TetraThionate, potassium

Sodium (and potassium) tetrathionate, M2S4O5, can be made by oxidation of thiosulfate by I2 (p. 714) and the free acid liberated (in aqueous solution) by addition of the stoichiometric amount of tartaric acid. 

The potassium salt may be prepared 4 in the same way if potassium thiosulfate is available. Otherwise, potassium tetrathionate (anhydrous) is formed by dissolving the sodium salt in its own weight of water at 40 0, adding 200% of the calculated amount of potassium acetate, and 1-2 volumes of alcohol. 

Potassium tetrathionate, K2S406.—The tetrathionate is formed by the interaction of potassium thiosulphate in aqueous solution and iodine, the salt being precipitated from the reaction-mixture by addition of alcohol. It is crystalline, and has a density of 2-296. The heat of formation from the elements is 897-21 Cal.7... 

Barium tetrathionate [82203-66-5] M 361.6. Purify the tetrathionate by dissolving it in a small volume of water and precipitating it with EtOH below 5°. After drying, the salt is stored in the dark at 0". [see FrehCT in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 399-401 1963 fw potassium tetrathionate K2S4O4.]... 

Until 1950 the only X-ray crystallographic work on polythionates was Zachariasen s structure determination of potassium trithionate (239) published in 1934, a partial structure analysis of thallium trithionate by Ketelaar and Sanders (151) in 1936, and unit cell and space group determinations of rubidium trithionate (161) and potassium tetrathionate (218). Since then, surveys of unit cells and space groups of tetra-, penta-, and hexathionates and selenotrithionates, selenopentathionates, and telluropentathionates have been made, and structure determinations of two tetrathionates, three pentathionates, one selenopentathionate, two telluropentathionates, and two hexathionates have been carried out. 

Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 399-401 1963 for potassium tetrathionate K2S4O4.]... 

The amount of sodium hypochlorite in a bleach solution can be determined by using a given volume of bleach to oxidize excess iodide ion to iodine CIO- is reduced to Cl-. The amount of iodine produced by the redox reaction is determined by titration with sodium thiosulfate, Na2S203 I2 is reduced to I-. The sodium thiosulfate is oxidized to sodium tetrathionate, Na2S406. In this analysis, potassium iodide was added in excess to 5.00 ml of bleach d = 1.00 g/cm3). If 25.00 mL of 0.0700 MNa2S203 was required to reduce all the iodine produced by the bleach back to iodide, what is the mass percent of NaCIO in the bleach ... 

A convenient method of preparing the potassium salt is to use this reaction, filter off the copper salt and to the concentrated filtrate add potassium acetate, when the tetrathionate separates this, after removal, should be washed with alcohol.10... 

Sulphur dioxide when passed through a solution of a thiosulphate gives rise not only to tetrathionate but also to trithionate and penta-thionate.12 Under suitable conditions, however, with a high concentration of sulphur dioxide, the tetrathionate separates. The reaction is accelerated by traces of potassium arsenite.13... 

In the interaction of sulphur monochloride with potassium thiosulphate, tetrathionate is obtained as the highest polythionate product.1... 

The tetrathionates are converted by nascent sulphur into penta-thionates, whilst by potassium sulphite solution they are reduced to trithionate.7 The latter reaction explains the erroneous assumption that trithionate could be directly produced by the action of iodine on an aqueous mixture of potassium thiosulphate and sulphite8 (see p. 210). With equivalent quantities of tetrathionate and sulphite, the reaction leads to the equilibrium 9... 

Potassium amalgam reduces an aqueous pentathionate solution to tetrathionate and thiosulphate. Metallic copper and silver are blackened by pentathionate solutions. 

Mercury fulminate dissolves readily in an aqueous solution of potassium cyanide to form a complex compound from which it is reprecipitated by the addition of strong acid. It dissolves in pyridine and precipitates again if the solution is poured into water. A sodium thiosulfate solution dissolves mercury fulminate with the formation of mercury tetrathionate and other inert compounds, and this reagent is used both for the destruction of fulminate and for its analysis.10 The first reaction appears to be as follows. 

Silicic acid gel, when evaporated with a slight excess of 30 per cent, peroxide, yields a highly active amorphous residue which continuously evolves ozonised oxygen. It liberates chlorine from hydrochloric acid, iodine from potassium iodide, decolorises permanganate, and evolves ozone with concentrated sulphuric acid.4 Possibly a persilicic acid is formed. Thiosulphates are at first oxidised to tetrathionates, the solution becoming alkaline 5... 

Ammonium trithionate, (NH4)2S306.—An aqueous solution of potassium trithionate reacts with hydrofluosilicic acid and ammonia to form the trithionate, which is precipitated from its aqueous solution by alcohol as a very deliquescent, unstable salt.15 It is also formed, along with the tetrathionate, by the action of sulphur dioxide on ammonium thiosulphate 16... 

To ensure that the bromination reaction proceeds quantitatively to the right-hand side, an excess of bromine is generated and the volume of bromine that does not react with resorcinol is determined by back titration. Bromine cannot be titrated easily, so the excess bromine is determined by addition of an excess of potassium iodide and titration of the liberated iodine with sodium thiosulfate, to give sodium iodide and sodium tetrathionate. 

Hertlein (US) in 1896 measured refraction, viscosity, and electrical conductivity of aqueous potassium tri-, tetra-, and pentathionates and decided in favor of uiibranched structures, and so did Martin and Metz (171) in 1924 on the basis of thermochemical measurements. Spacu and Popper (208) in 1939 reported the refraction of sodium tetrathionate Grinberg (186) has later commented on the ionic refraction of tetra thionate as indicating negative charge on the divalent sulfur atoms. However, from Hertlein s measurements the increments per sulfur atom, from tri-to tetra-thionate and tetra- to pentathionate, are about 9 cm3. This is the same as in other series, for example, in the polysulfur dichlorides (72) where the sulfur atoms are hardly negative. 

The first structure determination of a tetrathionate, the barium salt, was published in 1954, 20 years after that of potassium trithionate. 

The isomorphous potassium (218) and rubidium (91) salts have large cells with two tetrathionate ions in the asymmetric unit. 

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