Azide
Azide is the anion with the formula N3.  It is the conjugate base of hydrazoic acid.  Azide is also a functional group in organic chemistry,  RN3.  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.

# 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 Cl2. 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 -imino--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 Brnsted 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 by A. Hassner et al. .
- 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..