Effect of upper rim para-alkyl substituents on extraction of alkali and alkaline earth metal cations by di-ionizable calix[4]arenes

A series of new di-ionizable calix[4]arene N-(X-sulfonyl)carboxamides (X = CF3, Me, Ph and C6H4-4-NO2) and carboxylic acids with partially and completely removed upper rim p-tert-butyl groups was synthesized and utilized for competitive solvent extractions of alkali and alkaline earth metal cations. Removal of the para-alkyl substituents changes significantly both the efficiency and selectivity of metal ion separations by the carboxamide calix[4]arene extractants, while no such effect is observed for corresponding carboxylic acids.