Gold chloride From Wikipedia:
Gold(III) chloride, traditionally called auric chloride, is one of
the most common compounds of gold. It has the formula AuCl3. The
Roman numerals in the name indicate that the gold has an oxidation
state of +3, which is the most stable form for gold in its
compounds. Gold also forms another chloride, gold(I) chloride
(AuCl), which is less stable than AuCl3. Also, chlorauric acid
(HAuCl4), the product formed when gold dissolves in aqua regia, is
sometimes referred to rather loosely as "gold chloride", "acid gold
trichloride" or even "gold(III) chloride trihydrate".
Gold(III) chloride is very hygroscopic and highly soluble in water
and ethanol. It decomposes above 160 C or in light, and it forms a
variety of complexes with many ligands.
AuCl3 exists as a dimer both as a solid and as a vapour; the bromide
AuBr3 follows the same pattern. Each Au center is square planar.
This structure is reminiscent of the bitetrahedral structures
adopted by AlCl3 and FeCl3. The bonding in AuCl3 is mainly covalent,
reflecting the high oxidation state and relatively high
electronegativity (for a metal) of gold.
Anhydrous AuCl3 begins to decompose to AuCl at around 160 C;
however, this will in turn undergo 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 which readily forms complexes. For example
with hydrochloric acid, chlorauric acid (HAuCl4) is formed:
HCl(aq) + AuCl3(aq) -> H+AuCl4-(aq)
Ionic chlorides such as KCl will also form the AuCl4- ion with
Aqueous solutions of AuCl3 react with alkalis such as sodium
hydroxide to form a precipitate of impure 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(III) chloride is most often prepared by direct chlorination of
the metal at high temperatures:
2 Au + 3 Cl2 -> 2 AuCl3
Gold(III) chloride is one of the most common gold compounds and it
is therefore used as the starting point for the synthesis of many
other gold compounds, for example the water-soluble cyanide complex
AuCl3 + 4 KCN -> KAu(CN)4 + 3 KCl
Gold(III) salts, especially NaAuCl4 (made from AuCl3 + NaCl),
provide a non-toxic alternative to mercury(II) salts as catalysts
for alkyne reactions. One important reaction of this sort is the
hydration of terminal alkynes to produce methyl ketones.
Ketones are generally formed in over 90% yield under these
conditions. Also useful is the related amination of alkynes which
can use 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 find use in organic synthesis and in the
pharmaceutical industry. For example, 2-methylfuran (sylvan)
undergoes smooth alkylation by methyl vinyl ketone at the 5-position.
The reaction gives a 91% yield in only 40 minutes at room
temperature, using only 1 mole% of AuCl3 in acetonitrile. This yield
is noteworthy since 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
The reaction undergoes a complex rearrangement that leads to
formation of the new aromatic ring
Gold(III) chloride should be handled wearing gloves and goggles;
direct contact with the material should be avoided.