Hydrazoic acid

Hydrazoic acid
IUPAC name

Hydrogen azide
Identifiers
CAS number 7782-79-8 Y
PubChem 24530
ChemSpider 22937 Y
ChEBI CHEBI:29449 Y
ChEMBL CHEMBL186537 Y
Jmol-3D images Image 1
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 (verify) (what is: Y/N?)
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.

Contents

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 (pKa = 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]−

The ion H2N=N=N+ is isoelectronic to diazomethane.

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(s) + HCl(aq) → HN3(aq) + NaCl(aq)

Can also be prepared by treatment of barium azide solution with dilute sulfuric acid, filtering the insoluble barium sulfate.[6]

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

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
  2. ^  Chisholm, Hugh, ed (1911). "Azoimide". Encyclopædia Britannica (11th ed.). Cambridge University Press. 
  3. ^ Dictionary of Inorganic and Organometallic Compounds. Chapman & Hall. 
  4. ^ Curtius, Theodor (1890). Berichte 23: 3023. 
  5. ^ a b Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). "The Nitrogen Group". Inorganic chemistry. Academic Press. p. 625. ISBN 0123526515. 
  6. ^ Booth, Harold Simmons (1939). Inorganic Synthesis Vol.1. MCGRAW-HILL. doi:10.1002/9780470132326. ISBN 9780470131602. 

External links