View source for Chemistry:Bisulfite

{{Short description|Chemical compound or ion}}
[[Image:Bisulfite-equilibrium-2D.png|thumb|right|320px|Equilibrium reaction relating the two tautomers of bisulfite.]]
The '''bisulfite''' ion (IUPAC-recommended nomenclature: '''hydrogensulfite''') is the ion {{chem|HSO|3|−}}.  Salts containing the {{chem|HSO|3|−}} ion are also known as "sulfite lyes".<ref name = G&E>{{Greenwood&Earnshaw2nd}}</ref> Sodium bisulfite is used interchangeably with [[Chemistry:Sodium metabisulfite|sodium metabisulfite]] (Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub>). Sodium metabisulfite dissolves in water to give a solution of Na<sup>+</sup>{{chem|HSO|3|−}}.
:Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub>  +  H<sub>2</sub>O  →  2{{nbsp}}Na[HSO<sub>3</sub>]

==Structure==
The bisulfite anion exists in solution as a mixture of two [[Chemistry:Tautomer|tautomer]]s.  One tautomer has the proton attached to one of the three oxygen centers.  In the second tautomer the proton resides on sulfur. The S-protonated tautomer has [[Chemistry:Molecular symmetry|''C''<sub>3v</sub> symmetry]].  The O-protonated tautomer has only C<sub>s</sub> symmetry.

==Reactions==
===Tautomerization===
There exist two tautomers of bisulfite.  They interconvert readily but can be characterized individually by various spectroscopic methods.  They have been observed by [[Physics:Oxygen-17|<sup>17</sup>O]] [[Physics:Nuclear magnetic resonance spectroscopy|NMR]] spectroscopy:<ref name = G&E/><ref>
{{cite journal
 |last1=Horner |first1=D. A.
 |last2=Connick |first2=R. E.
 |year=1986
 |title=Equilibrium quotient for the isomerization of bisulfite ion from {{chem|HSO|3|−}} to SO<sub>3</sub>H<sup>−</sup>
 |journal=Inorganic Chemistry
 |volume=25 |issue= 14|pages=2414–2417
 |doi=10.1021/ic00234a026
|url=https://www.escholarship.org/uc/item/7vk7p7b8
 }}</ref>  
:HSO<sub>3</sub><sup>−</sup>  {{EqmR}}  SO<sub>2</sub>(OH)<sup>−</sup>   K = 4.2

===Acid-base reactions===
Solutions of bisulfite are typically prepared by treatment of [[Chemistry:Sulfur dioxide|sulfur dioxide]] with aqueous base:<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>
:SO<sub>2</sub>  +  OH<sup>−</sup>  →  {{chem|HSO|3|−}}

{{chem|HSO|3|−}} is the conjugate base of [[Chemistry:Sulfurous acid|sulfurous acid]], (H<sub>2</sub>SO<sub>3</sub>).

{{chem|HSO|3|−}} is a weak acidic species with a [[Chemistry:Acid dissociation constant|p''K''<sub>a</sub>]] of 6.97.  Its conjugate base is [[Chemistry:Sulfite|sulfite]], {{chem|SO|3|2−}}:
:{{chem|HSO|3|−}} ⇌ {{chem|SO|3|2−}} + H<sup>+</sup>

===Dehydration/hydration equilibria===
Attempted isolation of the common salts of bisulfite results in dehydration of the anion with formation of metabisulfite ({{chem|S|2|O|5|2−}}), also known as disulfite:
:2 {{chem|HSO|3|−}} ⇌ {{chem|S|2|O|5|2−}} + H<sub>2</sub>O
Because of this equilibrium, anhydrous sodium and potassium salts of bisulfite cannot be obtained. However, there are some reports of anhydrous bisulfites with large counter ions.<ref>{{cite journal |last1=Maylor |first1=R. |last2=Gill |first2=J. B. |last3=Goodall |first3=D. C. |title=Some studies on anhydrous cobalt sulphite |journal=Journal of Inorganic and Nuclear Chemistry |date=July 1971 |volume=33 |issue=7 |pages=1975–1979 |doi=10.1016/0022-1902(71)80558-4}}</ref>

