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 g ...
AuCl3 exists as a dimer both as a solid and as a vapour; the bromide AuBr3 follows the same pattern. This is similar (but not identical) to the tetrahedral dimers formed by AlCl3 and FeCl3. The bonding in AuCl3 is mainly covalent, reflecting the high oxidation state and relatively high electronegativity (for a metal) of the gold.
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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 KAu(CN)4:
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 ke ...
Anhydrous AuCl3 begins to decompose to AuCl at around 160 °C; however at 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 A ...
