azide

Azide refers to a chemical group consisting of three nitrogen atoms in a linear arrangement, with the azide ion having the formula N3−. The term also applies to compounds containing the azide group, including inorganic salts and organic azides. The azide ion is derived from hydrazoic acid (HN3), and in many salts the azide behaves as a pseudohalide, forming a wide range of coordination compounds.

In structure, the azide ion is linear and polyatomic, best described by resonance forms that distribute charge along the N–N–N chain. This results in a relatively stable yet energetic anion that can decompose to nitrogen gas under heat, shock, or catalytic conditions. Organic azides have the general formula R–N3, where a carbon-containing group is linked to the azide moiety; these compounds are used in various synthetic methods, notably in 1,3-dipolar cycloadditions.

Common inorganic azides include sodium azide (NaN3), potassium azide (KN3), and metal azides such as lead(II) azide (Pb(N3)2) and silver azide (AgN3). Organic azides, such as phenyl azide, are employed in chemical synthesis and in materials science. A notable application class is azide–alkyne cycloaddition, a widely used click chemistry reaction that forms triazoles rapidly under mild conditions.

Safety and hazards are significant: many azides are toxic and some metal azides are shock- or heat-sensitive explosives. Hydrolysis or acid treatment can release hydrazoic acid, a volatile and highly toxic gas.