Sodium nitrite

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Not to be confused with sodium nitrate or sodium nitride.
Sodium nitrite
Sodium nitrite
Natriumnitrit.png
The nitrite anion (space-filling model) The sodium cation
Identifiers
CAS number 7632-00-0 YesY
PubChem 24269
ChemSpider 22689 YesY
UNII M0KG633D4F YesY
EC number 231-555-9
UN number 1500
ChEBI CHEBI:78870 N
ChEMBL CHEMBL93268 YesY
RTECS number RA1225000
ATC code V03AB08
Jmol-3D images Image 1
Properties
Molecular formula NaNO2
Molar mass 68.9953 g/mol
Appearance white or slightly yellowish solid
Density 2.168 g/cm3
Melting point 271 °C (520 °F; 544 K) (decomposes at 320° C)
Solubility in water 71.4 g/100 mL (0 °C)
84.8 g/100 mL (25 °C)
160 g/100 mL (100 °C)
Solubility soluble in methanol (4.4 g/100 mL)
ethanol
slightly soluble in diethyl ether (0.3 g/100 mL)
very soluble in ammonia
Acidity (pKa) ~9
Refractive index (nD) 1.65
Structure
Crystal structure Trigonal
Thermochemistry
Std molar
entropy
So298
106 J/mol K
Std enthalpy of
formation
ΔfHo298
−359 kJ·mol−1[1]
Gibbs free energy ΔG -295 kJ/mol
Hazards
MSDS External MSDS
EU Index 007-010-00-4
EU classification Oxidizing Agent O Toxic T Dangerous for the Environment (Nature) N
R-phrases R8, R25, R50
S-phrases (S1/2), S45, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Autoignition temperature 489 °C (912 °F; 762 K)
LD50 180 mg/kg (rats, oral)
Related compounds
Other anions Lithium nitrite
Sodium nitrate
Other cations Potassium nitrite
Ammonium nitrite
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Sodium nitrite is the inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. It is a useful precursor to a variety of organic compounds, such as pharmaceuticals, dyes, and pesticides, but it is probably best known as a food additive to prevent botulism.

Production[edit]

The salt is prepared by treating sodium hydroxide with mixtures of nitrogen dioxide and nitric oxide:

2 NaOH + NO2 + NO → 2 NaNO2 + H2O

The conversion is sensitive to the presence of oxygen, which can lead to varying amounts of sodium nitrate.

In former times, sodium nitrite was prepared by reduction of sodium nitrate with various metals.[2]

Chemical reactions[edit]

In the laboratory, sodium nitrite can be used to destroy excess sodium azide.[3][4]

2 NaN3 + 2 Na NO2 + 2 H+ → 3 N2 + 2 NO + 2 Na+ + 2 H2O

Above 330 °C sodium nitrite decomposes (in air) to sodium oxide, nitrogen(II) oxide and nitrogen dioxide.[5]

2 NaNO2 → Na2O + NO + NO2

Sodium nitrite can also be used in the production of nitrous acid via sulfuric acid. This reaction first yields nitrous acid and sodium sulfate:

2NaNO
2
+ H
2
SO
4
→ 2HNO
2
+ Na
2
SO
4

The nitrous acid then, under normal conditions, decomposes:

2HNO2NO
2
+ NO + H
2
O

The nitrogen dioxide of the prior decomposition is then routed through a condensor or fractional distillation apparatus to react with water and yield nitric acid:

2NO
2
+ H
2
O
HNO
3
+ HNO
2

Uses[edit]

Industrial chemistry[edit]

The main use of sodium nitrite is for the industrial production of organonitrogen compounds. It is a reagent for conversion of amines into diazo compounds, which are key precursors to many dyes, such as diazo dyes. Nitroso compounds are produced from nitrites. These are used in the rubber industry.[2]

Other applications include uses in photography. It may also be used as an electrolyte in electrochemical grinding manufacturing processes, typically diluted to about 10% concentration in water. It is used in a variety of metallurgical applications, for phosphatizing and detinning.

Sodium nitrite is an effective corrosion inhibitor and is used as an additive in industrial greases,[6] as an aqueous solution in closed loop cooling systems, and in a molten state as a heat transfer medium.[7]

Medicine[edit]

Sodium nitrite can be used as part of an intravenous mixture with sodium thiosulfate to treat cyanide poisoning.

