Designing energetic materials that simultaneously exhibit high thermal stability, strong detonation performance, and chemical robustness remains a challenge in energetic materials chemistry. To that end, researchers from Nanjing University of Science and Technology and China Northern Industries Group Co., Ltd developed a direct hydrazine substitution strategy based on 3,5-diamino-4-nitropyrazole, providing an efficient route toward novel pyrazole-derived energetic frameworks with tunable structural and energetic properties. The study, published in Energetic Materials Frontiers , combines crystallographic analysis, electrostatic potential calculations, and energetic evaluation to establish a structure–property relationship linking molecular charge distribution, packing arrangement, and acid stability.
The team demonstrated that direct hydrazine functionalization can be used not only to construct fused heterocyclic energetic skeletons, but also to regulate molecular stability through positional isomerism and zwitterionic effects. "The direct hydrazine substitution reaction provides efficient access to pyrazole-based hydrazine derivatives," explains corresponding author Yong-xing Tang. "Meanwhile, zwitterionic structural characteristics significantly enhance acid stability while preserving energetic performance."
The researchers synthesized a fused-ring energetic framework identified as compound 3 , which exhibits exceptionally high thermal stability with a decomposition temperature of 305 °C. The compound also shows low impact and friction sensitivities, indicating strong intrinsic safety characteristics suitable for heat-resistant energetic applications.
"Further amination reactions produced two energetic derivatives, compounds 4 and 5 , which possess positional isomeric structures," shares Tang. "Structural analysis revealed that the location of the N–NH₂ group strongly influences intermolecular packing behavior." Notably, zwitterionic compound 4 adopts a wave-like packing arrangement, whereas compound 5 forms layered crystal stacks.
Further, although the two compounds exhibit comparable energetic performance, their chemical stability differs significantly under acidic conditions. "In nitric acid solution, zwitterionic compound 4 retains its original structure, while compound 5 undergoes decomposition through cleavage of the triazole ring," says Tang.
The researchers attributed this difference to electrostatic effects. In compound 4 , positive charge localization on the N–NH₂ group increases electropositivity of the triazole ring, effectively suppressing proton attack. By contrast, the neutral triazole ring in compound 5 is more vulnerable to proton-induced degradation.
"Energetic property evaluation further confirms the promise of these compounds," says Tang. "Due to incorporation of N-amino groups, compounds 4 and 5 exhibit high positive heats of formation exceeding those of conventional energetic materials such as TNT and RDX. Calculated detonation velocities reach 8550 m·s⁻¹ for compound 4 and 8621 m·s⁻¹ for compound 5 , demonstrating competitive energetic performance."
According to the researchers, the work not only expands the chemistry of direct hydrazine substitution reactions but also provides new insight into C–NH₂ functionalization strategies for advanced energetic materials.
"Our findings offer a promising pathway for designing next-generation energetic compounds that integrate thermal stability, detonation performance, and environmental robustness within a single molecular framework," Tang says.
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Contact the author: School of Chemistry and Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China ( zhiwei@njust.edu.cn ; zhiwei@njust.edu.cn ; yongxing@njust.edu.cn )
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Energetic Materials Frontiers
Constructing advanced pyrazole-based energetic materials via direct hydrazine substitution of a heterocyclic C–NH₂ bond
No potential conflict of interest was reported by the authors.