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The nitrite polyatomic ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. 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.
In the gas phase it exists predominantly as a trans-planar molecule.
| +0.94 |
| +0.86 |
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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):
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 hydrazine cation () the product of nitrite reduction is hydrazoic acid (HN3), an unstable and explosive compound:
This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states.
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.
The academic and industrial consensus is that nitrites also reduces growth and toxin production of Clostridium botulinum.
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. In the U.S., meat cannot be labeled as "cured" without the addition of nitrite. sodium nitrite and nitrate facts Accessed 12 Dec 2014 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. Other manufacture processes do not assure these conditions, and reduction of nitrite results in toxin production.
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. Adding nitrites to meat has been shown to generate known ; the World Health Organization (WHO) advises that eating of nitrite processed meat a day would raise the risk of getting bowel cancer by 18% over a lifetime.
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. Ingesting too much nitrite and/or nitrate through well water is suspected to cause methemoglobinemia.
95% of the nitrite ingested in modern diets comes from bacterial conversion of nitrates naturally found in vegetables. However, potentially cancer-causing nitroso compounds are not made in the pH-neutral colon. They are mostly made in the acidic stomach.
Addition of ascorbic acid, erythorbic acid, or one of their salts enhance the binding of nitrite to the iron atom in myoglobin. 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.
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.
Large doses of nitrite causes acute poisoning in the form of methemoglobinemia, which can lead to death.
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. (2025). 9783662437605 ISBN 9783662437605 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. Historians and epidemiology argue that the widespread use of nitrite in meat-curing is closely linked to the development of industrial meat-processing. French investigative journalist 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. 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).
Antidote for cyanide poisoning
Nitrites in the form of sodium nitrite and amyl nitrite are components of many cyanide antidote kits. 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 Mitochondrion, 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.
Organic nitrites
In organic chemistry, alkyl nitrites are 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 vasodilation 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; ; ; ; ; in which react with metallic nitrites to a mixture to nitroalkanes and nitrites.
Safety
Nitrite salts can react with secondary amines to produce Nitrosamine, which are suspected of causing stomach cancer. The World Health Organization (WHO) advises that each 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).
See also
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