View source for Nitrite

{{Short description|Portmanteau name for nitrite derivatives}}
{{Distinguish|nitride|nitrate|nitrogen dioxide}}
{{Use dmy dates|date=February 2023}}
{{Chembox
| ImageFileL1    = Nitrit-Ion2.svg
| ImageClassL1   = skin-invert
| ImageAltL1     = A nitrogen atom is bonded to two oxygen atoms, with bond strength 1.5, in a bent geometry; the collective ion bears a single negative charge
| ImageFileR1    = Nitrite-3D-vdW.png
| ImageAltR1     = [[Space-filling model]] of the nitrite ion
| ImageClassR1   = bg-transparent
| SystematicName = dioxidonitrate(1−)
| IUPACName      = Nitrite
| Section1       = {{Chembox Identifiers
| CASNo = 14797-65-0
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII = J39976L608
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 233-272-6
| PubChem = 946
| ChemSpiderID = 921
| SMILES = N(=O)[O-]
| InChI = 1/HNO2/c2-1-3/h(H,2,3)/p-1
| InChIKey = IOVCWXUNBOPUCH-REWHXWOFAR
| StdInChI = 1S/HNO2/c2-1-3/h(H,2,3)/p-1
| StdInChIKey = IOVCWXUNBOPUCH-UHFFFAOYSA-M
| RTECS = 
| MeSHName = 
| ChEBI = 16301 }}
| Section2       = {{Chembox Properties
| Formula = {{chem|NO|2|-}}
| N=1 | O=2
| Appearance =
| Solubility = 
| ConjugateAcid = [[Nitrous acid]]}}
| Section3       = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt = }}
}}

The '''nitrite''' [[polyatomic ion|ion]] has the [[chemical formula]] {{chem|NO|2|−}}. Nitrite (mostly [[sodium nitrite]]) is widely used throughout chemical and pharmaceutical industries.<ref name=Ullmann>{{Ullmann| first1 = Wolfgang | last1 = Laue | first2 = Michael | last2 = Thiemann | first3 = Erich | last3 = Scheibler | first4 = Karl Wilhelm | last4 = Wiegand | name-list-style = vanc | title= Nitrates and Nitrites |year = 2006 | doi = 10.1002/14356007.a17_265 | isbn = 978-3527306732 }}</ref> The nitrite anion is a pervasive intermediate in the [[nitrogen cycle]] in nature. The name nitrite also refers to organic compounds having the –ONO group, which are esters of [[nitrous acid]].

==Production==
[[Sodium nitrite]] is made industrially by passing a mixture of nitrogen oxides into aqueous [[sodium hydroxide]] or [[sodium carbonate]] solution:<ref name=p461/><ref name=Ullmann/>
:{{chem2|NO + NO2  + 2 NaOH  -> 2 NaNO2 + H2O}}
:{{chem2|NO + NO2  +  Na2CO3  -> 2 NaNO2 +  CO2}}
The product is purified by recrystallization. Alkali metal nitrites are thermally stable up to and beyond their melting point (441&nbsp;°C for KNO<sub>2</sub>). [[Ammonium nitrite]] can be made from [[dinitrogen trioxide]], N<sub>2</sub>O<sub>3</sub>, which is formally the [[anhydride]] of nitrous acid:
:2 NH<sub>3</sub> + H<sub>2</sub>O + N<sub>2</sub>O<sub>3</sub> → 2 NH<sub>4</sub>NO<sub>2</sub>

== Structure ==
[[Image:Nitrite-ion-canonical-structures.svg|thumb|200px|class=skin-invert-image|The two [[Resonance (chemistry)#Resonance as a diagrammatic tool|canonical structures]] of {{chem|NO|2|-}}, which contribute to the resonance hybrid for the nitrite ion]]
[[File:Trans-nitrous-acid-2D-dimensions.png|thumb|200px|class=skin-invert-image|Dimensions of ''trans''-HONO (from the [[rotational spectroscopy|microwave spectrum]])]]
The nitrite ion has a symmetrical structure (C<sub>2v</sub> [[molecular point group|symmetry]]), with both N–O bonds having equal length and a bond angle of about 115°. In [[valence bond theory]], it is described as a [[resonance hybrid]] with equal contributions from two canonical forms that are mirror images of each other. In [[molecular orbital theory]], there is a [[sigma bond]] between each oxygen atom and the nitrogen atom, and a delocalized [[pi bond]] made from the [[p orbitals]] on nitrogen and oxygen atoms which is perpendicular to the plane of the molecule. The negative charge of the ion is equally distributed on the two oxygen atoms. Both nitrogen and oxygen atoms carry a [[lone pair]] of electrons. Therefore, the nitrite ion is a [[Lewis base]].

In the gas phase it exists predominantly as a ''trans''-planar molecule.

