Method for synthesizing 3-methylpyridine

Abstract

The invention discloses a method for synthesizing an organic synthesis intermediate 3-methylpyridine. Most of the conventional methods for synthesizing the 3-methylpyridine have the problems of low yield and a large number of by-products. The method comprises the following steps of: under the action of ionic liquid, performing reaction on paraldehyde and urotropine which serve as raw materials atthe temperature of between 180 and 350 DEG C under the pressure of 1.2 to 20MPa; and cooling and directly demixing the reacted materials, wherein the obtained ionic liquid layer is reused; and the obtained product layer is extracted, concentrated and de-weighted to obtain the 3-methylpyridine. By taking the ionic liquid as a reaction medium, on the one hand, a high polarity environment can be provided, the improvement on the activity of aldol condensation reaction is facilitated, the reaction temperature can be effectively reduced and side reaction is reduced, and on the other hand, the ionicliquid can have a better pH value buffering effect to ensure that the reaction system keeps stable from beginning to end.

Description

Technical field [0001] The invention relates to the field of organic synthesis intermediates, in particular to a method for synthesizing 3-methylpyridine. Background technique [0002] The synthesis methods of 3-methylpyridine mainly include the following: a. Using formaldehyde, acetaldehyde, and ammonia as raw materials, various pyridine mixtures are directly obtained through a fixed bed reactor, and 3-methylpyridine, 3-methylpyridine is obtained after separation. The yield of pyridine is generally about 30%. b. Using 3-methylpiperidine as a raw material, 3-methylpyridine is obtained through dehydrogenation reaction. c. Using acetaldehyde and urotropine as raw materials, under the action of a salt solution such as diammonium phosphate, 3-methylpyridine is obtained through high temperature and high pressure reaction in an autoclave. The above-mentioned routes all have the problems of low yield and many by-products. The reason for these problems is that the reaction to form 3-me...

AI Technical Summary

Problems solved by technology

The above-mentioned routes all have the problems of low yield and many by-products. The reason for these problems is that the reaction to form 3-picoline will undergo four condensation and dehydration reactions to obtain the target product 3-picoline. Both formaldehyde and acetaldehyde have high reactivity, and it is easy to form a large number of by-products if the one-pot reaction is adopted

[0003] In view of the problem of many by-products in the synthesis of 3-picoline, U.S. patents US4481361 and US4482717 have also made relative improvements in the c method, using saline solution as a buffer solution system, and the aforementioned problems have been alleviated to a certain extent, but still not be fundamentally resolved

Disadvantages of using brine: 1. In order to reduce the formation of side reactions, a very low ratio of paraldehyde to brine is required, which will greatly affect the yield

2. The concentration of brine should not be very high, otherwise solid salt will precipitate out, which will affect its regulation of pH value. During the reaction process, excessive ammonia will be formed due to the decomposition of urotropine, and the pH value of the reaction system will rise, exceeding the value of brine. When adjusting the concentration, the response will become very poor

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