Lipophilic Crown-4 Derivatives as Lithium Ionophores

Article abstract of DOI:10.1021/ja00335a019

Crown-4 derivatives of 13- through 16-member rings bearing a long aliphatic chain have been synthesized in an effort to obtain highly selective ionophores for lithium ions.The measurements of potentiometric selectivity coefficients for polymeric membranes containing the crown ethers indicated that their lithium selectivities can be explained primarily in terms of the size-fit concept, the 14-crown-4 and 15-crown-4 derivatives being much more selective for lithium than the larger and the smaller macrocycles.It was found that incorporation of a methyl group geminal to the long aliphatic chain prevens formation of sandwich-type 2:1 crown ether-metal complexes with alkali metal ions other than lithium and, therefore, enhances the lithium selectivity of the original crown ether.Some of the lipophilic 14-crown-4 derivatives possess remarkably high preference of lithium over sodium which bears importantly upon their applications.