View source for Sodium thiosulfate

{{Chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 464404558
| Name           = Sodium thiosulfate
| ImageFile      = 
| ImageFile1     = Sodium thiosulfate.svg
| ImageClass1    = skin-invert-image
| ImageSize1     = 150px
| ImageName1     = Sodium thiosulfate
| ImageFile3     = Sodium thiosulfate.jpg
| ImageSize3     = 175px
| IUPACName      = Sodium thiosulfate
| OtherNames     = Sodium hyposulphite<br/>Hyposulphite of soda<br/>Hypo
| SystematicName = 
| Section1       = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 22885
| ChEBI_Ref = {{ebicite|changed|EBI}} 
| ChEBI = 132112
| ChEMBL1 = 2096650
| index_label = anhydrous
| index1_label = pentahydrate
| ChEMBL1_Ref = {{ebicite|correct|EBI}}
| EC_number = 231-867-5
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = L0IYT1O31N
| UNII1_Ref = {{fdacite|correct|FDA}}
| UNII1 = HX1032V43M
| InChI = 1/2Na.H2O3S2/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2
| InChIKey = AKHNMLFCWUSKQB-NUQVWONBAM
| SMILES = [Na+].[Na+].[O-]S(=O)(=O)[S-]
| SMILES1 = O.O.O.O.O.[Na+].[Na+].[O-]S(=O)(=O)[S-]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2Na.H2O3S2/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = AKHNMLFCWUSKQB-UHFFFAOYSA-L
| InChI1=1S/2Na.H2O3S2.5H2O/c;;1-5(2,3)4;;;;;/h;;(H2,1,2,3,4);5*1H2/q2*+1;;;;;;/p-2
| InChIKey1=PODWXQQNRWNDGD-UHFFFAOYSA-L
| CASNo = 7772-98-7
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo1 = 10102-17-7
| CASNo1_Ref = {{cascite|correct|CAS}}
| PubChem = 24477
| RTECS = XN6476000
  }}
| Section2       = {{Chembox Properties
| Formula = {{Chem2|Na2S2O3}}
| MolarMass = 158.11 g/mol (anhydrous) <br /> 248.18 g/mol (pentahydrate)
| Appearance = White crystals
| Odor = Odorless
| Density = 1.667 g/cm<sup>3</sup>
| Solubility = 70.1 g/100 mL (20&nbsp;°C)<ref>{{GESTIS|ZVG=2480}}</ref> <br /> 231 g/100 mL (100 °C)
| SolubleOther = negligible in [[ethanol|alcohol]]
| MeltingPtC = 48.3
| MeltingPt_notes = (pentahydrate)
| BoilingPtC = 100
| BoilingPt_notes = (pentahydrate, - 5H<sub>2</sub>O decomposition)
| pKb = 
| RefractIndex = 1.489
  }}
| Section3       = {{Chembox Structure
| Coordination = 
| CrystalStruct = monoclinic
| Dipole =
  }}
| Section4       = 
| Section5       = 
| Section6       = 
| Section7       = {{Chembox Hazards
| ExternalSDS = [https://commercialaquaticsupplies.com/2014%20MSDS%20Sodium%20Thiosulphate.pdf External MSDS]
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|315|319|335}}
| PPhrases = {{P-phrases|261|264|271|280|302+352|304+340|305+351+338|312|321|332+313|337+313|362|403+233|405|501}}
| GHS_ref  = 
| NFPA-H = 1
| NFPA-F = 0
| NFPA-R = 0
| FlashPt = Non-flammable
  }}
| Section9       = {{Chembox Related
| OtherAnions    = 
| OtherCations   = [[Thiosulfuric acid]]<br />[[Lithium thiosulfate]]<br />[[Potassium thiosulfate]]
| OtherFunction  = 
| OtherFunction_label = 
| OtherCompounds = 
  }}
}}
'''Sodium thiosulfate''' ('''sodium thiosulphate''') is an [[inorganic compound]] with the formula {{chem2|Na2S2O3*xH2O}}. Typically it is available as the white or colorless [[water of crystallization|pentahydrate]] (x = 5), which is a white solid that dissolves well in water. The compound is a [[reducing agent]] and a [[ligand]], and these properties underpin its applications.<ref name="Ullmann">{{Ullmann|vauthors=Barbera JJ, Metzger A, Wolf M |title=Sulfites, Thiosulfates, and Dithionites|doi=10.1002/14356007.a25_477|isbn=978-3-527-30673-2|date=2012}}</ref>

