Design, Synthesis And Detonation Performance Of New Nitropyrazole Energetic Compounds

Synthesis of energetic materials with high-energy, moderate sensitivity, and high thermal stability is always the research hotspot in the energetic materials field. It is the most promising methods for studying high energy density materials to design and synthesize new high energy density materials based on the ideas of molecular design and predict their related performance using effective technology and methods. The synthesis researches of nitrogen heterocyclic compounds, especially high nitrogen heterocyclic compound, have been attracted wide attention of worldwide scholars. The pyrazole compounds have high enthalpy and high crystal density, and easy to nitration of pyrazole ring electrophilic substitution reaction. The nitropyrazole compounds have potential application value because of its good explosion performance, stable performance, and good compatibility with most energetic materials.In this study, three synthesis reactions of the nitropyrazole compounds were designed using 4-chloropyrazole and 1-methylpyrazole as raw material. First, the structures of three kinds of monomers(4-FP, NO3-, and HX, X=F, Cl, CN), binary complexes, and ternary complexes were optimized by using the B3 LYP methods with the 6-311++G(2d,p) basis set. The cooperativity effects between the C???O interactions and O???HX or F???HX hydrogen bond interactions in 4-FP???NO3-???HX ternary complexe were investigated. The results show that the cooperativity effect appears in the 4-FP???NO3-???HX ternary complex and the HX molecules promotes the combination of the NO3- and 4-FP molecules. The cooperativity effects were confirmed further by atoms in molecule theory(AIM) analysis and natural bond orbital(NBO) analysis. Then, the structures of compounds in different reaction routes were also optimized by using the B3 LYP methods with the 6-311++G(2d,p) and cep-31 g basis set. The implementing possibility of three designed reaction was confirmed and reaction site was predict by calculating the surface electrostatic potential of each compound molecules. The nucleophilic substitution reaction could be carried out on C4 atom of 4-chloro-3,5-dinitropyrazole(4-CDNP) and C5 atom of 1-methyl-3,4-dinitro-5-iodopyrazole(MDNIP). Finally, three nitropyrazole compounds, 1-methyl-3,5-dinitro-4-nitroxypyrazole(4-MDNNP), 1-methyl-3,4-dinitro-5-nitroxypyrazole(5-MDNNP) and 1-methyl-3,4,5-trinitropyrazole(MTNP), were prepared according to the designed synthetic routes and the structure and performances were characterized by FTIR and 1H NMR methods. The influences of various factors on the product yield were also studied.The first new energetic compound, 1-methyl-3,5-dinitro-4-nitroxypyrazole, was synthesized via nitration, nucleophilic substitution reaction and methylation reaction using 4-chloropyrazole as raw material. The better reaction conditions of nucleophilic substitution reaction between nitrate and 4-CDNP are that n(Ag NO3):n(4-CDNP) is 2.5:1, the reaction temperature is 10℃, and the reaction time is 3 h. The yield of DNNP is 97.6% under this reaction condition. The better conditions of methylation reaction are that the reaction time is 10 h, the reaction temperature is 40℃, and the dosage of methyl iodide is twice of DNNP. The yield of 4-MDNNP is 55.2%, and the whole yield is 39.8%. At the same time, the detonation properties and impact sensitivity of4-MDNNP were calculated and researched. The melting range of 4-MDNNP is 93.6-95.2℃. For 4-MDNNP, the detonation temperature is 4124.8 K, detonation capacity is 768.70 L·kg-1, detonation heat is 6220.1 k J·kg-1, detonation velocity is 8.46 km·s-1, detonation pressure is 31.6 GPa, explosion percentage is 73%, and the characteristic height h50 is 23.0 cm, respectively. The detonation properties of 4-MDNNP are better than those of TNT and comparable with those of RDX, HMX and TNAZ. The impact sensitivity is higher than PETN and near to RDX. The TG-DSC-MS test results show that the decomposition temperature of 4-MDNNP is 200.4℃, and the gas phase decomposition products mainly include the N2, CO, H2 O and CO2.The other synthetic energetic compounds, 1-methyl-3,4-dinitro-5-nitroxypyrazole and 1-methyl-3,4,5-trinitropyrazole, were synthesized via iodination, nitration and nucleophilic substitution(nitrate or nitrite as nucleophilic substitution agent) using 1-methylpyrazole as raw material. When Ag NO3 was used as nucleophilic reagent, the better reaction conditions are that n(Ag NO3):n(MDNIP) is 2:1, the reaction temperature is 40℃, and the reaction time is 10 h. The yield of 5-MDNNP is 33.6% under this reaction condition and the whole yield is 28.7%. When Ag NO2 was used as nucleophilic reagent, the better reaction conditions are that n(Ag NO2):n(MDNIP) is 2:1, the reaction temperature is 40℃, and the reaction time is 10 h. The yield of 5-MDNNP is 30.2% under this reaction condition and the whole yield is 25.8%. At the same time, the detonation properties and impact sensitivity of 5-MDNNP and MTNP were calculated and researched. The melting range of 5-MDNNP and MTNP is 84.5-86.1 ℃ and 90.8-92.4 ℃, respectively. For 5-MDNNP, the detonation temperature is 4124.8 K, detonation capacity is 768.70 L·kg-1, detonation heat is 6220.1 k J·kg-1, detonation velocity is 8.46 km·s-1, detonation pressure is 31.6 GPa, and explosion percentage is 74%, respectively. For MTNP, the detonation temperature is 4024.6 K, detonation capacity is 825.35 L·kg-1, detonation heat is 6352.5 k J·kg-1, detonation velocity is 8.09 km·s-1, detonation pressure is 30.7 GPa, and explosion percentage is 75%, respectively. The detonation properties of 5-MDNNP and MTNP are better than those of TNT and comparable with those of RDX, HMX and TNAZ. The impact sensitivity is higher than PETN and near to RDX.