==Reactions==
=== Acid-base properties ===
Nitrite is the conjugate base of the weak acid [[nitrous acid]]:
:HNO<sub>2</sub> {{eqm}} H<sup>+</sup> + {{chem|NO|2|-}};{{spaces|5}} [[acid dissociation constant|p''K''<sub>a</sub>]] ≈ 3.3 at 18&nbsp;°C<ref name=scdb>[http://www.acadsoft.co.uk/scdbase/scdbase.htm IUPAC SC-Database] {{Webarchive|url=https://web.archive.org/web/20170619235720/http://www.acadsoft.co.uk/scdbase/scdbase.htm |date=19 June 2017 }} A comprehensive database of published data on equilibrium constants of metal complexes and ligands</ref>
Nitrous acid is also highly unstable, tending to [[disproportionate]]:
:3&nbsp;HNO<sub>2</sub> (aq) {{eqm}} H<sub>3</sub>O<sup>+</sup> + {{chem|NO|3|-}} + 2&nbsp;NO
This reaction is slow at 0&nbsp;°C.<ref name=p461/> Addition of acid to a solution of a nitrite in the presence of a [[reducing agent]], such as iron(II), is a way to make [[nitric oxide]] (NO) in the laboratory.

=== Oxidation and reduction ===
The formal [[oxidation state]] of the nitrogen atom in nitrite is +3. This means that it can be either oxidized to oxidation states +4 and +5, or reduced to oxidation states as low as −3. Standard [[reduction potential]]s for reactions directly involving nitrous acid are shown in the table below:<ref>{{Greenwood&Earnshaw2nd|page=431}}</ref> 
:{|class="wikitable"
|-
!Half-reaction||''E''<sup>0</sup> ([[Volt|V]])
|-
| {{chem|NO|3|-}} + 3 H<sup>+</sup> + 2 e<sup>−</sup> {{eqm}} HNO<sub>2</sub> + H<sub>2</sub>O|| +0.94
|-
| 2 HNO<sub>2</sub> + 4 H<sup>+</sup> + 4 e<sup>−</sup> {{eqm}} H<sub>2</sub>N<sub>2</sub>O<sub>2</sub> + 2 H<sub>2</sub>O||+0.86
|-
| N<sub>2</sub>O<sub>4</sub> + 2 H<sup>+</sup> + 2 e<sup>−</sup> {{eqm}} 2 HNO<sub>2</sub>||+1.065
|-
| 2 HNO<sub>2</sub>+ 4 H<sup>+</sup> + 4 e<sup>−</sup> {{eqm}} N<sub>2</sub>O + 3 H<sub>2</sub>O||+1.29
|}
The data can be extended to include products in lower oxidation states. For example:
:H<sub>2</sub>N<sub>2</sub>O<sub>2</sub> + 2 H<sup>+</sup> + 2 ''e''<sup>−</sup> {{eqm}} N<sub>2</sub> + 2 H<sub>2</sub>O;{{spaces|5}} ''E''<sup>0</sup> = +2.65&nbsp;V

Oxidation reactions usually result in the formation of the [[nitrate]] ion, with nitrogen in oxidation state +5. For example, oxidation with [[permanganate]] ion can be used for quantitative analysis of nitrite (by [[titration]]):
:5 {{chem|NO|2|-}} + 2 {{chem|MnO|4|-}} + 6 H<sup>+</sup> → 5 {{chem|NO|3|-}} + 2 Mn<sup>2+</sup> + 3 H<sub>2</sub>O

The product of reduction reactions with nitrite ion are varied, depending on the [[reducing agent]] used and its strength. With [[sulfur dioxide]], the products are NO and N<sub>2</sub>O; with tin(II) (Sn<sup>2+</sup>) the product is [[hyponitrous acid]] (H<sub>2</sub>N<sub>2</sub>O<sub>2</sub>); reduction all the way to ammonia (NH<sub>3</sub>) occurs with [[hydrogen sulfide]]. With the [[hydrazine|hydrazinium]] cation ({{chem|N|2|H|5|+}}) the product of nitrite reduction is [[hydrazoic acid]] (HN<sub>3</sub>), an unstable and explosive compound:

:HNO<sub>2</sub> + {{chem|N|2|H|5|+}} → HN<sub>3</sub> + H<sub>2</sub>O + H<sub>3</sub>O<sup>+</sup>
which can also further react with nitrite:
:HNO<sub>2</sub> + HN<sub>3</sub> → N<sub>2</sub>O + N<sub>2</sub> + H<sub>2</sub>O

This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states.<ref name=p461>{{Greenwood&Earnshaw2nd|pages=461–464}}</ref>

