NEW XANTHIC ACID-DERIVATIVES AS POTENTIAL REAGENTS IN THE SOLVENT-EXTRACTION OF PRECIOUS-METAL IONS - EXTRACTION OF PALLADIUM(II) WITH 1,3-BIS(O-BUTYLXANTHATO)PROPANE

Two series of new xanthic acid derivatives namely, the bis (O-butylxan thato) alkanes (abbreviated as BBXAs or simply as bis-xanthates in thi s paper) have been synthesized in connection with the solvent extracti on of precious metal ions. From an aqueous medium containing 0.1 M NaC lO4 (1 M=1 mol dm(-3)), these compounds exhibited high selectivity for extraction of Pd(II) and Ag(I) in dichloroethane, over most of the ba se metals as well as Pt(IV) and Au(III) ions. Towards Pd(II) and Ag(I) ions, the bis compounds act as SS chelating agents where the stabilit ies of the extractable complexes are determined by the length of the a lkylene chain existing between the donor atoms. Pd(II) extraction has been studied in detail taking 1,3-bis(O-n-butylxanthato)propane (BnBXP ) as the representative member of the series of bis-xanthates synthesi zed in this work. The extraction of palladium(II) was found to be quit e slow in pure chloride medium. But, a mixed acid medium containing H2 SO4 or HNO3 in the presence of smaller amount of chloride ion provided optimum reversible extraction of palladium in dichloroethane, where P d(II) forms 1:1 extractable complexes with BnBXP. Pd(II) extraction is described in terms of the aqueous phase compositions, extraction and back-extraction data, extraction equilibrium, selectivity consideratio ns and probable mechanisms of extraction.