JPS62164672A - Method for producing 1,2-dimethylimidazole - Google Patents

Abstract

PURPOSE:To obtain the titled high-purity substance, by reacting glyoxal with acetaldehyde, methylamine and ammonia, distilling the reaction solution to give a distillate of the titled substance containing a small amount of 1- methylimidazole and cooling the distillate. CONSTITUTION:Glyoxal is reacted with acetaldehyde, methylamine and ammonia in an aqueous medium and the resultant reaction product solution is distilled at 90-95 deg.C under 17-18Torr to give a distillate of the titled substance containing a small amount, e.g. about <=10wt%, 1-methylimidazole, which is then cooled to 5-7 deg.C to afford a wet cake containing a small amount of the 1-methylimidazole and water sticking to 1,2-dimethylimidazole. The liquid is then removed by using a means, e.g. centrifugal separation, etc., to provide the aimed substance almost completely free of the 1-methylimidazole which is an impurity. USE:An intermediate for organic chemicals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an industrially advantageous method for producing 1,2-dimethylimidazole of excellent quality.

[Prior Art 1] 1,2-Dimethylimidazole is a compound that is expected to be used as an intermediate for various chemicals.

The compound is prepared by reacting glyoxal, 7cetaldehyde, methylamine and ammonia.

[Problem to be solved by the invention 1 However, in the above method, a small amount of 1-methylimidazole is unavoidably produced, and it is necessary to remove this impurity to produce l111# 1,2-dimethylimidazole. However, since the boiling points of the two products are close to each other in normal distillation operations, complete purification is impossible.

[Means for Solving the Problems 1] However, the present inventors have conducted extensive research in order to solve the above problems and to find a method that can industrially advantageously incorporate 1,2-trimethylimidazole of good quality. As a result of stacking, (1)
A step of reacting glyoxal, acetaldehyde, methylamine and ammonia, (2) A step of distilling the reaction product to obtain a 1,2-dimethylimidazole distillate containing a small amount of 1-methylimidazole, (3) Distillation The objective can be achieved when carrying out a method consisting of a step of selectively crystallizing 1,2-dimethylimidazole by cooling the liquid, and (4) a step of removing 1-methylimidazole from the crystallized product. They discovered this and completed the present invention.

Each step of the present invention will be specifically explained below.

First Step Glyoxal, acetaldehyde, methylamine and ammonia are reacted to produce 1,2-dimethylimidazole.

The reaction medium is water, but if necessary, a small amount of an organic solvent compatible with water such as methanol, ethanol, propatool, etc. may be used. In the reaction, the method of charging the raw materials is not particularly limited, and any method such as batch charging, continuous charging, divided charging, etc. can be adopted. Typically, methylamine is introduced into an aqueous medium, followed by ammonia gas (
or ammonia water) is gradually introduced. Glyoxal and acetaldehyde are then added dropwise.

The charging composition of raw materials is glyoxal/acetaldehyde/methylamine/ammonia = 1/1.0 to 1 in molar ratio.
．． 5/1 to 1.5/1 to 1.5, preferably 1/1.0
A range of 1.2/1.0 to 1.2/1.0 to 1.2 is suitable. The amount of solvent used is per mole of glyoxal,
The reaction temperature when mixing methylamine and ammonia is preferably 100 to 300 m1 (including those serving as medium components such as water in the raw materials), and is preferably 30 to 30 °C, preferably 20 to 30 °C.
℃ is preferable. Also, when adding glyoxal and 7cetaldehyde, the temperature of the system should be 60 to 90°C, preferably 7°C.
A reaction product solution containing 1,2-dimethylimidazole can be obtained by adjusting the temperature to 0 to 80°C and aging for about 0.5 to 1.0 hours after the completion of the dropwise addition. After the reaction is completed, the vaginal fluid is sent to the next step either directly or after being concentrated as appropriate.

