Hydrazoic acid

Hydrazoic acid
IUPAC name	Hydrogen azide
Identifiers
CAS number	7782-79-8 Y
PubChem	24530
SMILES	N=N=N
Properties
Molecular formula	HN3
Molar mass	43.03 g/mol
Appearance	colorless, highly volatile liquid
Density	1.09 g/cm3
Melting point	-80 °C, 193 K, -112 °F
Boiling point	37 °C, 310 K, 99 °F
Solubility in water	highly soluble
Solubility	soluble in alkali, alcohol, ether
Acidity (pKa)	4.6 [1]
Structure
Molecular shape	approximately linear
Hazards
EU Index	Not listed
Main hazards	Highly toxic, explosive
Related compounds
Other cations	Sodium azide
Related nitrogen hydrides	Ammonia Hydrazine
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hydrazoic acid, also known as hydrogen azide or azoimide,^[2] is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN₃.^[3] It was first isolated in 1890 by Theodor Curtius.^[4] It is used primarily for preservation of stock solutions, and as a reagent.

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).

Its heavy metal salts are explosive and readily interact with the alkyl iodides. Azides of heavier alkali metals (excluding lithium) or alkaline earth metals are not explosive, but decompose in a more controlled way upon heating, releasing spectroscopically-pure N₂ gas.^[5]

In its properties hydrazoic acid shows some analogy to the halogen acids, since it forms poorly soluble (in water) lead, silver and mercury(I) salts. 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 (pK_a = 4.6-4.7).

Dissolution in the strongest acids produces explosive salts containing the H₂N=N=N⁺ ion, for example:^[5]

HN=N=N + HSbCl₆ → [H₂N=N=N]⁺[SbCl₆]⁻

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.

References

External links

• OSHA: Hydrazoic Acid