Hydrazoic acid

Hydrazoic acid, HN3, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure.

Applications
Hydrazoic acid is used primarily for preservation of stock solutions, and as a reagent.

History
It was first isolated in 1890 by Theodor Curtius (Berichte, 1890, 23, p. 3023).

Chemistry
It is soluble in water, and the solution dissolves many metals (e.g. zinc, iron) with liberation of hydrogen and formation of salts (azides, formerly also called azoimides or hydrazoates).

All the salts are explosive and readily interact with the alkyl iodides. In its properties it shows some analogy to the halogen acids, since it forms poorly soluble lead, silver and mercurous salts (in water). The metallic salts all crystallize in the anhydrous form and decompose on heating, leaving a residue of the pure metal. It is a weak acid (pKa 4.6-4.7).

Production
The acid is usually formed by acidification of an azide salt like sodium azide. Normally solutions of sodium azide in water contain trace quantities of hydrazoic acid in equilibrium with the azide salt, but introduction of a stronger acid can convert the primary species in solution to hydrazoic acid. The pure acid may be subsequently obtained by fractional distillation as an extremely explosive colorless liquid with an unpleasant smell.

Toxicity
Hydrazoic acid is volatile and highly toxic. It has a pungent smell and its vapor can cause violent headaches. The compound acts as a non-cumulative poison.