Improved extraction–separation of alkaline earths and lanthanides with the aid of an ion size-selective masking reagent

Abstract

A water-soluble macrocyclic compound, 4′-sulfobenzo-18-crown-6 (SB18C6), was prepared and utilized as an ion size-selective masking reagent with a view to establishing a highly selective extraction–separation system. In the synergistic extraction of alkaline earths with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone and trioctylphosphine oxide in cyclohexane or benzene, the extraction of those with larger ionic radii shifted to a higher pH region when SB18C6 was added to the aqueous phase, giving improved separations. A similar result was achieved in the extraction of lanthanides into chloroform with bis(2-ethylhexyl)phosphoric acid. The distribution of SB18C6 into cyclohexane, benzene or chloroform was so low in comparison with that of 18-crown-6 (18C6) and cryptand[2.2.2] that the synergistic extraction with 18C6, which usually reduces the selectivity, was not observed.