===Analysis of nitrite===
{{See also|Nitrite test}}
Nitrite is detected and analyzed by the [[Griess test|Griess Reaction]], involving the formation of a deep red-colored [[azo dye]] upon treatment of a {{chem|NO|2|-}}-containing sample with [[sulfanilic acid]] and naphthyl-1-amine in the presence of acid.<ref>{{Cite journal |last=Ivanov |first=V. M. |date=2004-10-01 |title=The 125th Anniversary of the Griess Reagent |journal=Journal of Analytical Chemistry |language=en |volume=59 |issue=10 |pages=1002–1005 |doi=10.1023/B:JANC.0000043920.77446.d7 |s2cid=98768756 |issn=1608-3199}}</ref>

=== Coordination complexes ===
{{main|Transition metal nitrite complex}}
Nitrite is an [[ambidentate ligand]] and can form a wide variety of [[coordination complex]]es by binding to metal ions in several ways.<ref name=p461/> Two examples are the red nitrito complex [Co(NH<sub>3</sub>)<sub>5</sub>(ONO)]<sup>2+</sup> is [[metastable]], [[isomer]]izing to the yellow [[Nitropentaamminecobalt(III) chloride|nitro complex [Co(NH<sub>3</sub>)<sub>5</sub>(NO<sub>2</sub>)]<sup>2+</sup>]]. Nitrite is processed by several enzymes, all of which utilize coordination complexes.

==Biochemistry==
[[File:Nitrogen Cycle - Reactions and Enzymes.svg|thumb|upright=1.5|class=skin-invert-image|A schematic representation of the microbial nitrogen cycle.<ref>{{Cite journal|last1=Sparacino-Watkins|first1=Courtney|last2=Stolz|first2=John F.|last3=Basu|first3=Partha|date=2013-12-16|title=Nitrate and periplasmic nitrate reductases|journal=Chem. Soc. Rev.|language=en|volume=43|issue=2|pages=676–706|doi=10.1039/c3cs60249d|pmid=24141308|issn=1460-4744|pmc=4080430}}</ref><ref>{{Cite journal|last1=Simon|first1=Jörg|last2=Klotz|first2=Martin G.|title=Diversity and evolution of bioenergetic systems involved in microbial nitrogen compound transformations|journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics|language=en|volume=1827|issue=2|pages=114–135|doi=10.1016/j.bbabio.2012.07.005|pmid=22842521|year=2013|doi-access=free}}</ref> [[Anammox|ANAMMOX]] is anaerobic ammonium oxidation, [[Dissimilatory nitrate reduction to ammonium|DNRA]] is dissimilatory nitrate reduction to ammonium, and [[Comammox|COMMAMOX]] is complete ammonium oxidation.]]

In [[nitrification]], [[ammonium]] is converted to nitrite.  Important species include ''[[Nitrosomonas]]''. Other bacterial species such as ''[[Nitrobacter]]'', are responsible for the oxidation of the nitrite into nitrate.

Nitrite can be reduced to [[nitric oxide]] or [[ammonia]] by many species of bacteria. Under hypoxic conditions, nitrite may release nitric oxide, which causes potent [[vasodilation]]. Several mechanisms for nitrite conversion to NO have been described, including enzymatic reduction by [[xanthine oxidoreductase]], [[nitrite reductase]], and [[Nitric oxide synthase|NO synthase]] (NOS), as well as nonenzymatic acidic [[disproportionation]] reactions.

==Uses==
===Chemical precursor===
[[Azo dye]]s and other colorants are prepared by the process called [[Diazonium compound#Preparation|diazotization]], which requires nitrite.<ref name=Ullmann/>

=== Nitrite in food preservation and biochemistry ===
{{See also|Warmed-over flavor|Sodium nitrite#Food additive and preservative}}
The addition of [[#Nitrite in food preservation and biochemistry|nitrites]] and [[nitrates]] to processed meats such as ham, bacon, and sausages speeds up the [[Curing (food preservation)|curing]] of meat and also impart an attractive colour.<ref name="Wilson">{{cite news 
 |last=Wilson
 |first=Bee
 |date=2018-03-01
 |title=Yes, bacon really is killing us
 |url=https://www.theguardian.com/news/2018/mar/01/bacon-cancer-processed-meats-nitrates-nitrites-sausages
 |url-status=live
 |work=The Guardian
 |location=London
 |language=en-GB
 |issn=0261-3077
 |archive-url=https://web.archive.org/web/20210210183650/https://www.theguardian.com/news/2018/mar/01/bacon-cancer-processed-meats-nitrates-nitrites-sausages
 |archive-date=2021-02-10
 |access-date=2021-02-14
 |quote=In trade journals of the 1960s, the firms who sold nitrite powders to ham-makers spoke quite openly about how the main advantage was to increase profit margins by speeding up production.}}</ref>

