New amino-functionalized 1,3-alternate calix[4]arene bis- and mono-(benzo-crown-6 ethers) for pH-switched cesium nitrate extraction

Four calix[4]arene benzo-crown-6 ethers functionalized with primary amine groups in various positions have been synthesized. The cesium extraction behavior under alkaline and acidic conditions has been measured for these compounds and compared with that of non-amine containing analogs. Extraction strength when the amine group is neutral is not affected by the amino substituent, but protonation causes a marked decrease in extraction strength, permitting pH-switched back-extraction.