Synthesis of Energetic 7-Nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one Based on a Novel Hofmann-Type Rearrangement.

Rearrangement reactions are efficient strategies in organic synthesis and contribute enormously to the development of energetic materials. Here, we report on the preparation of a fused energetic structure of 7-nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one (NPTO) based on a novel Hofmann-type rearrangement. The 1,2,3-triazine unit was introduced into the fused bicyclic skeleton from a pyrazole unit for the first time. The new compound of NPTO was fully characterized using multinuclear NMR and IR spectroscopy, elemental analysis as well as X-ray diffraction studies. The thermal behaviors and detonation properties of NPTO were investigated through a differential scanning calorimetry (DSC-TG) approach and EXPLO5 program-based calculations, respectively. The calculation results showed similar detonation performances between NPTO and the energetic materials of DNPP and ANPP, indicating that NPTO has a good application perspective in insensitive explosives and propellants.

A Family of Energetic Materials Based on 1,2,4-Oxadiazole and 1,2,5-Oxadiazole Backbones With Low Insensitivity and Good Detonation Performance.

Design and synthesis of new compounds with both high detonation performances and good safety properties have always been a formidable task in the field of energetic materials. By introducing -ONO2 and -NHNO2 moieties into 1,2,4-oxadiazole- and 1,2,5-oxadiazole-based backbones, a new family of energetic materials, including ammonium 3-nitramino-4-(5-hydroxymethyl-1,2,4-oxadiazol-3-yl)-furazan (4), 3,3'-bis[5-nitroxymethyl-1,2,4-oxadiazol-3-yl]-4,4'-azofuroxan (6), [3-(4-nitroamino-1,2,5-oxadiazol-3-yl)-1,2,4-oxadiazol-5-yl]-methylene nitrate (8), and its energetic ionic salts (10-12), were synthesized and fully characterized. The energetic and physical properties of the materials were investigated through theoretical calculations and experimental determination. The results show that the oxadiazole-based compounds exhibit high enthalpy of formations, good detonation performances, and extraordinary insensitivities. In particular, the hydrazinium salt (11) shows the best energetic properties (11: d = 1.821 g cm-3; P = 35.1 GPa, v D = 8,822 m s-1, IS = 40 J, FS > 360N). The ESP and Hirshfeld surface analysis indicated that a large number of hydrogen bonds as well as π-π stacking interactions within molecules might be the key reason for their low sensitivities and high energy-density levels.