Nitrite

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Nitrite
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
Space-filling model of the nitrite ion
Names
IUPAC name
Nitrite
Systematic IUPAC name
dioxidonitrate(1−)
Other names
nitrite
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
EC Number
  • 233-272-6
UNII
  • 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
  • N(=O)[O-]
Properties
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).

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.

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).

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 (C2v

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
;      pKa ≈ 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 E0 (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
2
H+
5
) the product of nitrite reduction is hydrazoic acid (HN3), an instable and explosive compound:

HNO2 + N
2
H+
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

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

Nitrite is an

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

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

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
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

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

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

alkyl halides
react with metallic nitrites to a mixture to nitroalkanes and nitrites.

Safety

Nitrite salts can react with secondary

Group 1).[10][26]

Nitrite (ingested) under conditions that result in endogenous

Group 2A) by the IARC.[27][28]

See also

References

  1. ^ .
  2. ^ a b c d Greenwood, pp. 461–464.
  3. ^ IUPAC SC-Database Archived 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. S2CID 98768756
    .
  6. .
  7. .
  8. .
  9. .
  10. ^ 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. Archived 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. .
  13. ^ sodium nitrite and nitrate facts Accessed 12 Dec 2014
  14. .
  15. .
  16. ^ "Is celery juice a viable alternative to nitrites in cured meats?". Office for Science and Society. Retrieved 14 September 2022.
  17. PMID 27894754
    .
  18. .
  19. OCLC 1011036745.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  20. .
  21. ^ "Guillaume Coudray on the Nitro Meat Cancer Connection". 14 April 2021.
  22. PMID 26543483
    .
  23. .
  24. .
  25. .
  26. ^ "IARC Monographs evaluate consumption of red meat and processed meat" (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. ^ "List of classifications, Volumes 1–116 – IARC Monographs on the Evaluation of Carcinogenic Risks to Humans". 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. ISBN 9789283212942. Retrieved 25 September 2016. {{cite book}}: |work= ignored (help
    )

Bibliography

External links