Disulfite

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 ;
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). verify (what is ?) Infobox references

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]

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

S
₂O²⁻
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

Disulfites salts are used for preserving food and beverages.

Examples of disulphites

Sodium metabisulphite (E223) and potassium metabisulphite (E224) are used as a preservative and antioxidant in food. Sulphites are implicated is 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.[7]

References

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.
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.
Lindqvist, I.; Mörtsell, M. "The Structure of Potassium Pyrosulfite and the Nature of the Pyrosulfite Ion". Acta Crystallogr. (1957". 10: 406–409. doi:10.1107/S0365110X57001322. {{cite journal}}: Cite journal requires |journal= (help)
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
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.
Bassam Z. Shakhashiri: Chemical demonstrations: a handbook for teachers of chemistry The University of Wisconsin Press, 1992, p.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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[redbookname-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. "The Structure of Potassium Pyrosulfite and the Nature of the Pyrosulfite Ion". Acta Crystallogr. (1957". 10: 406–409. doi:10.1107/S0365110X57001322. {{cite journal}}: Cite journal requires |journal= (help)

[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.

[Bassam-6] Bassam Z. Shakhashiri: Chemical demonstrations: a handbook for teachers of chemistry The University of Wisconsin Press, 1992, p.9

[pmid24834193-7] Vally H, Misso NL (2012). "Adverse reactions to the sulphite additives". Gastroenterol Hepatol Bed Bench. 5 (1): 16–23. PMC 4017440. PMID 24834193.