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sodium metabisulfite

{{chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 448850808

| Name =

| ImageFile =

| ImageFile1 = Sodium metabisulfite.jpg

| ImageName1 = Sodium metabisulfite

| ImageFile2 = Sodium-metabisulfite-2D.png

| ImageName2 = Structure of sodium metabisulfite

| OtherNames = {{Unbulleted list|Sodium pyrosulfite|Sodium disulfite}}

| IUPACName =

| SystematicName =

| Section1 = {{Chembox Identifiers

| CASNo = 7681-57-4

| CASNo_Ref = {{cascite|correct|CAS}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 4VON5FNS3C

| PubChem = 656671

| ChEMBL_Ref = {{ebicite|changed|EBI}}

| ChEMBL = 2016976

| ChEBI_Ref = {{ebicite|changed|EBI}}

| ChEBI = 114786

| EINECS = 231-673-0

| RTECS = UX8225000

| SMILES = [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]

| InChI = 1S/2Na.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2

}}

| Section2 = {{Chembox Properties

| Formula = Na2S2O5

| MolarMass = 190.107{{nbsp}}g/mol

| Appearance = White to yellow powder

| Odor = Faint SO2

| Density = 1.48{{nbsp}}g/cm3

| Solubility = {{ubl

| 45.1{{nbsp}}g/100{{thinsp}}mL (0{{nbsp}}°C)

| 65.3{{nbsp}}g/100{{thinsp}}mL (20{{nbsp}}°C)

| 81.7{{nbsp}}g{{thinsp}}100 mL (100{{nbsp}}°C)

}}

| SolubleOther = Very soluble in glycerol
Slightly soluble in ethanol

| MeltingPtC = 170

| MeltingPt_notes = decomposition begins at 150 °C

| BoilingPt =

}}

| Section3 =

| Section4 =

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| Section7 = {{Chembox Hazards

| ExternalSDS = [http://bulkpharm.mallinckrodt.com/_attachments/msds/S4378.htm Mallinckrodt MSDS]

| NFPA-H = 2

| NFPA-F = 0

| NFPA-R = 1

| NFPA-S =

| GHSPictograms = {{GHS05}}{{GHS07}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|302|318}}

| PPhrases = {{P-phrases|264|270|280|301+312|305+351+338|310|330|501}}

| PEL = None{{PGCH|0566}}

| IDLH = N.D.

| REL = TWA 5{{nbsp}}mg/m3

}}

| Section8 = {{Chembox Related

| OtherAnions = Sodium sulfite
Sodium bisulfite

| OtherCations = Potassium metabisulfite

| OtherCompounds = Sodium dithionite
Sodium thiosulfate
Sodium sulfate

}}

}}

Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent.{{Ullmann|doi=10.1002/14356007.a25_477|isbn=3527306730|title=Sulfites, Thiosulfates, and Dithionitesl Chemistry|year=2000|last1=Barberá|first1=José Jiménez|last2=Metzger|first2=Adolf|last3=Wolf|first3=Manfred}} When dissolved in water it forms sodium bisulfite.

Preparation

{{see also|Wellman–Lord process}}

Sodium metabisulfite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide.{{cite book

| title = Inorganic Chemistry, 3rd Edition

| chapter = Chapter 16: The group 16 elements

| author1 = Catherine E. Housecroft

| author2 = Alan G. Sharpe

| publisher = Pearson

| year = 2008

| isbn = 978-0-13-175553-6

| page = 520

}} When conducted in warm water, Na2SO3 initially precipitates as a yellow solid. With more SO2, the solid dissolves to give the disulfite, which crystallises upon cooling.{{cite book|doi=10.1002/9780470132333.ch49|isbn=9780470132333|chapter=Sulfites and Pyrosulfites of the Alkali Metals|year=1946|last1=Johnstone|first1=H. F.|title=Inorganic Syntheses|pages=162–167|volume=2}}

:SO2 + 2 NaOH → Na2SO3 + H2O

:SO2 + Na2SO3 → Na2S2O5

which yields a residue of colourless solid Na2S2O5.

Chemical structure

The anion metabisulfite consists of an SO2 group linked to an SO3 group, with the negative charge more localised on the SO3 end. The S–S bond length is 2.22 Å, and the "thionate" and "thionite" S–O distances are 1.46 and 1.50 Å, respectively.K. L. Carter, T. A. Siddiquee, K. L. Murphy, D. W. Bennett "The surprisingly elusive crystal structure of sodium metabisulfite" Acta Crystallogr. (2004). B60, 155–162. {{doi|10.1107/S0108768104003325}}

Reactivity

{{main|Bisulfite#Reactions}}

Upon dissolution in water, bisulfite is generated:

:Na2S2O5 + H2O → 2 Na+ + 2 HSO3−

Uses

Sodium and potassium metabisulfite have many major and niche uses. It is widely used for preserving food and beverages.

