Gold(III) chloride

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Gold(III) chloride


Crystal structure of AuCl3
Names
IUPAC name
Gold(III) trichloride
Other names
Auric chloride
Gold trichloride
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
100.033.280 Edit this at Wikidata
RTECS number
  • MD5420000
UNII
  • InChI=1S/Au.3ClH/h;3*1H/q+3;;;/p-3 checkY
    Key: RJHLTVSLYWWTEF-UHFFFAOYSA-K checkY
  • InChI=1/Au.3ClH/h;3*1H/q+3;;;/p-3
    Key: RJHLTVSLYWWTEF-DFZHHIFOAC
  • Cl[Au-]1(Cl)[Cl+][Au-]([Cl+]1)(Cl)Cl
Properties
AuCl3
(exists as Au2Cl6)
Molar mass 606.6511 g/mol
Appearance Red crystals (anhydrous); golden, yellow crystals (monohydrate)[1]
Density 4.7 g/cm3
Melting point 160 °C (320 °F; 433 K) (decomposes)
68 g/100 ml (20 °C)
Solubility soluble in ether and ethanol, slightly soluble in liquid ammonia, insoluble in benzene
−112·10−6 cm3/mol
Structure
monoclinic
P21/C
a = 6.57 Å, b = 11.04 Å, c = 6.44 Å
α = 90°, β = 113.3°, γ = 90°[2]
Square planar
Thermochemistry
Std enthalpy of
formation
fH298)
−117.6 kJ/mol[3]
Hazards[4]
Occupational safety and health (OHS/OSH):
Main hazards
Irritant
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P305+P351+P338
Related compounds
Other anions
Gold(III) fluoride
Gold(III) bromide
Other cations
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).
☒N verify (what is checkY☒N ?)

Gold(III) chloride, traditionally called auric chloride, is an

dimer of AuCl3. This compound has a few uses, such as an oxidizing agent and for catalyzing various organic reactions
.

Structure

AuCl3 exists as a

iodine(III) chloride
.

Each gold center is

square planar in gold(III) chloride, which is typical of a metal complex with a d8 electron count. The bonding in AuCl3 is considered somewhat covalent.[1]

Properties

Gold(III) chloride is a

hygroscopic. The anhydrous form absorbs moisture from the air to form the monohydrate which can be reversed by the addition of thionyl chloride.[5]

Preparation

Gold(III) chloride was first prepared in 1666 by Robert Boyle by the reaction of metallic gold and chlorine gas at 180 °C:[1][6][7]

2 Au + 3 Cl2 → Au2Cl6

This method is the most common method of preparing gold(III) chloride. It can also be prepared by reacting gold powder with iodine monochloride:[5]

2 Au + 6 ICl → 2 AuCl3 + 3 I2

The

lipophilic salt tetrabutylammonium tetrachloraurate.[8]

Another method of preparation is via chloroauric acid, which is obtained by first dissolving the gold powder in aqua regia to give chloroauric acid:[9]

Au + HNO3 + 4 HCl → H[AuCl4] + 2 H2O + NO

The resulting chloroauric acid is subsequently heated in an inert atmosphere at around 100 °C to give Au2Cl6:[10][11]

2 H[AuCl4] → Au2Cl6 + 2 HCl

Reactions

Concentrated aqueous solution of gold(III) chloride

Decomposition

Anhydrous AuCl3 begins to decompose to AuCl (gold(I) chloride) at around 160 °C (320 °F), however, this, in turn, undergoes disproportionation at higher temperatures to give gold metal and AuCl3:[5][10]

AuCl3 → AuCl + Cl2 (160 °C)
3 AuCl → AuCl3 + 2 Au (>210 °C)

Due to the disproportionation of AuCl, above 210 °C, most of the gold is in the form of elemental gold.[12][11]

Gold(III) chloride is more stable in a chlorine atmosphere and can sublime at around 200 °C without any decomposition. In a chlorine atmosphere, AuCl3 decomposes at 254 °C yielding AuCl which in turn decomposes at 282 °C to elemental gold.[2][13] This fact that no gold chlorides can exist above 400 °C is used in the Miller process.[14]

Other reactions

AuCl3 is a

complexes. For example, it reacts with hydrochloric acid to form chloroauric acid (H[AuCl4]):[15]

HCl + AuCl3 → H+ + [AuCl4]

Chloroauric acid is the product formed when gold dissolves in aqua regia.[15]

On contact with water, AuCl3 forms

conjugate base [AuCl3(OH)]. A Fe2+ ion may reduce it, causing elemental gold to be precipitated from the solution.[1][16]

Other chloride sources, such as

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.[15][17][18][19]

