Azide is the anion with the formula N₃⁻. It is the conjugate base of hydrazoic acid. 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.

Inorganic azides

Azide forms both covalent and ionic compounds with metals. Sodium azide, NaN₃, is a salt that is widely used as the propellant in airbags. Covalent azides are numerous, an example being [Co(NH₃)₅N₃]Cl₂, in which it is a monodentate ligand in a coordination complex of Co³⁺. A metal-organic azide is trimethylsilylazide, which is sometimes used as an anhydrous source of N₃⁻.

Azides in biochemistry

The azide anion is toxic, inhibiting the function of cytochrome c oxidase by binding irreversibly to the heme cofactor, in a process similar to that of cyanide. Azide salts are also used in studies of mutagenesis.

Organic azides

Organic azides engage in useful organic reactions. The terminal nitrogen is mildly nucleophilic. Azides easily extrude diatomic nitrogen, a tendency that is exploited in many reactions such as the Staudinger Ligation or the Curtius rearrangement or for example in the synthesis of γ-imino-β-enamino esters.

In the azide alkyne Huisgen cycloaddition, organic azides react as 1,3-dipoles. Examples of organic azides are the chemical reagent phenyl azide and the antiviral drug zidovudine (AZT).

Another azide regular is tosyl azide here in reaction with norbornadiene in a nitrogen insertion reaction:

Dutt-Wormall reaction

A classic method for the synthesis of azides is the Dutt-Wormall reaction in which a diazonium salt reacts with a sulfonamide first to a diazoaminosulfinate and then on hydrolysis the azide and a sulfinic acid.

Safety

• Sodium azide is toxic (LD₅₀ oral (rats) = 27 mg/kg) and can be absorbed through the skin.
• Heavy metal azides, such as lead azide are very unstable primary high explosives detonable when heated or shaken.
• Sodium azide decomposes explosively upon heating to above 275 °C.
• Sodium azide reacts vigorously with CS₂, bromine, nitric acid, dimethyl sulfate, and a series of heavy metals, including copper and lead.
• In reaction with water or Brønsted acids the highly toxic and explosive hydrogen azide is released.
• It has been reported that sodium azide and polymer-bound azide reagents react with dichloromethane and chloroform to form di- and triazidomethane resp., which are both unstable in high concentrations in solution. Various devastating explosions were reported while reaction mixtures were being concentrated on a rotary evaporator. The hazards of diazidomethane (and triazidomethane) have been well documented.
• Heavy-metal azides that are highly explosive under pressure or shock are formed when solutions of sodium azide or HN₃ vapors come into contact with heavy metals or their salts. Heavy-metal azides can accumulate under certain circumstances, for example, in metal pipelines and on the metal components of diverse equipment (rotary evaporators, freezedrying equipment, cooling traps, water baths, waste pipes), and thus lead to violent explosions. Some organic and other covalent azides are classified as highly explosive and toxic (inorganic azides as neurotoxins; azide ions as cytochrome c oxidase (COX) inhibitors).
• Solid iodoazide is explosive and should not be prepared in the absence of solvent.

References

External links

• Synthesis of organic azides, recent methods
• Synthesizing, Purifying, and Handling Organic Azides
• Preparation of Polyfunctional Acyl Azides
• Synthesis and Reduction of Azides