Nitrite

Not to be confused with nitride, nitrate, or nitrogen dioxide.

The nitrite ion has the chemical formula NO⁻
₂. Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries.^[1] 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.

Nitrite

Names
IUPAC name Nitrite
Systematic IUPAC name dioxidonitrate(1−)
Other names nitrite
Identifiers
CAS Number	14797-65-0^Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:16301
ChemSpider	921
EC Number	233-272-6
PubChem CID	946
UNII	J39976L608^Y
InChI InChI=1S/HNO2/c2-1-3/h(H,2,3)/p-1 Key: IOVCWXUNBOPUCH-UHFFFAOYSA-M InChI=1/HNO2/c2-1-3/h(H,2,3)/p-1 Key: IOVCWXUNBOPUCH-REWHXWOFAR
SMILES N(=O)[O-]
Properties
Chemical formula	NO^− 2
Molar mass	46.005 g·mol^−1
Conjugate acid	Nitrous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Production

Sodium nitrite is made industrially by passing a mixture of nitrogen oxides into aqueous sodium hydroxide or sodium carbonate solution:^[2][1]

NO + NO₂ + 2 NaOH → 2 NaNO₂ + H₂O

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 °C for KNO₂). Ammonium nitrite can be made from dinitrogen trioxide, N₂O₃, which is formally the anhydride of nitrous acid:

2 NH₃ + H₂O + N₂O₃ → 2 NH₄NO₂

Structure

 

The two canonical structures of NO⁻
₂, which contribute to the resonance hybrid for the nitrite ion

 

Dimensions of trans-HONO (from the microwave spectrum)

The nitrite ion has a symmetrical structure (C_2v 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:

HNO₂ ⇌ H⁺ + NO⁻
₂;      pK_a ≈ 3.3 at 18 °C^[3]

Nitrous acid is also highly volatile, tending to disproportionate:

3 HNO₂ (aq) ⇌ H₃O⁺ + NO⁻
₃ + 2 NO

This reaction is slow at 0 °C.^[2] 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 potentials for reactions directly involving nitrous acid are shown in the table below:^[4]

Half-reaction	E^0 (V)
NO^− 3 + 3 H^+ + 2 e^− ⇌ HNO2 + H2O	+0.94
2 HNO2 + 4 H^+ + 4 e^− ⇌ H2N2O2 + 2 H2O	+0.86
N2O4 + 2 H^+ + 2 e^− ⇌ 2 HNO2	+1.065
2 HNO2+ 4 H^+ + 4 e^− ⇌ N2O + 3 H2O	+1.29

The data can be extended to include products in lower oxidation states. For example:

H₂N₂O₂ + 2 H⁺ + 2 e⁻ ⇌ N₂ + 2 H₂O;      E⁰ = +2.65 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 NO⁻
₂ + 2 MnO⁻
₄ + 6 H⁺ → 5 NO⁻
₃ + 2 Mn²⁺ + 3 H₂O

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 N₂O; with tin(II) (Sn²⁺) the product is hyponitrous acid (H₂N₂O₂); reduction all the way to ammonia (NH₃) occurs with hydrogen sulfide. With the hydrazinium cation (N
₂H⁺
₅) the product of nitrite reduction is hydrazoic acid (HN₃), an instable and explosive compound:

HNO₂ + N
₂H⁺
₅ → HN₃ + H₂O + H₃O⁺

which can also further react with nitrite:

HNO₂ + HN₃ → N₂O + N₂ + H₂O

This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states.^[2]

Analysis of nitrite

See also: Nitrite test

Nitrite is detected and analyzed by the Griess Reaction, involving the formation of a deep red-colored azo dye upon treatment of a NO⁻
₂-containing sample with sulfanilic acid and naphthyl-1-amine in the presence of acid.^[5]

Coordination complexes

Main article: Transition metal nitrite complex

Nitrite is an ambidentate ligand and can form a wide variety of coordination complexes by binding to metal ions in several ways.^[2] Two examples are the red nitrito complex [Co(NH₃)₅(ONO)]²⁺ is metastable, isomerizing to the yellow nitro complex [Co(NH₃)₅(NO₂)]²⁺. Nitrite is processed by several enzymes, all of which utilize coordination complexes.