Gold(III) chloride is the starting point for the chemical synthesis of many other gold compounds. For example, the reaction with potassium cyanide produces the water-soluble complex, K[Au(CN)4]:[20]

AuCl3 + 4 KCN → K[Au(CN)4] + 3 KCl

Gold(III) fluoride can be also produced from gold(III) chloride by reacting it with bromine trifluoride.[15]

Gold(III) chloride reacts with

arenes undergo a similar reaction:[21]

2 PhH + Au2Cl6 → [PhAuCl2]2 + 2 HCl

Gold(III) chloride reacts with carbon monoxide in a variety of ways. For example, the reaction of anhydrous AuCl3 and carbon monoxide under SOCl2 produces gold(I,III) chloride with Au(CO)Cl as an intermediate:[22][23]

2 AuCl3 + 2 CO → Au4Cl8 + 2 COCl2

If carbon monoxide is in excess, Au(CO)Cl is produced instead.[24][25]

However, under tetrachloroethylene and at 120 °C, gold(III) chloride is first reduced to gold(I) chloride, which further reacts to form Au(CO)Cl. AuCl3 is also known to catalyze the production of phosgene.[25][26]

Applications

Although gold(III) chloride has no commercial uses, it has many uses in the laboratory.[5]

Organic synthesis

Since 2003, AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for various reactions,

acetyl compounds.[28]

Gold catalyses the

methyl vinyl ketone at the 5-position:[29]

The efficiency of this

tosyl):[29]

This reaction involves a rearrangement that gives a new aromatic ring.[30]

Another example of an AuCl3 catalyzed reaction is a hydroarylation, which is basically a

Friedel-Crafts reaction using metal-alkyne complexes. Example, the reaction of mesitylene with phenylacetylene:[31]

Gold(III) chloride can be used for the direct oxidation of primary

amines into ketones, such as the oxidation of cyclohexylamine to cyclohexanone.[5]

This reaction is pH sensitive, requiring a mildly acidic pH to proceed, however, it does not require any additional steps.[5]

In the production of organogold(III) compounds, AuCl3 is used as a source of gold. A main example of this is the production of monoarylgold(III) complexes, which are produced by direct

electrophilic auration of arenes by gold(III) chloride.[32]

Gold nanoparticles

Gold(III) chloride is used in the synthesis of gold nanoparticles, which are extensively studied for their unique size-dependent properties and applications in fields such as electronics, optics, and biomedicine. Gold nanoparticles can be prepared by reducing gold(III) chloride with a reducing agent such as sodium tetrafluoroborate, followed by stabilization with a capping agent.[33]

Photography

Gold(III) chloride has been used historically in the photography industry as a sensitizer in the production of photographic films and papers. However, with the advent of digital photography, its use in this field has diminished.[34]

Natural occurrence

This compound does not occur naturally; however, a similar compound with the formula AuO(OH,Cl)·nH2O is known as a product of natural gold oxidation.[35][36]

References

  1. ^ .
  2. ^ . Retrieved 2010-05-21.
  3. OCLC 930681942.{{cite book}}: CS1 maint: location missing publisher (link
    )
  4. ^ "Gold Chloride". American Elements. Retrieved July 22, 2019.
  5. ^ .
  6. ^ Robert Boyle (1666). The origine of formes and qualities. p. 370.
  7. .
  8. .
  9. .
  10. ^ a b Ya-jie Zheng; Wei Guo; Meng Bai; Xing-wen Yang (2006). "Preparation of chloroauric acid and its thermal decomposition". The Chinese Journal of Nonferrous Metals (in Chinese). 16 (11): 1976–1982. Archived from the original on March 27, 2024.
  11. ^ .
  12. .
  13. .
  14. .
  15. ^ .
  16. ^ Cotton, F.A.; Wilkinson, G.; Murillo, C.A.; Bochmann, M. Advanced Inorganic Chemistry; John Wiley & Sons: New York, 1999; pp. 1101-1102
  17. .
  18. McGraw-Hill
    , New York, 1968, p. 222
  19. ^ A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984, p. 909
  20. ^ Henry K. Lutz (1961). "Synthesis and Analyses of KAu(CN)4". Honors Theses. Union Digital Works.
  21. PMID 18613729
    .
  22. .
  23. .
  24. .
  25. ^ .
  26. .
  27. ^ 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
  28. .
  29. ^ .
  30. .
  31. .
  32. .
  33. .
  34. .
  35. ^ "UM1995-16-O:AuClH". mindat.org. Retrieved 27 April 2023.
  36. ^ John L. Jambor; Nikolai N. Pertsev; Andrew C. Roberts (1996). "New Mineral Names" (PDF). American Mineralogist. 81: 768.

External links