  • Sodium metabisulphite is one of the main ingredients in "Drywhite", a composition used to prevent chipped potatoes oxidising during storage prior to use in many fish and chip shops.{{cite book |last1=Cooper |first1=Lee |title=Principles of Frying Fish and Chips Learner Workbook |publisher=Seafood Academy |page=29 |url=https://seafoodacademy.org/pdfs/152k-principles-of-frying-fish-and-chips-v2.pdf |access-date=12 March 2025}}
  • Sodium metabisulfite is added as an excipient to medications which contain adrenaline (epinephrine), in order to prevent the oxidation of adrenaline. For example, it is added to combination drug formulations which contain a local anaesthetic and adrenaline,{{cite book |last1=McGee |first1=Douglas L. |editor1-last=Roberts |editor1-first=James R. |editor2-last=Jerris |editor2-first=R. Hedges |title=Roberts and Hedges' Clinical Procedures in Emergency Medicine |date=2013 |publisher=Elsevier/Saunders |isbn=9781455748594 |page=519 |edition=6th |chapter-url=https://books.google.com/books?id=slyLreFkHuIC&pg=PA519 |chapter=Local and topical anesthesia}} and to the formulation in epinephrine autoinjectors, such as the EpiPen.{{cite book |last1=Niazi |first1=Safaraz K. |title=Handbook of Pharmaceutical Manufacturing Formulations. Volume 6, Sterile Products |date=2009 |publisher=Informa Healthcare |location=New York |isbn=9781420081312 |page=410 |edition=2nd |url=https://books.google.com/books?id=HQbLBQAAQBAJ&pg=PA410}} This lengthens the shelf life of the formulation, although the sodium metabisulfite reacts with adrenaline, causing it to degrade and form epinephrine sulfonate.{{cite book |last=Barnes |first=Andrew R. |chapter=Chapter 48. Chemical stability in dosage forms|editor1-last=Aulton |editor1-first=Michael E. |editor2-last=Taylor |editor2-first=Kevin M.G. |title=Aulton's pharmaceutics : the design and manufacture of medicines |date=2013 |publisher=Churchill Livingstone/Elsevier |isbn=9780702053931 |page=833 |edition=4th |chapter-url=https://books.google.com/books?id=SZ43AAAAQBAJ&pg=PA833}}
  • In combination with sodium hydrosulfite it is used as a rust-stain remover{{cite web |title=Ingredients |url=https://summitbrands.com/ingredients/ |website=Summit Brands |date=31 October 2019 |access-date=25 April 2021}}
  • It is used in photography as an antioxidant in photographic film development.{{cite book|last1=Anchell|first1=Steve|title=The darkroom cookbook|url=https://archive.org/details/darkroomcookbook00anch|url-access=limited|date=2008|publisher=Focal Press|location=Amsterdam|isbn=978-0240810553|pages=[https://archive.org/details/darkroomcookbook00anch/page/n225 193]|edition=3rd}}{{Cite web |title=Sodium metabisulfite - Hazardous Agents {{!}} Haz-Map |url=https://haz-map.com/Agents/629 |access-date=2025-04-17 |website=haz-map.com}}
  • Concentrated sodium metabisulfite can be used to remove tree stumps. Some brands contain 98% sodium metabisulfite, and cause degradation of lignin in the stumps, facilitating removal.{{Cite web |title=Stump-Out DIY Stump Removal Granules |url=https://bonide.com/product/stump-out-diy-stump-removal-granules/ |access-date=2025-04-17 |website=Bonide |language=en-US}}
  • It is also used as an excipient in some tablets, such as paracetamol.
  • A very important health related aspect of this substance is that it can be added to a blood smear in a test for sickle cell anaemia (and other similar forms of haemoglobin mutation). The substance causes defunct cells to sickle (through a complex polymerisation) hence confirming disease.
  • It is used as a bleaching agent in the production of coconut cream.
  • It (or liquid SO2) is commonly used as an antimicrobial and antioxidant in winemaking; bottled wine indicates its use with the label "Contains Sulfites" in the US.
  • It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibres, thus allowing the garment to go back to its original shape after washing.
  • It is used as an SO2 source (mixed with air or oxygen) for the destruction of cyanide in commercial gold cyanidation processes.
  • It is used as an SO2 source (mixed with air or oxygen) for the precipitation of elemental gold in chloroauric (aqua regia) solutions.
  • It is used in the water treatment industry to quench residual chlorine.
