Chloroauric acid
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Other names
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Identifiers | |
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3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.037.211 |
EC Number |
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PubChem CID
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UNII |
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CompTox Dashboard (EPA)
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Properties | |
H[AuCl4] | |
Molar mass |
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Appearance | orange-yellow needle-like hygroscopic crystals
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Density | 3.9 g/cm3 (anhydrous) 2.89 g/cm3 (tetrahydrate) |
Melting point | 254 °C (489 °F; 527 K) (decomposes) |
350 g of H[AuCl4] in 100 g of H2O | |
Solubility | soluble in alcohol, ester, ether, ketone |
log P | 2.67510 [1] |
Conjugate base
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Tetrachloroaurate(III) |
Structure | |
monoclinic | |
Hazards | |
GHS labelling: | |
Danger | |
H302, H314, H317, H373, H411 | |
P260, P261, P264, P272, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P333+P313, P363, P405, P501 | |
NFPA 704 (fire diamond) | |
Safety data sheet (SDS) | JT Baker |
Related compounds | |
Other anions
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Tetrabromoauric acid |
Related compounds
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Gold(III) chloride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chloroauric acid is an
Properties
Structure
The tetrahydrate crystallizes as [H5O2]+[AuCl4]− and two water molecules.[2] The oxidation state of gold in H[AuCl4] and [AuCl4]− anion is +3. The salts of H[AuCl4] (tetrachloroauric(III) acid) are tetrachloroaurates(III), containing [AuCl4]− anions (tetrachloroaurate(III) anions), which have square planar molecular geometry. The Au–Cl distances are around 2.28 Å. Other d8 complexes adopt similar structures, e.g. tetrachloroplatinate(II) [PtCl4]2−.
Solute properties
When heated in air, solid H[AuCl4]·nH2O melts in the water of crystallization, quickly darkens and becomes dark brown.
Chemical reactions
Since [AuCl4]− is prone to hydrolyze,[6] upon treatment with an alkali metal base, chloroauric acid converts to gold(III) hydroxide.[7] The related thallium salt(Tl+[AuCl4]−) is poorly soluble in all nonreacting solvents. Salts of quaternary ammonium cations are known.[8] Other complex salts include [Au(bipy)Cl2]+[AuCl4]−[9] and [Co(NH3)6]3+[AuCl4]−(Cl−)2.
Partial reduction of chloroauric acid gives oxonium dichloridoaurate(1−).[10] Reduction may also yield other gold(I) complexes, especially with organic ligands. Often the ligand serves as reducing agent as illustrated with thiourea, CS(NH2)2:
- [AuCl4]− + 3 CS(NH2)2 + H2O → [Au(CS(NH2)2)2]+ + CO(NH2)2 + S + 2 Cl− + 2 HCl
Chloroauric acid is the precursor to gold nanoparticles by precipitation onto mineral supports.[11] Heating of H[AuCl4]·nH2O in a stream of chlorine gives gold(III) chloride (Au2Cl6).[12] Gold nanostructures can be made from chloroauric acid in a two-phase redox reaction whereby metallic clusters are amassed through the simultaneous attachment of self-assembled thiol monolayers on the growing nuclei. [AuCl4]− is transferred from aqueous solution to toluene using tetraoctylammonium bromide where it is then reduced with aqueous sodium borohydride in the presence of a thiol.[13]
Production
Chloroauric acid is produced by dissolving gold in aqua regia (a mixture of concentrated nitric and hydrochloric acids) followed by careful evaporation of the solution:[14][15]
- Au(s) + HNO3(aq) + 4 HCl(aq) → H[AuCl4](aq) + NO(g) + 2 H2O(l)
Under some conditions, oxygen can be used as an oxidant.[16] For higher efficiency, these processes are conducted in autoclaves, which allows greater control of temperature and pressure. Alternatively, a solution of H[AuCl4] can be produced by electrolysis of gold metal in hydrochloric acid:
- 2 Au(s) + 8 HCl(aq) → 2 H[AuCl4](aq) + 3 H2(g)
To prevent the deposition of gold on the cathode, the electrolysis is carried out in a cell equipped with a membrane. This method is used for refining gold. Some gold remains in solution in the form of [AuCl2]−.[17]
Uses
Chloroauric acid is the precursor used in the purification of gold by electrolysis.
Liquid–liquid extraction of chloroauric acid is used for the recovery, concentrating, purification, and analytical determinations of gold. Of great importance is the extraction of H[AuCl4] from hydrochloric medium by oxygen-containing extractants, such as alcohols, ketones, ethers and esters. The concentration of gold(III) in the extracts may exceed 1 mol/L.[3][4][5] Frequently used extractants for this purpose are dibutyl glycol, methyl isobutyl ketone, tributyl phosphate, dichlorodiethyl ether (chlorex).[18]
In
Health effects and safety
Chloroauric acid is a strong eye, skin, and mucous membrane irritant. Prolonged skin contact with chloroauric acid may result in tissue destruction. Concentrated chloroauric acid is
References
- ^ "hydrogen tetrachloroaurate(iii)_msds".
- ISSN 0002-7863.
- ^ S2CID 98015888.
- ^ a b Feather, A.; Sole, K. C.; Bryson, L. J. (July 1997). "Gold refining by solvent extraction—the minataur process" (PDF). Journal of the Southern African Institute of Mining and Metallurgy: 169–173. Retrieved 2013-03-17.
- ^ PMID 18960433.
- PMID 24760299.
- ISSN 0009-2673.
- S2CID 95581984.
- ^ Mironov, I. V.; Tsvelodub, L. D. (2001). "Equilibria of the substitution of pyridine, 2,2′-bipyridyl, and 1,10-phenanthroline for Cl− in AuCl4− in aqueous solution". Russian Journal of Inorganic Chemistry. 46: 143–148.
- PMID 20863096.
- S2CID 43671648.
- ^ Mellor, J. W. (1946). A Comprehensive Treatise on Inorganic and Theoretical Chemistry. vol. 3, p. 593.
- .
- ^ Brauer, G., ed. (1963). Handbook of Preparative Inorganic Chemistry (2nd ed.). New York: Academic Press.
- ISBN 9780470132357.
- ^ Novoselov, R. I.; Makotchenko, E. V. (1999). "Application of oxygen as ecologically pure reagent for the oxidizing of non-ferrous and precious metals, sulphide minerals". Chemistry for Sustainable Development. 7: 321–330.
- ^ Belevantsev, V. I.; Peschevitskii, B. I.; Zemskov, S. V. (1976). "New data on chemistry of gold compounds in solutions". Izvestiya Sibirskogo Otdeleniya AN SSSR, Ser. Khim. Nauk. 4 (2): 24–45.
- .
- ^ "Silver Impregnation". Archived from the original on April 21, 2016. Retrieved April 14, 2016.