Why is nitrogen gas used in airbags

Sodium azide is the sodium salt of hydrazoic acid.

Description / characteristics

In acidic solution, sodium azide decomposes to form hydrazoic acid (a low-boiling liquid, boiling point 37 ° C); when heated to over 300 ° C, the substance also decomposes:

(pure nitrogen by spectral analysis)

However, the azide can be melted undecomposed and only fizzle out when heated up or with a strong blow.

The fumes of the hydrazoic acid are very poisonous and burn the mucous membranes. Hydrazoic acid is extremely explosive with spontaneous decomposition and re-formation of nitrogen. The same applies to heavy metal azides such as Pb (N.3)2, which are used technically as detonators in cartridge cases, as well as many other azides, such. B. the halogen azides and methyl azide.

Azides, including sodium azide, specifically inhibit enzymes that contain heavy metals. They are therefore extremely toxic. The acid ion also has a strong blood pressure lowering effect. Even inhalation or ingestion of small amounts (for example 1.5 ml of 10% solution) can cause severe symptoms of intoxication. Hydrazoic acid and its solutions have an unbearably pungent odor and cause dizziness, headache and skin irritation upon exposure. Preparative work with sodium azide and hydrazoic acid solutions may only be carried out in an effective fume cupboard with the use of a protective shield. Wear safety glasses! The test instructions must be strictly observed, and hydrazoic acid must never be concentrated (spontaneous explosion possible). The solutions must be titrated before use.

The azide ion N3 belongs to the pseudohalides. It behaves like Cl in many reactions. The mesomeric stabilized ion is linear and symmetrical, with uniform distances between the nitrogen atoms (these are between those of the N-N double and triple bonds). This stabilization is absent in the case of the free acid and the heavy metal azides (Ref. [7,11]).


Sodium azide is formed when nitrous oxide is passed over sodium amide at 180 ° C:

In a preparatively more complex process, sodium azide is obtained from sodium amide and sodium nitrate in the melt at 175 ° C. Sodium hydroxide and ammonia are also produced:


Sodium azide is used in industrial synthesis for the preparation of lead azide and hydrazoic acid as well as tertiary alkyl azides and other organic azides such as tosyl azide (Hunnius, Römpp, Willmes). The reaction of carbonyl compounds with hydrazoic acid in a strongly acidic medium (SCHMIDT reaction) yields acid amides (from ketones) or the amine (from carboxylic acids) which is one carbon atom poorer with migration of an alkyl group. The hydrazoic acid required for this is generated directly in the reaction flask from sodium azide. SCHRÖTER used sodium azide to prepare alkyl isocyanates from acid chlorides. The generation of isocyanates from acid azides by thermal decomposition is called CURTIUS degradation (organic substance). Sodium azide has also been used in automotive airbag fuels to inflate the airbag.

Analytical use is made of the property of azides to only react with iodine in the presence of sulfhydryl or potential sulfhydryl compounds (such as penicillin) (so-called iodine azide test). This implementation is very sensitive; nitrogen and hydrogen iodide are produced. For detection, 1 ml of 0.1 N iodine solution is colored blue with starch, 1 ml of 10% aqueous sodium azide solution is added and the sample solution (mercaptans, thioethers, disulfides, thiones, S-heterocycles) is then added. After a short time, the solution becomes discolored with evolution of gas.

Sodium azide is also widely used in all areas in which the growth of microorganisms is to be prevented. Sodium azide can be used to keep consumables (beakers, etc.) aseptic for longer in laboratories. The chemical is also added to solutions, dispersions, etc. (approx. 0.1-0.001%) which, due to their composition, are very susceptible to microbial spoilage (e.g. solutions of biopolymers, protein dispersions).

Other possible uses described in the literature include: for rapid blood pressure lowering in emergencies, as a nitrification inhibitor (Römpp) and for the production of high-purity nitrogen.

Categories: Toxic Substance | Environmentally hazardous substance | Sodium compound | Azide