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.

Gold(III) chloride
IUPAC name
Gold(III) trichloride
Other names
Auric chloride
Gold trichloride
3D model (JSmol)
ECHA InfoCard 100.033.280
RTECS number
  • MD5420000
(exists as Au2Cl6)
Molar mass 303.325 g/mol
Appearance Red crystals (anhydrous); golden, yellow crystals (monohydrate)[1]
Density 4.7 g/cm3
Melting point 254 °C (489 °F; 527 K) (decomposes)
68 g/100 ml (cold)
Solubility soluble in ether, slightly soluble in liquid ammonia
112·10−6 cm3/mol
Square planar
Main hazards Irritant
Safety data sheet See: data page
GHS pictograms
GHS Signal word Warning
H315, H319, H335
P261, P305+351+338
Related compounds
Other anions
Gold(III) fluoride
Gold(III) bromide
Other cations
Gold(I) chloride
Silver(I) chloride
Platinum(II) chloride
Mercury(II) chloride
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references


AuCl3 exists as a chloride-bridged dimer both as a solid and as a vapour, at least at low temperatures.[3] Gold(III) bromide behaves analogously.[1] The structure is similar to that of iodine(III) chloride.

In gold(III) chloride, each gold center is square planar,[1] 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:[1]

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
(aq) + 6 H+(aq) Au3+(aq) + 3 NO2(g) + 3 H2O(l)
Au3+(aq) + 3 NOCl(g) + 3 NO
(aq) → AuCl3(aq) + 6 NO2(g)
AuCl3(aq) + Cl(aq) AuCl
2 HAuCl4(s) → Au2Cl6(s) + 2 HCl(g)


On contact with water, AuCl
forms acidic hydrates and the conjugate base [AuCl
. It may be reduced by Fe2+
causing elemental gold to be precipitated from solution.[1]

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 → AuCl + Cl2 (>160 °C)
3 AuCl → AuCl3 + 2 Au (>420 °C)

AuCl3 is Lewis acidic and readily forms complexes. For example, it reacts with hydrochloric acid to form chloroauric acid (HAuCl

HCl + AuCl
(aq) → H+
+ [AuCl

Other chloride sources, such as KCl, also convert AuCl3 into AuCl
. 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.[4][5][6][7][8]

Gold(III) chloride is the starting point for the synthesis of many other gold compounds. For example, reaction with potassium cyanide produces the water-soluble complex, K[Au(CN)4]:

+ 4 KCN → K[Au(CN)
+ 3 KCl

Applications in organic synthesis

AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for a variety of reactions,[9] 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.[10]

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):[11]

This reaction involves a rearrangement that gives a new aromatic ring.[12]

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:[13]

PhH + ½Au2Cl6 → ½[PhAuCl2]2 + HCl


  1. Egon Wiberg; Nils Wiberg; A. F. Holleman (2001). Inorganic Chemistry (101 ed.). Academic Press. pp. 1286–1287. ISBN 978-0-12-352651-9.
  2. "Gold Chloride". American Elements. Retrieved July 22, 2019.
  3. E. S. Clark; D. H. Templeton; C. H. MacGillavry (1958). "The crystal structure of gold(III) chloride". Acta Crystallogr. 11 (4): 284–288. doi:10.1107/S0365110X58000694. Retrieved 2010-05-21.
  4. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997
  5. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990
  6. The Merck Index. An Encyclopaedia of Chemicals, Drugs and Biologicals. 14. Ed., 2006, p. 780, ISBN 978-0-911910-00-1.
  7. H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968
  8. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984
  9. G. Dyker, An Eldorado for Homogeneous Catalysis?, in Organic Synthesis Highlights V, H.-G. Schmaltz, T. Wirth (eds.), pp 48−55, Wiley-VCH, Weinheim, 2003
  10. Y. Fukuda; K. Utimoto (1991). "Effective transformation of unactivated alkynes into ketones or acetals with a gold(III) catalyst". J. Org. Chem. 56 (11): 3729. doi:10.1021/jo00011a058.
  11. A. S. K. Hashmi; T. M. Frost; J. W. Bats (2000). "Highly Selective Gold-Catalyzed Arene Synthesis". J. Am. Chem. Soc. 122 (46): 11553. doi:10.1021/ja005570d.
  12. A. Stephen; K. Hashmi; M. Rudolph; J. P. Weyrauch; M. Wölfle; W. Frey; J. W. Bats (2005). "Gold Catalysis: Proof of Arene Oxides as Intermediates in the Phenol Synthesis". Angewandte Chemie International Edition. 44 (18): 2798–801. doi:10.1002/anie.200462672. PMID 15806608.
  13. Li, Zigang; Brouwer, Chad; He, Chuan (2008-08-01). "Gold-Catalyzed Organic Transformations". Chemical Reviews. 108 (8): 3239–3265. doi:10.1021/cr068434l. ISSN 0009-2665. PMID 18613729.
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