Intramolecular Cyclization and Energetic Group Modifications for Thermally Stable and Low-Sensitivity Monocyclic Dinitromethyl Zwitterionic Pyrazoles

Zwitterionic energetic materials offer a unique combination of high performance and stability, yet their synthesis and stability enhancement remain key challenges. In this study, we report the synthesis of a highly stable (dinitromethyl-functionalized zwitterionic compound, 1-(amino(iminio)methyl)-4,5-dihydro-1H-pyrazol-5-yl)dinitromethanide (4), with a thermal decomposition temperature of 215 °C, surpassing that of most previously reported energetic monocyclic zwitterions (T_d < 150 °C). This compound was synthesized via intramolecular cyclization of a trinitromethyl-functionalized hydrazone precursor. Further chemical modifications, including nitration and fluorination, enabled zwitterion-to-zwitterion transformations, resulting in the formation of nitramines 10 and 12. Additionally, the perchlorate salt (8) of 4 was synthesized, along with ammonium (13), guanidinium (14), and potassium (15) salts derived from 10, all retaining zwitterionic properties. Physicochemical evaluations reveal that zwitterion 12 exhibits excellent thermal stability (T_d = 181 °C) and an optimal balance between high energy output (detonation velocity: 8329 m s^–1, detonation pressure: 29.4 GPa) and reduced sensitivity (impact sensitivity: 35 J, friction sensitivity: 320 N). Notably, potassium salt 15 demonstrates superior thermal stability (T_d = 233 °C), exceeding that of RDX. These results expand the design framework for energetic zwitterions and contribute to the development of high-energy, low-sensitivity energetic materials.