Isomers of Dinitropyrazoles: Synthesis, Comparison and Tuning of their Physicochemical Properties

Three isomeric dinitropyrazoles (DNPs) were synthesized starting from readily available 1H-pyrazole by slightly improved methods than described in the literature. 3,4-Dinitropyrazole (3), 1,3-dinitropyrazole (4), and 3,5-dinitropyrazole (5) were obtained and compared to each other with respect to thermal stability, crystallography, sensitivity and energetic performance. Two isomers (3 and 4) show high densities (1.79 and 1.76 g cm^-3 ) and interesting thermal behavior as melt-castable materials (3: T_melt. =71 °C, T_dec. =285 °C; 5: T_melt. = 68 °C, T_dec. =171 °C). Furthermore, eight salts (sodium, potassium, ammonium, hydrazinium, hydroxylammonium, guanidinium, aminoguanidinium and 3,6,7-triamino-[1,2,4]triazolo[4,3-b][1,2,4]triazole (TATOT) of 3 and 5 were synthesized in order to tune performance and sensitivity values. These compounds were characterized using ¹ H, ¹³ C, ¹⁴ N, ¹⁵ N NMR and IR spectroscopy as well as mass spectrometry, elemental analysis and thermal analysis through differential scanning calorimetry. Crystal structures of 14 compounds were obtained (3-7, 10-12 and 15-20) by low-temperature single crystal X-ray diffraction. Impact, friction and electrostatic discharge (ESD) values were also determined by standard methods. The sensitivity values range between 8.5 and 40 J for impact and 240 N and 360 N for friction and show mainly insensitive character. The energetic performances were determined using recalculated X-ray densities, heats of formation and the EXPLO5 code and support the energetic character of the title compounds. The calculated energetic performances (V_D : 6245-8610 m s^-1 ; p_CJ : 14.1-30.8 GPa) were compared to RDX ((O₂ NNCH₂ )₃ ).