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.
3D model (JSmol)
CompTox Dashboard (EPA)
(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|
|GHS Signal word||Warning|
|H315, H319, H335|
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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.
- 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)
On contact with water, AuCl
3 forms acidic hydrates and the conjugate base [AuCl
. It may be reduced by Fe2+
causing elemental gold to be precipitated from solution.
- 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 of 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 acetyl compounds.
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, 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=tosyl):
As a stoichiometric reagent, auric chloride reacts with benzene (and a variety of other arenes) under extremely mild conditions (minutes at room temperature) to afford the dimeric phenylgold(III) dichloride:
PhH + ½Au2Cl6 → ½[PhAuCl2]2 + HCl
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