Nitrite
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Names | |||
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IUPAC name
Nitrite
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Systematic IUPAC name
dioxidonitrate(1−) | |||
Other names
nitrite
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Identifiers | |||
3D model (
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ChEBI | |||
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EC Number |
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PubChem CID
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Properties | |||
NO− 2 | |||
Molar mass | 46.005 g·mol−1 | ||
Conjugate acid
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Nitrous acid | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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).
- 2 NH3 + H2O + N2O3 → 2 NH4NO2
Structure
The nitrite ion has a symmetrical structure (C2v
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:
Nitrous acid is also highly volatile, tending to
- 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
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
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
Biochemistry
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
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
In mice, food rich in nitrites together with unsaturated fats can prevent
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
Organic nitrites
In
Safety
Nitrite salts can react with secondary
Nitrite (ingested) under conditions that result in endogenous
See also
- Curing (food preservation)
- Alkyl nitrites
References
- ^ ISBN 978-3527306732.
- ^ a b c d Greenwood, pp. 461–464.
- ^ 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
- ^ Greenwood, p. 431.
- S2CID 98768756.
- PMID 24141308.
- PMID 22842521.
- PMID 4572891.
- PMID 29531192.
- ^ 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.
- ^ 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.
- ISBN 978-0-8493-9488-1.
- ^ sodium nitrite and nitrate facts Accessed 12 Dec 2014
- ISBN 9781441908261.
- PMID 24843165.
- ^ "Is celery juice a viable alternative to nitrites in cured meats?". Office for Science and Society. Retrieved 14 September 2022.
- PMID 27894754.
- PMID 1107192.
- OCLC 1011036745.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - PMID 1999685.
- ^ "Guillaume Coudray on the Nitro Meat Cancer Connection". 14 April 2021.
- PMID 26543483.
- PMID 28041825.
- .
- .
- ^ "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.
- ^ "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.
- )
Bibliography
- ISBN 978-0-08-037941-8.
- Coudray, Guillaume, Who poisoned your bacon. London: Icon Books, 2021. ISBN 9-781-78578612-9
External links
- Material Safety Data Sheet, sodium nitrite (archive)
- ATSDR – Case Studies in Environmental Medicine – Nitrate/Nitrite Toxicity (archive) – US Department of Health and Human Services(public domain)
- Article about Toxicity of Nitrite