Synthesis And Reactivity Of Nitroazoles Energetic Compounds

Poly-nitrogen compounds have been developed rapidly in recent years as a new kind of energetic materials, especially nitroazoles. Because of novel properties, such as high nitrogen content, high density, high oxygen balance, positive heat of formation, better detonation property and environment-friendly, nitroazoles have been extensively used in high-energy insensitive explosives, low characteristic signal propellants and gas generators.Synthesis and modification of nitroazoles by introducting energetic groups to the C- and N-sites of azole rings to get better performances become a hot spot in energetic materials field.In this work, firstly, we developed a new synthesis method of nitroazoles; then, studied the reactivity of nitroazoles through C- and N-functionalization, obtaining a series of new nirtroazoles derivatives. Their structures and physicochemical properties have been investigated by combination of experimental and theoretical methods.We present an operationally simple, inherently safe, environmentally benign, and chemoselective conversion of a wide range of amineazoles to the corresponding nitroazoles using potassium peroxymonosulfate（Oxone） as the oxidant in water. The usefulness of the present method was demonstrated by the synthesis of two important energetic compounds,3,4,5-trinitro-1H-pyrazole and 5-amino-3-nitro-1H-1,2,4-triazole.N-dinitromethyl-5-nitrotetrazole, N-dinitromethyl-3-nitro-1,2,4-triazole,N-dinitromethyl-3-nitropyrazole, 2,2-Dinitro-2-（5-nitrotetrazol-2）ethanol and their nitrogen-rich salts were synthesized by introducting dinitromethyl to 5-nitrotetrazole,3-nitro-1,2,4-triazole and 3-nitropyrazole. With the help of N-dinitromethyl group, the densities and oxygen balance of nitroazoles got improved highly. The densities of most compounds are higher than 1.80 g cm^-3. In particular, N-dinitromethyl-5-nitrotetrazole has the highest measured density of 1.97 g cm^-3 to date of tetrazole-based CHNO energetic materials. With high OB, the specific impulses of some compounds are superior to those of AP and ADN. The calculated detonation pressures and velocities fall in the range of 24.8GPa-38.5 GPa and 7.98-9.23 km s^-1. Compounds 5 and 6 exhibit excellent detonation properties(38.5 GPa, 9.22 km s^-1; 37.0 GPa, 9.05 km s^-1), which are comparable to the high explosive HMX. The DSC results showed that the salts had better thermal stabilities than their neutral molecules, indicating the formation of salts could improve thermal stabilities.The results were proved by the data BDE and mulliken atomic charges and wiberg bond orders.3-Nitro-1,2,4-triazole and 3,5-dinitro-1H-pyrazole were C-aminated and N-aminated using different amination agents, yielding their respective C-amino and N-amino products.Based on the data and crystal structures in this work and available in the literature, the regularity of N-amino and C-amino group affecting energetic properties has been developed as follows:（i） the incorporation of an N-amino group into nitroazole ring can improve nitrogen content, heat of formation, and impact sensitivity. At the same time, it can also decrease density, oxygen balance, detonation velocity and pressure;（ii） the incorporation of a C-amino can increase density, nitrogen content, detonation velocity and pressure, while concomitantly decreasing heat of formation. Therefore, the introduction of the C-amino into nitroazole ring could contribute to the design of new high performance（high density and high detonation property） compounds. However, the addition of the N-amino into nitroazole ring is advantageous to the design of energetic compounds containing high heat of formation. The regularity is highly useful for the design and synthesis of novel high-energy-density materials（HEDM）.Tetrazolo[1,5-b][1,2,4]triazine and its C=O, C-CH₃ and N-NO₂ functionalized derivatives were synthesized. These compounds exhibit higher nitrogen contents, formation of heat and detonation performance than TNT. The calculated detonation pressures and velocities fall in the range of 13.8 GPa-34.1 GPa and 6.62-8.90 km s^-1. These ompounds show moderate to good thermal stabilities（178℃-205 ℃）. Careful characterization indicated that these compounds containing N₅ chains exhibited relatively high thermal stabilities. The study of the thermal decomposition mechanism indicates that the tetrazole rings opening of the fused aza-cyclic compounds, followed by N₂ elimination is predicted to be the primary decomposition channel, whether or not they are conjugated systems, and whether or not they have substituent groups. The results could lay the groundwork for the development of new fused heterocycles.