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The oxidation of ammonium thiosulfate with compressed oxygen in aqueous ammonia solution was examined. It was found that ammonium sulfamate and ammonium sulfate are mainly produced and a small amount of nitrite and imidodisulfonate obtained in the final solution. The most suitable conditions to produce ammonium sulfamate from ammonium thiosulfate industrially are as follows: reaction temperature 100°C, oxygen pressure 50 kg/cm2, concentration of ammonia 16 mol/l, concentration of cupric ion 0.1–0.2 mol/l. The electrolytic oxidation, hydrogen peroxide oxidation and ozone oxidation of ammonium thiosulfate were also examined.

The decomposition and oxygen oxidation of tetrathionate in aqueous ammonia solution have been investigated. In the decomposition, thiosulfate, sulfate and sulfamate were formed through penta- and trithionate as intermediate compounds. The molar ratio of the products (SO42−+SO3NH2−)/S2O32− was roughly equal to 2/7, where 0.1n ammonia solution was used. The deficient use of ammonia made the solution neutral or weakly acidic and the precipitation of sulfur and the formation of higher polythionates were observed. The polythionate was detected by means of TLC (Thin Layer Chromatography). In the oxidation, tetrathionate was supposed to go through the following three sequent steps. 1) Decomposition of tetrathionate to form thiosulfate, tri- and pentathionate, and further decomposition of pentathionate to thiosulfate. 2) Oxidation of thiosulfate to tetrathionate and partly to sulfate. 3) Decomposition of trithionate to form sulfate, sulfamate and thiosulfate.

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