Study On The Craft Of Continuous Preparation Of 3,4-Dinitropyrazole

In the synthesis process of 3,4-dinitropyrazole(DNP),there are problems such as high toxicity of thermal rearrangement reagent,high cost,cumbersome process,and large online quantity.In order to solve these problems,solid pyrazole was used as a raw material,the solvent1,2-dichloroethane is used as thermal rearrangement medium and a good solvent for solid raw materials to form a liquid-liquid system.Therefore,it can be combined with microfluidic technology to realize the safe,efficient and continuous preparation of DNP.First,using pyrazole as the raw material and nitric acid-acetic anhydride as the nitrating agent,N-nitropyrazole was synthesized in a microreactor,and 1,2-dichloroethane was used as the extractant to extract the product from the nitration solution.By optimizing the reaction temperature,residence time and other factors,it is determined that the optimal reaction conditions are 45°C,the material stays in the channel for 307.69 s,the nitrating agent is nitric acid and acetic anhydride with a volume ratio of 1:5.5,and the target product yield is 94.91 %.The 1,2-dichloroethane solution of N-nitropyrazole was directly added to the autoclave for thermal rearrangement reaction.By optimizing the reaction temperature,reaction time and other factors,it was determined that the optimal reaction conditions were 180℃,the reaction time was 4.5h,and the yield of the target product was 95.0%.The reaction kinetics was studied,and it was confirmed that it accorded with the first-order reaction kinetics.Finally,3-nitropyrazole dissolved in 1,2-dichloroethane and concentrated sulfuric acid is used as raw material,and nitric acid-concentrated sulfuric acid is used as the nitrating agent to prepare 3,4-dinitropyrazole in a microreactor.By optimizing the reaction temperature,residence time and other factors,it is determined that the optimal reaction condition is 75℃,the material stays in the channel for 104.65 s,the molar ratio of 3-nitropyrazole to nitrating agent is 1:2,the target product yield was 92.12%,and a process scale-up plan for the continuous preparation of DNP was formulated.N-nitropyrazole,3-nitropyrazole and 3,4-dinitropyrazole were characterized and analyzed by various analytical methods such as melting point instrument,infrared spectrometer,nuclear magnetic resonance spectrometer and high performance liquid chromatography.The results show that the quality of the target product is good,and the process has the advantages of no need to separate intermediate products,cheap and easy to obtain reagents,small online quantity,high safety,etc.It is expected to realize the continuous scale-up production of DNP.