Syntheses of phosphate diesters having p-tert-butylcalix[4]arene and alkyl group as ester moieties, and their selective lithium cation transport abilities through liquid membranes

Phospate diesters, 2a, 2b and 2c, having p-tert-butylcalix[4]arenes and alkyl groups as ester moieties exist as an equilibrium of cone and partial-cone conformations in solution and selectively transport Li+; however, the conformations of the calix[4]arene moieties in the Li and Na complexes of 2a as the methyl ester and/or 2b as the ethyl ester in solution are cone only, although that of the K complex exists as a mixture of cone and partial-cone conformers.