|Jmol 3D model||Interactive image|
(exists as Au2Cl6)
|Molar mass||303.325 g/mol|
|Appearance||Red crystals (anhydrous); golden, yellow crystals (monohydrate)|
|Melting point||254 °C (489 °F; 527 K) (decomposes)|
|68 g/100 ml (cold)|
|Solubility||soluble in ether, slightly soluble in liquid ammonia|
|Safety data sheet||See: data page|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Gold(III) chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula AuCl3, the name gold trichloride is a simplification, referring to the empirical formula. 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.
Gold(III) chloride is most often prepared by passing chlorine gas over gold powder at 180 °C:
- 2 Au + 3 Cl2 → 2 AuCl3
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:
- Au(s) + 3 NO−
3(aq) + 6 H+(aq) ⇌ Au3+(aq) + 3 NO2(g) + 3 H2O(l)
- Au3+(aq) + 3 NOCl(g) + 3 NO−
3(aq) → AuCl3(aq) + 6 NO2(g)
- AuCl3(aq) + Cl−(aq) ⇌ AuCl−
- 2 HAuCl4(s) → Au2Cl6(s) + 2 HCl(g)
- AuCl3 → AuCl + Cl2 (>160 °C)
- 3 AuCl → AuCl3 + 2 Au (>420 °C)
- HCl + AuCl
3 (aq) → H+
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.
3 + 4 KCN → K[Au(CN)
4] + 3 KCl
Applications in organic synthesis
AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for a variety reactions, although no transformations have been commercialized. Gold(III) salts, especially Na[AuCl4] (prepared from AuCl3 + NaCl), provide an alternative to mercury(II) salts as catalysts for reactions involving alkynes. An illustrative reaction is the hydration of terminal alkynes to produce methylketones:
Some alkynes undergo amination in the presence of gold(III) catalysts. Gold catalyses the alkylation of certain aromatic rings and a conversion of furans to phenols. For example, in acetonitrile solution, gold(III) chloride catalyses the alkylation of 2-methylfuran (sylvan) by methyl vinyl ketone at the 5-position:
The efficiency of this organogold reaction is noteworthy because both the furan and the ketone are sensitive to side-reactions such as polymerisation under acidic conditions. In some cases where alkynes are present, phenols sometimes form:
This reaction involves a rearrangement that gives a new aromatic ring.
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