Selenopentathionate. sodium

Sodium selenocyanate, 2 186, 187 Sodium selenopentathionate 3-hydrate, 4 88, 89 Sodium sulfate, removal of, in... 

Sodium selenopentathionate 3-hydrate, which was first isolated in 1949,1 is prepared by the reaction used by Norris and Fay2 for the iodometric analysis of selenious acid. Salts of telluropentathionic acid were also first isolated in 1949.3 The reaction utilized in their preparation was also discovered by Norris and Fay.2,4 Tellurous acid cannot be analyzed by a procedure analogous to that which Norris and Fay applied to the determination of selenious acid, because telluropentathionate is not indifferent to iodine but may be titrated directly with it 3... 

The crude product contains about 40 g. of sodium selenopentathionate 3-hydrate and about 4 mol per cent of sodium tetrathionate. It is dissolved in 50 ml. of 0.2 N hydrochloric acid at about 30°, and the solution is filtered with suction. One hundred milliliters of methanol is added, and the mixture is cooled in an ice-salt mixture. Pure sodium selenopentathionate 3-hydrate precipitates and is filtered, washed with ethanol, and dried in vacuo over sulfuric acid. The yield is about 25 g. (55%). 

Sodium selenopentathionate 3-hydrate crystallizes as small, voluminous, pale yellowish-green leaves or thin plates. It is veiy soluble in water and appreciably soluble in methanol, but insoluble in ethanol. Aqueous solutions of the substance are yellowish green. 

Sodium telluropentathionate 2-hydrate crystallizes as small plates or flat needles. A mass of crystals appears yellow with an orange tint single crystals are yellow with a greenish tint. Dilute aqueous solutions are yellow concentrated solutions are orange red. The salt is readily soluble in water, though less soluble than the analogous selenium compound. It is insoluble in ethanol and insoluble or very sparingly soluble in methanol. Its water of hydration, like that associated with sodium selenopentathionate, is lost very slowly in vacuo over sulfuric acid. 

Xanthates and dithioearbamates of bivalent selenium and tellurium may be conveniently prepared3-5 by allowing sodium selenopentathionate or sodium telluropenta-thionate to react with alkali xanthates or dithiocar-bamates. The reactions are rapid and quantitative, and the products separate from the aqueous reaction mixtures in a high state of purity. 

A solution of 0.025 mol of sodium or potassium xanthate or dithiocarbamate in 100 ml. of water is added, with stirring, to 3.5 g. of sodium selenopentathionate (0.01 mol) or 4.0 g. of sodium telluropentathionate (0.01 mol) (.synthesis 31) dissolved in 100 ml. of water. The product immediately precipitates, and after being stirred for several minutes, it coagulates, leaving a clear liquid. It is filtered, washed with water and methanol, and dried in vacuo over sulfuric acid. Conditions for crystallization of some of these compounds are outlined in Table I. Selenium ethyl-xanthate, which is an oil, is extracted from the aqueous layer with ether. The ether extract so obtained is dried over anhydrous sodium sulfate, after which the ether is removed by distillation. 

Selenopentathionic Acid, H2SeS4O0, is stated to be formed as the sodium salt when sodium thiosulphate and selenious acid interact in the presence of dilute hydrochloric acid. The reaction is described as taking place according to the equation... 

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