Sodium nitrite

Sodium nitrite, with chemical formula NaNO₂, is used as a color fixative and preservative in meats and fish. When pure, it is a white to slight yellowish crystalline powder. It is very soluble in water and is hygroscopic. It is also slowly oxidized by oxygen in the air to sodium nitrate, NaNO₃. The compound is a strong reducing agent.

It is also used in manufacturing diazo dyes, nitroso compounds, and other organic compounds; in dyeing and printing textile fabrics and bleaching fibers; in photography; as a laboratory reagent and a corrosion inhibitor; in metal coatings for phosphatizing and detinning; and in the manufacture of rubber chemicals. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator, an intestinal relaxant or a laxative, and an antidote for cyanide poisoning.

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Uses

Food additive

As a food additive, it serves a dual purpose in the food industry since it both alters the color of preserved fish and meats and also prevents growth of Clostridium botulinum, the bacteria which causes botulism. In the European Union it may be used only as a mixture with salt containing at most 0.6% sodium nitrite. It has the E number E250. Potassium nitrite (E249) is used in the same way.

While this chemical will prevent the growth of bacteria, it is also toxic for mammals. (LD₅₀ in rats is 180 mg/kg.)

Various dangers of using this as a food additive have been suggested and researched by scientists. A principal concern is the formation of carcinogenic N-nitrosamines by the reaction of sodium nitrite with amino acids in the presence of heat in an acidic environment.

Recent studies have found a link between high processed meat consumption and colon cancer, possibly due to preservatives such as sodium nitrite. publication from wiley

^[1]

Recent studies have also found a link between frequent ingestion of meats cured with nitrites and the COPD form of lung disease.^[2]

Disease treatment

Recently, sodium nitrite has been found to be an effective means to increase blood flow by dilating blood vessels, acting as a vasodilator. Research is ongoing to investigate its applicability towards treatments for sickle cell anemia, cyanide poisoning, heart attacks, brain aneurysms, and pulmonary hypertension in infants.^[3][4]

Synthetic reagent

Sodium nitrite is used to convert amines into diazo compounds. The synthetic utility of such a reaction is to render the amino group labile for nucleophilic substitution, as the N₂ group is a better leaving group.

In the laboratory, sodium nitrite is also used to destroy excess sodium azide.^[5][6]

2 NaN₃ + 2 HNO₂ → 3 N₂ + 2 NO + 2 NaOH

2 NaNO₂ + H₂SO₄ → 2 HNO₂ + Na₂SO₄

References

1. ^ A. W. Susanna C. Larsson (2006). "Meat consumption and risk of colorectal cancer: A meta-analysis of prospective studies". International Journal of Cancer 119 (11): 2657-2664. doi:10.1002/ijc.22170.
2. ^ Miranda Hitti. "Study: Cured Meats, COPD May Be Linked", WebMD Medical News, 17 April 2007. 
3. ^ Associated Press. "Hot dog preservative could be disease cure", 9/5/2005. 
4. ^ Roxanne Khamsi. "Food preservative fights cystic fibrosis complication", NewScientist.com, 27 January 2006. 
5. ^ Sodium Azide. Hazardous Waste Management. Northeastern University (March 2003).
6. ^ (1995) Prudent practices in the laboratory: handling and disposal of chemicals. National Academy Press. ISBN 0309052297. 

See also

• Nitrosamine
• Sodium nitrate