It is on the World Health Organization's List of Essential Medicines, a list of the most important medication needed in a basic health system.[8]

There is also research to investigate its applicability towards treatments for heart attacks, brain aneurysms, pulmonary hypertension in infants, and Pseudomonas aeruginosa infections.[9][10]

Food additive[edit]

In the early 1900s, irregular curing was commonplace. This led to further research surrounding the use of sodium nitrite as an additive in food, standardizing the amount present in foods to minimize the amount needed while maximizing its food additive role.[11] Through this research, sodium nitrite has been found to inhibit growth of disease-causing microorganisms; give taste and color to the meat; and inhibit lipid oxidation that leads to rancidity.[11] The ability of sodium nitrite to address the above-mentioned issues has led to production of meat with improved food safety, extended storage life and improving desirable color/taste.[11] In the European Union it may be used only as a mixture with salt containing at most 0.0625% sodium nitrite. It has the E number E250. Potassium nitrite (E249) is used in the same way. It is approved for usage in the EU,[12] USA[13] and Australia and New Zealand.[14]

Inhibition of microbial growth[edit]

Sodium nitrite is well known for its role in inhibiting the growth of Clostridium botulinum spores in refrigerated meats.[15] The mechanism for this activity results from the inhibition of iron-sulfur clusters essential to energy metabolism of Clostridium botulinum.[15] However, sodium nitrite has had varying degrees of effectiveness for controlling growth of other spoilage or disease causing microorganisms.[11] Even though the inhibitory mechanisms for sodium nitrite are not well known, its effectiveness depends on several factors including residual nitrite level, pH, salt concentration, reductants present and iron content.[16] Furthermore, the type of bacteria also affects sodium nitrites effectiveness.[16] It is generally agreed upon that sodium nitrite is not considered effective for controlling gram-negative enteric pathogens such as Salmonella and Escherichia coli.[16]

Taste and color[edit]

The appearance and taste of meat is an important component of consumer acceptance.[11] Sodium nitrite is responsible for the desirable red color (or shaded pink) of meat.[11] Very little nitrite is needed to induce this change.[11] It has been reported that as little as 2 to 14 parts per million (ppm), is needed to induce this desirable color change.[16] However, to extend the life-span of this color change significantly higher levels are needed.[16] The mechanism responsible for this color change is the formation of nitrosylating agents by nitrite, which has the ability to transfer nitric oxide that subsequently reacts with myoglobin to produce the cured meat color.[16] The unique taste associated with cured meat is also affected by the addition of sodium nitrite.[11] However, the mechanism underlying this change in taste is still not fully understood.[16]

Inhibition of lipid oxidation[edit]

Sodium nitrite is also able to effectively delay the development of oxidative rancidity.[16] Lipid oxidation is considered to be a major reason for the deterioration of quality of meat products (rancidity and unappetizing flavors).[16] Sodium nitrite acts as an antioxidant in a mechanism similar to the one responsible for the coloring affect.[16] Nitrite reacts with heme proteins and metal ions, neutralizing free radicals by nitric oxide (one of its byproducts).[16] Neutralization of these free radicals terminates the cycle of lipid oxidation that leads to rancidity.[16]

Toxicity[edit]

While this chemical will prevent the growth of bacteria, it can be toxic in high amounts for animals and humans. Sodium nitrite's LD50 in rats is 180 mg/kg and its human LDLo is 71 mg/kg, meaning a 65 kg person would likely have to consume at least 4.6 g to result in death.[17] To prevent toxicity, sodium nitrite (blended with salt) sold as a food additive is dyed bright pink to avoid mistaking it for plain salt or sugar. Nitrites are not naturally occurring in vegetables in significant quantities.[18] However, nitrites are found in commercially available vegetables and a study in an intensive agricultural area in northern Portugal found residual nitrite levels in 34 vegetable samples, including different varieties of cabbage, lettuce, spinach, parsley and turnips ranged between 1.1 and 57 mg/kg, e.g. white cauliflower (3.49 mg/kg) and green cauliflower (1.47 mg/kg).[19][20] Boiling vegetables lowers nitrate but not nitrite.[19] Fresh meat contains 0.4-0.5 mg/kg nitrite and 4–7 mg/kg of nitrate (10–30 mg/kg nitrate in cured meats).[18] The presence of nitrite in animal tissue is a consequence of metabolism of nitric oxide, an important neurotransmitter.[21] Nitric oxide can be created de novo from nitric oxide synthase utilizing arginine or from ingested nitrate or nitrite.[22] Most research on the negative effects of nitrites on humans predates the discovery of nitric oxide's importance to human metabolism and human endogenous metabolism of nitrite.[citation needed]

Humane toxin for feral hogs/wild boar control[edit]