Biochemistry

 

A schematic representation of the microbial nitrogen cycle.^[6][7] ANAMMOX is anaerobic ammonium oxidation, DNRA is dissimilatory nitrate reduction to ammonium, and 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 NO synthase (NOS), as well as nonenzymatic acidic disproportionation reactions.

Uses

Chemical precursor

Azo dyes and other colorants are prepared by the process called diazotization, which requires nitrite.^[1]

Nitrite in food preservation and biochemistry

See also: Warmed-over flavor

The addition of nitrites and nitrates to processed meats such as ham, bacon, and sausages reduces growth and toxin production of C. botulinum.^[8][9] Sodium nitrite is used to speed up the curing of meat and also impart an attractive colour.^[10] On the other hand a 2018 study by the British Meat Producers Association determined that legally permitted levels of nitrite have no effect on the growth of the Clostridium botulinum.^[11] In the U.S., meat cannot be labeled as "cured" without the addition of nitrite.^[12][13][14] In some countries, cured-meat products are manufactured without nitrate or nitrite, and without nitrite from vegetable source. Parma ham, produced without nitrite since 1993, was reported in 2018 to have caused no cases of botulism.^[10]

In mice, food rich in nitrites together with unsaturated fats can prevent hypertension, which is one explanation for the apparent health effect of the Mediterranean diet.^[15] Adding nitrites to meat has been shown to generate known carcinogens; the World Health Organization (WHO) advises that eating 50 g (1.8 oz) of nitrite processed meat a day would raise the risk of getting bowel cancer by 18% over a lifetime.^[10] However, 95% of the nitrite ingested in modern diets comes from bacterial conversion of nitrates naturally found in dietary vegetables.^[16]

The recommended maximum limits by the World Health Organization in drinking water are 3 mg L⁻¹ and 50 mg L⁻¹ for nitrite and nitrate ions, respectively.^[17]

Curing of meat

In a reaction with the meat's myoglobin, nitrite gives the product a desirable pink-red "fresh" color, such as with corned beef. 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.^[18] Historians^[19] and epidemiologists^[20] argue that the widespread use of nitrite in meat-curing is closely linked to the development of industrial meat-processing. French investigative journalist Guillaume Coudray 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.^[21] Some traditional and artisanal producers avoid nitrites.

Antidote for cyanide poisoning

Nitrites in the form of sodium nitrite and amyl nitrite are components of many cyanide antidote kits.^[22] Both of these compounds bind to hemoglobin and oxidize the Fe²⁺ ions to Fe³⁺ 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 mitochondria, which is the primary site of disruption caused by cyanide. Another mechanism by which nitrites are useful in treating 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.^[23]

Organic nitrites

 

A nitrite ester

In organic chemistry, alkyl nitrites are esters of nitrous acid and contain the nitrosoxy functional group. Nitro compounds contain the C–NO₂ group. Nitrites have the general formula RONO, where R is an aryl or alkyl group. Amyl nitrite and other alkyl nitrites have a 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^[24][25] in which alkyl halides 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 N-nitrosamines, which are suspected to cause stomach cancer. The World Health Organization (WHO) advises that each 50 g (1.8 oz) 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 (Group 1).^[10][26]

Nitrite (ingested) under conditions that result in endogenous nitrosation, specifically the production of nitrosamine, has been classified as Probably carcinogenic to humans (Group 2A) by the IARC.^[27][28]

