Gold(III) chloride

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Gold(III) chloride
AuCl3 structure.svg
Gold(III)-chloride-dimer-3D-balls.png
Gold(III)-chloride-xtal-3D-SF-B.png
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 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
RTECS number
  • MD5420000
UNII
  • InChI=1S/Au.3ClH/h;3*1H/q+3;;;/p-3 Yes check.svgY
    Key: RJHLTVSLYWWTEF-UHFFFAOYSA-K Yes check.svgY
  • 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
AppearanceRed 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 and ethanol, slightly soluble in liquid ammonia
−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
−117.6 kJ/mol [3]
Hazards [4]
Occupational safety and health (OHS/OSH):
Main hazards
Irritant
GHS labelling:
GHS-pictogram-exclam.svg
Warning
H315, H319, H335
P261, P305+P351+P338
Related compounds
Other anions
Gold(III) fluoride
Gold(III) bromide
Gold(III) nitrate
Other cations
Gold(I) chloride
Silver(I) chloride
Platinum(II) chloride
Mercury(II) chloride
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).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Gold(III) chloride, traditionally called auric chloride, is a compound of gold and chlorine with the molecular formula Au2 Cl 6. The "III" in the name indicates that the gold has an oxidation state of +3, typical for many gold compounds. Gold(III) chloride is hygroscopic and decomposes in visible light. This compound is a dimer of AuCl3. This compound has few uses, although it catalyzes various organic reactions.

Structure

AuCl3 exists as a chloride-bridged dimer both as a solid and vapour, at least at low temperatures. [2] Gold(III) bromide behaves analogously. [1] The structure is similar to that of iodine(III) chloride.

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

Preparation

Gold(III) chloride is most often prepared by passing chlorine gas over gold powder at 180 °C (356 °F): [1]

2 Au + 3 Cl2 → Au2Cl6

The chlorination reaction can be conducted in the presence of tetrabutylammonium chloride, the product being the lipophilic salt tetrabutylammonium tetrachloraurate. [5]

Another method of preparation is via chloroauric acid, which is obtained by first dissolving the gold powder in aqua regia to give chloroauric acid: [6]

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

The resulting chloroauric acid is subsequently heated to give Au2Cl6:

2 H[AuCl4] → Au2Cl6 + 2 HCl

Reactions

Concentrated aqueous solution of gold(III) chloride Gold(III) chloride solution.jpg
Concentrated aqueous solution of gold(III) chloride

On contact with water, AuCl3 forms acidic hydrates and the conjugate base [AuCl3(OH)]. An Fe 2+ ion may reduce it, causing elemental gold to be precipitated from the solution. [1]

Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C (320 °F), 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 a lewis acid and readily forms complexes. For example, it reacts with hydrochloric acid to form chloroauric acid (H[AuCl4]):

HCl + AuCl3 → H+ + [AuCl4]

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

Other chloride sources, such as KCl, also convert AuCl3 into [AuCl4]. 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. [7] [8] [9] [10] [11]

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]:

AuCl3 + 4 KCN → K[Au(CN)4] + 3 KCl

Gold(III) chloride reacts with benzene (and a variety of other arenes) under mild conditions (reaction times of a few minutes at room temperature) to produce the dimeric phenylgold(III) dichloride: [12]

2 PhH + Au2Cl6[PhAuCl2]2 + 2 HCl

Applications

Organic synthesis

As of 2003, AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for various reactions, [13] although no transformations have been commercialised. Gold(III) salts, especially Na[AuCl4], 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. [14]

Example of gold-catalyzed alkyne hydration reaction.svg

Gold catalyses the alkylation of certain aromatic rings and the conversion of furans to phenols. Some alkynes undergo amination in the presence of gold(III) catalysts. For example, a mixture of acetonitrile and gold(III) chloride catalyses the alkylation of 2-methylfuran by methyl vinyl ketone at the 5-position:

Alkylation reaction of 2-methylfuran with methyl vinyl ketone.svg

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 is an abbreviation for tosyl): [15]

AuCl3 phenol synthesis.svg

This reaction involves a rearrangement that gives a new aromatic ring. [16]

Production of gold nanoparticles

Gold(III) chloride is used in producing gold nanoparticles. Gold nanoparticles can be formed by the reaction of gold(III) chloride and sodium tetrafluoroborate and then coating with didodecyldimethylammonium bromide. Then washing with 1-dodecanethiol and ethanol proved to be the most effective method for forming nanoparticles. However, other methods work such as replacing the 1-dodecanethiol with dioctyl sulfide. [17] The gold(III) chloride is the source of gold in this production.

