A safe and efficient cyclic microreaction process for the synthesis of 3-methylpyridine-N-oxide_Industrial Additives

3-methylpyridine-N-oxide is an important intermediate for the preparation of 2-chloro-5-methylpyridine, which can be used to synthesize new nicotines such as imidacloprid and acetamiprid. Pesticide-like. The traditional method for preparing 3-methylpyridine-N-oxide is to catalytically oxidize 3-methylpyridine in a semi-batch reactor using hydrogen peroxide as the oxidant. The reaction is highly exothermic and the raw material 3-methylpyridine is a volatile and explosive compound. However, the existing batch process is limited by the performance of the reactor. In actual industrial production, there are many problems such as low reaction efficiency, poor selectivity and poor safety of boron trifluoride tetrahydrofuran complex, and it is impossible to achieve efficient and safe production. Therefore, it is very necessary to develop a safe and efficient 3-methylpyridine-N-oxide production process in industrial production. The emergence of microreactors provides reliable ideas for solving the above problems. Microreactors have the advantages of high heat and mass transfer efficiency, strong process controllability, intrinsic safety, and easy amplification. They have been widely used in many fields such as chemistry, chemical industry, and biology, especially in fine chemicals such as medicine, pesticides, and dyes. Manufacturing of goods.

This study uses microreactors to construct a continuous synthesis process of 3-methylpyridine-N-oxide to achieve process intensification of the reaction. In the study, the reaction performance of two forms of microreaction continuous processes (parallel flow microreaction process and cyclic microreaction process) was mainly tested. In the experiment, it was found that the oxidant hydrogen peroxide used has a strong self-decomposition side reaction during the reaction process, and this side reaction is mainly affected by the concentration of the reaction raw material 3-methylpyridine. It is necessary to maintain the concentration of 3-methylpyridine during the reaction process. High concentration can effectively control side reactions, improve hydrogen peroxide utilization, and ensure a high yield of the target product. Therefore, the cyclic microreaction process is more suitable for this reaction system. The experimental results also verified the above assumptions. Compared with the parallel flow microreaction process, the cyclic microreaction process has a higher product yield (more than 90%), fewer side reactions and better reaction controllability. Finally, after continuous optimization of reaction conditions, a practical and efficient cyclic microreaction process for the synthesis of 3-methylpyridine-N-oxide was developed. Compared with the traditional intermittent process, this process has significantly improved product stability and yield (~6%), greatly shortened the reaction cycle (~50%), significantly improved process safety, and enhanced the reaction process. This result has good guiding value for the subsequent transformation and upgrading of 3-methylpyridine-N-oxide production equipment, and the relevant experience of this part of the work can be extended to the research of other similar oxidation reaction systems. middle.

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