The academic and industrial consensus is that nitrites also reduces growth and toxin production of ''[[Clostridium botulinum]]''.<ref>{{cite journal | vauthors = Christiansen LN, Johnston RW, Kautter DA, Howard JW, Aunan WJ | title = Effect of nitrite and nitrate on toxin production by Clostridium botulinum and on nitrosamine formation in perishable canned comminuted cured meat | journal = Applied Microbiology | volume = 25 | issue = 3 | pages = 357–62 | date = March 1973 | pmid = 4572891 | pmc = 380811 | doi = 10.1128/AEM.25.3.357-362.1973 }}</ref><ref>{{Cite journal |last1=Lee |first1=Soomin |last2=Lee |first2=Heeyoung |last3=Kim |first3=Sejeong |last4=Lee |first4=Jeeyeon |last5=Ha |first5=Jimyeong |last6=Choi |first6=Yukyung |last7=Oh |first7=Hyemin |last8=Choi |first8=Kyoung-Hee |last9=Yoon |first9=Yohan |date=August 2018 |title=Microbiological safety of processed meat products formulated with low nitrite concentration — A review |journal=Asian-Australasian Journal of Animal Sciences |volume=31 |issue=8 |pages=1073–1077 |doi=10.5713/ajas.17.0675 |issn=1011-2367 |pmc=6043430 |pmid=29531192}}</ref><ref>{{cite journal |last1=Sindelar |first1=Jeffrey J. |last2=Milkowski |first2=Andrew L. |title=Human safety controversies surrounding nitrate and nitrite in the diet |journal=Nitric Oxide |date=May 2012 |volume=26 |issue=4 |pages=259–266 |doi=10.1016/j.niox.2012.03.011}}</ref>
On the other hand, a 2018 study (full text not available) by the British Meat Producers Association determined that legally permitted levels of nitrite do not affect the growth of ''C. botulinum''.<ref>{{cite news 
 |last=Doward
 |first=Jamie
 |date=2019-03-23
 |title=Revealed: no need to add cancer-risk nitrites to ham
 |url=https://www.theguardian.com/food/2019/mar/23/nitrites-ham-bacon-cancer-risk-additives-meat-industry-confidential--report
 |url-status=live
 |work=The Observer
 |location=London
 |archive-url=https://web.archive.org/web/20210126134441/https://www.theguardian.com/food/2019/mar/23/nitrites-ham-bacon-cancer-risk-additives-meat-industry-confidential--report
 |archive-date=2021-01-26
 |access-date=2021-02-14
 |quote=The results show that there is no change in levels of inoculated ''C. botulinum'' over the curing process, which implies that the action of nitrite during curing is not toxic to ''C. botulinum'' spores at levels of 150ppm [parts per million] ingoing nitrite and below.}}</ref> In the U.S., meat cannot be labeled as "cured" without the addition of nitrite.<ref>{{Cite book|title=Food Safety and Toxicity |first=John |last=De Vries|publisher=CRC Press |year=1997|isbn=978-0-8493-9488-1|page=70}}</ref><ref>[https://web.archive.org/web/20090617075537/http://www.meatami.com/ht/a/GetDocumentAction/i/44170 sodium nitrite and nitrate facts] Accessed 12 Dec 2014</ref><ref name="CMSFB">{{cite book | url=https://books.google.com/books?id=5IS2n8MBpf8C&pg=PA78 | title=Compendium of the Microbiological Spoilage of Foods and Beverages | page=78| isbn=978-1-4419-0826-1 | last1=Doyle | first1=Michael P. | last2=Sperber | first2=William H. | date=23 September 2009 | publisher=Springer }}</ref> In some countries, cured-meat products are manufactured without [[nitrate]] or nitrite, and without nitrite from vegetable sources. [[Parma ham]], produced without nitrite since 1993, was reported in 2018 to have caused no cases of botulism. This is because the interior of the muscle is sterile and the surface is exposed to oxygen.<ref name=Wilson/> Other manufacture processes do not assure these conditions, and reduction of nitrite results in toxin production.<ref>{{cite journal |last1=Lebrun |first1=S. |last2=Van Nieuwenhuysen |first2=T. |last3=Crèvecoeur |first3=S. |last4=Vanleyssem |first4=R. |last5=Thimister |first5=J. |last6=Denayer |first6=S. |last7=Jeuge |first7=S. |last8=Daube |first8=G. |last9=Clinquart |first9=A. |last10=Fremaux |first10=B. |title=Influence of reduced levels or suppression of sodium nitrite on the outgrowth and toxinogenesis of psychrotrophic Clostridium botulinum Group II type B in cooked ham |journal=International Journal of Food Microbiology |date=December 2020 |volume=334 |article-number=108853 |doi=10.1016/j.ijfoodmicro.2020.108853}}</ref>

