Ammonium thiosulfate

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]

Ammonium thiosulfate

Names
IUPAC name Diammonium thiosulfate
Other names Ammonium thiosulphate, ATS
Identifiers
CAS Number	7783-18-8 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:147402
ChemSpider	4807475 Y
ECHA InfoCard	100.029.074
PubChem CID	6096946
UNII	BKH1729645 Y
CompTox Dashboard (EPA)	DTXSID6029703
InChI InChI=1S/2H3N.H2O3S2/c;;1-5(2,3)4/h2*1H3;(H2,1,2,3,4) Y Key: XYXNTHIYBIDHGM-UHFFFAOYSA-N Y InChI=1S/2H3N.H2O3S2/c;;1-5(2,3)4/h2*1H3;(H2,1,2,3,4)
SMILES [O-]S([O-])(=O)=S.[NH4+].[NH4+]
Properties
Chemical formula	[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
Solubility in water	173 g/100 mL (20 °C)
Solubility	slightly soluble in acetone insoluble in alcohol
Structure
Crystal 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). Y verify (what is YN ?) Infobox references

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]

Safety

LD50 (oral, rat) is 2890 mg/kg.^[2]

See also

• Thiosulfate
• Sodium thiosulfate
• Ammonium sulfate