Synthesis of calix[4]arene-based dipodal receptors: Competitive solvent extraction and liquid bulk membrane transport for selective recovery of Cu²⁺

A series of new p-tert-butylcalix[4]arene-based dipodal receptors are synthesised in high yields. The calix[4]arene units of all the receptors have been found to be present in cone conformation. To optimise the good extraction ability and high transport rate, we synthesised the receptors that differ from each other in their end groups. These receptors extract Cu²⁺ ion selectively from the buffered aqueous medium containing a mixture of metal ions. The receptor bearing four sp³ nitrogens has by far the greater ability to extract Cu²⁺ than the other receptors. All these receptors were effectively used for Cu²⁺ ion transport from the aqueous buffered source phase to the aqueous receiving phase.