Because of sodium nitrite's high level of toxicity to swine (Sus scrofa) it is now being developed in Australia to control feral pigs and wild boar.[23][24] The sodium nitrite induces methemoglobinemia in swine, i.e., it reduces the amount of oxygen that is released from hemoglobin, so the animal will feel faint and pass out, and then die in a humane manner after first being rendered unconscious.[25]

Nitrosamines[edit]

A principal concern about sodium nitrite is the formation of carcinogenic nitrosamines in meats containing sodium nitrite when meat is charred or overcooked. Such carcinogenic nitrosamines can also be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats. Dietary sources of nitrosamines include US cured meats preserved with sodium nitrite as well as the dried salted fish eaten in Japan. In the 1920s, a significant change in US meat curing practices resulted in a 69% decrease in average nitrite content. This event preceded the beginning of a dramatic decline in gastric cancer mortality.[26] About 1970, it was found that ascorbic acid (vitamin C), an antioxidant, inhibits nitrosamine formation.[27] Consequently, the addition of at least 550 ppm of ascorbic acid is required in meats manufactured in the United States. Manufacturers sometimes instead use erythorbic acid, a cheaper but equally effective isomer of ascorbic acid. Additionally, manufacturers may include alpha-tocopherol (vitamin E) to further inhibit nitrosamine production. Alpha-tocopherol, ascorbic acid, and erythorbic acid all inhibit nitrosamine production by their oxidation-reduction properties. Ascorbic acid, for example, forms dehydroascorbic acid when oxidized, which when in the presence of nitrous anhydride, a potent nitrosating agent formed from sodium nitrate, reduces the nitrous anhydride into nitric oxide.[28] Note that nitrous anhydride does not exist in vitro.[29]

Sodium nitrite consumption has also been linked to the triggering of migraines in individuals who already suffer from them.[30]

One study has found a correlation between highly frequent ingestion of meats cured with pink salt and the COPD form of lung disease. The study's researchers suggest that the high amount of nitrites in the meats was responsible; however, the team did not prove the nitrite theory. Additionally, the study does not prove that nitrites or cured meat caused higher rates of COPD, merely a link. The researchers did adjust for many of COPD's risk factors, but they commented they cannot rule out all possible unmeasurable causes or risks for COPD.[31][32]

Mechanism of action[edit]

Carcinogenic nitrosamines are formed when amines that occur naturally in food react with sodium nitrite found in cured meat products.

R2NH (amines) + NaNO2 (sodium nitrite) → R2N-N=O (nitrosamine)

In the presence of acid (such as in the stomach) or heat (such as via cooking), nitrosamines are converted to diazonium ions.

R2N-N=O (nitrosamine) + (acid or heat) → R-N2+ (diazonium ion)

Certain nitrosamines such as N-nitrosodimethylamine[33] and N-nitrosopyrrolidine[34] form carbocations that react with biological nucleophiles (such as DNA or an enzyme) in the cell.

R-N2+ (diazonium ion) → R+ (carbocation) + N2 (leaving group) + :Nu (biological nucleophiles) → R-Nu

If this nucleophilic substitution reaction occurs at a crucial site in a biomolecule, it can disrupt normal cell functions, leading to cancer or cell death.

References[edit]

