Guijuan Fan

5,6-Di(2-fluoro-2,2-dinitroethoxy)furazano[3,4- b ]pyrazine: a high performance melt-cast energetic material and its polycrystalline properties

5,6-Di(2-fluoro-2,2-dinitroethoxy)furazano[3,4-b]pyrazine was synthesized in a three-step process starting from 3,4-diaminofurazan (DAF) including a significant nucleophilic substitution reaction under the catalytic effect of trisodium phosphate dodecahydrate. Characterization of this molecule indicates that it possesses a higher crystal density than that of 2,4,6-trinitrotoluene (TNT) at ambient temperature with acceptable melting-point and energetic properties approaching those of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) but with a higher thermal stability and lower sensitivity towards impact and friction. To investigate its polycrystalline properties, differential scanning calorimetry (DSC), powder-X-ray-diffraction (PXRD) and ab initio calculation using the Viena Ab initio simulation package (VASP) were employed.

Formation of trinitromethyl functionalized 1,2,4-triazole-based energetic ionic salts and a zwitterionic salt directed by an intermolecular and intramolecular metathesis strategy

Ionic salts of 5,5′-bis(trinitromethyl)-3,3′-bi-1H-1,2,4-triazole and an unexpected energetic zwitterion 5-diazonium-3-trinitromethyl-1,2,4-triazolate were synthesized via an intermolecular and intramolecular metathesis strategy. Compared with its ammonium (6), hydrazinium (7) and hydroxylammonium (8) salts, 5,5′-bis(trinitromethyl)-3,3′-bi-1H-1,2,4-triazole (5) exhibits lower sensitivities (IS: 22.5 J and FS: 252 N). It is worth noting that energetic salt 8 exhibits a high density of 1.97 g cm−3 and an excellent calculated detonation velocity of 9468 m s−1, and that the energetic zwitterion 5-diazonium-3-trinitromethyl-1,2,4-triazolate (14) exhibits a high density of 1.893 g cm−3 and an excellent calculated detonation velocity of 9317 m s−1, which are both superior to that of HMX (9254 m s−1).

Synthesis, and single crystal structure of fully-substituted polynitrobenzene derivatives for high-energy materials

New energetic fully-substituted polynitrobenzene derivatives were synthesized via the reaction of 1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) with 1,2,4-triazole followed by the nucleophilic substitution of the halo groups by aqueous ammonia or sodium azide. These compounds were charactered by 1H NMR, 13C NMR and HRMS. Additionally, the structures of amino derivatives 6, 8 and azido derivative 7 were further confirmed by single crystal X-ray diffraction analysis. Their decomposition temperatures and impact sensitivities were also determined. The derivative 1,2-di-1H-triazol-4,6-diamino-3,5-dinitrobenzene (8) exhibits good thermal stability (Td = 314 °C) and low impact sensitivity (IS = 30 J), which are both superior to that of TNT (Td = 295 °C, IS = 15 J). These synthesized compounds showed high heat of formation ranging from 31.77 to 1014.68 kJ mol−1, and reasonable detonation velocities and pressures.

Towards understanding the stability of the N5+-containing salts: the role of counterions

The thermal stabilities of the N5+M− species (M = Sb(OH)6, Sb(OH)4F2, AlF6, AlF4, BF4, B(CF3)4, PF6, AsF6 and SbF6) have been studied by means of density functional theory. The present calculations indicate that their thermal stabilities (represented by activation enthalpy, ΔH≠ in kcal mol−1) decrease in the order N5+ (47.2) > N5B(CF3)4 (34.1) ≈ N5SbF6 (31.6) ≈ N5AsF6 (31.5) > N5PF6 (30.5) > N5AlF4 (27.1) ≈ N5BF4 (27.1) > N5AlF6 (8.5). Only N5SbF6 has a small positive reaction enthalpy, ΔrH. The thermal stability of the N5+ salt depends on the amount of electron transfer from the counterion to N5+ in the reaction. The high electronegativite atoms or groups in the counterion are essential. Another crucial factor is bond strength between the central ion and the ligand. Studies of the N5Sb(OH)4F2 isomers indicate that the OH rather than the fluorine ions in the axial coordination positions could stabilize the decomposition transition structure through partial dissociation of the Sb–OH bond, which is used to explain the reason why there is an obvious difference in the decomposition activation enthalpies of the three isomers.