Precious Metal Extraction with Thiol and Dithioether Derivatives of a Trident Molecule

Thiol and dithioether derivatives of tripodal extraction reagents have been newly prepared and employed to investigate the extraction behavior of precious metals. Both sulfur-containing compounds did not exhibit a pH dependency for precious metal extraction. The thiol type derivative exhibited a high extraction ability for gold(III), silver and palladium(II), and a 1 : 3 (extractant : metal) stoichiometry for gold(III) and silver. The results showed that the thiol derivative exhibited little structural effect due to the strong functionality of thiol group. The dithioether derivative also extracted gold(III), silver and palladium(II), however the silver extraction is caused by the structural effect of the tripodal framework, while gold(III) and palladium(II) extraction is probably attributed to a partial structural effect. The tripodal derivative possesses a high extraction ability compared with the corresponding monopodal compound. Tripodal and monopodal derivatives showed 1 : 1 and 1 : 2 (extractant : metal) stoichiometry for silver. This means that the tripodal derivative exhibited the structural effect as a size effect, converging effect of the multi functionality, complementary effect. The coordination site of the tripodal derivative was confirmed by 1H-NMR spectra before and after the silver loading. Stripping of the loaded silver from the tripodal derivative was also investigated. Finally, the stepwise separation of silver and palladium(II) was carried out and roughly achieved by using different eluents.