Selective extraction of silver(I) over palladium(II) with ketonic derivatives of calixarenes from highly concentrated nitric acid

Solvent extraction of silver(I) and palladium(II) ions with 37,38,39,40,41,42-hexakis(acetomethoxy)-5,11,17,23,29,35-hexakis(1,1,3,3-tetramethylbutyl)calix[6]-arene, 26,27,28-tetrakis(acetomethoxy)-5,11,17,23-tetrakis(1,1,3,3-tetramethylbutyl)calix[4]arene, and p-(1,1,3,3-tetramethylbutyl)phenoxyacetone as a monomeric analog, from highly concentrated HCl or HNO3 into chloroform was investigated. For comparison, the corresponding carboxylate derivatives and the unmodified calixarenes were also examined. Since both silver and palladium ions strongly form complexes with chloride anions, the extraction of both metals was found to be suppressed in highly acidic media. Among the compound employed in the present work, tetrameric ketone was found to be capable of selectively extracting silver over palladium at about 1 mol dm(-3) HNO3 and was suitable for removing traces of silver from a large excess of palladium. It was suggested from the observation of the chemical shift of proton nuclear magnetic resonance that the ketonic derivative of calix[4]arene forms a complex with silver ion surrounded by phenoxy oxygen and carbonyl groups.