Properties of the gold(I) sulfite complex in acidic chloride solutions

Abstract

The effects of various factors on the redox stability of the gold(I) sulfite complex Au(SO₃)₂^3- in acidic chloride solutions is studied. Increased concentrations of gold and H⁺, as well as temperature, reduce the time before traces of gold(0) emerge; increased concentrations of sulfite and especially of Cl^– increase this time. The beaker material (quartz, glass, or polypropylene) is found to have no significant effect. Added organic solvents have different effects. It is shown using UV spectroscopy and pH measurements that the average number of SO₃^2- ions bound to one gold(I) ion can be much greater than two even at an excessive amount of sulfite in the acidic region (pH 2–4) due to the equilibrium Au(SO₃)Cl^2– + SO₃^2- = Au(SO₃)₂^3- + Cl^– with the constant logK₂ = 6.4 ± 0.1 at 25°C and I = 1 M (NaCl).