Study On The Technology Of Microchannel Continuous Flow Synthesis Of 3,5-Dinitrobenzoic Acid

Nitration is one of the most widely used organic reactions in chemical production operations.Because of its intense heat release,it has great potential safety hazards in production unit operations.In this paper,the nitration of benzoic acid is taken as an example,and the microchannel continuous flow reaction technology is introduced into the nitration,and the safety problems caused by intense heat release due to the strong mass and heat transfer effect of micro-reaction technology are solved.Microchannel continuous flow technology can strictly control the reaction time,no amplification effect,high continuous production efficiency,especially suitable for high temperature and high pressure strong exothermic organic reaction process.3,5-Dinitrobenzoic acid is an important intermediate in organic synthesis.It is mainly used in medicine to produce positive contrast agent,such as panthenic acid and borneol.In other aspects,it is mainly used for synthetic explosive plasticizer and coordination polymer,etc.These new products have a great application prospect.At present,3,5-dinitrobenzoic acid is mainly benzoic acid or m-nitrobenzoic acid as raw material by nitrification reaction in the kettle reaction.The production process of traditional kettle reactor is complicated,and the process control is unstable.Therefore,it is an urgent matter to design a microchannel continuous flow reaction process with high efficiency,strong mass transfer and green environmental protection for nitration of benzoic acid.3,5-Dinitrobenzoic acid was synthesized in a microchannel continuous flow silicon carbide reaction system in two steps using benzoic acid and fuming 25%sulfuric acid as reaction substrates and 98%nitric acid as nitration agent.3-Nitrobenzoic acid was obtained by nitration of benzoic acid in the first step,and then the target product 3,5-dinitrobenzoic acid was obtained by nitration of 3-nitrobenzoic acid,in order to explore the influence of different technological conditions on the nitration of benzoic acid to synthesis 3-nitrobenzoic acid and 3,5-dinitrobenzoic acid.The better technological conditions for continuous synthesis of 3-nitrobenzoic acid and 3,5dinitrobenzoic acid were obtained.Compared to the traditional kettle reaction,the final yield and selectivity of benzoic acid nitration have reached a higher level,the yield of 3-nitrobenzoic acid increased from 78.37%to 86.88%,and the yield of 3,5dinitrobenzoic acid increased from 65.34%to 76.58%,and improve the safety of the reaction,suitable for large-scale industrial production.In addition,isothermal solution equilibrium method was used to determine the solubilities of benzoic acid,3-nitrobenzoic acid and 3,5-dinitrobenzoic acid in seven pure solvents,water,methanol,ethanol,acetonitrile,dichloromethane,toluene,and ethyl acetate over a temperature range from 273.15 to 323.15 K under 101.3kPa in this paper.The results will help to compare the solubility differences of benzoic acid,3nitrobenzoic acid and 3,5-dinitrobenzoic acid,and optimize the industrial nitration of benzoic acid.