Gold(III) chloride, traditionally called auric chloride, is the chemical compound with the formula AuCl3. The Roman numerals in the name indicate that the gold has an oxidation 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 in aqua regia, is sometimes referred to as "gold chloride", "acid gold trichloride" or even "gold(III) chloride trihydrate."
AuCl3 exists as a dimer 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 high electronegativity (for a metal) of gold.
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 to gold(III) oxide, Au2O3, and then to gold metal.
Another method of preparation is the reaction in which solid gold is placed in a solution of aqua regia.
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 as alkylation of aromatics and a conversion of furans to phenols (see below). Such reactions are of potential value in organic synthesis, for example for the preparation of pharmaceuticals. For example, in acetonitrile, 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 alkynes are present, a phenol may be formed:
The reaction undergoes a complex rearrangement that leading to a new aromatic ring.
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Apr 03, 2013; By a News Reporter-Staff News Editor at Biotech Week -- According to news reporting originating from Washington, D.C., by NewsRx...