enhanced potentiometric selectivity for Na⁺over K⁺when a linear alkyl R group is replaced by a branched alkyl group appears to result from decreased complexation of K⁺only.