(NH4)2S2O3
Ammonium thiosulfat

Chemical properties

Ammonium thiosulfate forms colorless, elongated crystals. The commercially available crystalline powder appears white. The hygroscopic salt is very soluble in water, it dissolves very little in ethyl alcohol and not at all in organic solvents.

Ammonium thiosulfate is chemically more reactive than sodium thiosulfate. It decomposes already at heat and in warm, concentrated, aqueous solutions with yellowing and formation of sulphur. Strong heating to over 150 °C also produces sulphur dioxide, ammonia and nitrogen oxides.

Production

Ammonium thiosulfate is obtained by the reaction of sulfur with ammonium sulfite. The latter is obtained by introducing sulphur dioxide into ammonia solution.

(NH4)2SO3 + S → (NH4)2S2O3

Use

Ammonium thiosulphate is used as a rapid fixing salt (similar to sodium thiosulphate) for the production of fixing baths in film technology, photographic and X-ray technology and as a fertiliser.