Disulfite: Difference between revisions

| Watchedfields = changed

| verifiedrevid = 423158544

| ImageFile = Structure of metabisulfite ion.png

| ImageSize = 190px

| ImageFile1 = Metabisulfite-ion-from-xtal-3D-bs-17.png

| IUPACName = disulfite<ref name=redbookname>{{RedBookRef|page=130}}</ref>

| SystematicName = pentaoxido-1''κ''³''O'',2''κ''²''O''-disulfate(S—S)(2−)<ref name=redbookname/>

| CASNo = 23134-05-6

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

| ChemSpiderID = 140610

| UNII = 7992SO049K

| SMILES = [O-][S+2]([O-])([O-])[S+]([O-])[O-]

| StdInChI=1S/H2O5S2/c1-6(2)7(3,4)5/h(H,1,2)(H,3,4,5)/p-2

| StdInChIKey = WBZKQQHYRPRKNJ-UHFFFAOYSA-L

| Formula = {{chem|S|2|O|5|2−}}

| ConjugateAcid = [[Disulfurous acid]]

A '''disulfite''', commonly known as '''metabisulfite''' or '''pyrosulfite''', is a [[chemical compound]] containing the ion {{chem|S|2|O|5|2−}}. 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 {{chem|H|S|O|3|−}} anion. These salts act equivalently to [[Sodium hydrogen sulfite|sodium hydrogensulfite]] or [[Potassium hydrogen sulfite|potassium hydrogensulfite]].<ref>{{cite book|doi=10.1002/9780470132333.ch49|isbn=9780470132333|chapter=Sulfites and Pyrosulfites of the Alkali Metals|series=Inorganic Syntheses|year=1946|last1=Johnstone|first1=H. F.|title=Inorganic Syntheses|pages=162–167|volume=2}}</ref>

==Structure==

In contrast to [[disulfate]] ({{chem|S|2|O|7|2−}}), disulfite ion ({{chem|S|2|O|5|2−}}) 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.<ref>{{cite journal|first1=I.|last1=Lindqvist|first2=M.|last2=Mörtsell|title=The Structure of Potassium Pyrosulfite and the Nature of the Pyrosulfite Ion". |journal=[[Acta Crystallographica]] |date= 1957|volume=10 |pages=406–409 |doi=10.1107/S0365110X57001322 |doi-access=free}}</ref>

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&nbsp;Å, and the "thionate" and "thionite" S–O distances are 1.46 and 1.50&nbsp;Å respectively.<ref>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}}</ref>

===Production===

Salts of disulfite ion are produced by dehydration of salts of [[hydrogensulfite]] ion ({{chem|HSO|3|−}}). When solutions of [[sodium bisulfite|sodium hydrogensulfite]] or [[potassium bisulfite|potassium hydrogensulfite]] are evaporated, [[sodium metabisulfite]] and [[potassium metabisulfite]] result.<ref>{{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}}</ref>

:{{chem2|2 HSO3−}} [[File:Equilibrium left.svg|40px]] {{chem2|S2O5(2−) + H2O}}

Although the equilibrium lies far to the left, evaporation of a bisulfite salt will produce a substantial amount of disulfite.<ref name=Bassam>Bassam Z. Shakhashiri: [https://books.google.com/books?id=btNF9aLXtPcC&pg=PA9&lpg=PA9 ''Chemical demonstrations: a handbook for teachers of chemistry''] The University of Wisconsin Press, 1992, p.9</ref>

Disulfite is the conjugate base of [[disulfurous acid]] (pyrosulfurous acid), which originates from [[sulfurous acid]] in accordance with the dehydration reaction above:<br />

:2 H₂SO₃ → 2 {{chem|HSO|3|−}} + 2 H⁺ → H₂S₂O₅ + H₂O

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

|{{chem|HSO|3|−}} [[File:Equilibrium left.svg|40px]] {{chem|SO|3|2−}} + H⁺<br /><br />SO₃²⁻ + SO₂ [[File:Equilibrium left.svg|40px]] {{chem|S|2|O|5|2−}} || &nbsp; || [[File:Disulfite-Synthese.png|center|300px]]

==Use==

Disulfite salts are used for [[Sulfite food and beverage additives|preserving food and beverages]] and as [[Antioxidant|antioxidants]], with the main species used for this purpose being [[Sodium metabisulphite|sodium metabisulfite]] ([[E number|E223]])<ref>{{Cite journal |last=Noorafshan |first=A. |last2=Asadi-Golshan |first2=R. |last3=Monjezi |first3=S. |last4=Karbalay-Doust |first4=S. |date=2014 |title=Sodium metabisulphite, a preservative agent, decreases the heart capillary volume and length, and curcumin, the main component of Curcuma longa, cannot protect it |url=https://pubmed.ncbi.nlm.nih.gov/25629268 |journal=Folia Biologica |volume=60 |issue=6 |pages=275–280 |issn=0015-5500 |pmid=25629268}}</ref> and [[potassium metabisulphite|potassium metabisulfite]] (E224).<ref>{{Cite web |last=PubChem |title=Potassium metabisulfite |url=https://pubchem.ncbi.nlm.nih.gov/compound/28019 |access-date=2024-04-19 |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref> Sulfites are implicated in asthmatic reactions and may also cause symptoms in non-asthmatic individuals, namely [[dermatitis]], [[hives|urticaria]], [[flushing (physiology)|flushing]], [[hypotension]], [[abdominal pain]] and [[diarrhea]], and even life-threatening [[anaphylaxis]].<ref name="pmid24834193">{{cite journal |vauthors=Vally H, Misso NL |title=Adverse reactions to the sulphite additives |journal=Gastroenterol Hepatol Bed Bench |volume=5 |issue=1 |pages=16–23 |date=2012 |pmid=24834193 |pmc=4017440 |doi= |url=}}</ref>

[[Category:Metabisulfites| ]]

[[Category:Sulfur oxyanions]]