Metal ion extraction by lariat ethers with ‘tunable’ proton-ionizable groups

Compared with crown ethers and lariat ethers with neutral side arms, proton-ionizable lariat ethers have an important advantage for metal ion separations. Due to ion-exchange of the metal ion and a proton from the pendent acidic function, transfer of an aqueous phase anion into the organic medium is avoided. A new type of proton-ionizable group, the N-(X)sulfonyl carbamoyl function, has now been incorporated into lariat ethers. For competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform, variation of the X group is found to change the acidity without concomitant steric effects. A series of N-(X)sulfonyl sym-(decyl)dibenzo-16-crown-5-oxyacetamides exhibits very high Na+ selectivity. The effect of varying the crown ether ring size on alkali metal cation extraction is explored with dibenzo-14-crown-4 and dibenzo-19-crown-6 analogs.