  • It is used in tint etching iron-based metal samples for microstructural analysis.{{cite web | url=https://vacaero.com/information-resources/metallography-with-george-vander-voort/991-color-metallography.html | title=Color Metallography| date=2011-05-04}}{{cite web|url=https://www.asminternational.org/documents/10192/1874035/htp00102p025.pdf/ace8f01d-bf9a-4048-b948-a3aeb2d8a536|format=PDF|title=ETCHING ISOTHERMALLY TREATED STEELS|author=George F. Vander Voort|website=Asminternational.org|access-date=24 January 2022|archive-date=16 October 2022|archive-url=https://web.archive.org/web/20221016054106/https://www.asminternational.org/documents/10192/1874035/htp00102p025.pdf/ace8f01d-bf9a-4048-b948-a3aeb2d8a536|url-status=dead}}
  • It is used as a fungicide for anti-microbe and mould prevention during shipping of consumer goods such as shoes and clothing. Plastic stickers and packaging (such as Micro-Pak™) containing the anhydrous, sodium metabisulfite solid active ingredient are added prior to shipping. The devices absorb moisture from the atmosphere during shipping and release low levels of sulfur dioxide.{{cite web | url=http://hawaii.gov/hdoa/labels/8979.1.pdf | title=Micro-Pak Enhanced Packaging Stickers| date=2020-05-05}}
  • It is used for preserving fruit during shipping.{{cite book | chapter-url=https://www.sciencedirect.com/science/article/pii/B9781845697358500152 | title=Postharvest Biology and Technology of Tropical and Subtropical Fruits| chapter=15 - Litchi (Litchi chinensis Sonn.)| series=Woodhead Publishing Series in Food Science, Technology and Nutrition| doi=10.1533/9780857092885.361 |date=2020-05-05| pages=361–409e| publisher=Woodhead| isbn=9781845697358| last1=Sivakumar| first1=D.| last2=Korsten| first2=L.}}
  • It is used as an additive in the extraction of starch from tubers,{{cite journal|last1=Manek|first1=Rahul V.|last2=Builders|first2=Philip F.|last3=Kolling|first3=William M.|last4=Emeje|first4=Martins|last5=Kunle|first5=Olobayo O.|date=June 2012|title=Physicochemical and binder properties of starch obtained from Cyperus esculentus|journal=AAPS PharmSciTech|volume=13|issue=2|pages=379–388|doi=10.1208/s12249-012-9761-z|issn=1530-9932|pmc=3364391|pmid=22350737}} fruit,{{cite journal|last1=Nawab|first1=Anjum|last2=Alam|first2=Feroz|last3=Haq|first3=Muhammad Abdul|last4=Hasnain|first4=Abid|date=2016|title=Biodegradable film from mango kernel starch: Effect of plasticizers on physical, barrier, and mechanical properties|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/star.201500349|journal=Starch - Stärke|language=en|volume=68|issue=9–10|pages=919–928|doi=10.1002/star.201500349|issn=1521-379X}} and cereal crops.{{cite journal|last1=Nyakabau|first1=Tatenda|last2=Wokadala|first2=Obiro Cuthbert|last3=Emmambux|first3=Mohammad Naushad|date=2013|title=Effect of steeping additives on tef starch extraction and its quality|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/star.201200241|journal=Starch - Stärke|language=en|volume=65|issue=9–10|pages=738–746|doi=10.1002/star.201200241|issn=1521-379X|hdl=2263/41924|hdl-access=free}}{{cite journal|last1=Park|first1=S. H.|last2=Bean|first2=S. R.|last3=Wilson|first3=J. D.|last4=Schober|first4=T. J.|date=2006|title=Rapid Isolation of Sorghum and Other Cereal Starches Using Sonication|url=https://onlinelibrary.wiley.com/doi/abs/10.1094/CC-83-0611|journal=Cereal Chemistry|language=en|volume=83|issue=6|pages=611–616|doi=10.1094/CC-83-0611|issn=1943-3638}}
  • It is used as a pickling agent to treat high pressure reverse osmosis and nanofiltration water desalination membranes for extended storage periods between uses.
  • It is used to create a bisulfite adduct from ketones to aid in separation of the ketone product. The usage of metabisulfite versus the sulfite is also more entropically favourable.

Safety

Sodium metabisulfite, despite not being flammable, decomposes in 150 °C of heat releasing toxic gasses when decomposed. It is corrosive when dissolved in water. Some people who are sulfite sensitive may experience an allergic reaction to sodium meta bisulfite, sometimes severe, resulting in labeling requirements for food safety.{{cite web | url=https://www.webmd.com/allergies/sulfite-sensitivity | title=What is Sulfite Sensitivity? }} In 2024, it was named ‘allergen of the year 2024’ by the American Contact Dermatitis Society. {{cite web | url=https://www.liebertpub.com/doi/10.1089/derm.2023.0154 | title= Sulfites: Allergen of the Year 2024 }}

References

{{reflist}}

External links

  • [http://www.inchem.org/documents/icsc/icsc/eics1461.htm International Chemical Safety Card 1461]
  • [https://www.ncbi.nlm.nih.gov/pubmed/15017087 The surprisingly elusive crystal structure of sodium metabisulfite]
  • [https://www.cdc.gov/niosh/npg/npgd0566.html CDC - NIOSH Pocket Guide to Chemical Hazards]

{{Sodium compounds}}

{{DEFAULTSORT:Sodium Metabisulfite}}

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