Highly Lipophilic, Mono-ionizable Calix[4]arene-benzocrown-6 Extractants for Removal of Radiocesium from Nuclear Wastes

A series of lipophilic, proton-ionizable calix[4]arene-benzocrown-6 compounds with calixarene units locked in the 1,3-alternate conformation was prepared for evaluation of their potential as radiocesium ion extractants. Upon ionization of the pendant acidic function, the ligand provides the requisite anion for the formation of an electroneutral extraction complex, thereby markedly increasing Cs+ extraction efficiency. To enhance the lipophilicity, each proton-ionizable calix[4]arene-crown-6 ligand bears a (2-ethylhexyl)benzo unit and two octyl groups. By use of radiotracer techniques for Cs+ and Na+ and ICP spectrometry for K+, the ligands were evaluated in terms of the efficiency and selectivity with which they extract Cs+ from aqueous solutions into toluene. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplementary file.