Polythionates are oxoanions with the formula (''n'' ≥ 0). They occur naturally and are the products of redox reactions of

thiosulfate Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...

. Polythionates are readily isolable, unlike the parent polythionic acids.

Preparation

Many members of the polythionates have been characterized:

dithionate The dithionate (or metabisulfate) anion, , is a sulfur oxoanion derived from dithionic acid, H2S2O6. Its chemical formula is sometimes written in a semistructural format, as 3SSO3sup>2−. It is the first member of the polythionates. The su ...

, trithionate,

tetrathionate The tetrathionate anion, , 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 viewe ...

, pentathionate, etc. These salts are often generated by oxidation of thiosulfate. For example,

is obtained by oxidation of thiosulfate ion with iodine (reaction is used in

iodometry Iodometry, known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point. Note that iodometry involves indirect titration of iodin ...

): : More specialized routes involve reactions of sulfur chlorides with bisulfite salts: : : : Potassium pentathionate ion has been obtained from ,

sodium thiosulfate Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula . Typically it is available as the white or colorless pentahydrate, . The solid is an efflorescent (loses water readily) crystalline substance that dissolves well ...

, and

potassium acetate Potassium acetate (CH3COOK) is the potassium salt of acetic acid. It is a hygroscopic solid at room temperature. Preparation It can be prepared by treating a potassium-containing base such as potassium hydroxide or potassium carbonate with acetic ...

. 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. Potassium hexathionate has been synthesized by combining and in concentrated HCl at low temperatures.

References

{{Reflist Sulfur compounds