Sodium Nitrite
Properties
| State | Solid at room temperature |
| Color | White to slightly yellowish crystalline powder |
| Solubility | Very soluble in water (820 g/L at 20 °C); also soluble in methanol |
| Melting Point | 271 °C |
| Boiling Point | 320 °C (decomposes to Na2O, NO, NO2) |
About Sodium Nitrite
Sodium nitrite (NaNO2, MW 68.995) is the lower oxidation state cousin of sodium nitrate, and the difference of one oxygen atom puts it in a completely different functional and toxicological category. Industrially it's made by absorbing NOx (a mix of NO and NO2 from the catalytic ammonia oxidation step of the Ostwald process) into NaOH or Na2CO3 solution: NO + NO2 + 2NaOH -> 2NaNO2 + H2O. As the curing salt E250 (used as Prague Powder #1, a 6.25% NaNO2 / 93.75% NaCl mixture for short-cure products like bacon, hot dogs, ham, and bologna), it's the workhorse that prevents Clostridium botulinum spores from germinating in vacuum-packed cured meats and produces the characteristic pink color via nitrosomyoglobin formation. The mechanism: NaNO2 is reduced in the meat matrix by ascorbate or muscle reductases to nitric oxide (NO), which displaces water from the sixth coordination site of the heme Fe2+ in myoglobin to form the stable pink nitrosomyoglobin pigment, then on cooking the heat-stable pink nitrosohemochrome. In medicine, sodium nitrite is the first injection of the classic cyanide-poisoning antidote (followed by sodium thiosulfate); it oxidizes hemoglobin Fe2+ to Fe3+, generating methemoglobin that scavenges CN- as cyanmethemoglobin. In organic synthesis, NaNO2 in cold acidic solution (HCl or H2SO4 at 0-5 °C) generates the diazonium ion ArN2+ from a primary aromatic amine, the foundational diazotization that opens onto the Sandmeyer halogenation, the Schiemann fluorination, the Japp-Klingemann coupling, and most azo dye chemistry (methyl orange, sunset yellow, the entire 'azo' class).
Where you'll encounter it
If you've ever cured your own bacon at home with Prague Powder #1, eaten a hot dog at a baseball game, or run a Sandmeyer reaction in graduate organic chemistry to install a Br or CN onto an aniline-derived diazonium salt, you've used NaNO2 chemistry. In a meat-processing plant, the USDA mandates an ingoing nitrite limit of 156 ppm in cured meats (200 ppm with ascorbate) and a 120 ppm minimum for bacon, with mandatory 550 ppm sodium ascorbate or erythorbate co-addition specifically to suppress nitrosamine formation when bacon is fried. In an emergency room treating a cyanide poisoning, the antidote sequence is a 300 mg IV push of sodium nitrite over 5 minutes (driving methemoglobin to about 25%), then 12.5 g IV sodium thiosulfate over 10 minutes; modern practice has largely shifted to hydroxocobalamin (Cyanokit), but the older nitrite-thiosulfate kit remains in many ambulances. In a synthesis lab, the diazotization of aniline at 0-5 °C with NaNO2 and HCl, followed by coupling to beta-naphthol in cold alkali, gives the brilliant red Sudan I dye in a single class period.
Common Uses
- Active curing agent in Prague Powder #1 for bacon, hot dogs, ham, and bologna
- First-line cyanide poisoning antidote (paired with sodium thiosulfate)
- Diazotization reagent for Sandmeyer, Schiemann, and azo coupling reactions
- Corrosion inhibitor in closed-loop cooling water and antifreeze formulations
- Brass and bronze color treatment (chemical patination)
- Photographic fixer accelerator in some legacy emulsion processes
- Vasodilator research reagent (releases NO, the endothelium-derived relaxing factor)
- Reducing agent in textile dyeing for color stripping and discharge printing
Safety Information
Acute oral toxicity is significant: rat LD50 is 180 mg/kg, and the human lethal oral dose is roughly 33 mg/kg (about 2.5 g for an adult), making it one of the more dangerous food additives by mass. The mechanism is methemoglobinemia: NO2- oxidizes hemoglobin Fe2+ to Fe3+, which cannot bind O2; cyanosis appears at MetHb above 15% and is lethal above 70%. Methylene blue (1-2 mg/kg IV) is the antidote. Cured meats deliver only milligram-level doses well below the toxic threshold, but bulk NaNO2 has been used for both suicide and homicide and is now restricted online. Carcinogenicity: nitrite itself is not classified, but during high-temperature cooking it can react with secondary amines in meat to form N-nitrosamines (N-nitrosodimethylamine, N-nitrosopyrrolidine), several of which are IARC Group 2A. No firm substance-specific occupational exposure limit is established, though the advisory dust limits that exist are low. GHS classifications: H272 (may intensify fire; oxidizer), H301 (toxic if swallowed), H319 (serious eye irritation), H400 (very toxic to aquatic life). Pictograms: Flame over circle, Skull-and-crossbones, Exclamation mark, Environment. Store away from acids (releases brown NO2 gas) and organics.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.