Effect of coexisting alkaline metal ions on the extraction selectivity of lanthanide ions with calixarene carboxylate derivatives

Extraction behavior of nine types of trivalent lanthanide ions from three types of aqueous solutions containing an alkaline metal ion such as lithium, sodium or potassium ion into chloroform was investigated with three types of extradants: 37,38,39,40,41,42-hexakis(carboxymethoxy)-5,11,17,23,29,35-hexakis(1,1,3,3- tetramethylbutyl)calix[6]arene and the cone conformational type of 25,26,27,28-tetrakis(carboxymethoxy)-5,11,17,23-tetrakis(1,1,3,3- tetramethylbutyl)calix[4]arene as well as p-(1,1,3,3-tetrametylbutyl)phenoxyacetic acid as the monomeric analog of their calixarene derivatives. The uptake behaviors of the three types of coexisting alkaline metal ions with the calix[4]arene carboxylate derivative and the monomeric analog were also investigated by measuring the chemical shifts of proton NMR spectra. It was found that the calix[4]arene derivative selectively extracted sodium ions, while lithium and potassium ions were hardly extracted, and also found that when sodium ion is contained in the feed solution, the order of extraction selectivity for rare earth metal ions with the calix[4]arene derivative was much changed from an ordinary system containing no sodium ion. That is, in the absence of sodium ion, the calix[4]arene derivative preferentially extracted the light lanthanides with greater ionic radii while in the presence of sodium ion it extracts the heavy lanthanides with smaller ionic radii. It was suggested that the cyclic tetramer preferentially extracts sodium ion at first and then the sodium-loaded calix[4]arene extract lanthanide ions, as a "preorganized" extractant.