[[File:Structure of metabisulfite ion.png|right|thumb|200px|Structure of disulfite (aka metabisulfite) ion.<ref>{{cite journal |last1=Carter |first1=Kay L. |last2=Siddiquee |first2=Tasneem A. |last3=Murphy |first3=Kristen L. |last4=Bennett |first4=Dennis W. |title=The surprisingly elusive crystal structure of sodium metabisulfite |journal=Acta Crystallographica Section B: Structural Science |date=18 March 2004 |volume=60 |issue=2 |pages=155–162 |doi=10.1107/S0108768104003325|pmid=15017087 }}</ref>]]

===Redox reactions===
Bisulfite is a good [[Chemistry:Reducing agent|reducing]] agent, especially for oxygen scrubbing:
:2 {{chem|HSO|3|−}} +  O<sub>2</sub>   →  2 {{chem|SO|4|2−}} + 2 H<sup>+</sup>
Its reducing properties are exploited to precipitate gold from auric acid (gold dissolved in [[Chemistry:Aqua regia|aqua regia]]) and reduce chromium(VI) to chromium(III).  In [[Chemistry:Water chlorination|water chlorination]], sodium bisulfite is used to reduce the residual 'chlorine' which can have a negative impact on aquatic life.

===Organic synthesis===
:[[Image:Bisulfite adduct.svg|Bisulfite adduct]]{{clear|left}}
In [[Chemistry:Organic chemistry|organic chemistry]], "[[Chemistry:Sodium bisulfite|sodium bisulfite]]" is used to form [[Chemistry:Adduct|adduct]]s with [[Chemistry:Aldehyde|aldehyde]] and with certain cyclic ketones. These adducts are α-hydroxy[[Chemistry:Sulfonic acid|sulfonic acid]]s.<ref>{{OrgSynth | collvol = 7 | collvolpages = 381 | year = 1990 | title = 2-Methyl-2-(Trimethylsiloxy)pentan-3-one | first1 = Steven D. |last1=Young |first2=Charles T. |last2=Buse |first3= Clayton H. |last3=Heathcock | prep = cv7p0381}}</ref> This reaction is useful for the separation and purification of aldehydes.<ref>{{Cite journal |last1=Furigay |first1=Maxwell H. |last2=Boucher |first2=Maria M. |last3=Mizgier |first3=Nikola A. |last4=Brindle |first4=Cheyenne S. |date=2018-04-02 |title=Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol |journal=Journal of Visualized Experiments |issue=134 |pages=57639 |doi=10.3791/57639 |issn=1940-087X |pmc=5933314 |pmid=29658940}}</ref>  The bisulfite adducts are charged and so are more soluble in polar solvents. The reaction can be reversed in base or strong acid.<ref>{{OrgSynth | collvol = 7 | collvolpages = 361 | year = 1990 | title = 2-Methyl-3-phenylpropanal | first1 = S. A. |last1=Buntin |first2=Richard F. |last2=Heck | prep = cv7p0361}}</ref> Examples of such procedures are described for [[Chemistry:Benzaldehyde|benzaldehyde]],<ref>{{OrgSynth | title = α-(''N'',''N''-Dimethylamino)phenylacetonitrile | first1 = Harold M. |last1=Taylor |first2=Charles R. |last2=Hauser |author2-link=Charles R. Hauser | collvol = 5 | collvolpages = 437 | year = 1973 | prep = cv5p0437}}</ref> [[Chemistry:2-Tetralone|2-tetralone]],<ref>{{OrgSynth | title = β-Tetralone | first1 = M. D. |last1=Soffer |first2=M. P. |last2=Bellis |first3=Hilda E. |last3=Gellerson |first4=Roberta A. |last4=Stewart | collvol = 4 | collvolpages = 903 | year = 1963 | prep = cv4p0903}}</ref> [[Chemistry:Citral|citral]],<ref>{{OrgSynth | title = Pseudoionone | first1 = Alfred |last1=Russell |first2=R. L. |last2=Kenyon | collvol = 3 | collvolpages = 747 | prep = cv3p0747 | year = 1955}}</ref> the ethyl ester of [[Chemistry:Pyruvic acid|pyruvic acid]]<ref>{{OrgSynth | title = Ethyl Pyruvate | first = J. W. |last=Cornforth | year = 1963 | collvol = 4 | collvolpages = 467 | prep = cv4p0467}}</ref> and [[Chemistry:Glyoxal|glyoxal]].<ref>{{OrgSynth | first1 = Anthony R. |last1=Ronzio |first2=T. D. |last2=Waugh | title = Glyoxal Bisulfite | collvol = 3 | collvolpages = 438 | prep = cv3p0438 | year = 1955}}</ref> In the ring-expansion reaction of [[Chemistry:Cyclohexanone|cyclohexanone]] with [[Chemistry:Diazald|diazald]], the bisulfite reaction is reported to allow differentiation between the primary reaction product [[Chemistry:Cycloheptanone|cycloheptanone]] and the main contaminant cyclooctanone.<ref>{{OrgSynth | prep = cv4p0221 | title = Cycloheptanone | first1 = Hyp J., Jr. |last1=Dauben |first2=Howard J. |last2=Ringold |first3=Robert H. |last3=Wade |first4=David L. |last4=Pearson |first5=Arthur G., Jr. |last5=Anderson |doi=10.15227/orgsyn.034.0019 | collvol = 4 | collvolpages = 221 }}</ref>

