Sodium azide is an inorganic compound with the formula NaN3. This colorless salt is the gas-forming component in some car airbag systems. It’s primarily used in laboratories and industry, especially in airbag systems for vehicles where it rapidly decomposes to release nitrogen gas (N₂) in an explosion-like manner to inflate airbags. It is used for the preparation of other azide compounds. It is an ionic substance, is highly soluble in water, and is acutely poisonous.
Despite its usefulness, sodium azide is highly toxic and can be dangerous if ingested, inhaled, or absorbed through the skin. Its toxicity stems from its ability to disrupt cellular respiration by inhibiting cytochrome c oxidase in mitochondria.
Structure
Sodium azide is an ionic solid. Two crystalline forms are known, rhombohedral and hexagonal. Both adopt layered structures. The azide anion is very similar in each form, being centrosymmetric with N–N distances of 1.18 Å. The Na+ ion has an octahedral geometry. Each azide is linked to six Na+ centers, with three Na–N bonds to each terminal nitrogen center.
Properties
It is typically a white, crystalline solid. It can appear as a powder or in solid form. It is moderately soluble in water. Its solubility is about 68 grams per 100 milliliters of water at room temperature.
- Chemical formula: NaN3
- Molar mass: 65.0099 g/mol
- Appearance: Colorless to white solid
- Odor: Odorless
- Density: 1.846 g/cm3 (20 °C)
- Melting point: 275 °C (527 °F; 548 K) violent decomposition
- Solubility in water: 38.9 g/100 mL (0 °C), 55.3 g/100 mL (100 °C)
- Solubility: Very soluble in ammonia,
- Slightly soluble in benzene
- Insoluble in diethyl ether, acetone, hexane, chloroform
- Solubility in methanol: 2.48 g/100 mL (25 °C)
- Solubility in ethanol: 0.22 g/100 mL (0 °C)
Preparation
The common synthesis method is the “Wislicenus process”, which proceeds in two steps in liquid ammonia. In the first step, ammonia is converted to sodium amide by metallic sodium:
2 Na + 2 NH3 → 2 NaNH2 + H2
It is a redox reaction in which metallic sodium gives an electron to a proton of ammonia which is reduced in hydrogen gas. Sodium easily dissolves in liquid ammonia to produce solvated electrons responsible for the blue color of the resulting liquid. The Na+ and NH−2 ions are produced by this reaction.
The sodium amide is subsequently combined with nitrous oxide:
2 NaNH2 + N2O → NaN3 + NaOH + NH3
These reactions are the basis of the industrial route, which produced about 250 tons per year in 2004, with production increasing due to the increased use of airbags.
Industrial Use
One of the primary uses of sodium azide is in automotive airbags. It is also used in some biological and chemical applications, such as a preservative in laboratory reagents, and in the synthesis of other chemicals, including azides for pharmaceutical or agricultural products.
Natural Occurrence
Sodium azide does not naturally occur in significant quantities in the environment, but it can form under specific conditions in certain chemical processes.
Toxicity
Sodium azide is toxic if ingested or inhaled, and exposure to it can cause severe health effects such as nausea, headaches, dizziness, and even death. It is also hazardous to the environment, particularly aquatic life.
