E250 (Sodium nitrite) is a chemical compound, an inorganic sodium salt ion and a physiological derivative of nitric oxide to which it can be bioactivated.  It is very soluble in water and liquid ammonia, stable under anaerobic conditions. Slightly soluble in ether, ethanol, methanol and other organic solvents. It reacts with oxygen to form sodium nitrate when exposed to air.

The name defines the structure of the molecule

• "Sodium". It's an alkali metal, symbol Na, with atomic number 11. It's an essential element for life and plays a key role in regulating blood pressure and plasma volume.
• "Nitrite". Refers to the salt or ester of nitrous acid and has the chemical formula NO2-. Nitrites are used as food preservatives and as antimicrobial agents.

Description of the raw materials used in its production:

• Nitrogen Oxides (NO and NO₂) - These gases are generated during high-temperature combustion operations.
• Sodium Hydroxide (NaOH) or Sodium Carbonate (Na₂CO₃) - These alkaline reagents react with nitrogen oxides to form sodium nitrite.

Industrial chemical synthesis of Sodium Nitrite, step by step:

• Production of Nitrogen Oxides - During high-temperature combustion, nitrogen and oxygen from the air react to form nitrogen oxides (NO and NO₂).
• Absorption of Nitrogen Oxides - The nitrogen oxides are absorbed into an aqueous solution of sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃). This reaction yields sodium nitrite (NaNO₂):
• Crystallization - The sodium nitrite solution is cooled to allow for the crystallization of sodium nitrite.
• Isolation and Filtration - The crystals of sodium nitrite are separated from the solution by filtration.
• Drying - The filtered crystals are dried to remove residual water.

It occurs as a white or yellowish crystalline powder.

What it is used for and where

It is used in medicine, food, fertiliser, fixative in dyes, biological insecticide, antifreeze, raw material in the production of caffeine and saccharin, corrosion inhibitor for steel, bleaching agent for silk and linen, heat treatment agent for metals, bleaching, electroplating.

Chromatography: to determine mercury, potassium and chlorate. Nitrification and diazotization reagent (temporary generation of sodium nitrite and hydrochloric acid). Soil analysis.  Serum bilirubin measured in liver function test.

Food

Ingredient listed in the European food additives list as E250, preservative.

Nitrites and nitrates are inserted into processed meat to give it a characteristic colour and preserve it. In the 1800s saltpetre was used to preserve meat, but it was in the 1950s and 1960s that nitrites were used regularly. Sodium salts or potassium salts were also used as alternatives.

The use of sodium nitrite is now permitted but at concentrations strictly laid down in European legislation on food additives (Regulation (EC) No 1333/2008). Sodium nitrite is labelled with the number E250 in the list of European additives as a preservative. It is subject to an Acceptable Daily Intake (ADI) of 0-0.07 mg/kg body weight per day by the SCF (1997) and JECFA (2002).

Sodium nitrite is a common curing agent that performs its protective action against lipid oxidation, however this study notes that while there is a rapid expansion of meat products using natural nitrate derivatives, there is a fundamental lack of understanding regarding the safety and chemical implications of curing agents, whether derived from synthetic or natural sources. A high intake of nitrites poses a risk to consumers due to vasodilatory effects and the production of carcinogenic nitrosamines (1). Meat products treated with sodium nitrite may be contaminated with carcinogenic N-nitrosamines depending on the method of processing (ageing, maturing, fermentation, smoking, heat treatment and storage) (2).

A report by the World Cancer Research Fund in 2007 emphasised the importance of limiting red meat intake and avoiding processed meat as compelling evidence points to an association between processed red meat and cancer (3) and this study, referring to a workshop held in Oslo, Norway in November 2013 where the health aspect of red and processed meat was discussed, draws attention to an unbalanced red meat-dominated diet that may increase the risk of colorectal cancer (4).

Prolonged intake of large amounts of nitrite is associated with an increased risk of developing stomach cancer and oesophageal cancer. Foods containing potassium nitrite (E249), sodium nitrite (E250) and potassium nitrate (E252) should therefore be avoided or greatly reduced, especially in canned meat, sausages and processed meats (5).

In 2017, the Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion on the safety of sodium nitrite concluding that there is evidence to attribute NDMA (n-nitrosodimethylamine) a link to colorectal cancers (6).

Cosmetics

Anticorrosive. It is a restricted ingredient III/17 as a relevant item in the Annexes of the European Cosmetics Regulation 1223/2009. Maximum concentration in the ready-for-use preparation 0.2%. Do not use with secondary and/or tertiary amines or other nitrosamine-forming substances. 

