Abstract
A series of new mono-ionizable cone calix[4]arenes, with either a pendent carboxylic acid or a N-(X-sulfonyl)carboxamide group, is synthesized and their alkali metal cation extraction behavior determined and compared with that for conformationally mobile analogues. These new proton-ionizable, cone calixarenes exhibit good (for the sulfonylcarboxamides) to excellent (for the carboxylic acid) Li+-selectivity. Surprisingly, the Li+-selectivity decreases on going from the conformationally flexible to the cone ionophores due to enhanced Na+ binding by the latter. During the ligand synthesis, unusual behavior of cone tributoxy-N-(trifluoromethylsulfonyl)carbamoylmethoxy-p-tert-butylcalix[4]arene suggests a strong tendency for molecular association.
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