Neutral 5-nitrotetrazoles: easy initiation with low pollution

Abstract

5-Nitro-2H-tetrazole (1), 1-methyl-5-nitrotetrazole (2) and 2-methyl-5-nitrotetrazole (3) were synthesized starting from the corresponding 5-amino-substituted tetrazoles in good yields and purities. The compounds were fully characterized by analytical and spectroscopic methods and their solid state structures were determined by low temperature X-ray diffraction techniques. Due to the potential of tetrazoles as energetic materials an extensive computational study (CBS-4M) was performed in order to estimate the energies of formation (Δ_fU°) of the molecules, which are highly endothermic (1, 2527 kJ kg⁻¹; 2, 2253 kJ kg⁻¹ and 3, 2006 kJ kg⁻¹). The EXPLO5 software was used to calculated the corresponding detonation velocities (D_det) and detonation pressures (p_det) (1, D_det = 9457 m s⁻¹ and p_det = 390 kbar; 2, D_det = 8085 m s⁻¹ and p_det = 257 kbar and 3, D_det = 8109 m s⁻¹ and p_det = 262 kbar) by combining the Δ_fU° values of the materials with the (X-ray calculated) densities and molecular formulas, giving performances comparable to commonly used secondary explosives (e.g., RDX). Lastly, all three neutral compounds can be easily initiated by impact (<2 J) and with high detonation velocities and excellent combined oxygen and nitrogen contents offer a more powerful and environmentally friendly alternative to commonly used primary explosives in initiating devices.