1,3,4-Oxadiazole-Bridged 3,5-Dinitropyrazoles: Powerful Alliance toward High Performance and High Thermal Stability.

Abstract

The ever-increasing demand for heat-resistant energetic materials in deep mining and space exploration has led to significant interest in developing new materials with exceptional thermal stability and detonation performance. In this work, a novel heat-resistant energetic compound, 2,5-bis(3,5-dinitro-1H-pyrazol-4-yl)-1,3,4-oxadiazole (3), was achieved through a simple and straightforward method where two 3,5-dinitropyrazole moieties are linked through a 1,3,4-oxadiazole ring. Compound 3, a symmetrical conjugated molecule, demonstrates superior thermal stability (T_dec = 325 °C), good energetic performance (D_v = 8464 m s^-1), and improved physical stability (IS = 7.5 J) compared to the industrially used heat-resistant explosive, HNS. The properties of 3 were further optimized by forming energetic salts, 4 and 5. An attempted reaction to synthesize zwitterionic compound 7, having 3,5-dinitropyrazole and 3,5-diamino-1,2,4-triazole ring connected via a C-C bond, resulted in another zwitterionic compound 6. Energetic salts 4 (T_dec = 291 °C) and 5 (T_dec = 275 °C), as well as zwitterionic compound 6 (T_dec = 286 °C), demonstrated excellent decomposition temperatures with good physical stability. The dihydroxylammonium salt (5) (D_v = 8507 m s^-1, P = 31.25 GPa) exhibited the best energetic properties, approaching the performance of RDX. The remarkable overall performance of compounds 3-5 makes them suitable candidates for high-performance, heat-resistant explosives.