Tetrathionate

The structure of the tetrathionate anion

The tetrathionate anion, S₄O₆²⁻, is a sulfur oxoanion derived from the compound tetrathionic acid, H₂S₄O₆. Two of the sulfur atoms present in the ion are in oxidation state 0 and two are in oxidation state +5. Alternatively, the compound can be viewed as the adduct resulting from the binding of the Lewis base S₂²⁻ to SO₃. Tetrathionate is one of the polythionates, a family of anions with the formula [S_n(SO₃)₂]²⁻. Its IUPAC name is (sulfonatodisulfanyl)sulfonate, the name of its corresponding acid is (sulfodisulfanyl)sulfonic acid. The Chemical Abstracts Service identifies tetrathionate by the CAS Number 15536-54-6.

Tetrathionate is a product of the oxidation of thiosulfate, S₂O₃²⁻, by iodine, I₂:

2S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2I⁻

Structure

Tetrathionate's structure can be visualized by following three edges of a cube, as in the diagram below. The structure shown is the configuration of S₄O₆²⁻ in BaS₄O₆·2H₂O and Na₂S₄O₆·2H₂O. Dihedral S-S-S-S angles approaching 90° are common in polysulfides.

Compounds

Compounds containing the tetrathionate anion include sodium tetrathionate, Na₂S₄O₆, potassium tetrathionate, K₂S₄O₆, and barium tetrathionate dihydrate, BaS₄O₆·2H₂O.

Properties

As other reduced species of sulfur, such as thiosulfate, tetrathionate can be responsible for the pitting corrosion of carbon steel and stainless steel.

See also

• Corrosion
• Dithionite
• Polysulfides
• Thiosulfate

References

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.