See also

• Curing (food preservation)
• Alkyl nitrites

References

1. Laue W, Thiemann M, Scheibler E, Wiegand KW (2006). "Nitrates and Nitrites". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_265. ISBN 978-3527306732.
2. Greenwood, pp. 461–464.
3. IUPAC SC-Database 19 June 2017 at the Wayback Machine A comprehensive database of published data on equilibrium constants of metal complexes and ligands
4. Greenwood, p. 431.
5. Ivanov, V. M. (1 October 2004). "The 125th Anniversary of the Griess Reagent". Journal of Analytical Chemistry. 59 (10): 1002–1005. doi:10.1023/B:JANC.0000043920.77446.d7. ISSN 1608-3199. S2CID 98768756.
6. Sparacino-Watkins, Courtney; Stolz, John F.; Basu, Partha (16 December 2013). "Nitrate and periplasmic nitrate reductases". Chem. Soc. Rev. 43 (2): 676–706. doi:10.1039/c3cs60249d. ISSN 1460-4744. PMC 4080430. PMID 24141308.
7. Simon, Jörg; Klotz, Martin G. (2013). "Diversity and evolution of bioenergetic systems involved in microbial nitrogen compound transformations". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1827 (2): 114–135. doi:10.1016/j.bbabio.2012.07.005. PMID 22842521.
8. Christiansen LN, Johnston RW, Kautter DA, Howard JW, Aunan WJ (March 1973). "Effect of nitrite and nitrate on toxin production by Clostridium botulinum and on nitrosamine formation in perishable canned comminuted cured meat". Applied Microbiology. 25 (3): 357–62. doi:10.1128/AEM.25.3.357-362.1973. PMC 380811. PMID 4572891.
9. Lee, Soomin; Lee, Heeyoung; Kim, Sejeong; Lee, Jeeyeon; Ha, Jimyeong; Choi, Yukyung; Oh, Hyemin; Choi, Kyoung-Hee; Yoon, Yohan (August 2018). "Microbiological safety of processed meat products formulated with low nitrite concentration — A review". Asian-Australasian Journal of Animal Sciences. 31 (8): 1073–1077. doi:10.5713/ajas.17.0675. ISSN 1011-2367. PMC 6043430. PMID 29531192.
10. Wilson, Bee (1 March 2018). "Yes, bacon really is killing us". The Guardian. London. ISSN 0261-3077. from the original on 10 February 2021. Retrieved 14 February 2021. 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.
11. Doward, Jamie (23 March 2019). "Revealed: no need to add cancer-risk nitrites to ham". The Observer. London. from the original on 26 January 2021. Retrieved 14 February 2021. 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.
12. De Vries, John (1997). Food Safety and Toxicity. CRC Press. p. 70. ISBN 978-0-8493-9488-1.
13. Accessed 12 Dec 2014
14. Doyle, Michael P.; Sperber, William H. (23 September 2009). Compendium of the Microbiological Spoilage of Foods and Beverages. Springer. p. 78. ISBN 9781441908261.
15. Charles, R. L.; Rudyk, O.; Prysyazhna, O.; Kamynina, A.; Yang, J.; Morisseau, C.; Hammock, B. D.; Freeman, B. A.; Eaton, P. (2014). "Protection from hypertension in mice by the Mediterranean diet is mediated by nitro fatty acid inhibition of soluble epoxide hydrolase". Proceedings of the National Academy of Sciences. 111 (22): 8167–72. Bibcode:2014PNAS..111.8167C. doi:10.1073/pnas.1402965111. PMC 4050620. PMID 24843165.
16. "Is celery juice a viable alternative to nitrites in cured meats?". Office for Science and Society. Retrieved 14 September 2022.
17. Bagheri, H.; Hajian, A.; Rezaei, M.; Shirzadmehr, A. (2017). "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 of Hazardous Materials. 324 (Pt B): 762–772. doi:10.1016/j.jhazmat.2016.11.055. PMID 27894754.
18. Binkerd, E. F.; Kolari, O. E. (1 January 1975). "The history and use of nitrate and nitrite in the curing of meat". Food and Cosmetics Toxicology. 13 (6): 655–661. doi:10.1016/0015-6264(75)90157-1. ISSN 0015-6264. PMID 1107192.
