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

Abstract

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: Tmelt.=71 °C, Tdec.=285 °C; 5: Tmelt. = 68 °C, Tdec.=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 1H, 13C, 14N, 15N 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 (VD: 6245–8610 m s−1; pCJ: 14.1–30.8 GPa) were compared to RDX ((O2NNCH2)3).

Combining Performance with Thermal Stability: Synthesis and Characterization of 5‐(3,5‐Dinitro‐1H‐pyrazol‐4‐yl)‐1H‐tetrazole and its Energetic Derivatives

“…The signals are all in the range for C-substituted tetrazoles and 3,5-dinitropyrazoles. [26,28,39,40] For the neutral compound 3 C4 can be observed at δ = 153.6 ppm, C1/C3 at δ = The signal for the carbon atom in the cation can be found at δ = 153.1 for 5 which is a usual shift for tetrazolium cations. [41] The guanidinium and aminoguanidinium derivatives show a resonance at δ = 157.9 and 158.8 ppm, respectively.…”

“…The assignments were based on comparison with theoretical calculations using Gaussian 09 [42] and literature values with similar 3,5-dinitropyrazoles and electron poor 5-substituted tetrazoles. [18,40,43] The spectrum shows two sharp signals at δ = -9.5 and -25.4 ppm. Additionally, two broad signals at δ = -93.8 and -98.0 ppm are observed.…”

Recent Advances in Synthesis and Properties of Nitrated-Pyrazoles Based Energetic Compounds

“…These compounds showed extraordinary insensitivity to impact (>60 J), as the detonation properties of 40i and 41k were comparable to those of TATB ( Energetic salts often possess superior properties comparing with non-ionic species since they always show lower vapor pressures, lower impact and friction sensitivities, and enhanced thermal stabilities [19]. In addition to the derivatives mentioned above, Klapötke group [26] developed the ionic salts of 3,4-DNP and 3,5-DNP shown in Figure 15, and these salts were extremely insensitive in Table 7. Comparing with 3,4-DNP, 36 and 38 owned much lower decomposition temperatures, similar to that of 37, 39 and 3,5-DNP.…”

“…Therefore, the exploration and development of high energy density compounds with low sensitivity have been a priority. A significant amount of effort has been made to resolve this problem, such as recrystallization of Ems [20], preparing polymer bonded explosives (PBXs) [21,22], forming energetic cocrystals [23][24][25], and synthesizing novel energetic compounds [26][27][28][29]. In contrast with other technologies, synthesizing new HEDMs may be the most direct and effective method.…”

Synthesis and Characterization of Salts of the 3,6‐Dinitro‐[1,2,4]triazolo[4,3‐b][1,2,4]triazolate Anion: Insensitive Energetic Materials Available From Economical Precursors

“…3,6,7‐Triamino‐[1,2,4]triazolo[4,3‐b][1,2,4]triazole (TATOT) has been shown to be a very promising energetic cation in the design of new energetic materials , , . This moiety has the advantage that it is prepared in an easily‐scaled two‐step two‐pot procedure; first inexpensive guanidinium chloride is reacted with hydrazine hydrate giving triaminoguanidinium chloride .…”