Commercial applications 

Preservative in Food Products. Sodium nitrite is used as a preservative, especially in processed meats like sausages, to prevent the growth of bacteria.

Coloring Agent in Foods. It acts as a color fixative in processed meats, helping to maintain an appealing red color.

Corrosion Inhibitor. Used in engine cooling solutions and other industrial applications to prevent corrosion of metals.

Reagent in Chemical Analysis. Used as a reagent in various chemical tests to analyze and determine the presence of specific compounds.

Rubber Production. Used in the production of rubber as a maturing agent to improve strength and processing properties.

Sodium nitrite studies

Typical optimal commercial product characteristics Sodium nitrite

Appearance	Colorless or yellow crystal
Content of sodium nitrite %	≥98.5
Boiling Point	320 °C
Melting Point	271 °C(lit.)
Density	1.29 g/mL at 25 °C
PSA	52.49000
LogP	0.25060
Water Solubility	820 g/L (20 ºC)
Water insoluble matter	≤0.05%
Sodium nitrate	≤0.8%
Chloride	≤50ppm
Moisture %	≤2.0
Storage	2-8°C
Safety

• Molecular Formula : NNaO₂
• Molecular Weight : 68.995
• Exact Mass   68.982674
• CAS : 7632-00-0
• UNII M0KG633D4F
• EC Number   231-555-9
• DSSTox Substance ID DTXSID0020941
• IUPAC  sodium;nitrite
• InChI=1S/HNO2.Na/c2-1-3;/h(H,2,3);/q;+1/p-1  
• InChl Key      LPXPTNMVRIOKMN-UHFFFAOYSA-M
• SMILES   N(=O)[O-].[Na+]
• MDL number  MFCD00011118
• PubChem Substance ID 329752451
• ChEBI  78870
• ICSC    1120
• NSC   77391
• RTECS   RA1225000
• UN   1500   3287

Sinonimi :

• Nitrous acid, sodium salt
• Nitrite, Sodium

References_____________________________________________________________________

(1) Rivera N, Bunning M, Martin J. Uncured-Labeled Meat Products Produced Using Plant-Derived Nitrates and Nitrites: Chemistry, Safety, and Regulatory Considerations. J Agric Food Chem. 2019 Jul 24;67(29):8074-8084. doi: 10.1021/acs.jafc.9b01826. 

(3) De Mey E, De Maere H, Paelinck H, Fraeye I. Volatile N-nitrosamines in meat products: Potential precursors, influence of processing, and mitigation strategies. Crit Rev Food Sci Nutr. 2017 Sep 2;57(13):2909-2923. doi: 10.1080/10408398.2015.1078769.

(3) Demeyer D, Honikel K, De Smet S. The World Cancer Research Fund report 2007: A challenge for the meat processing industry. Meat Sci. 2008 Dec;80(4):953-9. doi: 10.1016/j.meatsci.2008.06.003. 

(4) Oostindjer M, Alexander J, Amdam GV, Andersen G, Bryan NS, Chen D, Corpet DE, De Smet S, Dragsted LO, Haug A, Karlsson AH, Kleter G, de Kok TM, Kulseng B, Milkowski AL, Martin RJ, Pajari AM, Paulsen JE, Pickova J, Rudi K, Sødring M, Weed DL, Egelandsdal B. The role of red and processed meat in colorectal cancer development: a perspective. Meat Sci. 2014 Aug;97(4):583-96. doi: 10.1016/j.meatsci.2014.02.011.

(5) http://www.airc.it/cancro/disinformazione/additivi-conservanti-alimentari/  (italian)

(6) EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), Mortensen A, Aguilar F, Crebelli R, Di Domenico A, Dusemund B, Frutos MJ, Galtier P, Gott D, Gundert-Remy U, Lambré C, Leblanc JC, Lindtner O, Moldeus P, Mosesso P, Oskarsson A, Parent-Massin D, Stankovic I, Waalkens-Berendsen I, Woutersen RA, Wright M, van den Brandt P, Fortes C, Merino L, Toldrà F, Arcella D, Christodoulidou A, Cortinas Abrahantes J, Barrucci F, Garcia A, Pizzo F, Battacchi D, Younes M. Re-evaluation of potassium nitrite (E 249) and sodium nitrite (E 250) as food additives. EFSA J. 2017 Jun 15;15(6):e04786. doi: 10.2903/j.efsa.2017.4786.