4-tert-Butylcalix[4]arene tetrahydroxamate chelators for the selective extraction of actinide ions: synthesis and preliminary metal ion extraction studies1

Abstract

Organic extractants capable of selective and efficient removal of actinides such as plutonium and americium from aqueous process waste streams are potentially useful in radioactive waste remediation. In this context, with the help of molecular modelling, the 4-tert-butylcalix[4]arene tetrahydroxamate chelators 1 and 2 have been identified as structures capable of achieving the selective solvent extraction of actinide(IV) ions from aqueous solutions. The syntheses of 1 and 2 from 4-tert-butylcalix[4]arene have been accomplished in moderate yields using short synthetic sequences. Some extraction studies have been performed using Th⁴⁺ (as a surrogate for Pu⁴⁺), Fe³⁺, UO₂²⁺ and Cu²⁺ to estimate the metal ion selectivity and extraction efficacy of these chelators. Our preliminary results show these ligands are capable of extracting thorium(IV) efficiently but that they may not be selective for its extraction in the presence of iron(III).