Sodium thiosulfate
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IUPAC name
Sodium thiosulfate
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Other names
Sodium hyposulphite
Hyposulphite of soda Hypo | |
Identifiers | |
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3D model (
JSmol ) |
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ChEBI | |
ChEMBL |
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ChemSpider | |
ECHA InfoCard
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100.028.970 |
EC Number |
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E number | E539 (acidity regulators, ...) |
PubChem CID
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RTECS number
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UNII |
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CompTox Dashboard (EPA)
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Properties | |
Na2S2O3 | |
Molar mass | 158.11 g/mol (anhydrous) 248.18 g/mol (pentahydrate) |
Appearance | White crystals |
Odor | Odorless |
Density | 1.667 g/cm3 |
Melting point | 48.3 °C (118.9 °F; 321.4 K) (pentahydrate) |
Boiling point | 100 °C (212 °F; 373 K) (pentahydrate, - 5H2O decomposition) |
70.1 g/100 mL (20 °C)[1] 231 g/100 mL (100 °C) | |
Solubility | negligible in alcohol |
Refractive index (nD)
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1.489 |
Structure | |
monoclinic | |
Hazards | |
GHS labelling: | |
Warning | |
H315, H319, H335 | |
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501 | |
NFPA 704 (fire diamond) | |
Flash point | Non-flammable |
Safety data sheet (SDS) | External MSDS |
Related compounds | |
Other cations
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Thiosulfuric acid Lithium thiosulfate Potassium thiosulfate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na2S2O3·(H2O)(x). Typically it is available as the white or colorless pentahydrate (x = 5). It is a white solid that dissolves well in water. The compound is a reducing agent and a ligand, and these properties underpin its applications.[2]
Uses
Sodium thiosulfate is used predominantly in dyeing. It converts some dyes to their soluble colorless "leuco" forms. It is also used to bleach "wool, cotton, silk, ...soaps, glues, clay, sand, bauxite, and... edible oils, edible fats, and gelatin."[2]
Medical uses
Sodium thiosulfate is used in the treatment of
Photographic processing
In photography, sodium thiosulfate is known as a fixer, sometimes still called 'hypo' from the original chemical name, hyposulphite of soda.[12] It functions to dissolve silver halides, e.g., AgBr, components of photographic emulsions. It is used for both film and photographic paper processing. Ammonium thiosulfate is typically preferred to sodium thiosulfate for this application.[2] The ability of thiosulfate to dissolve silver ions is related to its ability to dissolve gold ions described below.
Neutralizing chlorinated water
It is used to dechlorinate tap water including lowering
In pH testing of bleach substances, sodium thiosulfate neutralizes the color-removing effects of bleach and allows one to test the pH of bleach solutions with liquid indicators. The relevant reaction is akin to the iodine reaction: thiosulfate reduces the hypochlorite (the active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:
- 4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O
Similarly, sodium thiosulfate reacts with bromine, removing the free bromine from the solution. Solutions of sodium thiosulfate are commonly used as a precaution in chemistry laboratories when working with bromine and for the safe disposal of bromine, iodine, or other strong oxidizers.
Structure
Two polymorphs are known as pentahydrate. The anhydrous salt exists in several polymorphs.
Production
Sodium thiosulfate is prepared by oxidation of sodium sulfite with sulfur.[2] It is also produced from waste sodium sulfide from the manufacture of sulfur dyes.[13]
This salt can also be prepared by boiling aqueous sodium hydroxide and sulfur according to the following equation.[14][15] However, this is not recommended outside of a laboratory, as exposure to hydrogen sulfide can result if improperly handled.
- 6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O
Principal reactions
Upon heating to 300 °C, it decomposes to sodium sulfate and sodium polysulfide:
- 4 Na2S2O3 → 3 Na2SO4 + Na2S5
Thiosulfate salts characteristically decompose upon treatment with acids. Initial protonation occurs at sulfur. When the protonation is conducted in diethyl ether at −78 °C, H2S2O3 (thiosulfuric acid) can be obtained. It is a somewhat strong acid with pKas of 0.6 and 1.7 for the first and second dissociations, respectively. Under normal conditions, acidification of solutions of this salt excess with even dilute acids results in complete decomposition to sulfur, sulfur dioxide, and water:[13]
- 8 Na2S2O3 + 16 HCl → 16 NaCl + S8 + 8 SO2 + 8 H2O
Coordination chemistry
Thiosulfate is a potent ligand for
Iodometry
Some analytical procedures exploit the oxidizability of thiosulfate anion by iodine. The reaction produces tetrathionate:
- 2 S2O2−3 + I2 → S4O2−6 + 2 I−
Due to the quantitative nature of this reaction, as well as because Na2S2O3·5H2O has an excellent shelf-life, it is used as a
experiments.This particular use can be set up to measure the oxygen content of water through a long series of reactions in the
Organic chemistry
Alkylation of sodium thiosulfate gives S-alkylthiosulfates, which are called Bunte salts.[18] The alkylthiosulfates are susceptible to hydrolysis, affording the thiol. This reaction is illustrated by one synthesis of thioglycolic acid:
- ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H] + NaCl
- Na[O3S2CH2CO2H] + H2O → HSCH2CO2H + NaHSO4
Safety
Sodium thiosulfate has low toxicity. LDLo for rabbits is 4000 mg/kg.[2]
References
- ^ Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
- ^ ISBN 978-3527306732.
- ^ ISBN 978-92-4-154765-9.
- hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
- hdl:10665/345533. WHO/MHP/HPS/EML/2021.02.
- S2CID 75657768.
- S2CID 28366905.
- PMID 35489339.
- S2CID 11381393.
- ^ Winstead, Edward (October 6, 2022). "Sodium Thiosulfate Reduces Hearing Loss in Kids with Cancer". National Cancer Institute. Retrieved March 9, 2023.
- ^ "FDA approves sodium thiosulfate to reduce the risk of ototoxicity associated with cisplatin in pediatric patients with localized, non-metastatic solid tumors". U.S. Food and Drug Administration. 20 September 2022. Retrieved 9 March 2023.
- ^ Gibson CR (1908). The Romance of Modern Photography, Its Discovery & Its Achievements. Seeley & Co. pp. 37.
hyposulphite-of-soda herschel fixer hypo.
- ^ ISBN 978-0-12-352651-9.
- ^ Gordin HM (1913). Elementary Chemistry. Vol. 1. Inorganic Chemistry. Chicago: Medico-Dental Publishing Co. pp. 162 & 287–288.
- ISBN 978-0-08-037941-8.
- .
- ^ Малусел, Виорел Александру. "TECHNOLOGY OF GOLD AND SILVER EXTRACTION". Google Patents. Retrieved January 10, 2023.