Dissolution of Gold as Involved a Strong Oxidant and a Ligating Agent

Many of the chemical reactions of gold compounds are conducted in solution and so it is appropriate to initially consider how soluble gold compounds are obtained from this most attractive but inert metal. Traditionally, the dissolution of gold has involved a strong oxidant and a ligating agent. Thus,gold can be dissolved by treatment with aqua regia (a mixture of nitric acid [the oxidant] and hydrochloric acid [the ligand source], neither of which alone dissolves gold) to form [AuCl4]⋅n(H2O) or by oxidation by O2 in the presence of cyanide ion. However, there are reports of metallic gold dissolving under less harsh conditions.

O2 appears to be the oxidant in this dissolution process, which would appear to have significant implications in the handling of gold nanoclusters that frequently are stabilized by coatings of thiolate ligands.

In related work,dithoxamide/dihalogen compounds have been demonstrated to act as oxidations that are capable of dissolving gold. Exposure of metallic gold to chloroform solutions of cetyltrimethylammonium bromide also results in dissolution with the formation of [AuIIIBr4]. Again O2 from air is the oxidant. Under rather different anhydrous and anaerobic conditions,Me3AsI2 and Me3PI2 in diethyl ether solution will dissolve metallic gold to produce gold(III) complexes in reactions. This products have been isolated as crystalline solids.