In mice, food rich in nitrites together with unsaturated fats can prevent [[hypertension]] by forming nitro fatty acids that inhibit soluble [[epoxide hydrolase]], which is one explanation for the apparent health effect of the [[Mediterranean diet]].<ref>{{Cite journal | doi = 10.1073/pnas.1402965111| title = Protection from hypertension in mice by the Mediterranean diet is mediated by nitro fatty acid inhibition of soluble epoxide hydrolase| journal = Proceedings of the National Academy of Sciences| volume = 111| issue = 22| pages = 8167–72| year = 2014| last1 = Charles | first1 = R. L.| last2 = Rudyk | first2 = O.| last3 = Prysyazhna | first3 = O.| last4 = Kamynina | first4 = A.| last5 = Yang | first5 = J.| last6 = Morisseau | first6 = C.| last7 = Hammock | first7 = B. D.| last8 = Freeman | first8 = B. A.| last9 = Eaton | first9 = P. | pmid=24843165 | pmc=4050620
| bibcode = 2014PNAS..111.8167C| doi-access = free}}</ref> Adding nitrites to meat has been shown to generate known [[carcinogen]]s; the [[World Health Organization]] (WHO) advises that eating {{convert|50|g|abbr=on}} of nitrite processed meat a day would raise the risk of getting [[bowel cancer]] by 18% over a lifetime.<ref name=Wilson/>

The recommended maximum limits by the World Health Organization in [[drinking water]] are 3&nbsp;mg&nbsp;L<sup>−1</sup> and 50&nbsp;mg&nbsp;L<sup>−1</sup> for nitrite and [[nitrate]] ions, respectively.<ref name="ReferenceB">{{Cite journal | doi = 10.1016/j.jhazmat.2016.11.055| pmid = 27894754| title = Composite of Cu metal nanoparticles—multiwall carbon nanotubes—reduced graphene oxide as a novel and high performance platform of the electrochemical sensor for simultaneous determination of nitrite and nitrate| journal = Journal of Hazardous Materials| volume = 324| issue = Pt B| pages = 762–772| year = 2017| last1 = Bagheri | first1 = H.| last2 = Hajian | first2 = A.| last3 = Rezaei | first3 = M.| last4 = Shirzadmehr | first4 = A.| bibcode = 2017JHzM..324..762B}}</ref> Ingesting too much nitrite and/or nitrate through well water is suspected to cause [[methemoglobinemia]].<ref>{{Cite journal |display-authors=6 |vauthors=Powlson DS, Addiscott TM, Benjamin N, Cassman KG, de Kok TM, van Grinsven H, L'Hirondel JL, Avery AA, van Kessel C |year=2008 |title=When does nitrate become a risk for humans? |url=https://digitalcommons.unl.edu/agronomyfacpub/102 |journal=Journal of Environmental Quality |volume=37 |issue=2 |pages=291–295 |bibcode=2008JEnvQ..37..291P |doi=10.2134/jeq2007.0177 |pmid=18268290 |s2cid=14097832|url-access=subscription }}</ref>

95% of the nitrite ingested in modern diets comes from bacterial conversion of nitrates naturally found in vegetables.<ref>{{Cite web |title=Is celery juice a viable alternative to nitrites in cured meats? |url=https://www.mcgill.ca/oss/article/food/celery-juice-viable-alternative-nitrites-cured-meats |access-date=2022-09-14 |website=Office for Science and Society |language=en}}</ref> However, potentially cancer-causing nitroso compounds are not made in the pH-neutral colon. They are mostly made in the acidic stomach.<ref>{{cite journal | pmid = 7285009 | volume=41 | issue=10 | title=Absence of volatile nitrosamines in human feces |date=October 1981 | journal=Cancer Res. | pages=3992–4 | last1 = Lee | first1 = L | last2 = Archer | first2 = MC | last3 = Bruce | first3 = WR}}</ref><ref>{{cite journal | doi = 10.1016/j.freeradbiomed.2007.03.011 | pmid = 17761300 | volume=43 | issue=7 | title=Diet-induced endogenous formation of nitroso compounds in the GI tract |date=October 2007 | journal=Free Radic. Biol. Med. | pages=1040–7 | last1 = Kuhnle | first1 = GG | last2 = Story | first2 = GW | last3 = Reda | first3 = T |display-authors=etal }}</ref>

