Disulfite

A disulfite, commonly known as metabisulfite or pyrosulfite, is a chemical compound containing the ion S
2O2−
5. It is a colorless dianion that is primarily marketed in the form of sodium metabisulfite or potassium metabisulfite. When dissolved in water, these salts release the hydrogensulfite HSO−
3 anion. These salts act equivalently to sodium hydrogensulfite or potassium hydrogensulfite.[2]

Not to be confused with Bisulfite.
Disulfite ion
Names
IUPAC name
disulfite[1]
Systematic IUPAC name
pentaoxido-1κ3O,2κ2O-disulfate(S—S)(2−)[1]
Other names
metabisulfite ion
pyrosulfite
Identifiers
3D model (JSmol)
ChemSpider
UNII
  • InChI=1S/H2O5S2/c1-6(2)7(3,4)5/h(H,1,2)(H,3,4,5)/p-2
    Key: WBZKQQHYRPRKNJ-UHFFFAOYSA-L
  • [O-][S+2]([O-])([O-])[S+]([O-])[O-]
Properties
S
2O2−
5
Conjugate acid Disulfurous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure

In contrast to disulfate (S
2O2−
7), disulfite ion (S
2O2−
5) has an unsymmetrical structure with an S-S bond. The oxidation state of the sulfur atom bonded to 3 oxygen atoms is +5 while oxidation number of other sulfur atom is +3.[3]

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.[4]

Production

Salts of disulfite ion are produced by dehydration of salts of hydrogensulfite ion (HSO−
3). When solutions of sodium hydrogensulfite or potassium hydrogensulfite are evaporated, sodium metabisulfite and potassium metabisulfite result.[5]

2 HSO−3 S2O2−5 + H2O

Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.[6]

Disulfite is the conjugate base of disulfurous acid (pyrosulfurous acid), which originates from sulfurous acid in accordance with the dehydration reaction above:

2 H2SO3 → 2 HSO−
3 + 2 H+ → H2S2O5 + H2O

The disulfite ion also arises from the addition of sulfur dioxide to the sulfite ion:

HSO−
3 SO2−
3 + H+

SO32− + SO2 S
2O2−
5		 

Use

Disulfite salts are used for preserving food and beverages and as antioxidants, with the main species used for this purpose being sodium metabisulfite (E223)[7] and potassium metabisulfite (E224).[8] Sulfites are implicated in asthmatic reactions and may also cause symptoms in non-asthmatic individuals, namely dermatitis, urticaria, flushing, hypotension, abdominal pain and diarrhea, and even life-threatening anaphylaxis.[9]

References
  1. International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 130. Electronic version.
  2. Johnstone, H. F. (1946). "Sulfites and Pyrosulfites of the Alkali Metals". Inorganic Syntheses. Inorganic Syntheses. Vol. 2. pp. 162–167. doi:10.1002/9780470132333.ch49. ISBN 9780470132333.
  3. Lindqvist, I.; Mörtsell, M. (1957). "The Structure of Potassium Pyrosulfite and the Nature of the Pyrosulfite Ion"". Acta Crystallographica. 10: 406–409. doi:10.1107/S0365110X57001322.
  4. 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
  5. Barberá, José Jiménez; Metzger, Adolf; Wolf, Manfred (2000). "Sulfites, Thiosulfates, and Dithionitesl Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a25_477. ISBN 3527306730.
  6. Bassam Z. Shakhashiri: Chemical demonstrations: a handbook for teachers of chemistry The University of Wisconsin Press, 1992, p.9
  7. Noorafshan, A.; Asadi-Golshan, R.; Monjezi, S.; Karbalay-Doust, S. (2014). "Sodium metabisulphite, a preservative agent, decreases the heart capillary volume and length, and curcumin, the main component of Curcuma longa, cannot protect it". Folia Biologica. 60 (6): 275–280. ISSN 0015-5500. PMID 25629268.
  8. PubChem. "Potassium metabisulfite". pubchem.ncbi.nlm.nih.gov. Retrieved 2024-04-19.
  9. Vally H, Misso NL (2012). "Adverse reactions to the sulphite additives". Gastroenterol Hepatol Bed Bench. 5 (1): 16–23. PMC 4017440. PMID 24834193.
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