Promising Thermally Stable Energetic Materials with the Combination of Pyrazole–1,3,4-Oxadiazole and Pyrazole–1,2,4-Triazole Backbones: Facile Synthesis and Energetic Performance

Abstract

Thermally stable energetic materials have broad applications in the deep mining, oil and natural exploration, and aerospace industries. The quest for thermally stable (heat-resistant) energetic materials with high energy output and low sensitivity has fascinated many researchers worldwide. In this study, two different series of thermally stable energetic materials and salts based on pyrazole-oxadiazole and pyrazole-triazole (<b>3-23</b>) with different explosophoric groups have been synthesized in a simple and straightforward manner. All the newly synthesized compounds were fully characterized by IR, ESI-MS, multinuclear NMR spectroscopy, elemental analysis, and thermogravimetric analysis-differential scanning calorimetry measurements. The structures of <b>3</b>, <b>7</b>, and <b>22</b> were supported by single-crystal X-ray diffraction studies. The density, heat of formation, and energetic properties (detonation velocity and detonation pressure) of all the compounds range between 1.75 and 1.94 g cm^-3, 0.73 to 2.44 kJ g^-1, 7689 to 9139 m s^-1, and 23.3 to 31.5 GPa, respectively. All the compounds are insensitive to impact (>30 J) and friction (>360 N). In addition, compounds <b>4</b>, <b>6</b>, <b>10</b>, <b>14</b>, <b>17</b>, <b>21</b>, <b>22</b>, and <b>23</b> show high onset decomposition temperature (<i>T</i>_d between 238 and 397 °C) than the benchmark energetic materials RDX (<i>T</i>_d = 210 °C), HMX (279 °C), and thermally stable HNS (318 °C). It is noteworthy that the pyrazole-oxadiazole and pyrazole-triazole backbones greatly influence their physicochemical and energetic properties. Overall, this study offers a perspective on insensitive and thermally stable nitrogen-rich materials and explores the relationship between the structure and performance.