Azide

Azide is the anion with the formula N₃⁻. It is the conjugate base of hydrazoic acid (HN₃). N₃⁻ is a linear anion that is isoelectronic with CO₂ and N₂O. Per valence bond theory, azide can be described by several resonance structures, an important one being N⁻=N⁺=N⁻. Azide is also a functional group in organic chemistry, RN₃. The dominant application of azides is as a propellant in air bags.

Preparation

Inorganic azides

Sodium azide is made industrially by the reaction of nitrous oxide, N₂O with sodium amide in liquid ammonia as solvent:

Many inorganic azides can be prepared directly or indirectly from sodium azide. For example, lead azide, used in detonators, may be prepared from the metathesis reaction between lead nitrate and sodium azide. An alternative route is direct reaction of the metal with silver azide dissolved in liquid ammonia. Some azides are produced by treating the carbonate salts with hydrazoic acid.

Organic azides

The principal source of the azide moiety is sodium azide. As a pseudohalogen compound, sodium azide generally displaces an appropriate leaving group (e.g. Br, I, OTs) to give the azido compound. Aryl azides may be prepared by displacement of the appropriate diazonium salt with sodium azide, or trimethylsilyl azide; nucleophilic aromatic substitution is also possible, even with chlorides. Anilines and aromatic hydrazines undergo diazotization, as do alkyl amines and hydrazines.