Sodium nitrite

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Sodium nitrite
Sodium nitrite sample.jpg
Sodium nitrite sample on a watch glass.
Names
IUPAC name
Sodium nitrite
Other names
Nitrous acid, sodium salt
Identifiers
Jmol-3D images Image
Properties
NaNO2
Molar mass 68.9953 g/mol
Appearance White or slight yellowish solid
Density 2.168 g/cm3
Melting point 271 °C (520 °F; 544 K)
Boiling point 320 °C (608 °F; 593 K) (decomposes)
71.4 g/100 mL (0 °C)
84.8 g/100 mL (25 °C)
160 g/100 mL (100 °C)
Solubility Very soluble in anhydrous ammonia
Soluble in ethanol
Solubility in ethanol 3 g/100 ml
Solubility in methanol 4.4 g/100 ml
Solubility in diethyl ether 0.3 g/100 mL
Acidity (pKa) ~9
Thermochemistry
106 J·mol-1·K-1
−359 kJ/mol
Hazards
Safety data sheet ScienceCompany
Lethal dose or concentration (LD, LC):
180 mg/kg (rats, oral)
Related compounds
Related compounds
Sodium nitrate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium nitrite is the inorganic compound, the nitrate salt of nitrous acid with the chemical formula NaNO2.

Properties

Chemical

Sodium nitrite will react with sodium chloroacetate in aqueous solution to give nitromethane:

NaNO2 + ClCH2COONa + H2O → CH3NO2 + NaCl + NaHCO3

Sodium nitrite is a poor oxidizing agent, compared to its nitrate cousin.

Physical

Sodium nitrite is a white or white-yellowish hygroscopic solid, soluble in water and slightly soluble in primary alcohols, while insoluble in alkanes and chlorocarbons. It has a density of 2.168 g/cm3. It melts when heated to 271 °C, and will also decompose, with significant decomposition starting above 320 °C.

Availability

Sodium nitrite can be found as food additive. It is usually dyed pink to differentiate it from table salt. The dye can be removed by washing it with a solvent and further purification can be achieved by recrystallizing the sodium nitrite.

Preparation

There are many ways to prepare sodium nitrite.

A known process involves the reduction of sodium nitrate with metallic lead. About 8.5 g of powdered NaNO3 is mixed with 21 g of lead and heated until it melts. The mixture is kept liquid and stirred/agitated for 30-45 minutes until all the lead is oxidized to lead(II) oxide and forming sodium nitrite.

NaNO3 + Pb → NaNO2 + PbO

The resulting slag is grounded and the sodium nitrite is purified by recrystallizing it from water. This procedure has the disadvantage of contaminating the product with lead oxide, making it less safe to handle without proper protection. It is also temperature sensitive.

The thermal reduction of sodium nitrate with calcium sulfite will also yield sodium nitrite.[1]

NaNO3 + CaSO3 → NaNO2 + CaSO4

Calcium sulfamate can also be used.

Another method involves heating sodium nitrite with carbon in the presence of sodium hydroxide or calcium hydroxide.

2 NaNO3 + 2 NaOH + C → 2 NaNO2 + Na2CO3 + H2O
2 NaNO3 + Ca(OH)2 + C → 2 NaNO2 + CaCO3 + H2O

The latter method is preferred as calcium carbonate is insoluble in water and can be easily removed from the slag.[2]

A mixture of aluminium powder and sodium nitrate heated for 40 minutes will yield sodium nitrite.

The industrial route involves treating an aqueous solution of sodium hydroxide with a mixture of nitrogen dioxide and nitric oxide:

2 NaOH + NO2 + NO → 2 NaNO2 + H2O

This reaction is air-sensitive and traces of oxygen will lead to sodium nitrate.

Very pure sodium nitrite can be obtained by reacting nitrous acid (which can be obtained by adding dinitrogen trioxide to pure water) with sodium hydroxide.

2 NaOH + N2O3 → 2 NaNO2 + H2O

An interesting method involves reducing sodium nitrate using starch and sodium hydroxide.[3]

Projects

  • Make alkyl nitrites
  • Make nitromethane
  • Destroy azides
  • Make azo compounds
  • Electrochemical grinding
  • Meat curing
  • Intravenous mixture of sodium nitrite and sodium thiosulfate can be used as antidote for cyanide poisoning.

Handling

Safety

Sodium nitrite is harmful if inhaled or ingested and proper protection should be worn when handling the compound.

Storage

In closed bottles, away from light and oxygen-rich environment.

Disposal

Heating sodium nitrite above 300 °C will cause it to decompose, leaving behind sodium oxide/hydroxide which can be safely disposed of.

Adding sodium percarbonate to sodium nitrite will oxidize it to sodium nitrate.

References

  1. https://www.google.com/patents/US670021
  2. http://www.google.com/patents/US792515
  3. http://www.sciencemadness.org/talk/viewthread.php?tid=77186

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