Gold(III) chloride

Gold(III) chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula Au2Cl6, the name gold trichloride is a simplification, referring to the empirical formula, AuCl3. The Roman numerals in the name indicate that the gold has an oxidation state of +3, which is common for gold compounds. There is also another related chloride of gold, gold(I) chloride (AuCl). Chloroauric acid, HAuCl4, the product formed when gold dissolves in aqua regia, is sometimes referred to as 'gold chloride' or 'acid gold trichloride'. Gold(III) chloride is very hygroscopic and highly soluble in water as well as ethanol. It decomposes above 160 °C or in light.PhH + ½Au2Cl6 → ½2 + HCl Gold(III) chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula Au2Cl6, the name gold trichloride is a simplification, referring to the empirical formula, AuCl3. The Roman numerals in the name indicate that the gold has an oxidation state of +3, which is common for gold compounds. There is also another related chloride of gold, gold(I) chloride (AuCl). Chloroauric acid, HAuCl4, the product formed when gold dissolves in aqua regia, is sometimes referred to as 'gold chloride' or 'acid gold trichloride'. Gold(III) chloride is very hygroscopic and highly soluble in water as well as ethanol. It decomposes above 160 °C or in light. AuCl3 exists as a chloride-bridged dimer both as a solid and as a vapour, at least at low temperatures. Gold(III) bromide behaves analogously. The structure is similar to that of iodine(III) chloride. In gold(III) chloride, each gold center is square planar, which is typical of a metal complex with a d8 electron count. The bonding in AuCl3 is considered somewhat covalent. Gold(III) chloride is most often prepared by passing chlorine gas over gold powder at 180 °C: Another method of preparation is by reacting Au3+ species with chloride to produce tetrachloroaurate. Its acid, chloroauric acid, is then heated to eliminate hydrogen chloride gas. Reaction with aqua regia produces gold(III) chloride: On contact with water, AuCl3 forms acidic hydrates and the conjugate base −. It may be reduced by Fe2+ causing elemental gold to be precipitated from solution. Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C; however, this in turn undergoes disproportionation at higher temperatures to give gold metal and AuCl3. AuCl3 is Lewis acidic and readily forms complexes. For example, it reacts with hydrochloric acid to form chloroauric acid (HAuCl4): Other chloride sources, such as KCl, also convert AuCl3 into AuCl−4. Aqueous solutions of AuCl3 react with aqueous base such as sodium hydroxide to form a precipitate of Au(OH)3, which will dissolve in excess NaOH to form sodium aurate (NaAuO2). If gently heated, Au(OH)3 decomposes to gold(III) oxide, Au2O3, and then to gold metal.