Extraction of alkali metal cations from aqueous solutions by a crown ether carboxylic acid

Solvent extraction of alkali metal cations from aqueous solutions by sym-dibenzo-16-crown-5-oxyacetic acid in chloroform is reported. Influence of pH, metal ion identity and concentration in the aqueous phase, and anion identity in the aqueous phase upon the concentrations of metal and complexing agent in the organic phase are assessed for single ion extractions. Extraction efficiency is insensitive to changing the aqueous phase anion from chloride to sulfate which demonstrates that the anion is not transferred to the organic phase during extraction. Extraction efficiency is very sensitive to the pH of the aqueous phase. For competitive ion extractions, the selectivity is K > Na > Rb greater than or equal to Cs > Li for pH 6 to 7 and Na > K > Rb approx. = Cs > Li for pH 8 to 12. The crown ether carboxylic acid exhibits extraction efficiencies and selectivities which surpass those of sym-dibenzo-16-crown-5 methyl ether or phenoxyacetic acid.