====Curing of meat====
Nitrite reacts with the meat's [[myoglobin]] by attaching to the heme iron atom, forming reddish-brown nitrosomyoglobin and the characteristic pink "fresh" color of nitrosohemochrome or nitrosyl-heme upon cooking.<ref name=ind>{{cite journal |last1=Pappenberger |first1=Günter |last2=Hohmann |first2=Hans-Peter |title=Industrial Production of l-Ascorbic Acid (Vitamin C) and d-Isoascorbic Acid |journal=Biotechnology of Food and Feed Additives |series=Advances in Biochemical Engineering/Biotechnology |date=2013 |volume=143 |pages=143–188 |doi=10.1007/10_2013_243|pmid=24258144 |isbn=978-3-662-43760-5 }}</ref> In the US, nitrite has been formally used since 1925. According to scientists working for the industry group [[American Meat Institute]], this use of nitrite started in the [[Middle Ages]].<ref>{{Cite journal|last1=Binkerd|first1=E. F.|last2=Kolari|first2=O. E.|date=1975-01-01|title=The history and use of nitrate and nitrite in the curing of meat|journal=Food and Cosmetics Toxicology|volume=13|issue=6|pages=655–661|doi=10.1016/0015-6264(75)90157-1|issn=0015-6264|pmid=1107192}}</ref> Historians and [[epidemiology|epidemiologist]]s argue that the widespread use of nitrite in meat-curing is closely linked to the development of industrial meat-processing.<ref>{{cite book |last=Coudray |first=Guillaume |year=2017 |title=Cochonneries: Comment la charcuterie est devenue un poison |language=fr |location=Paris |publisher=La Découverte |pages=40–70 |isbn=978-2-7071-9358-2}}</ref><ref>{{Cite journal|last=Lauer|first=Klaus|date=1991-01-01|title=The history of nitrite in human nutrition: A contribution from German cookery books|url=https://www.jclinepi.com/article/0895-4356(91)90037-A/abstract|journal=Journal of Clinical Epidemiology|language=en|volume=44|issue=3|pages=261–264|doi=10.1016/0895-4356(91)90037-A|issn=0895-4356|pmid=1999685|url-access=subscription}}</ref> French investigative journalist {{interlanguage link|Guillaume Coudray|fr}} asserts that the meat industry chooses to cure its meats with nitrite even though it is established that this chemical gives rise to cancer-causing [[nitroso]]-compounds.<ref>{{cite web |url=https://www.corporatecrimereporter.com/news/200/guillaume-coudray-on-the-nitro-meat-cancer-connection/ |title=Guillaume Coudray on the Nitro Meat Cancer Connection |author=<!--Editor byline, no author name given.--> |date=14 April 2021 |website=Corporate Crime Reporter |access-date=2024-10-13}}</ref> Some traditional and artisanal producers avoid nitrites. As many researches nowadays try to point out the hazardous generation of nitrosamines as nitrites link with free peptides in the gastrointestinal system, the EU published a regulation which obliges the reduction of nitrites on meat curing from 150 to 80 ppm (mg/kg).<ref>{{Cite news |title=COMMISSION DECISION (EU) 2024/1225 of 30 April 2024 concerning national provisions notified by Denmark on the addition of nitrite to certain meat products |url=https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ:L_202401225}}</ref>

{{see also|Nitrosamine formation during digestion}}
Addition of [[ascorbic acid]], [[erythorbic acid]], or one of their salts enhance the binding of nitrite to the iron atom in myoglobin.<ref name=ind/> These chemicals also reduce the formation of nitrosamine in the stomach, but only when the fat content of a meal is less than 10%, beyond which they instead increase the formation of nitrosamine.<ref>{{cite journal |pmid=17785370 |pmc=2095705 |year=2007 |last1=Combet |first1=E. |title=Fat transforms ascorbic acid from inhibiting to promoting acid-catalysed ''N''-nitrosation |journal=Gut |volume=56 |issue=12 |pages=1678–1684 |last2=Paterson |first2=S |last3=Iijima |first3=K |last4=Winter |first4=J |last5=Mullen |first5=W |last6=Crozier |first6=A |last7=Preston |first7=T |last8=McColl |first8=K. E. |doi=10.1136/gut.2007.128587}}</ref><ref>{{cite journal |pmid=20026204 |year=2010 |last1=Combet |first1=E |title=Dietary phenolic acids and ascorbic acid: Influence on acid-catalyzed nitrosative chemistry in the presence and absence of lipids |journal=Free Radical Biology and Medicine |volume=48 |issue=6 |pages=763–771 |last2=El Mesmari |first2=A |last3=Preston |first3=T |last4=Crozier |first4=A |last5=McColl |first5=K. E. |doi=10.1016/j.freeradbiomed.2009.12.011}}</ref>

