REMARKABLY SELECTIVE AG+ EXTRACTION AND TRANSPORT BY THIOLARIAT ETHERS

Synthesis and metal binding properties of thiolariat ethers, where a s ulfide side chain is introduced into a framework of a crown ether, hav e been performed. Remarkably high Ag+ selectivity among heavy metal io ns was observed in solvent extraction and transport across a liquid me mbrane using thiolariat ethers with a 15-crown-5 ring as carriers. Thi olariat ethers with a 12-crown-4 or a 18-crown-6 do not exhibit such a high Agi selectivity. The former binds metal ions weakly, and the lat ter recognizes Pb2+ as well as Ag+. The corresponding oxygen analogs, i.e. lariat ethers, do not show Ag+ selectivity. The Ag+ binding stren gth of the sulfoxide and sulfone analogs is much lower than that of th iolariat ethers. Thiolariat ethers with a benzocrown framework contain ing a sulfide chain at the 4 position of the benzene nucleus showed ve ry low affinity to Ag+. Extractability and transport ability using var ious thiolariat ether derivatives strongly suggested that this high Ag + selectivity is a result of the synergistic coordination of the ring oxygen and the sulfur atom of the thiolariat ether. NMR chemical shift s of protons and carbons in the proximity of the sulfur atom of the th iolariat ether were changed significantly in accordance with the syner gistic coordination described above. 1:1 Complexation between a thiola riat ether and Ag+ were supported by a Job plot using the chemical shi ft of the methylene protons adjacent to the sulfur atom.