Hydrazoic acid

Hydrazoic acid

Names
IUPAC name Hydrogen azide
Identifiers
CAS Number	7782-79-8 Y
ChEBI	CHEBI:29449 Y
ChEMBL	ChEMBL186537 Y
ChemSpider	22937 Y
Jmol 3D model	Interactive image
PubChem	24530
InChI InChI=1S/HN3/c1-3-2/h1H Y Key: JUINSXZKUKVTMD-UHFFFAOYSA-N Y InChI=1/HN3/c1-3-2/h1H Key: JUINSXZKUKVTMD-UHFFFAOYAO
SMILES [N-]=[N+]=[N@H]
Properties
Chemical formula	HN3
Molar mass	43.03 g/mol
Appearance	colorless, highly volatile liquid
Density	1.09 g/cm3
Melting point	−80 °C (−112 °F; 193 K)
Boiling point	37 °C (99 °F; 310 K)
Solubility in water	highly soluble
Solubility	soluble in alkali, alcohol, ether
Acidity (pKa)	4.6
Structure
Molecular shape	approximately linear
Vapor pressure	{{{value}}}
Related compounds
Other cations	Sodium azide
Related nitrogen hydrides	Ammonia Hydrazine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN₃. It was first isolated in 1890 by Theodor Curtius. The acid has few applications, but its conjugate base, the azide ion, is useful in specialized processes.

Hydrazoic acid is soluble in water. Undiluted hydrazoic acid is dangerously explosive with a standard enthalpy of formation Δ_fH^o (l, 298K) = +264 kJmol⁻¹). When dilute, the gas and aqueous solutions (<10%) can be safely handled.

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.

NaN₃ + HCl → HN₃ + NaCl

Its aqueous solution can also be prepared by treatment of barium azide solution with dilute sulfuric acid, filtering the insoluble barium sulfate.

It was originally prepared by the reaction of aqueous hydrazine with nitrous acid.

N₂H₅⁺ + HNO₂ → HN₃ + H⁺ + 2 H₂O

Other oxidizing agents, such as hydrogen peroxide, NOCl, NCl3 or nitric acid, can also be used.

Reactions

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 = 4.75.) 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 N
₂ gas. Solutions of hydrazoic acid dissolve many metals (e.g. zinc, iron) with liberation of hydrogen and formation of salts, which are called azides (formerly also called azoimides or hydrazoates).

Dissolution in the strongest acids produces explosive salts containing the H
₂N=N=N⁺
ion, for example:

HN=N=N + HSbCl
₆ → [H
₂N=N=N]⁺
[SbCl
₆]⁻

The ion H
₂N=N=N⁺
is isoelectronic to diazomethane.

The decomposition of hydrazoic acid, triggered by shock, friction, spark, etc. goes as follows:

2HN
₃ → H
₂ + 3N
₂

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.

Applications

2-Furonitrile, a pharmaceutical intermediate and potential artificial sweetening agent has been prepared in good yield by treating furfural with a mixture of hydrazoic acid (HN₃) and perchloric acid in the presence of magnesium perchlorate in the benzene solution at 35 °C.

The all gas-phase iodine laser (AGIL) mixes gaseous hydrazoic acid with chlorine to produce excited nitrogen chloride, which is then used to cause iodine to lase; this avoids the liquid chemistry requirements of COIL lasers.

External links

• OSHA: Hydrazoic Acid