=== Antidote for cyanide poisoning===
Nitrites in the form of [[sodium nitrite]] and [[amyl nitrite]] are components of many [[cyanide]] [[antidote]] kits.<ref>{{Cite journal |last1=Meillier |first1=Andrew |last2=Heller |first2=Cara |date=2015 |title=Acute Cyanide Poisoning: Hydroxocobalamin and Sodium Thiosulfate Treatments with Two Outcomes following One Exposure Event |journal=Case Reports in Medicine |volume=2015 |article-number=217951 |doi=10.1155/2015/217951 |issn=1687-9627 |pmc=4620268 |pmid=26543483|doi-access=free }}</ref> Both of these compounds bind to [[hemoglobin]] and oxidize the Fe<sup>2+</sup> ions to Fe<sup>3+</sup> ions forming [[methemoglobin]]. Methemoglobin, in turn, binds to cyanide (CN), creating cyanmethemoglobin, effectively removing cyanide from the [[complex IV]] of the [[electron transport chain]] (ETC) in [[Mitochondrion|mitochondria]], which is the primary site of disruption caused by cyanide. Another mechanism by which nitrites help treat cyanide toxicity is the generation of [[nitric oxide]] (NO). NO displaces the CN from the [[cytochrome c oxidase]] (ETC complex IV), making it available for methemoglobin to bind.<ref>{{Cite journal |last1=Bebarta |first1=Vikhyat S. |last2=Brittain |first2=Matthew |last3=Chan |first3=Adriano |last4=Garrett |first4=Norma |last5=Yoon |first5=David |last6=Burney |first6=Tanya |last7=Mukai |first7=David |last8=Babin |first8=Michael |last9=Pilz |first9=Renate B. |last10=Mahon |first10=Sari B. |last11=Brenner |first11=Matthew |title=Sodium Nitrite and Sodium Thiosulfate Are Effective Against Acute Cyanide Poisoning when Administered by Intramuscular Injection |date=June 2017 |journal=Annals of Emergency Medicine |volume=69 |issue=6 |pages=718–725.e4 |doi=10.1016/j.annemergmed.2016.09.034 |issn=0196-0644 |pmc=5446299 |pmid=28041825}}</ref>

==Organic nitrites==
[[Image:Nitrite-group-2D.svg|thumb|right|upright=0.5|class=skin-invert-image|A nitrite ester]]

In [[organic chemistry]], [[alkyl nitrites]] are [[ester]]s of nitrous acid and contain the nitrosoxy functional group. Nitro compounds contain the C–NO<sub>2</sub> group. Nitrites have the general formula RONO, where R is an [[aryl]] or [[alkyl]] group. [[Amyl nitrite]] and other alkyl nitrites have a [[vasodilation|vasodilating action]] and must be handled in the laboratory with caution. They are sometimes used in medicine for the treatment of heart diseases. A classic [[named reaction]] for the synthesis of alkyl nitrites is the '''Meyer synthesis'''<ref>{{cite journal 
| title = Ueber die Nitroverbindungen der Fettreihe  
| author = Victor Meyer  
| journal = [[Justus Liebig's Annalen der Chemie]] 
| volume = 171 
| issue = 1
| pages = 1–56 
| year = 1872 
| url = https://zenodo.org/record/1427331
| doi = 10.1002/jlac.18741710102   | author-link = Victor Meyer 
}}; {{cite journal 
| title = Ueber die Pseudonitrole, die Isomeren der Nitrolsäuren
| author = Victor Meyer, J. Locher
| journal = [[Justus Liebig's Annalen der Chemie]] 
| volume = 180 
| issue = 1–2
| pages = 133–55
| year = 1876 
| url = https://zenodo.org/record/1427351
| doi = 10.1002/jlac.18761800113}}; {{cite journal 
| title = Vorläufige Mittheilung
| author = V. Meyer and Stüber
| journal = [[Chemische Berichte]] 
| volume = 5 
| pages = 203–05
| year = 1872
| url = https://zenodo.org/record/1425020
| doi = 10.1002/cber.18720050165}}; {{cite journal 
| title = Ueber die Nitroverbindungen der Fettreihe 
| author = Victor Meyer, O. Stüber
| journal = [[Chemische Berichte]] 
| volume = 5 
| pages = 399–406
| year = 1872
| url = https://zenodo.org/record/1427331
| doi = 10.1002/cber.187200501121| s2cid = 95188274
}}; {{cite journal 
| title = Ueber die Nitroverbindungen der Fettreiche. Dritte Mittheilung 
| author = Victor Meyer, A. Rilliet
| journal = [[Chemische Berichte]] 
| volume = 5 
| issue = 2
| pages = 1029–34
| year = 1872
| url = https://zenodo.org/record/1425028
| doi = 10.1002/cber.187200502133}};  {{cite journal 
| title = Ueber die Nitroverbindungen der Fettreihe. Vierte Mittheilung
| author = Victor Meyer, C. Chojnacki
| journal = [[Chemische Berichte]] 
| volume = 5 
| issue = 2
| pages = 1034–38
| year = 1872
| url = https://zenodo.org/record/1425030
| doi = 10.1002/cber.187200502134}}</ref><ref>{{cite journal 
| title = The Relationship of the Constitution of Certain Alky Halides to the Formation of Nitroparaffins and Alkyl Nitrites
| author = Robert B. Reynolds, Homer Adkins 
| journal = [[Journal of the American Chemical Society]] 
| volume = 51 
| issue = 1
| pages = 279–87 
| year = 1929
| doi = 10.1021/ja01376a037| bibcode = 1929JAChS..51..279R 
}}</ref> in which [[alkyl halide]]s react with metallic nitrites to a mixture to nitroalkanes and nitrites.

