Preparation method of methyl isocyanate

Abstract

The invention provides a preparation method of methyl isocyanate. A reaction product synthesized at the high temperature is directly fed into a first organic solvent for treatment at the temperature of 200-300 DEG C, effective separation of the methyl isocyanate and hydrogen chloride is realized, the fact that the methyl isocyanate reacts with the hydrogen chloride to produce methyl carbamyl chloride is avoided, the once-through yield of the methyl isocyanate is increased, repeated heating and condensation are not required, energy consumption and production of by-products are reduced, meanwhile, multiple decomposition reactors are not required and the number of condensers is decreased in the aspect of devices, and the investment cost and the production cost are greatly reduced.

Description

technical field [0001] The invention relates to the field of organic synthesis, in particular to a method for preparing methyl isocyanate. Background technique [0002] Methyl isocyanate is an important pesticide intermediate, mainly used in the synthesis of carbamate pesticides, such as: carbofuran, methomyl, amethomyl, isoprocarb (Yechansan), secbucarb (Barba Sand), carbaryl, propoxur, haoanwei, thiodicarb, carbosulfan and butylthiuron, etc. [0003] At present, there are many reports about the preparation method of methyl isocyanate, such as German published patents 2422211, 2503270, U.S. patent 8969889, Japanese patents 42-8911, 46-24123, Chinese patents CN86100286, CN102976976A, etc.; The preparation method of base isocyanate all is to prepare methylcarbamoyl chloride first with phosgene and monomethylamine as raw material, then in the presence of inert solvent (such as carbon tetrachloride, trichloromethane, toluene etc.), methylcarbamoyl chloride Acyl chloride is de...

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Problems solved by technology

[0003] At present, there are many reports about the preparation method of methyl isocyanate, such as German published patents 2422211, 2503270, U.S. patent 8969889, Japanese patents 42-8911, 46-24123, Chinese patents CN86100286, CN102976976A, etc.; The preparation method of base isocyanate all is to prepare methylcarbamoyl chloride first with phosgene and monomethylamine as raw material, then in the presence of inert solvent (such as carbon tetrachloride, trichloromethane, toluene etc.), methylcarbamoyl chloride Acyl chloride is decomposed and rectified to produce methyl isocyanate. Since the reaction of methyl carbamoyl chloride to generate methyl isocyanate and hydrogen chloride is a reversible reaction, the single-pass yield is low, and the molar percentage is about 60%. Therefore, the existing methyl In the preparation method of isocyanate, the whole preparation process requires repeated heating and condensation, and the preparation process is relatively long. On the one hand, there are more reaction by-products, trimeric methyl isocyanate, which in turn reduces the yield of methyl isocyanate and increases the three wastes; on the other hand, On the one hand, because the yield of methyl isocyanate prepared by the decomposition of methylcarbamoyl chloride is low, it is necessary to configure multiple decomposition reactors, which leads to large equipment investment

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