Synthesis and properties of 5-nitrotetrazole derivatives as new energetic materials

Abstract

An improved procedure for the synthesis of ammonium 5-nitrotetrazolate (3) is given here, which allows the preparation of the material on a large scale. 3 was selectively alkylated with bromoacetonitrile yielding 5-nitrotetrazol-2-ylacetonitrile (4). The 1,3-dipolar cycloaddition of azide ion to 4 rendered 5-(5-nitrotetrazol-2-ylmethyl)tetrazole monohydrate (5a) after recrystallization from water, which was used to synthesize energetic salts with ammonium (6a), guanidinium (7) and aminoguanidinium (8) cations. The water of crystallization in the hydrated species 5a and 6a was conveniently removed under vacuum forming the anhydrous materials 5b and 6b. All compounds were characterized by analytical (elemental analysis and mass spectrometry) and spectroscopic methods (IR, Raman and NMR spectroscopy), and the crystal structures of 4 (orthorhombic, P2₁2₁2₁, ρ = 1.747 g cm⁻³), 5a (monoclinic, P2₁, ρ = 1.796 g cm⁻³), 6a (triclinic, P, ρ = 1.594 g cm⁻³) and 8 (monoclinic, P2₁/n, ρ = 1.633 g cm⁻³) were determined by low temperature X-ray crystallography. Due to the interest in tetrazole derivatives as energetic materials, the sensitivities and energetic properties of all compounds were determined. The high detonation pressures (P) and velocities (D) of the materials (4: 29.5 GPa, 8356 m s⁻¹, 5a: 28.7 GPa, 8341 m s⁻¹, 5b: 30.2 GPa, 8688 m s⁻¹, 6a: 21.3 GPa, 7658 m s⁻¹, 6b: 22.8 GPa, 7861 m s⁻¹, 7: 24.3 GPa, 8066 m s⁻¹ and 8: 25.0 GPa, 8202 m s⁻¹) make them interesting candidates to find application as environmentally friendly nitrogen-rich energetic materials.