Study On Synthesis Of Nitropyrazole And Its Derivatives

Nitrogen heterocyclic compounds are widely used in the construction of the basic skeleton of the molecular structure of energetic compounds due to containing carbon-nitrogen single bond,nitrogen-nitrogen single bond and carbon-nitrogen double bond with high bond energy.Therefore,the synthesis of nitropyrazole compounds has gradually become a research hotspot in the field of energetic materials.The nitropyrazole compounds have excellent characteristics of low sensitivity,high thermal stability,high formation enthalpy and high energy.Hence,the research on the synthesis of nitropyrazole and its derivatives is particularly important.In this study,based on the synthesis of the raw material pyrazole,through methylation reaction and substitution reaction,respectively prepared methylpyrazole,bis（1-pyrazolyl）methane and tri（1-pyrazolyl）methane;3,4-dinitropyrazole was synthesized from pyrazole by three steps of nitrogen nitrification,thermal rearrangement and carbon-nitrification;1-methyl-3,4,5-trinitropyrazole was synthesized by direct nitration of methylpyrazole in one step;using N-NP as a nitrating agent and intermolecular nitro transfer as a means,the green synthesis method of 1-methyl-4-nitropyrazole was studied,and the structural characterization and purity analysis of the product were carried out.Single factor experiment method and orthogonal experiment method were used to optimize the synthesis process route of the target products.（1）By optimizing the feeding order of pyrazole synthesis process（glycerin→hydrazine hydrate→sulfuric acid）,the glycerin and hydrazine hydrate were mixed thoroughly before adding sulfuric acid,which improved the utilization rate of raw material hydrazine hydrate,and the new process pyrazole yield increased by 5%.（2）The new synthesis process of 3,4-dinitropyrazole（113 g 3-nitropyrazole,250 mL of H₂SO₄,180 mL of HNO₃,reaction temperature of 70℃,reaction time of 20 min）adopted liquid feeding method,and the exothermic heat of the reaction was controlled by the flow rate of nitric acid,which solved the problem of flying temperature of solid feed in the old process.The reaction time was reduced by 50%,the reaction temperature was reduced by 30℃.The new process improved the safety of the production process and reduced energy consumption.（3）The new synthesis process of 1-methyl-3,4,5-trinitropyrazole（volume ratio of H₂SO₄,HNO₃ and N-methylpyrazole was 36:12:1,reaction temperature of 80℃,reaction time of 6.5h）was catalyzed by the recoverable mesoporous（SO₄）^2-/ZrO₂-CeO₂ super acid catalyst,which reduced the reaction temperature by 50℃.（4）Under mild reaction conditions(concentrated sulfuric acid 8 mL,material ratio n_{（1-methylpyrazole）}:n_（N-NP）=1:2,reaction temperature of 60℃,reaction time of 6 h),using1-methylpyrazole as the nitro acceptor and N-NP as the nitrating agent,the intermolecular transfer of nitro group from N-NP to 1-methylpyrazole was realized.The nitro donor of this process was N-NP,not was nitric acid.And this was a new green nitrification process.The five-second delay burst temperatures of DNP and MTNP were measured to be548.55 K and 548.05 K,respectively;the thermal performance of DNP and MTNP were analyzed using a differential scanning calorimeter.It was proved that DNP and MTNP had good thermal stability,good safety and practicality.The theoretical calculations showed that the detonation velocities of DNP and MTNP were 8777.75 m·s^-1 and 8348.85 m·s^-1respectively;and the burst pressures were 35.40 GPa and 30.69 GPa,respectively.The research results proved that the application value and competitive potential of DNP and MTNP.