==Uses==
Sodium thiosulfate is used predominantly in [[dyeing]].  It converts some dyes to their soluble colorless [[Leuco dye|"leuco"]] forms.  It is also used to bleach "wool, cotton, silk, soaps, glues, clay, sand, bauxite, and edible oils, edible fats, and gelatin."<ref name=Ullmann/>

===Medical uses===
{{main|Sodium thiosulfate (medical use)}}
Sodium thiosulfate is used in the treatment of [[cyanide poisoning]].<ref name="WHO2008">{{cite book | title = WHO Model Formulary 2008 | year = 2009 | isbn = 978-92-4-154765-9 | veditors = Stuart MC, Kouimtzi M, Hill SR | hdl = 10665/44053 | publisher = World Health Organization | hdl-access=free | page=66 }}</ref> It is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]].<ref name="WHO21st">{{cite book| last1 = Organization | first1 = World Health | title = World Health Organization model list of essential medicines: 21st list 2019 | year = 2019 | hdl = 10665/325771 | publisher = World Health Organization | location = Geneva | id = WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO | hdl-access=free }}</ref><ref name="WHO22nd">{{cite book | last1 = Organization | first1 = World Health | title = World Health Organization model list of essential medicines: 22nd list (2021) | year = 2021 | hdl = 10665/345533 | publisher = World Health Organization | location = Geneva | id = WHO/MHP/HPS/EML/2021.02 | hdl-access=free }}</ref> Other uses include topical treatment of [[ringworm]] and [[tinea versicolor]],<ref name=WHO2008/><ref name="sune">{{Cite journal|vauthors=Sunenshine PJ, Schwartz RA, Janniger CK|date=2002|title=Tinea versicolor |journal=[[International Journal of Dermatology|Int. J. Dermatol.]]|volume=37|issue=9|pages=648–55|doi=10.1046/j.1365-4362.1998.00441.x|pmid=9762812|s2cid=75657768}}</ref> and treating some side effects of [[hemodialysis]]<ref name="auriemma">{{Cite journal |display-authors=3|vauthors=Auriemma M, Carbone A, Di Liberato L, Cupaiolo A, Caponio C, De Simone C, Tulli A, Bonomini M, Amerio P|date=2011|title=Treatment of Cutaneous Calciphylaxis with Sodium Thiosulfate: Two Case Reports and a Review of the Literature|journal=[[American Journal of Clinical Dermatology|Am. J. Clin. Dermatol.]]|volume=12|issue=5|pages=339–46|doi=10.2165/11587060-000000000-00000|pmid=21834598|s2cid=28366905}}</ref> and [[chemotherapy]].<ref name="pmid35489339">{{cite journal |vauthors=Orgel E, Villaluna D, Krailo MD, Esbenshade A, Sung L, Freyer DR |title=Sodium thiosulfate for prevention of cisplatin-induced hearing loss: updated survival from ACCL0431 |journal=The Lancet. Oncology |volume=23 |issue=5 |pages=570–572 |date=May 2022 |pmid=35489339 |pmc=9635495 |doi=10.1016/S1470-2045(22)00155-3}}</ref><ref>{{Cite journal|display-authors=3 |vauthors=Dickey DT, Wu YJ, Muldoon LL, Neuwelt EA|date=2005|title=Protection against Cisplatin-Induced Toxicities by ''N''-Acetylcysteine and Sodium Thiosulfate as Assessed at the Molecular, Cellular, and in ''Vivo'' Levels|journal=[[Journal of Pharmacology and Experimental Therapeutics|J. Pharmacol. Exp. Ther.]]|volume=314|issue=3|pages=1052–8 |doi=10.1124/jpet.105.087601|pmid=15951398|s2cid=11381393}}</ref> In September 2022, the U.S. [[Food and Drug Administration]] (FDA) approved sodium thiosulfate under the trade name Pedmark to lessen the risk of [[ototoxicity]] and [[hearing loss]] in infant, child, and adolescent cancer patients receiving the chemotherapy medication [[cisplatin]].<ref name="Winstead 2022">{{cite web |last=Winstead |first=Edward |title=Sodium Thiosulfate Reduces Hearing Loss in Kids with Cancer |website=National Cancer Institute |date=October 6, 2022 |url=https://www.cancer.gov/news-events/cancer-currents-blog/2022/fda-sodium-thiosulfate-cisplatin-hearing-loss-children |access-date=March 9, 2023}}</ref><ref name="FDA 2022">{{cite web |title=FDA approves sodium thiosulfate to reduce the risk of ototoxicity associated with cisplatin in pediatric patients with localized, non-metastatic solid tumors  |website=U.S. Food and Drug Administration |date=20 September 2022 |url=https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-sodium-thiosulfate-reduce-risk-ototoxicity-associated-cisplatin-pediatric-patients |access-date=9 March 2023}}</ref>

