Sodium nitrite
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| Sodium nitrite | |||
|---|---|---|---|
| Sodium nitrite | |||
| The sodium cation | The nitrite anion (space-filling model) | ||
| Identifiers | |||
| CAS number | 7632-00-0 7px | ||
| PubChem | 24269 | ||
| ChemSpider | 22689 7px | ||
| UNII | M0KG633D4F 7px | ||
| EC number | 231-555-9 | ||
| UN number | 1500 | ||
| ChEMBL | CHEMBL93268 7px | ||
| RTECS number | RA1225000 | ||
| Jmol-3D images | Image 1 | ||
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| Molecular formula | NaNO2 | ||
| Molar mass | 68.9953 g/mol | ||
| Appearance | white or slightly yellowish solid | ||
| Density | 2.168 g/cm3 | ||
| Melting point |
271 °C decomp. | ||
| Solubility in water | 82 g/100 ml (20 °C) | ||
| Structure | |||
| Crystal structure | Trigonal | ||
| Hazards | |||
| MSDS | External MSDS
|
EU Index | 007-010-00-4 |
| EU classification | Oxidant (O) Toxic (T) Dangerous for the environment (N) | ||
| R-phrases | R8, R25, R50 | ||
| S-phrases | (S1/2), S45, S61 | ||
| NFPA 704 | |||
| Autoignition temperature |
489 °C | ||
| LD50 | 180 mg/kg (rats, oral) | ||
| Related compounds | |||
| Other anions | Lithium nitrite Sodium nitrate | ||
| Other cations | Potassium nitrite Ammonium nitrite | ||
| 14px (verify) (what is: 10px/10px?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |||
| Infobox references | |||
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.
Sodium nitrite is also used in the manufacture of diazo dyes, nitroso compounds, and other organic compounds; in dyeing and printing textile fabrics and bleaching fibers; in photography; as a laboratory reagent; in metal coatings for phosphatizing and detinning; and in the manufacture of rubber chemicals. It may also be used as an electrolyte in electrochemical grinding manufacturing processes, typically diluted to about 10% concentration in water. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator, and an antidote for cyanide poisoning.
Contents
Uses
In normal human diet
Nitrites are a normal part of human diet, found in most vegetables.[1][2][3] Spinach and lettuce can have as high as 2500 mg/kg, curly kale (302.0 mg/kg) and green cauliflower (61.0 mg/kg), to a low of 13 mg/kg for asparagus. 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).[4][1] Boiling vegetables lowers nitrate but not nitrite.[1] 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).[3] The presence of nitrite in animal tissue is a consequence of metabolism of nitric oxide, an important neurotransmitter.[5] Nitric oxide can be created de novo from nitric oxide synthase utilizing arginine or from ingested nitrate or nitrite.[6] Most research on negative effects of nitrites on humans predates discovery of nitric oxide's importance to human metabolism and human endogenous metabolism of nitrite.
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 bacterium 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 can be toxic in high amounts for animals, including 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 4.615 g to result in death.[7] 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.
Humane toxin for feral hogs/wild boar control
Because of sodium nitrite's high level of toxicity to swine (Sus scrofa) it is now being developed in Australia as a new toxin to contol feral pigs and wild boar (which are the same species), with the intention to market the toxic baits in the USA and other countries in the future[8][9].
The toxin's mode of action is that 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[10].
Medical uses
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.[11][12]
An intravenous mixture including sodium nitrite solution has been used as an emergency treatment for cyanide poisoning (see Cyanide#Antidote).
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.[13][14]
- NaNO2 + H2SO4 → HNO2 + NaHSO4
- 2 NaN3 + 2 HNO2 → 3 N2 + 2 NO + 2 NaOH
Heated to high temperatures, sodium nitrite decomposes, providing sodium oxide, nitrogen(II) oxide and oxygen. This possibly allowed the crew of the first operable submarine not to die due to the high concentration of the carbon dioxide, as the sodium oxide absorbs the CO2, forming sodium carbonate.[15]
Health concerns
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 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.[16] About 1970, it was found that ascorbic acid (vitamin C), an antioxidant, inhibits nitrosamine formation.[17] 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 the nitric oxide gas.[18] Note that Nitrous Anhydride does not exist[19] in vitro.
Sodium nitrite consumption has also been linked to the triggering of migraines in individuals who already suffer from them.[20]
A recent 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.[21][22]
Mechanism of action
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[23] and N-nitrosopyrrolidine[24] 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 functioning leading to cancer or cell death.
References
- ↑ 1.0 1.1 1.2 Script error
- ↑ http://www.wholesomebabyfood.com/nitratearticle.htm
- ↑ 3.0 3.1 Script error
- ↑ Script error
- ↑ Script error
- ↑ Script error
- ↑ http://msds.chem.ox.ac.uk/SO/sodium_nitrite.html
- ↑ Script error
- ↑ Script error
- ↑ Script error
- ↑ Associated Press (9/5/2005). "Hot dog preservative could be disease cure". USA Today. http://www.usatoday.com/news/health/2005-09-05-hot-dog-drug_x.htm.
- ↑ Roxanne Khamsi (27 January 2006). "Food preservative fights cystic fibrosis complication". NewScientist.com. http://www.newscientist.com/article.ns?id=dn8643.
- ↑ "Sodium Azide". Hazardous Waste Management. Northeastern University. March 2003. http://www.ehs.neu.edu/hazardous_waste/fact_sheets/sodium_azide/.
- ↑ Script error
- ↑ Hoshino Y., Utsunomiya T., Abe O. The Thermal Decomposition of Sodium Nitrate and the Effects of Several Oxides on the Decomposition. // Bulletin of the Chemical Society of Japan Vol. 54, No.5 (1981). - p.1389.
- ↑ "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
- ↑ Script error
- ↑ http://lpi.oregonstate.edu/f-w00/nitrosamine.html Nitrosamines and Cancer by Richard A. Scanlan, Ph.D.
- ↑ Script error
- ↑ "Heading Off Migraine Pain". FDA Consumer magazine. U.S. Food and Drug Administration. 1998. http://www.fda.gov/FDAC/features/1998/398_pain.html.
- ↑ Miranda Hitti (17 April 2007). "Study: Cured Meats, COPD May Be Linked". WebMD Medical News. http://www.webmd.com/news/20070417/study-copd-cured-meats-may-be-linked.
- ↑ Script error
- ↑ Script error
- ↑ Script error
External links
- ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity U.S. Department of Health and Human Services (public domain)
- International Chemical Safety Card 1120.
- European Chemicals Bureau.
- National Center for Home Food Preservation Nitrates and Nitrites.
- TR-495: Toxicology and Carcinogenesis Studies of Sodium Nitrite (CAS NO. 7632-00-0) Drinking Water Studies in F344/N Rats and B6C3F1 Mice.
- FOX news article concerning carcinogicity and hot dogs
- Nitrite in Meat
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