Ammonium thiosulfate (ammonium thiosulphate in British English) is an inorganic compound with the formula [NH4]2S2O3. It is white crystalline solid with ammonia odor, readily soluble in water, slightly soluble in acetone and insoluble in ethanol and diethyl ether.[1]
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| Names | |
|---|---|
| IUPAC name Diammonium thiosulfate | |
| Other names Ammonium thiosulphate, ATS | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.029.074 |
PubChem CID | |
| UNII | |
CompTox Dashboard (EPA) | |
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| Properties | |
| [NH4]2S2O3 | |
| Molar mass | 148.20 g·mol−1 |
| Appearance | colorless or white, hygroscopic solid |
| Density | 1.679 g/cm3 |
| Melting point | decomposes at 100 °C |
| 173 g/100 mL (20 °C) | |
| Solubility | slightly soluble in acetone insoluble in alcohol |
| Structure | |
| monoclinic | |
| Hazards | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 2980 mg/kg (rat, oral) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Production
It is produced by treating ammonium sulfite with sulfur at temperatures between 85 and 110 °C:[2]
- [NH4]2SO3 + S → [NH4]2S2O3
Applications
Ammonium thiosulfate is used in photographic fixer. It is a so-called rapid fixer, acting more quickly than sodium thiosulfate fixers.[3] Fixation involves these chemical reactions (illustrated for silver bromide):[4]
- AgBr + 2 [NH4]2S2O3 → [NH4]3[Ag(S2O3)2] + [NH4]Br
- AgBr + 3 [NH4]2S2O3 → [NH4]5[Ag(S2O3)3] + [NH4]Br
Also exploiting the stability of thiosulfate coordination complexes, ammonium thiosulfate is also used for leaching of gold and silver. It works with presence of copper as a catalyst. This process is a nontoxic alternative gold cyanidation.[5] The advantage to ammonium thiosulfate is that the pyrolysis of its silver complexes leaves a residue solely of silver sulfide, in contrast to complexes derived from sodium thiosulfate.[2]
Other
Ammonium thiosulfate can be used as a fertilizer.[6] As suggested by some research studies, it can also be used as an additive to coal-waste mixtures to reduce formation of dioxins and furans during combustion.[7]