Thiosulfate

Thiosulfate (S₂O₃²⁻), sometimes spelled thiosulphate, Its fully deprotonated structural IUPAC name is sulfanidesulfonate, the name of its corresponding acid is S-sulfosulfanethiol. When the sulfanyl moiety is deprotonated, its name is sulfosulfanide, when the oxidanyl moiety is deprotonated, its name is S-sulfonatosulfanethiol. The preferred IUPAC name for the protonated species is thiosulfuric acid.

Thiosulfates are stable only in neutral or alkaline solutions, but not in acidic solutions, due to decomposition to sulfite and sulfur, the sulfite being dehydrated to sulfur dioxide:

:S₂O₃²⁻ (aq) + 2 H⁺ (aq) → SO₂ (g) + S (s) + H₂O

This reaction may be used to generate a temporary aqueous suspension of particles and demonstrate the Rayleigh scattering of light in physics. If white light is shone from below, blue light is seen from sideways and orange from above, due to the same mechanisms that color the sky at mid-day and dusk.

Thiosulfates react with halogens differently, which can be attributed the decrease of oxidizing power down the halogen group:

:2 S₂O₃²⁻ (aq) + I₂ (aq) → S₄O₆²⁻ (aq) + 2 I⁻ (aq)

:S₂O₃²⁻ (aq) + 4 Br₂ (aq) + 5 H₂O(l) → 2 SO₄²⁻ (aq) + 8 Br⁻ (aq) + 10 H⁺ (aq)

:S₂O₃²⁻ (aq) + 4 Cl₂ (aq) + 5 H₂O (l) → 2 SO₄²⁻ (aq) + 8 Cl⁻ (aq) + 10 H⁺ (aq)

Thiosulfate causes rapid corrosion of metals; steel and stainless steel are particularly sensitive to pitting corrosion induced by thiosulfate. Addition of molybdenum to stainless steel is needed to improve its resistance to pitting (AISI 316L hMo). Thiosulfates are also often produced by incomplete oxidation of sulfides (pyrite oxidation) or partial reduction of sulfate (Kraft paper).

The natural occurrence of the thiosulfate group is practically restricted to a very rare mineral sidpietersite, Pb₄(S₂O₃)O₂(OH)₂, as the presence of this anion in the mineral bazhenovite was recently disputed.

References

* Category:Corrosion