Gold(III) chloride, traditionally called auric chloride, is a

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...

and

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

with the

molecular formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

. The "III" in the name indicates that the gold has an

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

of +3, typical for many gold compounds. Gold(III) chloride is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...

and decomposes in visible light. This compound is a

dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...

of . This compound has few uses, although it catalyzes various

organic reactions Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemi ...

Structure

exists as a chloride-bridged

both as a

solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...

and

vapour In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Herr ...

, at least at low temperatures.

Gold(III) bromide Gold(III) bromide is a dark-red to black crystalline solid.Macintyre, J. E. (ed.) ''Dictionary of Inorganic Compounds''; Chapman & Hall: London, 1992; vol. 1, pp. 121Greenwood, N.N.; Earnshaw, A. ''Chemistry of the Elements''; Butterworth-Heineman ...

behaves analogously. The structure is similar to that of

iodine(III) chloride Iodine trichloride is an interhalogen compound of iodine and chlorine. It is bright yellow but upon time and exposure to light it turns red due to the presence of elemental iodine. In the solid state is present as a planar dimer I2Cl6, with two b ...

. Each gold center is

square planar The square planar molecular geometry in chemistry describes the stereochemistry (spatial arrangement of atoms) that is adopted by certain chemical compounds. As the name suggests, molecules of this geometry have their atoms positioned at the corne ...

in gold(III) chloride, which is typical of a metal complex with a d⁸ electron count. The bonding in is considered somewhat

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

Preparation

Gold(III) chloride is most often prepared by passing

gas over

powder at : : The

chlorination reaction 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 polymer ...

can be conducted in the presence of

tetrabutylammonium chloride Tetrabutylammonium chloride is the organic compound with the formula (C4H9)4NCl. A white water-soluble solid, it is a quaternary ammonium salt of chloride. It is a precursor to other tetrabutylammonium salts. Often tetrabutylammonium bromide ...

, the product being the

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipo ...

salt tetrabutylammonium tetrachloraurate. Another method of preparation is via

chloroauric acid Chloroauric acid is an inorganic compound with the chemical formula . It forms hydrates . Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar anion. Often chloroauric acid is handled as a soluti ...

, which is obtained by first dissolving the gold powder in '' aqua regia'' to give chloroauric acid: : The resulting chloroauric acid is subsequently heated to give : :

Reactions

On contact with water, forms acidic hydrates and the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

. An ion may reduce it, causing elemental gold to be precipitated from the solution.

Anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achi ...

begins to decompose to AuCl at around , however, this, in turn, undergoes

disproportionation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...

at higher temperatures to give gold metal and AuCl₃: : (>160 °C) : (>420 °C) is a

lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

and readily forms complexes. For example, it reacts with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

to form chloroauric acid (): :

Chloroauric acid Chloroauric acid is an inorganic compound with the chemical formula . It forms hydrates . Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar anion. Often chloroauric acid is handled as a soluti ...

is the product formed when gold dissolves in '' aqua regia''. Other chloride sources, such as KCl, also convert into .

Aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...

solutions of react with an aqueous base such as

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and al ...

to form a precipitate of , which will dissolve in excess NaOH to form sodium aurate (). If gently heated, decomposes to gold(III) oxide, , and then to gold metal.''The

Merck Index ''The Merck Index'' is an encyclopedia of chemicals, drugs and biologicals with over 10,000 monograph on single substances or groups of related compounds published online by the Royal Society of Chemistry. History The first edition of the Mer ...

. An Encyclopaedia of Chemicals, Drugs and Biologicals''. 14. Ed., 2006, p. 780, . Gold(III) chloride is the starting point for the

chemical synthesis As a topic of chemistry, chemical synthesis (or combination) is the artificial execution of chemical reactions to obtain one or several products. This occurs by physical and chemical manipulations usually involving one or more reactions. In mod ...

of many other gold compounds. For example, the reaction with

potassium cyanide Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications inc ...

produces the water-soluble complex, : : Gold(III) chloride reacts with benzene (and a variety of other

arenes Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupi ...

) under mild conditions (reaction times of a few minutes at room temperature) to produce the dimeric phenylgold(III) dichloride: :

Applications

Organic synthesis

although no transformations have been commercialised. Gold(III)

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...

, especially , provide an alternative to mercury(II) salts as catalysts for reactions involving

alkynes \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne 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 ...

. An illustrative reaction is the hydration of terminal alkynes to produce

acetyl In organic chemistry, acetyl is a functional group with the chemical formula and the structure . It is sometimes represented by the symbol Ac (not to be confused with the element actinium). In IUPAC nomenclature, acetyl is called ethanoyl, ...

compounds. : Example of gold-catalyzed alkyne hydration reaction

Gold catalyses the

alkylation Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effectin ...

of certain

aromatic rings In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to saturat ...

and the conversion of

furans Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...

phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...

. Some alkynes undergo

amination Amination is the process by which an amine group is introduced into an organic molecule. This type of reaction is important because organonitrogen compounds are pervasive. Reactions ;Aminase enzymes Enzymes that catalysis, catalyse this reaction a ...

in the presence of gold(III) catalysts. For example, a mixture of

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile ( hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

and gold(III) chloride catalyses the alkylation of 2-methylfuran by

methyl vinyl ketone Methyl vinyl ketone (MVK, IUPAC name: butenone) is the organic compound with the formula CH3C(O)CH=CH2. It is a reactive compound classified as an enone, in fact the simplest example thereof. It is a colorless, flammable, highly toxic liquid w ...

at the 5-position: : Alkylation reaction of 2-methylfuran with methyl vinyl ketone

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 In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or Tos) is a univalent functional group with the chemical formula –. It consists of a tolyl group, –, joined to a sulfonyl group, ––, with the open valence o ...

): :

This reaction involves a rearrangement that gives a new aromatic ring.

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 Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

proved to be the most effective method for forming nanoparticles. However, other methods work such as replacing the 1-dodecanethiol with dioctyl sulfide. The gold(III) chloride is the source of gold in this production.

References

External links

* {{Chlorides Chlorides Metal halides Gold(III) compounds Deliquescent substances Photographic chemicals Gold–halogen compounds