Hydrazoic acid, also known as hydrogen azide, azic acid or azoimide, This also contains a detailed description of the contemporaneous production process. is a compound with the chemical formula . It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, and is therefore a pnictogen hydride. The Oxidation state of the nitrogen atoms in hydrazoic acid is fractional and is -1/3. It was first isolated in 1890 by Theodor Curtius. The acid has few applications, but its conjugate acid, the azide ion, is useful in specialized processes.
Hydrazoic acid, like its fellow , is soluble in water. Undiluted hydrazoic acid is dangerously explosive with a standard enthalpy of formation ΔfHo (l, 298K) = +264 kJ/mol. 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.Gonzalez-Bobes, F. et al Org. Process Res. Dev. 2012, 16, 2051-2057.Treitler, D. S. et al Org. Process Res. Dev. 2017, 21, 460-467.
Its aqueous solution can also be prepared by treatment of barium azide solution with dilute sulfuric acid, filtering the insoluble barium sulfate.L . F. Audrieth, C. F. Gibbs Hydrogen Azide in Aqueous and Ethereal Solution" Inorganic Syntheses 1939, vol. 1, pp. 71-79.
It was originally prepared by the reaction of aqueous hydrazine with nitrous acid:
With the hydrazine cation this reaction is written as:
Other oxidizing agents, such as hydrogen peroxide, nitrosyl chloride, trichloramine or nitric acid, can also be used to produce hydrazoic acid from hydrazine.
This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states.Greenwood, pp. 461–464.
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 called Schmidt reaction or Schmidt rearrangement.
Dissolution in the strongest acids produces explosive salts containing the aminodiazonium ion , for example:
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. In addition, these unimolecular rates have been analyzed theoretically, and the experimental and calculated rates are in reasonable agreement.
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 .
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