- Gold(III) chloride
Chembox new
Name = Gold(III) chloride
ImageFile =
ImageName = Gold(III) chloride solution
IUPACName = Gold(III) chloride
OtherNames = Auric chloride
Gold trichloride
Section1 = Chembox Identifiers
CASNo = 13453-07-1
RTECS = MD5420000 (anhydrous)
Section2 = Chembox Properties
Formula = AuCl3
(exists as Au2Cl6)
MolarMass = a poop
Appearance = Red crystalline solid
Density = 3.9 g/cm3 (solid)
Solubility = 68 g/100 ml (cold)
MeltingPt = 254 °C (527 K)
(decomposes)
Section4 = Chembox Structure
Coordination = Square planar
CrystalStruct =monoclinic
Section7 = Chembox Hazards
MainHazards = Irritant
RPhrases = R36/37/38
SPhrases = S26-36
Section8 = Chembox Related
OtherAnions =Gold(III) fluoride Gold(III) bromide
OtherCations =Gold(I) chloride Silver(I) chloride Platinum(II) chloride Mercury(II) chloride Gold(III) chloride, traditionally called auric chloride, is the chemical compound with the formula AuCl3. The
Roman numeral s in the name indicate that the gold has anoxidation state of +3, which is common for gold in its compounds. The other chloride of gold, gold(I) chloride (AuCl), is less stable than AuCl3.Chloroauric acid , HAuCl4, the product formed when gold dissolves inaqua regia , is sometimes referred to as "gold chloride", "acid gold trichloride" or even "gold(III) chloride trihydrate."Gold(III) chloride is very
hygroscopic and highly soluble in water andethanol . It decomposes above 160 °C or in light.tructure
AuCl3 exists as a both as a solid and as a vapour at low temperatures; the bromide AuBr3 follows the same pattern. Each gold center is square planar, a similar structure to
iodine(III) chloride . The bonding in AuCl3 is mainly covalent, reflecting the high oxidation state and relatively highelectronegativity (for a metal) of gold.Properties and inorganic chemistry
Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C; however, this in turn undergoesdisproportionation 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 with
hydrochloric acid , chloroauric acid (H [AuCl4] ) is formed::HCl + AuCl3(aq) → H+ [AuCl4] −
Other chloride sources, such as KCl, also convert AuCl3 into [AuCl4] −. 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 togold(III) oxide , Au2O3, and then to gold metal. [N. N. Greenwood, A. Earnshaw, "Chemistry of the Elements", 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997] ["Handbook of Chemistry and Physics", 71st edition, CRC Press, Ann Arbor, Michigan, 1990] ["The Merck Index", 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960] [H. Nechamkin, "The Chemistry of the Elements", McGraw-Hill, New York, 1968] [A. F. Wells, "Structural Inorganic Chemistry", 5th ed., Oxford University Press, Oxford, UK, 1984] [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]Gold(III) chloride is the starting point for the synthesis of many other gold compounds, for example the water-soluble
cyanide complex K [Au(CN)4] ::AuCl3 + 4 KCN → K [Au(CN)4] + 3 KClPreparation
Gold(III) chloride is most often prepared by direct
chlorination of the metal at high temperatures:Fact|date=February 2008:2 Au + 3 Cl2 → 2 AuCl3
Another method of preparation is the reaction in which solid gold is placed in a solution of aqua regia.
Applications in organic synthesis
Gold(III)
salt s, especially Na [AuCl4] (prepared from AuCl3 + NaCl), provide a non-toxic alternative to mercury(II) salts ascatalyst s foralkyne reactions. An illustrative reaction is the hydration of terminal alkynes to produce methylketone s: [cite journal | author = Y. Fukuda and K. Utimoto | title = Effective transformation of unactivated alkynes into ketones or acetals with a gold(III) catalyst | journal =J. Org. Chem. | year = 1991 | volume = 56 | issue = 11 | doi = 10.1021/jo00011a058 | pages = 3729]Also, alkynes undergo
amination in the presence of gold(III) catalysis. In recent years AuCl3 has begun to attract the interest of organic chemists as a mild acid catalyst for other reactions such asalkylation of aromatics and a conversion offuran s tophenol s (see below). Such reactions are of potential value inorganic synthesis , for example for the preparation ofpharmaceutical s. For example, inacetonitrile ,2-methylfuran (sylvan) undergoes smooth alkylation by methyl vinyl ketone at the 5-position:The efficiency of this reaction is noteworthy because both the furan and the ketone are normally very sensitive to side-reactions such as polymerisation under acidic conditions. In some cases where
alkyne s are present, a phenol may be formed: [cite journal | author = A. S. K. Hashmi, T. M. Frost and J. W. Bats | title = Highly Selective Gold-Catalyzed Arene Synthesis | journal =J. Am. Chem. Soc. | year = 2000 | volume = 122 | issue = 46 | doi = 10.1021/ja005570d | pages = 11553]The reaction undergoes a complex rearrangement that leading to a new aromatic ring. [cite journal | author = A. Stephen, K. Hashmi, M. Rudolph, J. P. Weyrauch, M. Wölfle, W. Frey and J. W. Bats | title = Gold Catalysis: Proof of Arene Oxides as Intermediates in the Phenol Synthesis | journal = Angewandte Chemie International Edition| year = 2005 | volume = 44 | issue = 18 | doi = 10.1002/anie.200462672 | pages = 2798]
References
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