==Safety==
{{see also|Curing (food preservation)#Nitrates and nitrites}}

Nitrite salts can react with secondary [[amines]] to produce [[Nitrosamine|''N''-nitrosamines]], which are suspected of causing [[stomach cancer]]. The [[World Health Organization|World Health Organization (WHO)]] advises that each {{convert|50|g|abbr=on}} of processed meat eaten a day would raise the risk of getting bowel cancer by 18% over a lifetime; processed meat refers to meat that has been transformed through fermentation, nitrite curing, salting, smoking, or other processes to enhance flavor or improve preservation. The World Health Organization's review of more than 400 studies concluded in 2015 that there was sufficient evidence that processed meats caused cancer, particularly colon cancer; the WHO's [[International Agency for Research on Cancer]] (IARC) classified processed meats as carcinogenic to humans ([[List of IARC Group 1 carcinogens|Group 1]]).<ref name=Wilson/><ref>{{cite journal |vauthors=Bouvard V, Loomis D, Guyton KZ, Grosse Y, El Ghissassi F, Benbrahim-Tallaa L, Guha N, Mattock H, Straif K |display-authors=6 |date=December 2015 |title=Carcinogenicity of consumption of red and processed meat |url=https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(15)00444-1/fulltext |journal=The Lancet Oncology |volume=16 |issue=16 |pages=1599–1600 |doi=10.1016/S1470-2045(15)00444-1 |pmid=26514947 |url-access=registration |access-date=2024-10-13}}</ref>

Nitrite (ingested) under conditions that result in endogenous [[nitrosation]], specifically the production of [[nitrosamine]], has been classified as ''Probably carcinogenic to humans'' ([[List of IARC Group 2A carcinogens|Group 2A]]) by the IARC.<ref>{{cite journal |vauthors=Grosse Y, Baan R, Straif K, Secretan B, El Ghissassi F, Cogliano V |date=August 2006 |title=Carcinogenicity of nitrate, nitrite, and cyanobacterial peptide toxins |url=https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(06)70789-6/fulltext |journal=The Lancet Oncology |volume=7 |issue=8 |pages=628–629 |doi=10.1016/S1470-2045(06)70789-6 |pmid=16900606 |url-access=registration |access-date=2024-10-13}}</ref>

Large doses of nitrite causes acute poisoning in the form of [[methemoglobinemia]], which can lead to death.<ref>{{cite journal | vauthors = Katabami K, Hayakawa M, Gando S | title = Severe Methemoglobinemia due to Sodium Nitrite Poisoning | journal = Case Reports in Emergency Medicine | volume = 2016 | article-number = 9013816 | date = 3 August 2016 | pmid = 27563472 | pmc = 4987464 | doi = 10.1155/2016/9013816 | doi-access = free}}</ref>

==See also==
*[[Curing (food preservation)]]
*[[Alkyl nitrites]]

==References==
{{Reflist}}

==External links==
{{Commons category|Nitrites}}
*[http://msds.chem.ox.ac.uk/SO/sodium_nitrite.html Material Safety Data Sheet, sodium nitrite] ([https://web.archive.org/web/20111211073524/http://msds.chem.ox.ac.uk:80/SO/sodium_nitrite.html archive])
*[https://www.atsdr.cdc.gov/csem/csem.html ATSDR – Case Studies in Environmental Medicine – Nitrate/Nitrite Toxicity] ([https://web.archive.org/web/20100304080534/http://www.atsdr.cdc.gov/csem/nitrate/no3cover.html archive]) – US [[Department of Health and Human Services]] (public domain)
*[http://www.merckvetmanual.com/mvm/toxicology/nitrate_and_nitrite_poisoning/overview_of_nitrate_and_nitrite_poisoning.html Article about Toxicity of Nitrite]

{{Nitrogen compounds}}
{{Nitrites}}
{{Nitric oxide signaling}}
{{Authority control}}

[[Category:Nitrites|*]]
[[Category:Nitrogen oxyanions]]
[[Category:Curing agents]]
[[Category:Garde manger]]
[[Category:Nitrogen cycle]]
[[Category:Preservatives]]