The second step reaction product liquid is subjected to distillation. Since the reaction solution contains many impurities, it is usually distilled under reduced pressure. Any known distiller can be used. Suitable distillation conditions are 17-18 Torr and 90-95°C.

The composition of the distillate is mainly composed of 1,2-dimethylimidazole and a small amount (approximately 10% by weight or less) of 1-dimethylimidazole as an impurity.
Contains methylimidazole and solvent (water).

Third step The distillate obtained above is then cooled.

By this operation, only 1,2-dimethylimidazole is selectively precipitated as crystals. The efficient cooling temperature is 10°C or less, preferably about 5 to 7°C. At high temperatures, sufficient precipitation does not occur and the yield of the target product decreases. Since 1-methylimidazole exists in a liquid state at such a cooling temperature, a wet cake in which a small amount of 1-methylimidazole and water are attached to 1,2-dimethylimidazole is obtained by such crystallization.

Fourth step: The liquid is removed from the wet cake by known means such as centrifugation. By this repeated operation, 1-methylimidazole, which is an impurity, can be almost completely removed.

If necessary, the desired 1,2-dimethylimidazole of high purity can be obtained by purifying the above crystals of 1,2-dimethylimidazole by a well-known process such as recrystallization.

[Function 1] In the present invention, high purity 1,2-dimethylimidazole containing almost no 1-methylimidazole can be produced by carrying out steps (1) to (4).

[Example 1] Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 133.8 g (1.8 mol) of a 42% methylamine solution was introduced at room temperature into a reaction vessel containing 122.4 g of water. 25% ammonia aqueous solution 122. while maintaining the same temperature. h
(1.8 mol) was slowly charged. The system was heated to 70°C and 40% glyoxal 2611? (1,8 mol) and 132 g (1,8 mol) of 60% acetaldehyde aqueous solution
mol) was gradually added dropwise. After completion of the dropwise addition, the mixture was aged for 1 hour to complete the reaction.

The reaction product liquid was concentrated using a rotary evaporator at a bath temperature of 140'C''C'', and the concentrated liquid was subjected to vacuum distillation under the conditions of 90-95°C/1.7-18 Torr. A distillate containing ,2-no'methyl imiguzole as the main component was obtained.

(Composition ratio of 1,2-methylimidazole 90%, 1-methylimidazole 9.6%, water 0.4%) Next, this distillate was cooled to 5°C with stirring and the 1.2-methylimidazole was cooled to 5°C with stirring. Methylimidazole crystals were selectively crystallized to obtain a wet cake of the above crystals.

The 1-methylimidazole and water contained in the wet cake were removed under aspirator vacuum using a Nutsche suction bottle. The obtained 1,2-trimethylimidazole contained only 1% of 1-methylimidazole.

The yield of 1,2-dimethylimidazole was 74% based on the glyoxal charged.

As a control example, the distillate was further subjected to distillation and purified.
Separation of methylimidazole was insufficient, and results similar to those of the Examples were not obtained.

Example 2 The same method as in Example 1 was carried out. Then the obtained 1, 2-
The crystals of trimethylimidazole were heated and melted again, and then 2
It was cooled to 5°C and recrystallized.

1. The purity of 2-dimethylimidazole is further improved1.
- The content of methylimidazole was 0.1%), and crystals of excellent quality and no coloring were obtained.

[Effect 1] 1,2-trimethylimidazole obtained by the method of the present invention is useful as an intermediate for various compounds including medicines and agricultural chemicals.

Claims (4)

[Claims] (1) A step of reacting glyoxal, acetaldehyde, methylamine and ammonia, (2) a step of distilling the reaction product liquid to obtain a 1,2-dimethylimidazole distillate containing a small amount of 1-methylimidazole; (3) cooling the distillate to selectively crystallize 1,2-dimethylimidazole; (4) A method for producing 1,2-dimethylimidazole comprising the steps of removing 1-methylimidazole from a crystallized product.