Boron triazide, also known as triazidoborane, is a thermally unstable compound of
boron and
nitrogen with a nitrogen content of 92.1 % (by the
standard atomic weight). Formally, it is the triazido derivative of
borane and is a covalent inorganic
azide. The high-energy compound, which has the propensity to undergo spontaneous explosive decomposition, was first described in 1954 by
Egon Wiberg and Horst Michaud of the
University of Munich.[1]
Preparation
The first method is by the addition of
diborane to a solution of
hydrazoic acid in
diethyl ether at a temperature range between −20 °C and −10 °C. This synthesis proceeds via the intermediates monoazidoborane, BH2N3, and diazidoborane, BH(N3)2.[1]
A similar gas-phase synthesis uses the spontaneous reaction of
boron trichloride with hydrazoic acid.[3][4]
BCl3 + 3 HN3 → B(N3)3 + 3 HCl
Properties
The compound forms colorless crystals that are only stable at low temperatures. Above −35 °C, an explosive decomposition may occur.[1] In the gas phase, generated boron triazide decomposes at
room temperature within 60 minutes via loss of nitrogen gas to form boron nitrides with formulas BN3 and
BN. These reactions can also be initiated
photochemically by UV radiation in the compounds absorption range at about 230 nm.[3][4][5]
B(N3)3 → BN3 + 3 N2
B(N3)3 → BN + 4 N2
In contact with water, it undergoes hydrolysis to hydrazoic acid and
boron trioxide.[3]
The parent tetraazidoboric acid, H[B(N3)4, can be obtained at temperatures lower than −60 °C.[1]
Uses
Due to the low stability, the compound itself is not used as a high-energy substance. However, the tetraazidoborate derivatives and adducts with bases such as
quinoline,
pyrazine or
2,2,6,6-tetramethylpiperidine have potential for this usage.[7] The gas-phase decomposition of the compound is also of interest as a method of coating surfaces with boron nitride.[3]
Fraenk, W.;
Klapötke, T. M. (2002). "Recent Developments in the Chemistry of Covalent Main Group Azides.". In Meyer, G.; Naumann, D.; Wesemann, L. (eds.). Inorganic Chemistry Highlights. Wiley-VCH Verlag. pp. 259–265.
ISBN3-527-30265-4.