Gold(III) chloride

Gold trichloride

Red crystalline solid

Fixed

3.9 g · cm -3

254 ° C ( decomposition)

Readily soluble in water: 680 g · l-1 (20 ° C)

Risk

Not yet determined

-117.6 KJ / mol

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Gold (III ) chloride is one of the most important gold compounds with the empirical formula AuCl 3. Other gold chlorides are AuCl and AuCl2. However AuCl2 is not gold ( II) compound, but a mixed-valence Au ( I) -/Au ( III) compound.

Production and representation

Gold (III ) chloride is prepared by passing chlorine gas over finely divided gold at 250 ° C.

Properties

Physical Properties

AuCl3 is present both in the solid state and in the vapor phase as a dimer Au2Cl6. The same applies to the Goldbromid AuBr3. In contrast to the dimeric aluminum chloride also the gold ( III) chloride dimer are precisely arranged the AuCl4 - unit is square - planar. At ( AlCl3 ) 2 is established tetrahedral and bridging atoms are above and below the plane. The Au - Cl bond is built up strong covalent, this is due to the ( relatively ) high electronegativity of gold and the high oxidation state.

Gold (III ) chloride is very hygroscopic and readily soluble in water and ethanol.

Chemical Properties

This is the most stable 3 oxidation state of gold in compounds and complexes.

At temperatures above 250 ° C decomposes into AuCl and AuCl 3 Cl2.

AuCl3 is a Lewis acid and forms complexes of the form, many M AuCl4 ( Tetrachloroaurate ). M can be for example potassium ( Kaliumtetrachloridoaurat (III ) ). This AuCl4 - ion is not very stable in aqueous solution.

Add hydrochloric acid to dissolve to form AuCl3 tetrachloroauric.

In aqueous solution of AuCl 3 reacts with alkali hydroxides (eg, sodium hydroxide) to Au ( OH ) 3 This reacts when heated in air to gold (III ) oxide Au2O3 and further to metallic gold.

Use

Gold ( III) chloride is widely used as a starting material for the preparation of other gold compounds and complexes. An example is the production of cyanide complex KAu (CN) 4

Applications in organic chemistry:

Gold ( III) salts, especially NaAuCl4 ( of AuCl3 and sodium chloride) ) can be used in reactions with alkynes in the organic synthesis as a catalyst. They are there as a non-toxic substitute for mercury (II ) salts. An important example is the hydration of terminal alkynes to obtain a high yield of methyl ketones. Amines can be prepared in a similar manner.

Gold ( III) chloride can be used as a mild catalyst for the alkylation of aromatic and heteroaromatic compounds. An example is the alkylation of 2- methylfuran with methyl vinyl ketone.

For furan derivatives and alkynes can be formed in a rearrangement catalyzed by gold (III ) chloride is a phenol.