===Photographic processing===
{{See also|Collodion#Wet-plate collodion photography}}
In photography, sodium thiosulfate is used in both [[photographic film|film]] and [[photographic paper]] processing as a [[photographic fixer|fixer]], sometimes still called 'hypo' from the original chemical name, hyposulphite of soda.<ref>{{cite book|url=https://archive.org/details/romancemodernph00gibsgoog|quote=hyposulphite-of-soda herschel fixer hypo.|title=The Romance of Modern Photography, Its Discovery & Its Achievements|vauthors=Gibson CR|publisher=Seeley & Co|year=1908|pages=[https://archive.org/details/romancemodernph00gibsgoog/page/n47 37]}}</ref> It functions to dissolve [[silver halide]]s, e.g., [[silver bromide|AgBr]], components of photographic emulsions. [[Ammonium thiosulfate]] is typically preferred to sodium thiosulfate for this application.<ref name=Ullmann/> 

The ability of thiosulfate to dissolve silver ions is related to its ability to dissolve gold ions.

===Neutralizing chlorinated water===
It is used to dechlorinate tap water including lowering [[chlorine]] levels for use in aquariums, swimming pools, and spas (e.g., following [[superchlorination]]) and within [[water treatment]] plants to treat settled backwash water prior to release into rivers.<ref name=Ullmann/> The reduction reaction is analogous to the iodine reduction reaction.

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:
:{{Chem2|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==
[[Image:Sodium-thiosulfate-xtal-3D-balls.png|thumb| Structure of sodium thiosulfate according to [[X-ray crystallography]], showing the tetrahedral thiosulfate anion embedded in a network of sodium ions. Color code: red = O, yellow = S|left]]

Two polymorphs are known as pentahydrate. The anhydrous salt exists in several polymorphs.<ref name=Ullmann/>  In the solid state, the [[thiosulfate]] [[anion]] is tetrahedral in shape and is notionally derived by replacing one of the oxygen atoms by a sulfur atom in a [[sulfate]] anion. The S-S distance indicates a single bond, implying that the terminal sulfur holds a significant negative charge and the S-O interactions have more double-bond character.

