Polythionates

Polythionates are oxyanions with the formula ⁻O₃S−S_n−SO−3 (n ≥ 0). They occur naturally and are the products of redox reactions of thiosulfate. Polythionates are readily isolable, unlike the parent polythionic acids.[2]

Structure of the hexathionate dianion.[1]

Preparation

Many members of the polythionates have been characterized: dithionate, trithionate, tetrathionate, pentathionate, etc.

These salts are often generated by oxidation of thiosulfate. For example, tetrathionate is obtained by oxidation of thiosulfate ion with iodine (reaction is used in iodometry):

S₂O2−3 + I₂ → S₄O2−6 + 2 I⁻

More specialized routes involve reactions of sulfur chlorides with bisulfite salts:

SCl₂ + 2 HSO−3 → [O₃SSSO₃]²⁻ + 2 HCl

S₂Cl₂ + 2 HSO−3 → [O₃SS₂SO₃]²⁻ + 2 HCl

SCl₂ + 2 HS₂O−3 → [O₃SS₃SO₃]²⁻ + 2 HCl

Potassium pentathionate ion has been obtained from SCl₂, sodium thiosulfate, and potassium acetate. Initially prismatic crystals of potassium tetrathionate appear, then lamellar crystals of potassium pentathionate, from which the influence of tartaric acid makes an aqueous solution of pentathionic acid.[3]

Potassium hexathionate K₂S₆O₆ has been synthesized by combining KNO₂ and K₂S₂O₃ in concentrated HCl at low temperatures.[4]

References

Marøy, Kjartan (1973). "Refinement of the Crystal Structure of trans-Dichlorobis(ethylenediamine)cobalt(III) Hexathionate Monohydrate". Acta Chemica Scandinavica. 27: 1705–1716. doi:10.3891/acta.chem.scand.27-1705.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
P. W. Schenk (1963). "Sulfur, Selenium, Tellurium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY,NY: Academic Press. p. 401.
P. W. Schenk (1963). "Sulfur, Selenium, Tellurium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY,NY: Academic Press. p. 403.

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[1] Marøy, Kjartan (1973). "Refinement of the Crystal Structure of trans-Dichlorobis(ethylenediamine)cobalt(III) Hexathionate Monohydrate". Acta Chemica Scandinavica. 27: 1705–1716. doi:10.3891/acta.chem.scand.27-1705.

[2] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[3] P. W. Schenk (1963). "Sulfur, Selenium, Tellurium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY,NY: Academic Press. p. 401.

[4] P. W. Schenk (1963). "Sulfur, Selenium, Tellurium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY,NY: Academic Press. p. 403.