Related Research Articles

Alkyne Hydrocarbon compound containing one or more carbon-carbon triple bonds

In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature. Like other hydrocarbons, alkynes are generally hydrophobic.

The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.

In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons.

In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -COCl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride.

Hydrogen bromide Chemical compound

Hydrogen bromide is the inorganic compound with the formula HBr. It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a constant-boiling azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H2O until the constant-boiling mixture composition is reached.

An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class provides common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names, applications, and properties. Organochlorine compounds have wide use in many applications, though some are of profound environmental concern, with TCDD being one of the most notorious.

Aluminium chloride Chemical compound

Aluminium chloride (AlCl3), also known as aluminium trichloride, describe compounds with the formula AlCl3(H2O)n (n = 0 or 6). They consist of aluminium and chlorine atoms in a 1:3 ratio, and one form also contains six waters of hydration. Both are white solids, but samples are often contaminated with iron(III) chloride, giving a yellow color.

Sulfonic acid Class of chemical compounds

A sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula R−S(=O)2−OH, where R is an organic alkyl or aryl group and the S(=O)2(OH) group a sulfonyl hydroxide. As a substituent, it is known as a sulfo group. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent. The parent compound (with the organic substituent replaced by hydrogen) is the parent sulfonic acid, HS(=O)2(OH), a tautomer of sulfurous acid, S(=O)(OH)2. Salts or esters of sulfonic acids are called sulfonates.

In organic chemistry, an electrophilic aromatic halogenation is a type of electrophilic aromatic substitution. This organic reaction is typical of aromatic compounds and a very useful method for adding substituents to an aromatic system.

Diazonium compound Diazonium salts of formula R-N≡N+

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.

Hafnium tetrachloride Chemical compound

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

Chloroplatinic acid Chemical compound

Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6
). Hexachloroplatinic acid is highly hygroscopic.

The Gattermann reaction, (also known as the Gattermann formylation and the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by a mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl3. It is named for the German chemist Ludwig Gattermann and is similar to the Friedel–Crafts reaction.

Barrelene Chemical compound

Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by Howard Zimmerman in 1960, the name derives from the resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels–Alder adduct of benzene and acetylene. Due to its unusual molecular geometry, the compound is of considerable interest to theoretical chemists.

Chloro(triphenylphosphine)gold(I) Chemical compound

Chloro(triphenylphosphine)gold(I) or triphenylphosphinegold(I) chloride is a coordination complex with the formula (Ph3P)AuCl. This colorless solid is a common reagent for research on gold compounds.

Chloroauric acid Chemical compound

Chloroauric acid refers to inorganic compounds with the chemical formula H[AuCl4nH2O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4] anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.

Organogold chemistry is the study of compounds containing gold–carbon bonds. They are studied in academic research, but have not received widespread use otherwise. The dominant oxidation states for organogold compounds are I with coordination number 2 and a linear molecular geometry and III with CN = 4 and a square planar molecular geometry. The first organogold compound discovered was gold(I) carbide Au2C2, which was first prepared in 1900.

Ynone

In organic chemistry, an ynone is a compound containing a ketone function and a C≡C triple bond. Many ynones are α,β-ynones, where the carbonyl and alkyne groups are conjugated. Capillin is a naturally occurring example. Some ynones are not conjugated.

Gold(III) sulfide or auric sulfide is an inorganic compound with the formula Au2S3. Little evidence has been published supporting the existence of macroscopic quantities of this material.

References

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  2. 1 2 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.
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  4. "Gold Chloride". American Elements . Retrieved July 22, 2019.
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  15. 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.
  16. 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.
  17. M. Lin; C. M. Sorensen; K. J. Klabunde (1999). "Ligand-Induced Gold Nanocrystal Superlattice Formation in Colloidal Solution". Chemistry of Materials. 11 (2): 198–202. doi:10.1021/cm980665o.