Ion-pair sorption of alkali metal chlorides by crown ether carboxamide resins

Ten crown ether carboxamide resins are prepared by condensation polymerization of N,N-dialkyl sym-(R)dibenzo-16-crown-5-oxyacetamide monomers with formaldehyde in formic acid. Competitive ion-pair sorption of alkali metal chlorides from aqueous methanol solutions by these novel resins reveals that both sorption selectivity and efficiency are influenced by: 1) the conformational positioning of the pendant carboxamide group with respect to the crown ether cavity; 2) the length of the N,N-dialkyl chains on the pendant carboxamide group; 3) the methanol content of the aqueous methanol solution; 4) the concentration of alkali metal chlorides in the sample solution; and 5) the temperature of the sample solution. The highest sorption efficiency and Na+ selectivity are obtained for a resin prepared from N,N-dibutyl sym-(propyl)dibenzo-16-crown-5-oxacetamide monomer in which the geminal propyl group orients the carboxamide-containing side arm over the crown ether cavity. Lengthening the alkyl chains in the carboxamide group is detrimental to both sorption efficiency and selectivity. A very sharp response of alkali metal chloride sorption to the methanol content of the sample solution is noted for the crown ether resins which possess preorganized carboxamide side arms.