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Ten crown ethers with pendant carboxylic acid groups are synthesized from corresponding hydroxy crown ethers. Within this series of crown ether carboxylic acids there is systematic variation of the following: (a) the crown ether cavity size, while holding the pendant carboxylic acid group constant, (b) the length of the linkage which joins the carboxylic acid group to a common polyether ring, and (c) the lipophilicity, while keeping the polyether ring and linkage which joins the carboxylic acid and polyether ring portions invariant. Dissociation constants of the crown ether carboxylic acids in water are determined.

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Solvent extraction of Mg, Ca, Sr, and Ba cations from aqueous solutions by sym-dlbenzo-16-crown-5-oxyacetlc acid (1), sym-dlbenzo-13-crown-4-oxyacetic acid (2), and sym-dlbenzo-19-crown-6-oxyacetlc acid (3) In chloroform has been Investigated. Influences of pH and metal Ion concentration In the aqueous phase upon the concentrations of metal(s) and complexing agent In the organic phase are assessed for single Ion (with 1) and competitive (with 1, 2, or 3) extractions. Marked differences In the efficiency and selectivity order for single Ion and competitive extractions uslrig 1 are noted.Although chloroform phase extraction complexes of MAZ are Indicated for each crown ether carboxylic acid, 1 surpasses 2 and 3 In extraction efficiency and selectivity. The crown ether carboxylic acids 1, 2, and 3 are superior extraction agents to closely related neutral crown ethers and to phenoxyacetic acid.

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