Taming of 4-azido-3,5-dinitropyrazole based energetic materials

Abstract

4-Azido-3,5-dinitropyrazole (AzDNP) and its derivatives are attractive candidates as high-performance energetic materials due to their excellent energetic properties and high nitrogen and oxygen contents. However, they are often more sensitive (primary explosives) and have poor thermal stability (T_d < 150 °C), attributed to the presence of the azido functionality. In this work, we have tried to fine-tune the properties of 4-azido-3,5-dinitropyrazole by connecting it to 5-nitramino-1,2,4-oxadiazole moieties via N-methylene-C bridges. Furthermore, a series of nitrogen-rich energetic salts (compounds 7–17) were prepared from neutral compound 6 by reacting with different nitrogen-rich bases. All compounds were thoroughly characterized using IR and multinuclear NMR spectroscopy, differential scanning calorimetry (DSC), elemental analysis, and HRMS studies. Compounds 4, 7, and 9 were further confirmed through single-crystal X-ray diffraction studies. The physicochemical and energetic properties of all energetic compounds were also investigated. A hydroxylammonium salt, 12 (D_v: 8961 m s⁻¹; P: 33.0 GPa), has been found to be the most energetic derivative of AzDNP to date. Compounds 6 (D_v: 8734 m s⁻¹; P: 33.9 GPa; IS < 2.5 J) and 12 (D_v: 8961 m s⁻¹; P: 33.0 GPa; IS < 2.5 J) show potential to be used as metal-free high-performance primary explosives. The most comprehensive properties are shown by ammonium salt 7 (D_v: 8591 m s⁻¹; P: 30.6 GPa, T_d: 173 °C; IS: 14 J). The structure–property relationship was studied using Hirshfeld surface and non covalent interaction (NCI) analyses.