Liquid-Liquid Distribution of Ion Associates of Tetrahalogenoaurate(III) with Quaternary Ammonium Counter Ions

Abstract

The solvent extraction of ion associates of tetrahalogenoaurate(III) ions, AuX₄^-(X^-=chloride or bromide), with quaternary ammonium cations (Q⁺) has been studied. The extraction constants (K_ex) were determined for the ion associates of AuX₄^- with Q⁺ between an aqueous phase and several organic phases (chloroform (CF), chlorobenzene (Cl-B), benzene (B), toluene (T) and carbon tetrachloride (CTC)). The extractability of AuX₄^- was in the order AuBr₄^- >AuCl₄^-; the difference in logK_ex between tetrachloroaurate(III) and tetrabromoaurate(III) was about 1.16 on the average. Among the ion associates examined, the extractability of the extracting solvent was generally in the order CF>Cl-B>B>T>CTC; the differences in logK_ex between two successive solvents in this order were about 0.26, 0.40, 0.09 and 0.10 on the average. The contribution of a methylene group in Q⁺ to logK_ex was about 0.5 on the average. From the obtained extraction constants, possible extraction systems for the spectrophotometry of gold are predicted: tetrabutylammonium cation•AuCl₄^--chloroform, tetraamylammonium cation•AuCl₄^--chloroform, tetra-butylammonium cation•AuBr₄^-chloroform, tetrabutylammonium cation•AuBr₄^--chlorobenzene and tetraamylammonium cation•AuCl₄^--benzene.