Another use of bisulfite in organic chemistry is as a mild [[Chemistry:Reducing agent|reducing agent]], for example to remove traces or excess amounts of [[Chemistry:Chlorine|chlorine]], [[Chemistry:Bromine|bromine]], [[Chemistry:Iodine|iodine]], [[Chemistry:Hypochlorite|hypochlorite]] salts, [[Chemistry:Osmium tetroxide|osmate]] esters, [[Chemistry:Chromium trioxide|chromium trioxide]] and [[Chemistry:Potassium permanganate|potassium permanganate]].  Sodium bisulfite is a decoloration agent in purification procedures because it reduces strongly coloured oxidizing agents, conjugated alkenes and carbonyl compounds.

Bisulfite is also the key ingredient in the [[Chemistry:Bucherer reaction|Bucherer reaction]]. In this reaction an aromatic hydroxyl group is converted to the corresponding [[Chemistry:Amine|amine]] group. This is a [[Physics:Reversible reaction|reversible reaction]]. The first step in this reaction is an [[Chemistry:Addition reaction|addition reaction]] of sodium bisulfite to an aromatic [[Chemistry:Double bond|double bond]]. The [[Chemistry:Bucherer carbazole synthesis|Bucherer carbazole synthesis]] is a related [[Chemistry:Organic reaction|organic reaction]] that uses sodium bisulfite as a reagent.

===Bisulfite DNA sequencing===
{{further|Biology:Bisulfite sequencing}}
[[Image:Bisulfite-reaction.png|thumb|left|300px|The chemical reaction that underlies the bisulfite-mediated conversion of cytosine to uracil.]]

Sodium bisulfite is used in the analysis of the [[Biology:Methylation|methylation]] status of cytosines in [[Biology:DNA|DNA]].

In this technique, sodium bisulfite deaminates [[Chemistry:Cytosine|cytosine]] into [[Chemistry:Uracil|uracil]], but does not affect 5-methylcytosine, a methylated form of cytosine with a methyl group attached to carbon 5.

When the bisulfite-treated DNA is amplified via [[Biology:Polymerase chain reaction|polymerase chain reaction]], the uracil is amplified as thymine and the methylated cytosines are amplified as cytosine. [[Biology:DNA sequencing|DNA sequencing]] techniques are then used to read the sequence of the bisulfite-treated DNA. Those cytosines that are read as cytosines after sequencing represent methylated cytosines, while those that are read as thymines represent unmethylated cytosines in the genomic DNA.<ref>{{cite journal | journal = PNAS | year = 1992 | volume = 89 | issue = 5 | pages = 1827–1831 |author1=Frommer, M. |author2=McDonald, L. E. |author3=Millar, D. S. |author4=Collis, C. M. |author5=Watt, F. |author6=Grigg, G. W. |author7=Molloy P. L. |author8=Paul, C. L. | title = A genomic sequencing protocol that yields a positive display of 5-methylcytosine residues in individual DNA strands | pmid = 1542678 | doi = 10.1073/pnas.89.5.1827 |doi-access=free | pmc = 48546| bibcode = 1992PNAS...89.1827F }}</ref>

==References==
<references/>

[[Category:Bisulfites| ]]
[[Category:Sulfur ions]]

{{Sourceattribution|Bisulfite}}