Lithium ion selective electrodes based on 14-crown-4 derivatives bearing lipophilic substituents as ionophores.

Abstract

Eight 14-crown-4 derivatives carrying two, three or four bulky substituents have been synthesized in an attempt to improve the selectivity of the parent macrocycles for Li+ The bulky lipophilic substituents are expected to suppress the formation of stable 2 : 1 (crown ether/cation) complexes with Na+. The selectivity for Li+ against Na+ increased with bulkiness of the substituents up to bearing two benzyl groups and then leveled off with bulkier substituents. In the cases of multi-substituted 14-crown-4 derivatives, however, there was a pronounced drop in the Li+ preference over the other cations except for Na+, compared to dibenzyl- and/or dodecyl methyl-14-crown-4.