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Atoms & ions
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The periodic table
What is thiosulfate ion?
Thiosulfate (S2O32-) is an oxyanion of sulfur
produced by the reaction of sulfite ions with elemental sulfur in boiling water,
S(s) + SO32-(aq) S2O3-2(aq)
Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes.
In the body, thiosulfate converts small amounts of cyanide ion into harmless products and plays a role in the biosynthesis of cysteine, a sulfur-containing amino acid that locks proteins into their correct three-dimensional shapes.
Thiosulfate is not found in large quantities in nature. Solutions of thiosulfate break down into sulfur, sulfites, and sulfates when exposed to acids, light, metal ions, and bacteria.
Thiosulfate is a reducing agent. It is routinely used as a titrant to determine concentrations of oxidants such as hypochlorite in bleach and dissolved oxygen in water. It instantly dechlorinates water, and is used to stop bleaching action in the paper-making industry. Thiosulfate forms water-soluble complexes with many metals, making it useful in photoprocessing (where it dissolves excess silver bromide on the surface of exposed film, preventing excessive darkening). Thiosulfate is also useful in the extraction of silver from silver ore, in leather manufacture, and as a mordant in the textile industry.
What is the structure of the thiosulfate ion?
Structurally, thiosulfate is similar to sulfate. The molecule has a slightly distorted tetrahedral shape with a central and a peripheral sulfur (S-SO3). Sulfur is larger than oxygen and forms weaker bonds,
so the S-S bond is somewhat longer than the S-O bonds (1.99 +/- 0.03 A vs. 1.48 +/- 0.06 A, respectively) [Nardelli].
|Structure of the thiosulfate ion.|
Yellow = sulfur, Red = oxygen.
Click the image for a 3D Chime model.
What are some common thiosulfate compounds?
Common thiosulfate compounds.
(ammo hypo, Amthio
||fungicide; fixative in photographic development; lubricants for metalworking; metal cleaning agent
||manufacture of explosives and matches; photographic processes
||liquid lime/sulfur agricultural treatments
||gold(I) sodium thiosulfate dihydrate
(Auricidine, Aurocidin; Aurolin; Auropex;Auropin; Aurosan; Aurothion)
||screening for gold allergies; antirheumatic
||fixative in photographic development; liquid lime/sulfur agricultural treatments
||fixative in photographic development; water dechlorination; paper manufacture; whitening agent
Solubility data compiled from the CRC Handbook of Chemistry and Physics (CRC). Commercial and medical uses compiled from the Merck Index (Merck) and Web/paper references cited below.
What is thiosulfate used for?
Most of thiosulfate's usefulness stems from its ability to convert certain insoluble metal compounds into soluble complexes, and its ability to act
as a mild reducing agent.
How does thiosulfate ion affect health and the environment?
Thiosulfate is an antidote for cyanide poisoning. It reacts with cyanide to produce sulfite and thiocyanate ions:
CN- + S2O32- SCN- + SO32-
This reaction is catalyzed by an enzyme produced by cell mitochondria to neutralize small quantities of ingested cyanide (which occurs naturally in cassava root, lima beans, and almonds!).
Thiosulfate is an intermediate in several biochemical pathways, including the synthesis of L-cysteine (an amino acid).
Thiosulfate is manufactured by some cells by oxidation of elemental sulfur and by degradation of L-cysteine.
Thiosulfates break down rapidly in the environment due to the action of air and certain bacteria, eventually producing sulfides and sulfates.
Where does thiosulfate ion come from?
Thiosulfate is produced industrially by several different reactions:
- Reaction of sulfur with sodium sulfite in boiling aqueous solution,
S8 + 8 SO32- 8 S2O32-
- Reaction of SO2 gas with sulfide/carbonate liquor (a byproduct of paper manufacturing).
- As a byproduct in the manufacture of sulfur dyes.
References and Resources
- Crystallographic structure of the thiosulfate ion (M. Nardelli, G. Fava)
- Acta Cryst., 15, 477 (1962).
- The Merck Index (Merck & Co., Inc.)
- An encyclopedia of drugs and chemicals. (8th ed., Rahway, NJ 1968.
- Thiosulfate (S. W. Dahwak)
- J. Chem. Ed., 70, 12 (1993).
- Garments: Discoloration/Yellowing from Age (NCSU)
- Chemical mixtures for fabric whitening.
- Biochemical Oxygen Demand (RPI)
- Procedure for determining the extent to which oxygen in a sample can support microbial life. Thiosulfate is used as a titrant in the procedure.