Abstract
Extraction of platinum (IV) from hydrochloric acid solutions by using dihexylsulfide (DHS) containing micro amount of trioctylmethylammonium chloride (TOMAC) was investigated under irradiation of light. Although the complex of Pt (IV) with DHS is not formed by the extraction, on this extraction system, Pt (IV) was extracted quantitatively by DHS because (TOMA)2PtCl6 complex activated by irradiation of ultraviolet rays acts as catalyst. The stoichiometric composition of the DHS complex formed in the organic phase was deduced to be PtCl4DHS. Therefore, the following equilibrium equations are proposed: PtCl62 -(aq) + 2TOMAC (org) ⇔ (TOMA)2PtCl6(org) + 2Cl- (aq) (TOMA)2PtCl6(org)→hv(TOMA) 2PtCl6*(org) (activated complex) (TOMA)2PtCl6*(org) + 2DHS(org) ⇔ PtCl4 · 2DHS(org) + 2TOMAC(org) . In the equilibrium reactions, it was found that Pt (IV) in the complex is not reduced to Pt (II). The examination of diluent effects proved that aromatic diluents with electron-donating groups, such as m-xylene and toluene, promote the activation of TOMAC-Pt (IV) complex, whereas aromatic diluents with electron-accepting groups, such as chlorobenzene and nitrobenzene, and aliphatic diluents, such as hexane and dodecane, suppress that activation. Furthermore, it was found that from the examination of effects of high molecular-weight amine, the catalytic effect of amine-Pt (IV) complexes depends on their activated degree by irradiation of ultraviolet rays, which is promoted by electron-donating groups of amines, and ability of replacement between the chlorine atoms coordinated to Pt (IV) in the activated complex and DHS, which is affected by steric hindrance of amines.
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