==Production==
Sodium thiosulfate is prepared by oxidation of [[sodium sulfite]] with [[sulfur]].<ref name=Ullmann/>  It is also produced from waste [[sodium sulfide]] from the manufacture of sulfur [[dye]]s.<ref name="holleman">{{Cite book|title=Inorganic Chemistry|vauthors=Holleman AF, Wiberg E, Wiberg N|publisher=Academic Press|year=2001|isbn=978-0-12-352651-9|location=San Diego}}</ref>

This salt can also be prepared by boiling aqueous [[sodium hydroxide]] and sulfur according to the following equation.<ref>{{cite book|url=https://books.google.com/books?id=FgfnAAAAMAAJ&q=sodium+thiosulfate&pg=PA287|title=Elementary Chemistry|vauthors=Gordin HM|publisher=Medico-Dental Publishing Co.|year=1913|volume=1. Inorganic Chemistry|location=Chicago|pages=162 & 287–288}}</ref><ref>{{Greenwood&Earnshaw2nd|paage=678}}</ref> However, this is not recommended outside of a laboratory, as exposure to [[hydrogen sulfide]] can result if improperly handled.
:{{Chem2|6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O}}

==Principal reactions==
Upon heating to 300&nbsp;°C, it decomposes to [[sodium sulfate]] and [[sodium polysulfide]]:
:{{Chem2|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&nbsp;°C, {{Chem2|H2S2O3}} ([[thiosulfuric acid]]) can be obtained. It is a somewhat strong acid with p''K''<sub>a</sub>s 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]]:<ref name="holleman" />
:{{Chem2|8 Na2S2O3 + 16 HCl → 16 NaCl + S8 + 8 SO2 + 8 H2O}}

===Coordination chemistry===
Thiosulfate forms complexes with [[transition metal thiosulfate complex|transition metal ions]].  One such complex is [[Sodium aurothiosulfate|{{Chem2|[Au(S2O3)2](3−)}}]].

===Iodometry===
Some [[analytical chemistry|analytical procedures]] exploit the oxidizability of [[thiosulfate]] anion by [[iodine]].  The reaction produces [[tetrathionate]]:
:{{Chem2|2 S2O3(2-) + I2 → S4O6(2-) + 2 I−}}

Due to the quantitative nature of this reaction, as well as because {{Chem2|Na2S2O3*5H2O}} has an excellent shelf-life, it is used as a [[titrant]] in [[iodometry]]. {{Chem2|Na2S2O3*5H2O}} is also a component of [[iodine clock reaction|iodine clock]] experiments.

This particular use can be set up to measure the oxygen content of water through a long series of reactions in the [[Winkler test for dissolved oxygen]]. It is also used in estimating volumetrically the concentrations of certain compounds in solution ([[hydrogen peroxide]], for instance) and in estimating the chlorine content in commercial bleaching powder and water.

===Organic chemistry===
[[Alkylation]] of sodium thiosulfate gives ''S''-alkylthiosulfates, which are called [[Bunte salt]]s.<ref>{{cite journal|vauthors=Alonso ME, Aragona H|date=1978|title=Sulfide Synthesis in Preparation of Unsymmetrical Dialkyl Disulfides: Sec-butyl Isopropyl Disulfide|journal=[[Organic Syntheses|Org. Synth.]]|volume=58|page=147|doi=10.15227/orgsyn.058.0147}} {{free access}}</ref> The alkylthiosulfates are susceptible to hydrolysis, affording the thiol. This reaction is illustrated by one synthesis of [[thioglycolic acid]]:
:{{Chem2|ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H] + NaCl}}
:{{Chem2|Na[O3S2CH2CO2H] + H2O → HSCH2CO2H + NaHSO4}}

==Safety==
Sodium thiosulfate has low toxicity. LDLo for rabbits is 4000 mg/kg.<ref name=Ullmann/>

==References==
{{reflist}}

{{Commons category}}

{{Sodium compounds}}
{{Antifungals}}
{{Antidotes}}

[[Category:Thiosulfates]]
[[Category:Sodium compounds]]
[[Category:Photographic chemicals]]
[[Category:Antidotes]]
[[Category:Antifungals for dermatologic use]]
[[Category:Orphan drugs]]
[[Category:Specialty drugs]]
[[Category:World Health Organization essential medicines]]