Sodium metabisulfite

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.

Sodium metabisulfite
Other names
Sodium pyrosulfite
Sodium disulfite
3D model (JSmol)
ECHA InfoCard 100.028.794
EC Number
  • 231-673-0
E number E223 (preservatives)
RTECS number
  • UX8225000
Na2S2O5, Na-O-(S=O)-O-(S=O)-O-Na
Molar mass 190.107 g/mol
Appearance White to yellow powder
Odor Faint SO2
Density 1.48 g/cm3
Melting point 170 °C (338 °F; 443 K) decomposition begins at 150 °C
  • 45.1 g/100mL (0 °C)
  • 65.3 g/100mL (20 °C)
  • 81.7 g100 mL (100 °C)
Solubility Very soluble in glycerol
Slightly soluble in ethanol
Safety data sheet Mallinckrodt MSDS
GHS pictograms
GHS Signal word Danger
H302, H318
P264, P270, P280, P301+312, P305+351+338, P310, P330, P501
NFPA 704 (fire diamond)
NIOSH (US health exposure limits):
PEL (Permissible)
REL (Recommended)
TWA 5 mg/m3[1]
IDLH (Immediate danger)
Related compounds
Other anions
Sodium sulfite
Sodium bisulfite
Other cations
Potassium metabisulfite
Related compounds
Sodium dithionite
Sodium thiosulfate
Sodium sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references


Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide:

2 HSO3 ⇌ H2O + S2O52−

which yields a residue of colorless solid Na2S2O5.[2]

Chemical structure

The anion metabisulfite is a hybrid of dithionite (S2O42−) and dithionate (S2O62−). The anion consists of an SO2 group linked to an SO3 group, with the negative charge more localized 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.[3]


Food preservation and additive

It is used as a preservative and antioxidant in food and is also known as E223.[4] It can be used to preserve color of some fruits, such as bananas.[5]

It may cause allergic reactions in those who are sensitive to sulfites, including respiratory reactions in asthmatics, anaphylaxis, and other allergic reactions in sensitive individuals.[6][7]

Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.[8]

The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight.[9] Sodium metabisulfite oxidizes in the liver to harmless sulfate which is excreted in the urine.[9]

Sanitization and cleaning agent

It is commonly used in homebrewing and winemaking to sanitize equipment. It is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems. It is also used to remove monochloramine from drinking water after treatment.

Other uses

  • Sodium metabisulphite is added as an excipient to medications which contain adrenaline (epinephrine), in order to prevent the oxidation of adrenaline.[10] For example, it is added to combination drug formulations which contain a local anaesthetic and adrenaline,[10] and to the formulation in epinephrine autoinjectors, such as the EpiPen.[11] This lengthens the shelf life of the formulation,[10] although the sodium metabisulphite reacts with adrenaline, causing it to degrade and form epinephrine sulphonate.[12]
  • It is used in photography.[13]
  • 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.[14]
  • 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 substances causes defunct cells to sickle (through a complex polymerisation) hence confirming disease.
  • It is used as the source of SO2 in wine, an important anti-oxidant and bactericide
  • It is also used to precipitate gold from auric acid (gold dissolved in aqua regia).
  • It is used in waste treatment to chemically reduce hexavalent chromium to trivalent chromium which can then be precipitated and removed from an aqueous waste stream.
  • It is used as a bleaching agent in the production of coconut cream
  • It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibers, 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 in the oil and gas industry as a corrosion inhibitor/oxygen scavenger.
  • It is used in the water treatment industry to quench chlorine residual
  • It is used in tint etching iron-based metal samples for microstructural analysis. [15] [16]

Chemical properties

When mixed with water, sodium metabisulfite releases sulfur dioxide (SO2), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people. For this reason, sodium metabisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent.

Sodium metabisulfite releases sulfur dioxide in contact with strong acids:

Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

On heating to high temperature, it releases sulfur dioxide, leaving sodium sulfite behind:[17]

Na2S2O5 → Na2SO3 + SO2

See also


  1. NIOSH Pocket Guide to Chemical Hazards. "#0566". National Institute for Occupational Safety and Health (NIOSH).
  2. Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6.
  3. 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
  4. "Food Additives approved by the EU" (PDF). Retrieved 12 March 2015.
  5. "DRIED FRUIT" (PDF). Food and Agriculture Organization of the United Nations. p. 3.
  6. Dean D. Metcalfe, Ronald A. Simon, Food allergy: adverse reactions to food and food additives, Wiley-Blackwell 2003, p. 324–339
  7. "Archived copy". Archived from the original on 2009-04-16. Retrieved 2009-06-07.CS1 maint: archived copy as title (link)
  8. Milne, George W. A. (2005). Gardner's commercially important chemicals: synonyms, trade names, and properties. New York: Wiley-Interscience. p. 568. ISBN 978-0-471-73518-2.
  9. " : E-numbers : E223: Sodium disulphite".
  10. McGee, Douglas L. (2013). "Local and topical anesthesia". In Roberts, James R.; Jerris, R. Hedges (eds.). Roberts and Hedges' Clinical Procedures in Emergency Medicine (6th ed.). Elsevier/Saunders. p. 519. ISBN 9781455748594.
  11. Niazi, Safaraz K. (2009). Handbook of Pharmaceutical Manufacturing Formulations. Volume 6, Sterile Products (2nd ed.). New York: Informa Healthcare. p. 410. ISBN 9781420081312.
  12. Barnes, Andrew R. (2013). "Chapter 48. Chemical stability in dosage forms". In Aulton, Michael E.; Taylor, Kevin M.G. (eds.). Aulton's pharmaceutics : the design and manufacture of medicines (4th ed.). Churchill Livingstone/Elsevier. p. 833. ISBN 9780702053931.
  13. Anchell, Steve (2008). The darkroom cookbook (3rd ed.). Amsterdam: Focal Press. p. 193. ISBN 978-0240810553.
  15. "Color Metallography". 2011-05-04.
  17. Sodium sulfite.
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