19. coudray, guillaume, eric (2017). Cochonneries : comment la charcuterie est devenue un poison. paris: Decouverte. pp. part I, chapter 2 (p. 40–55) and chapter 3 (p. 56–70). ISBN 9782707193582. OCLC 1011036745.{{cite book}}: CS1 maint: multiple names: authors list (link)
20. Lauer, Klaus (1 January 1991). "The history of nitrite in human nutrition: A contribution from German cookery books". Journal of Clinical Epidemiology. 44 (3): 261–264. doi:10.1016/0895-4356(91)90037-A. ISSN 0895-4356. PMID 1999685.
21. "Guillaume Coudray on the Nitro Meat Cancer Connection". 14 April 2021.
22. Meillier, Andrew; Heller, Cara (2015). "Acute Cyanide Poisoning: Hydroxocobalamin and Sodium Thiosulfate Treatments with Two Outcomes following One Exposure Event". Case Reports in Medicine. 2015: 217951. doi:10.1155/2015/217951. ISSN 1687-9627. PMC 4620268. PMID 26543483.
23. Bebarta, Vikhyat S.; Brittain, Matthew; Chan, Adriano; Garrett, Norma; Yoon, David; Burney, Tanya; Mukai, David; Babin, Michael; Pilz, Renate B.; Mahon, Sari B.; Brenner, Matthew (June 2017). "Sodium Nitrite and Sodium Thiosulfate Are Effective Against Acute Cyanide Poisoning when Administered by Intramuscular Injection". Annals of Emergency Medicine. 69 (6): 718–725.e4. doi:10.1016/j.annemergmed.2016.09.034. ISSN 0196-0644. PMC 5446299. PMID 28041825.
24. Victor Meyer (1872). "Ueber die Nitroverbindungen der Fettreihe". Justus Liebig's Annalen der Chemie. 171 (1): 1–56. doi:10.1002/jlac.18741710102.; Victor Meyer, J. Locher (1876). "Ueber die Pseudonitrole, die Isomeren der Nitrolsäuren". Justus Liebig's Annalen der Chemie. 180 (1–2): 133–55. doi:10.1002/jlac.18761800113.; V. Meyer and Stüber (1872). "Vorläufige Mittheilung". Chemische Berichte. 5: 203–05. doi:10.1002/cber.18720050165.; Victor Meyer, O. Stüber (1872). "Ueber die Nitroverbindungen der Fettreihe". Chemische Berichte. 5: 399–406. doi:10.1002/cber.187200501121. S2CID 95188274.; Victor Meyer, A. Rilliet (1872). "Ueber die Nitroverbindungen der Fettreiche. Dritte Mittheilung". Chemische Berichte. 5 (2): 1029–34. doi:10.1002/cber.187200502133.; Victor Meyer, C. Chojnacki (1872). "Ueber die Nitroverbindungen der Fettreihe. Vierte Mittheilung". Chemische Berichte. 5 (2): 1034–38. doi:10.1002/cber.187200502134.
25. Robert B. Reynolds, Homer Adkins (1929). "The Relationship of the Constitution of Certain Alky Halides to the Formation of Nitroparaffins and Alkyl Nitrites". Journal of the American Chemical Society. 51 (1): 279–87. doi:10.1021/ja01376a037.
26. (PDF). International Agency for Research on Cancer. 26 October 2015. Archived from the original (PDF) on 18 January 2021. Retrieved 14 February 2021. Processed meat was classified as carcinogenic to humans (Group 1), based on sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.
27. . International Agency for Research on Cancer (IARC) – World Health Organization (WHO). 2010. Archived from the original on 10 June 2017. Retrieved 25 September 2016.
28. VOLUME 94 – Ingested Nitrate and Nitrite, and Cyanobacterial Peptide Toxins – IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. 2010. ISBN 9789283212942. Retrieved 25 September 2016. {{cite book}}: |work= ignored (help)

Bibliography

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Coudray, Guillaume, Who poisoned your bacon. London: Icon Books, 2021. ISBN 9-781-78578612-9

External links

 

Wikimedia Commons has media related to Nitrites.

• Material Safety Data Sheet, sodium nitrite ()
• ATSDR – Case Studies in Environmental Medicine – Nitrate/Nitrite Toxicity () – US Department of Health and Human Services (public domain)
• Article about Toxicity of Nitrite