Study On Synthesis And Properties Of 3,4-dinitropyrazole

The search of new melt-cast explosive carriers has been a hotspot as the conventionalmelt-cast explosives with various disadvantages. As a substitution of TNT for melt-castexplosive carrier, 3,4-dinitropyrazole（DNP） with excellent performance has been reportedrecently. It have been synthesized, its properties have been investigated, and the metallic ionhave an affect on its sensitivity has been calculated. On the one hand, it can be as a guide forthe synthesis and theoretical investigation of DNP; on the other hand , it increases the subjectinvestigated of the melt-cast explosive carriers. In addition, it gives a theory evidence forreducing the explosive sensitivity in theory and experiment.N-Nitropyrazole has been synthesized from pyrazole with the nitration reaction in nitricacid and phosphorus pentoxide or acetic anhydride. In the system of the nitric acid and aceticanhydride, the optimum process conditions has been obtained by orthogonal test and when itis at 30℃for two hours and the proportion of pyrazole, nitro acid, acetic anhydride and aceticacid is 1g：0.92mL : 3.17mL : 2.5mL, the yield of N-nitropyrazole is the largest。3-Nitropyrazole has been obtained from N-nitropyrazole by thermal rearrangement withoil bath or microwave. The optimum process conditions in microwave has been obtained byorthogonal test, and the rearrangement reaction of 1g N-nitropyrazole in 90 mL anisole can getmost products at 140℃for two hours.3,4-Dinitropyrazole（DNP） has been synthesized from 3-nitropyrazole in fuming nitro andsulphuric acid. In system of the nitro and sulphuric acid the optimum process conditions ofobtaining DNP from 3-nitropyrazole has been obtained by orthogonal test, and when it is at100℃for one hour and the proportion of 3-nitropyrazole, nitro acid and sulphuric acid is 1g：1.4mL : 5.4mL, the yield of 3,4-dinitropyrazole is largest.The crystalstructure of DNP has been investigated. It shows DNP is of P2（1）/n pointgroup and its molecular is layer stacking. The properties of DNP are simply concluded,containing detonation performance, thermal behavior（TG） and solubility property. In additionthe sensitivity of DNP affected by metallic ion has been calculated with quantum chemistry theory. The explosive sensitivity with the formation of molecule-cation interaction between thenitro group of 3,4-dinitropyrazole （DNP） and H+, Li+, Na+, Be²⁺or Mg²⁺has been investigatedusing the B3LYP and MP2（full） methods with the 6-311++G** and 6-311++G（2df,2p） basissets. The bond dissociation energy of the C3–N7 trigger bond has also been discussed for theDNP monomer and the corresponding complex. The ionic bond character is obvious betweenthe oxygen atom of nitro group and H+in DNP…H+. The molecule-cation interaction andbond dissociation energy of the C3–N7 trigger bond follow the order of DNP…Be²⁺>DNP…Mg²⁺>DNP…Li⁺>DNP…Na⁺. Except for DNP…H+, the increment of the bond dissociationenergy of the trigger bond correlates well with the molecule-cation interaction energy, naturalcharge of the nitro group, electron densityρBCP（C3–N7）, delocalization energy E（2）and NBOcharge transfer. The analyses of atoms in molecules （AIM）, natural bond orbital （NBO） andelectron density shifts have shown that the conjugated system of nitro group is slightlydestroyed and the electron density of the nitro group shifts toward the C3–N7 trigger bondwith the formation of the molecule-cation interaction. Thus, the trigger bond is strengthenedand the sensitivity of DNP is reduced.