Sensitivity and performance of azole-based energetic materials.
Imidazole, pyrazole, 1,2,3-triazole-, 1,2,4-triazole-, and tetrazole-based energetic materials are theoretically investigated by employing density functional theory (DFT). Heats of formation (ΔfH(0)'s) for the studied compounds (298 K) in the gas phase are determined at the B3P86/6-311G (d, p) theory level through isodesmic reactions. The bond dissociation energies (BDEs) corresponding to NO2, NH2, CH3, and Cl removal from carbon or nitrogen positions of the azole ring are also calculated at the B3P86/6-311G (d, p) theory level. The substituent effect of electron-withdrawing (NO2, Cl) and electron-donating (NH2, CH3) groups on the ΔfH(0)s and BDEs is discussed. Both electron-withdrawing groups and electron-donating groups (except the CH3 group) dramatically increase the ΔfH(0)s of these energetic materials when the substituent is at an N position on the azole ring. For substitution at a C atom on the azole ring, electron-withdrawing and electron-donating groups have different effects on the ΔfH(0)s for different azole compounds. A correlation is developed for this series of energetics between impact sensitivity h50% and the defined sensitivity index (SI): based on this empirical relationship and its extrapolation, the impact sensitivities of compounds for which experiments are not available are provided. The promising energetic compounds in each groups, which have potentially good energetic performance and low sensitivity, are 1-amino-2,4,5-trinitroimidazole, 1-amino-3,4,5-trinitropyrazole, 1,4-dinitro-1,2,3-triazole, 1,3-dinitro-1,2,4-triazole, and 1-nitrotetrazole.