Ball-and-stick model of AuCl3
Crystal structure of AuCl3
3D model (JSmol)
CompTox Dashboard (EPA)
(exists as Au2Cl6)
|Molar mass||606.6511 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 and ethanol, slightly soluble in liquid ammonia|
|Occupational safety and health (OHS/OSH):|
|H315, H319, H335|
|Supplementary data page|
|Gold(III) chloride (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 compound of gold and chlorine with the molecular formula Au2Cl6. The "III" in the name indicates the gold has an oxidation state of +3, which is typical for many gold compounds. Gold(III) chloride is hygroscopic and decomposes in visible light. This compound is a dimer of AuCl3. This compound has few uses, although it does catalyze a variety of organic reactions.
AuCl3 exists as a chloride-bridged dimer both as a solid and a vapour, at least at low temperatures. Gold(III) bromide behaves analogously. The structure is similar to that of iodine(III) chloride.
The resulting chloroauric acid is subsequently heated to give Au2Cl6:
Other chloride sources, such as KCl, also convert AuCl3 into AuCl−
4. Aqueous solutions of AuCl3 react with an 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.
Gold(III) chloride reacts with benzene (and a variety of other arenes) under mild conditions (reaction times of a few minutes at room temperature) to produce the dimeric phenylgold(III) dichloride:
PhH + ½ Au2Cl6 → ½ [PhAuCl2]2 + HCl
As of 2003, AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for a variety of reactions,[update]  although no transformations have been commercialised. Gold(III) salts, especially Na[AuCl4], provide an alternative to mercury(II) salts as catalysts for reactions involving alkynes. An illustrative reaction is the hydration of terminal alkynes to produce acetyl compounds.
Some alkynes undergo amination in the presence of gold(III) catalysts. Gold catalyses the alkylation of certain aromatic rings and the conversion of furans to phenols. For example, a mixture of acetonitrile and gold(III) chloride catalyses the alkylation of 2-methylfuran 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 (Ts is an abbreviation for tosyl):
This reaction involves a rearrangement that gives a new aromatic ring.