 | |
-chloride-dimer-3D-balls.png) Ball-and-stick model of AuCl3 | |
-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 |
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| ECHA InfoCard | 100.033.280 |
| RTECS number |
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| UNII | |
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| Properties | |
| AuCl3 (exists asAu2Cl6) | |
| Molar mass | 606.6511 g/mol (forAu2Cl6) |
| 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 inether andethanol, slightly soluble in liquidammonia, insoluble inbenzene |
| −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(ΔfH⦵298) | −117.6 kJ/mol[3] |
| Hazards[4] | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Irritant |
| GHS labelling: | |
 | |
| Warning | |
| H315,H319,H335 | |
| P261,P264,P271,P280,P302+P352,P305+P351+P338 | |
| Related compounds | |
Otheranions | Gold(III) fluoride Gold(III) bromide |
Othercations | 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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Gold(III) chloride, traditionally calledauric chloride, is aninorganic compound ofgold andchlorine with themolecular formulaAu2Cl6. The "III" in the name indicates that the gold has anoxidation state of +3, typical for many gold compounds. It has two forms, the monohydrate (AuCl3·H2O) and the anhydrous form, which are bothhygroscopic and light-sensitive solids. This compound is adimer ofAuCl3. This compound has a few uses, such as an oxidizing agent and forcatalyzing variousorganic reactions.
AuCl3 exists as achloride-bridgeddimer both as asolid andvapour, at least at low temperatures.[2]Gold(III) bromide behaves analogously.[1] The structure is similar to that ofiodine(III) chloride.
Each gold center issquare planar in gold(III) chloride, which is typical of a metal complex with ad8 electron count. The bonding inAuCl3 is considered somewhatcovalent.[1]
Gold(III) chloride is adiamagnetic light-sensitive red crystalline solid that forms the orange monohydrate, AuCl3 · H2O; the anhydrous and monohydrate are bothhygroscopic. The anhydrous form absorbs moisture from the air to form the monohydrate which can be reversed by the addition ofthionyl chloride.[5]
Gold(III) chloride was first prepared in 1666 byRobert Boyle by the reaction of metallic gold andchlorine gas at 180 °C:[1][6][7]
This method is the most common method of preparing gold(III) chloride. It can also be prepared by reacting gold powder withiodine monochloride:[5]
Thechlorination reaction can be conducted in the presence oftetrabutylammonium chloride, the product being thelipophilic salt tetrabutylammonium tetrachloraurate.[8]
Another method of preparation is viachloroauric acid, which is obtained by first dissolving the gold powder inaqua regia to give chloroauric acid:[9]
The resulting chloroauric acid is subsequently heated in an inert atmosphere at around 100 °C to giveAu2Cl6:[10][11]
_chloride_solution.jpg)
AnhydrousAuCl3 begins to decompose toAuCl (gold(I) chloride) at around 160 °C (320 °F); however, this, in turn, undergoesdisproportionation at higher temperatures to give gold metal and AuCl3:[5][10]
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 theMiller process.[14]
AuCl3 is aLewis acid and readily formscomplexes. For example, it reacts withhydrochloric acid to form chloroauric acid (H[AuCl4]):[15]
Chloroauric acid is the product formed when gold dissolves inaqua regia.[15]
On contact with water,AuCl3 formsacidic hydrates and theconjugate base[AuCl3(OH)]−. AFe2+ ion may reduce it, causing elemental gold to beprecipitated from the solution.[1][16]
Other chloride sources, such asKCl, also convertAuCl3 into[AuCl4]−.Aqueous solutions ofAuCl3 react with an aqueous base such assodium hydroxide to form a precipitate ofAu(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.[15][17][18][19]
Gold(III) chloride is the starting point for thechemical synthesis of many other gold compounds. For example, the reaction withpotassium cyanide produces the water-soluble complex,K[Au(CN)4]:[20]
Gold(III) fluoride can be also produced from gold(III) chloride by reacting it withbromine trifluoride.[15]
Gold(III) chloride reacts withbenzene under mild conditions (reaction times of a few minutes at room temperature) to produce the dimeric phenylgold(III) dichloride; a variety of otherarenes undergo a similar reaction:[21]
Gold(III) chloride reacts withcarbon monoxide in a variety of ways. For example, the reaction of anhydrous AuCl3 and carbon monoxide under SOCl2 producesgold(I,III) chloride with Au(CO)Cl as an intermediate:[22][23]
If carbon monoxide is in excess, Au(CO)Cl is produced instead.[24][25]
However, undertetrachloroethylene 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 ofphosgene.[25][26]
Gold(III) chloride has many uses in the laboratory, and primarily thrives in this environment.[5]
Since 2003,AuCl3 has attracted the interest of organic chemists as a mild acid catalyst for various reactions,[27] although no transformations have been commercialised. Gold(III)salts, especiallyNa[AuCl4], provide an alternative tomercury(II) salts as catalysts for reactions involvingalkynes. An illustrative reaction is the hydration of terminal alkynes to produceacetyl compounds.[28]
Gold catalyses thealkylation of certainaromatic rings and the conversion offurans tophenols. Some alkynes undergoamination in the presence of gold(III) catalysts. For example, a mixture ofacetonitrile and gold(III) chloride catalyses the alkylation of2-methylfuran bymethyl vinyl ketone at the 5-position:[29]
The efficiency of thisorganogold 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 fortosyl):[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 aFriedel-Crafts reaction using metal-alkyne complexes. Example, the reaction ofmesitylene withphenylacetylene:[31]
Gold(III) chloride can be used for the direct oxidation of primaryamines into ketones, such as the oxidation ofcyclohexylamine tocyclohexanone.[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 directelectrophilic auration of arenes by gold(III) chloride.[32]
Gold(III) chloride is used in the synthesis ofgold 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 assodium tetrafluoroborate, followed by stabilization with a capping agent.[33]
Gold(III) chloride has been used historically in thephotography 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]
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]
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