Calix[4]arenes with a novel proton-ionizable group: synthesis and metal ion separations

Abstract

New calix[4]arenes with two N-(X)sulfonyl carboxamide groups of ‘tunable’ acidity are synthesized from the corresponding calixarene dicarboxylic acid and exhibit good to excellent extraction selectivity for Pb²⁺ over most alkali, alkaline earth and transition metal ions.