1,2,4‐Oxadiazole‐Bridged Polynitropyrazole Energetic Materials with Enhanced Thermal Stability and Low Sensitivity

A family of mono or di(1,2,4‐oxadiazole)‐bridged polynitropyrazole derivatives with C‐nitro/N‐nitro functionalities is reported. All compounds were fully characterized by IR, NMR (¹H, ¹³C), elemental analysis and differential scanning calorimetry (DSC). The solid‐state structure features were further investigated with X‐ray diffraction. Of these, compounds 3,5‐bis(3,4‐dinitro‐1H‐pyrazol‐5‐yl)‐1,2,4‐oxadiazole (3 a) and 5,5′‐bis(3,4‐dinitro‐1H‐pyrazol‐5‐yl)‐3,3′‐bi(1,2,4‐oxadiazole) (3 b) possess high thermal stability (3 a: T_dec=274 °C; 3 b: T_dec=272 °C), sensitivity (IS >30 J, FS >360 N) and comparable detonation properties (3 a: D_v=8741 m s⁻¹, P=34.0 GPa; 3 b: D_v=8685 m s⁻¹, P=33.4 Gpa) to RDX. In addition, 3,5‐bis(4‐nitro‐1H‐pyrazol‐3‐yl)‐1,2,4‐oxadiazole (4 a) and 5,5′‐bis(4‐nitro‐1H‐pyrazol‐3‐yl)‐3,3′‐bi(1,2,4‐oxadiazole) (4 b) have high decomposition temperature (4 a: T_dec=314 °C; 4 b: T_dec=317 °C), low sensitivity (IS >40 J; FS>360 N) and superior detonation performances (4 a: D_v=8027 m s⁻¹, P=26.4 GPa; 4 b: D_v=7991 m s⁻¹, P=25.2 Gpa) than conventional heat‐resistant explosive hexanitrostilbene (HNS: T_dec=318 °C; IS=5 J; FS=240 N; D_v=7612 m s⁻¹, P=24.3 GPa), thus suggesting their potential application as heat‐resistant explosives.