Chloroauric acid

Chloroauric acid
Other names Hydrogen tetrachloroaurate, Aurochloric acid, Aurate(1-), tetrachloro-, hydrogen, (SP-4-1)-
Identifiers
CAS number	16903-35-8 Y
ChemSpider	26171 Y
Jmol-3D images	Image 1
SMILES [H+].Cl[Au-](Cl)(Cl)Cl
InChI InChI=1S/Au.4ClH/h;4*1H/q+3;;;;/p-3 Y Key: VDLSFRRYNGEBEJ-UHFFFAOYSA-K Y InChI=1/Au.4ClH.Na/h;4*1H;/q+3;;;;;+1/p-4/rAuCl4.Na/c2-1(3,4)5;/q-1;+1 Key: IXPWAPCEBHEFOV-ACHCXQQJAP InChI=1/Au.4ClH/h;4*1H/q+3;;;;/p-3/rAuCl4/c2-1(3,4)5/q-1/p+1 Key: VDLSFRRYNGEBEJ-ZXMCYSOYAI
Properties
Molecular formula	HAuCl4
Molar mass	339.785 g/mol (anhydrous) 393.833 g/mol (trihydrate) 411.85 g/mol (tetrahydrate)
Appearance	golden yellow crystals hygroscopic
Density	3.9 g/cm3 (tetrahydrate)
Melting point	254°C
Solubility in water	soluble
Solubility	soluble in alcohol, ether
Related compounds
Other anions	Tetrabromoauric acid
Y acid (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chloroauric acid is a inorganic compound with the formula HAuCl₄. This pale yellow compound is a common precursor to gold (Au) in a variety of purposes. The term chloroauric acid is also sometimes used to describe other gold chlorides.

Preparation and structure

Chloroauric acid is obtained by dissolving gold in aqua regia followed by evaporation of these solutions.^[1] Upon heating, chloroauric acid liberates hydrogen chloride, giving gold(III) chloride. This reaction is reversible: dissolving gold(III) chloride in hydrochloric acid:

Au₂Cl₆ + 2 HCl 2 HAuCl₄

In aqueous solution, chloroauric acid consists of the square planar [AuCl₄]⁻ ion. It is a common precursor to other gold coordination complexes.^[2]

Reactions

Chloroauric acid is readily reduced by most metals to precipitate elemental gold.

This compound is reduced by dimethyl sulfide to give chloro(dimethyl sulfide)gold(I), which is also useful as a precursor to other gold complexes.^[3]

Applications

Chloroauric acid is used as the electrolyte in the Wohlwill process for refining gold.

Generally, colloidal gold and gold nanoparticles are produced in a solution ("liquid chemical methods") by reduction of chloroauric acid with trisodium citrate, although alternative methods exist, such as the Norrish reaction and the aldehyde reduction used in Angel gilding.

References

1. ^ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1057.
2. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
3. ^ Marie-Claude Brandys , Michael C. Jennings and Richard J. Puddephatt (2000). "Luminescent gold(I) macrocycles with diphosphine and 4,4-bipyridyl ligands". J. Chem. Soc., Dalton Trans. (24): 4601–4606. doi:10.1039/b005251p.