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| Names | |
|---|---|
| IUPAC name Hydrogen azide | |
| Other names Hydrogen azide Azoimide | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
|
| ECHA InfoCard | 100.029.059 |
| EC Number |
|
| 773 | |
| UNII | |
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| |
| Properties | |
| HN3 | |
| Molar mass | 43.029 g·mol−1 |
| 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) |
| highly soluble | |
| Solubility | soluble inalkali,alcohol,ether |
| Acidity (pKa) | 4.6[1] |
| Conjugate base | Azide |
| Structure | |
| approximately linear | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Highly toxic, explosive, reactive |
| GHS labelling: | |
   | |
| Danger | |
| H200,H319,H335,H370 | |
| P201,P202,P260,P264,P270,P271,P280,P281,P304+P340,P305+P351+P338,P307+P311,P312,P321,P337+P313,P372,P373,P380,P401,P403+P233,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Othercations | Sodium azide Lithium azide Potassium azide |
| Ammonia Hydrazine | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Hydrazoic acid, also known ashydrogen azide orazoimide,[2] is a compound with the chemical formulaHN3.[3] It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound ofnitrogen andhydrogen, and is therefore apnictogen hydride. It was first isolated in 1890 byTheodor Curtius.[4] The acid has few applications, but itsconjugate base, theazide ion, is useful in specialized processes.
Hydrazoic acid, like its fellowmineral acids, is soluble in water. Undiluted hydrazoic acid is dangerously explosive[5] with astandard enthalpy of formation ΔfHo (l, 298K) = +264 kJ/mol.[6] When dilute, the gas and aqueous solutions (<10%) can be safely prepared but should be used immediately; because of its low boiling point, hydrazoic acid is enriched upon evaporation and condensation such that dilute solutions incapable of explosion can form droplets in the headspace of the container or reactor that are capable of explosion.[7][8]
The acid is usually formed by acidification of an azide salt likesodium 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 byfractional distillation as an extremely explosive colorless liquid with an unpleasant smell.[2]
Its aqueous solution can also be prepared by treatment ofbarium azide solution with dilutesulfuric acid, filtering the insolublebarium sulfate.[9]
It was originally prepared by the reaction of aqueoushydrazine withnitrous acid:
With thehydrazinium cation[N2H5]+ this reaction is written as:
Other oxidizing agents, such ashydrogen peroxide,nitrosyl chloride,trichloramine ornitric acid, can also be used to produce hydrazoic acid from hydrazine.[10]
Hydrazoic acid reacts with nitrous acid:
This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states.[11]
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.[2] It is a weak acid (pKa = 4.75.[6]) Its heavy metal salts are explosive and readily interact with thealkyl iodides. Azides of heavieralkali metals (excludinglithium) oralkaline earth metals are not explosive, but decompose in a more controlled way upon heating, releasing spectroscopically-pureN2 gas.[12] Solutions of hydrazoic acid dissolve many metals (e.g.zinc,iron) with liberation of hydrogen and formation of salts,[13] which are calledazides (formerly also called azoimides or hydrazoates).
Hydrazoic acid may react with carbonyl derivatives, including aldehydes, ketones, and carboxylic acids, to give an amine or amide, with expulsion of nitrogen. This is calledSchmidt reaction or Schmidt rearrangement.
Dissolution in the strongest acids produces explosive salts containing the aminodiazonium ion[H2N=N=N]+ ⇌ [H2N−N≡N]+, for example:[12]
The ion[H2N=N=N]+ isisoelectronic todiazomethaneH2C=N+=N−.
The decomposition of hydrazoic acid, triggered by shock, friction, spark, etc. produces nitrogen and hydrogen:
Hydrazoic acid undergoes unimolecular decomposition at sufficient energy:
The lowest energy pathway produces NH in the triplet state, making it a spin-forbidden reaction. This is one of the few reactions whose rate has been determined for specific amounts of vibrational energy in the ground electronic state, by laser photodissociation studies.[14] In addition, these unimolecular rates have been analyzed theoretically, and the experimental and calculated rates are in reasonable agreement.[15]
Hydrazoic acid is volatile and highly toxic. It has a pungent smell and its vapor can cause violentheadaches. The compound acts as a non-cumulative poison.
2-Furonitrile, a pharmaceutical intermediate and potential artificial sweetening agent has been prepared in good yield by treatingfurfural with a mixture of hydrazoic acid (HN3) andperchloric acid (HClO4) in the presence of magnesium perchlorate in thebenzene solution at 35 °C.[16][17]
Theall gas-phase iodine laser (AGIL) mixes gaseous hydrazoic acid withchlorine to produce excitednitrogen chloride, which is then used to causeiodine to lase; this avoids the liquid chemistry requirements ofCOIL lasers.
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