Carboxyl-substituted derivatives of S-decyl dithizone as solvent extractants for precious metal ions
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abstract
Novel ortho-, meta- and para-monocarboxyl-substituted derivatives of S-decyldithizone (D-oC, D-mC and D-pC) and the unsubstituted parent compound (D-H) were synthesized and their extraction properties towards precious and base metal ions investigated. Dissolved in p-xylene or chloroform, the formazan compounds were spontaneously oxidized to the corresponding tetrazolium salts by contact with aqueous Au(III) solution. Towards palladium the dithizone derivatives acted via chelation. The mode of coordination was strongly influenced by the position of the carboxylic acid group. As a consequence, only the o-COOH-derivative D-oC formed exclusively one 1:1:1 (Pd(II)-ligand-Cl) complex, whereas the other extracting agents yielded a mixture of different isomeric palladium chelates in the organic phase. D-oC removed Pd(II) from hydrochloric acid solutions effectively and selectively. Compared to the other compounds the co-extraction of Pt(IV), Os(IV), as well as Fe(III) and other base metals was drastically reduced. Stripping was achieved by acidic thiourea solution and thiocyanate, however, the tendency of D-oC to pile up traces of precious metal ions was obvious.Novel ortho-, meta- and para-monocarboxyl-substituted derivatives of S-decyldithizone (D-oC, D-mC and D-pC) and the unsubstituted parent compound (D-H) were synthesized and their extraction properties towards precious and base metal ions investigated. Dissolved in p-xylene or chloroform, the formazan compounds were spontaneously oxidized to the corresponding tetrazolium salts by contact with aqueous Au(III) solution. Towards palladium the dithizone derivatives acted via chelation. The mode of coordination was strongly influenced by the position of the carboxylic acid group. As a consequence, only the o-COOH-derivative D-oC formed exclusively one 1:1:1 (Pd(II)-ligand-Cl) complex, whereas the other extracting agents yielded a mixture of different isomeric palladium chelates in the organic phase. D-oC removed Pd(II) from hydrochloric acid solutions effectively and selectively. Compared to the other compounds the co-extraction of Pt(IV), Os(IV), as well as Fe(III) and other base metals was drastically reduced. Stripping was achieved by acidic thiourea solution and thiocyanate, however, the tendency of D-oC to pile up traces of precious metal ions was obvious.
