Sodium Nitrite (NaNO2)

Sodium Nitrite

Other Names: Nitrous acid sodium salt, Sodium nitrite(III)
Chemical Formula: NaNO₂
Molar Mass: 68.995 g/mol
CAS Number: 7632-00-0
Appearance: White to slightly yellow crystalline solid
Odor: Odorless
SMILES: [Na+].[O-]N=O

Sodium nitrite is an inorganic ionic compound consisting of sodium cations (Na⁺) and nitrite anions (NO₂⁻). The nitrite ion has a bent molecular geometry and its electronic structure is described by resonance between equivalent N–O bonding arrangements. Sodium nitrite is highly soluble in water, producing solutions containing freely solvated sodium and nitrite ions. The nitrite ion participates in a broad range of acid–base, redox and coordination reactions, making sodium nitrite an important reagent in inorganic chemistry, analytical chemistry and synthetic chemistry.

In acidic media, nitrite is protonated to form nitrous acid (HNO₂), an unstable weak acid that participates in equilibria and decomposition pathways involving nitrogen oxides. This chemistry makes sodium nitrite a convenient laboratory source of nitrite and reactive nitrogen species under controlled conditions. Its reactions with amines, transition-metal complexes and other nitrogen-containing compounds have consequently been studied extensively in mechanistic and coordination chemistry.

Chemical and physical properties

Sodium nitrite is a crystalline solid under ambient conditions. It has a molar mass of 68.995 g/mol and a density of approximately 2.17 g/cm³ at room temperature. It melts at approximately 271 °C; at higher temperatures it undergoes chemical decomposition rather than exhibiting ordinary distillation behavior.

The compound is highly soluble in water, and its solubility increases substantially with temperature. Dissolution produces the nitrite anion, which is the conjugate base of nitrous acid. Consequently, aqueous sodium nitrite solutions are generally mildly alkaline as a result of hydrolysis of NO₂⁻.

The nitrite ion contains nitrogen in the +3 oxidation state and can therefore participate in both oxidation and reduction reactions depending on the reaction partner and conditions. Oxidation can produce nitrate species, whereas reduction pathways can generate nitrogen-containing products with lower nitrogen oxidation states. This intermediate oxidation state accounts for much of the versatile redox chemistry of sodium nitrite.

Sodium nitrite is a strong oxidizing substance under appropriate conditions and can intensify the combustion of combustible materials. It is also toxic if swallowed and must be handled with suitable laboratory precautions. Reactions with acids require particular care because acidification can generate nitrous acid and nitrogen oxides.

Applications

Sodium nitrite is widely used as a reagent in organic synthesis, particularly for generating nitrous acid and nitrosating or diazotizing species in situ. A particularly important transformation is the diazotization of primary aromatic amines, which produces arenediazonium compounds that can subsequently participate in substitution, coupling and other synthetic reactions.

In analytical chemistry, sodium nitrite is used as a source of accurately controlled nitrite concentrations and as a reagent in colorimetric and spectrophotometric procedures. Nitrite determination is itself an important analytical topic, and reactions involving diazotization followed by formation of strongly absorbing azo compounds provide highly sensitive methods for its detection.

Sodium nitrite is also used in corrosion-control research and in selected industrial aqueous systems. Nitrite ions can promote passivation of ferrous materials by supporting the formation and maintenance of protective oxide layers on steel surfaces. The effectiveness of nitrite-based corrosion inhibition depends strongly on concentration, solution composition, pH, chloride content and electrochemical conditions.

In inorganic and coordination chemistry, sodium nitrite serves as a convenient source of the ambidentate nitrite ligand. Nitrite can coordinate to metal centers through nitrogen or oxygen, producing nitro and nitrito coordination modes. This structural versatility has made nitrite-containing complexes important model systems for studies of linkage isomerism, photochemistry, spectroscopy and metal–ligand bonding.

Sodium nitrite is additionally employed in chemical research involving nitrogen oxides, reactive nitrogen species, oxidation–reduction chemistry and reaction kinetics. Its well-defined composition and high water solubility make it a practical laboratory source of NO₂⁻ for controlled physicochemical and mechanistic investigations.

Scientific references

National Institute of Standards and Technology. NIST Chemistry WebBook, SRD 69. Sodium nitrite, CAS Registry Number 7632-00-0.

National Center for Biotechnology Information. PubChem Compound Summary for CID 24269, Sodium Nitrite. PubChem, U.S. National Library of Medicine.

Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd ed.; Butterworth-Heinemann: Oxford, 1997.

Butler, A. R.; Feelisch, M. “Therapeutic Uses of Inorganic Nitrite and Nitrate: From the Past to the Future.” Circulation, 2008, 117, 2151–2159. DOI: 10.1161/CIRCULATIONAHA.107.753814.

Moorcroft, M. J.; Davis, J.; Compton, R. G. “Detection and Determination of Nitrate and Nitrite: A Review.” Talanta, 2001, 54, 785–803. DOI: 10.1016/S0039-9140(01)00323-X.

Griess, P. “Bemerkungen zu der Abhandlung der HH. Weselsky und Benedikt ‘Ueber einige Azoverbindungen’.” Berichte der Deutschen Chemischen Gesellschaft, 1879, 12, 426–428.

Handling and Storage

• Storage Conditions: Store in a tightly closed container in a cool, dry, well-ventilated place away from combustible materials and reducing agents

• Handling Precautions: Avoid contact with skin, eyes, and clothing. Handle with proper protective equipment