Disulfite

Not to be confused with Bisulfite.

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]

Disulfite ion

Names
IUPAC name disulfite[1]
Systematic IUPAC name pentaoxido-1κ3O,2κ2O-disulfate(S—S)(2−)[1]
Other names metabisulfite ion pyrosulfite
Identifiers
CAS Number	23134-05-6 Y
3D model (JSmol)	Interactive image
ChemSpider	140610
PubChem CID	159940
UNII	7992SO049K
CompTox Dashboard (EPA)	DTXSID70945813
InChI InChI=1S/H2O5S2/c1-6(2)7(3,4)5/h(H,1,2)(H,3,4,5)/p-2 Key: WBZKQQHYRPRKNJ-UHFFFAOYSA-L
SMILES [O-][S+2]([O-])([O-])[S+]([O-])[O-]
Properties
Chemical formula	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). Y verify (what is YN ?) 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.