HN3

Hydrazoic acid, also known as hydrogen azide and abbreviated as HN3, is a highly toxic chemical with the formula HN3. In practical terms it exists as a volatile, colorless gas and, in solution, as hydrazoic acid. It is related to the azide ion (N3−) and forms various azide derivatives used in synthesis.

Chemically, HN3 is a linear molecule with a resonance-stabilized azide group. The conjugate base is the azide ion, N3−. Hydrazoic acid is a weak acid, with acidity in water described by a pKa around 4.7. It is extremely hazardous due to its volatility and tendency to decompose explosively under heat, shock, or friction. Exposure can be highly toxic, and inhalation of vapors poses severe health risks.

Preparation and occurrence: Hydrazoic acid can be generated by the controlled acidification of solutions containing sodium azide or related azide compounds. It is also encountered transiently during certain chemical syntheses involving azide chemistry. Because of its instability and energetic decomposition, HN3 is handled with significant safety precautions in specialized facilities.

Uses and history: Hydrazoic acid and azide chemistry have been used as intermediates in organic synthesis, including the preparation of diazo compounds. Historically, azide-based compounds have been employed in propellant formulations and other energetic materials; however, safety concerns limit direct use of hydrazoic acid today. The related sodium azide salt remains common in applications such as airbags, where it releases nitrogen gas upon decomposition.

Safety: Due to its toxicity and explosive potential, HN3 is handled only in appropriate containment with protective equipment, under strict procedures, and away from acids and organic materials.