  1. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X. 
  2. ^ a b Wolfgang Laue, Michael Thiemann, Erich Scheibler, Karl Wilhelm Wiegand “Nitrates and Nitrites” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim.doi:10.1002/14356007.a17_265. Article Online Posting Date: 15 June 2000
  3. ^ "Sodium Azide". Hazardous Waste Management. Northeastern University. March 2003. 
  4. ^ Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, Board on Chemical Sciences and Technology, Commission on Physical Sciences, Mathematics, and Applications, National Research Council. (1995). Prudent practices in the laboratory: handling and disposal of chemicals. Washington, D.C.: National Academy Press. ISBN 0-309-05229-7. 
  5. ^ Stern, Kurt H. (1972). "High Temperature Properties and Decomposition of Inorganic Salts; Part 3. Nitrates and Nitrites". J. Phys. Chem. (US Naval Research Laboratory) 1 (3): 750–751. Retrieved 15 March 2014. 
  6. ^ Krakhmalev, S. I.; V. A. Vorotnikova, N. V. Ten and N. V. Taranova (1984). "Determination of sodium nitrite in complex sodium grease". Chemistry And Technology Of Fuels And Oils 20 (12): 612–613. doi:10.1007/BF00726438. 
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  8. ^ "WHO Model List of EssentialMedicines". World Health Organization. October 2013. Retrieved 28 April 2014. 
  9. ^ "Hot dog preservative could be disease cure". USA Today. Associated Press. Sep 5, 2005. 
  10. ^ Roxanne Khamsi (27 January 2006). "Food preservative fights cystic fibrosis complication". NewScientist.com. 
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  12. ^ UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 27 October 2011. 
  13. ^ US Food and Drug Administration: "Listing of Food Additives Status Part II". Retrieved 27 October 2011. 
  14. ^ Australia New Zealand Food Standards Code"Standard 1.2.4 - Labelling of ingredients". Retrieved 27 October 2011. 
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  16. ^ a b c d e f g h i j k l Sindelar, Jeffrey; Andrew Milkowski (November 2011). "Sodium Nitrite in Processed Meat and Poultry Meats: A Review of Curing and Examining the Risk/Benefit of Its Use". American Meat Science Association 3: 1–14. 
  17. ^ http://msds.chem.ox.ac.uk/SO/sodium_nitrite.html
  18. ^ a b Dennis, M J; Wilson, L A (2003). "Encyclopedia of Food Sciences and Nutrition". p. 4136. doi:10.1016/B0-12-227055-X/00830-0. ISBN 978-0-12-227055-0.  |chapter= ignored (help)
  19. ^ a b Leszczyńska, Teresa; Filipiak-Florkiewicz, Agnieszka; Cieślik, Ewa; Sikora, ElżBieta; Pisulewski, Paweł M. (2009). "Effects of some processing methods on nitrate and nitrite changes in cruciferous vegetables". Journal of Food Composition and Analysis 22 (4): 315. doi:10.1016/j.jfca.2008.10.025. 
  20. ^ Correia, Manuela; Barroso, ÂNgela; Barroso, M. FáTima; Soares, DéBora; Oliveira, M.B.P.P.; Delerue-Matos, Cristina (2010). "Contribution of different vegetable types to exogenous nitrate and nitrite exposure". Food Chemistry 120 (4): 960. doi:10.1016/j.foodchem.2009.11.030. 
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  24. ^ Cowled, BD; SJ Lapidge; S. Humphrys; L Staples (2008). "Nitrite Salts as Poisons in Baits for Omnivores". International Patent WO/2008/104028. 
  25. ^ S. Porter & T. Kuchel (2010). Assessing the humaness and efficacy of a new feral pig bait in domestic pigs. Study PC0409. Canberra, South Australia: Veterinary Services Division, Institute of Medical and Veterinary Science. p. 11. 
  26. ^ "The epidemiological enigma of gastric cancer rates in the US: was grandmother's sausage the cause?", International Journal of Epidemiology (2000) accessdate 2000-08-01
  27. ^ C.W. Mackerness, S.A. Leach, M.H. Thompson and M.J. Hill (1989). "The inhibition of bacterially mediated N-nitrosation by vitamin C: relevance to the inhibition of endogenous N-nitrosation in the achlorhydric stomach". Carcinogenesis 10 (2): 397–9. doi:10.1093/carcin/10.2.397. PMID 2492212. 
  28. ^ Nitrosamines and Cancer by Richard A. Scanlan, Ph.D.
  29. ^ Williams, D (2004). "Nitrosation Reactions and the Chemistry of Nitric Oxide". p. 1. doi:10.1016/B978-044451721-0/50002-5. ISBN 978-0-444-51721-0.  |chapter= ignored (help)
  30. ^ "Heading Off Migraine Pain". FDA Consumer magazine. U.S. Food and Drug Administration. 1998. 
  31. ^ Miranda Hitti (17 April 2007). "Study: Cured Meats, COPD May Be Linked". WebMD Medical News. 
  32. ^ Jiang, R.; Paik, D. C.; Hankinson, J. L.; Barr, R. G. (2007). "Cured Meat Consumption, Lung Function, and Chronic Obstructive Pulmonary Disease among United States Adults". American Journal of Respiratory and Critical Care Medicine 175 (8): 798–804. doi:10.1164/rccm.200607-969OC. PMC 1899290. PMID 17255565. 
  33. ^ Najm, Issam; Trussell, R. Rhodes (February 2001). "NDMA Formation in Water and Wastewater". Journal AWWA 93 (2): 92–99. 
  34. ^ Donald D. Bills, Kjell I. Hildrum, Richard A. Scanlan, Leonard M. Libbey (May 1973). "Potential precursors of N-nitrosopyrrolidine in bacon and other fried foods". J. Agric. Food Chem. 21 (5): 876–7. doi:10.1021/jf60189a029. PMID 4739004. 

External links[edit]