JPH0372214B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Fields] Imidazole is useful as a raw material for fungicides, other agricultural chemicals, medicines, etc. The present invention relates to a new method for producing such compounds. [Prior art] Imidazole is glyoxal, formalin,
It has been widely known that it can be obtained by reacting ammonia, and after the reaction is completed, the reaction solution is concentrated and subjected to reduced pressure and distillation to condense and crystallize the desired imidazole. This is commonly done. [Problems to be Solved by the Invention] However, as a result of studies by the present inventors, in addition to imidazole, the reaction solution contains unreacted raw materials, urotropin, etc. produced by the reaction of formalin and ammonia, etc. It contains various impurities, and in particular, residual formalin and urotropin easily react with imidazole when heated, resulting in a problem in that the yield of imidazole is reduced. [Means for solving the problem] However, the present inventors believe that the fundamental cause of the above problem lies in formalin used as a raw material,
As a result of various studies on new methods for producing imidazole that do not use formalin, we have found that when the reaction is carried out using glyoxal, glyoxylic acid, and ammonia, the above-mentioned problems can be avoided.
It was discovered that imidazole could be obtained in good yield,
The present invention has now been completed. The reaction of glyoxal, glyoxylic acid and ammonia is carried out in an aqueous medium, and usually glyoxal and glyoxylic acid aqueous solutions are mixed separately or in advance in an ammonia aqueous solution and the temperature of the liquid is maintained at 50 to 90°C. Just drop it little by little. Of course, it is also possible to charge the raw materials all at once or to adopt an addition procedure other than those described above. Further, a small amount of an organic solvent compatible with water may be present in the aqueous medium as necessary. The optimum molar ratio for each charge is, in pure terms, 1.0 to 1.5 mol of glyoxylic acid, more preferably 1.0 to 1.2 mol, and 2.0 to 3.0 mol of ammonia, more preferably 2.0 to 2.2 mol, per 1 mol of glyoxal. . Generally, the raw materials glyoxal and glyoxylic acid are commercially available as aqueous solutions, so they may be used as they are at the above-mentioned charge ratio, but they may be diluted or concentrated as necessary. The preferred concentration range of the raw material aqueous solution is 10 to 80% by weight, more preferably 35 to 50% by weight for the glyoxal aqueous solution and glyoxylic acid aqueous solution. Although ammonia may be introduced as a gas into the aqueous medium, it is usually supplied to the system as an aqueous ammonia solution. The concentration of the solution is preferably 5 to 40% by weight, more preferably 30 to 40% by weight.
During the reaction, carbon dioxide gas is generated, so if necessary, the generated gas is appropriately removed from the system to allow the reaction to proceed.
After the generation of carbon dioxide gas is completed, aging is further performed for about 0.5 to 1 hour to complete the reaction. The reaction solution obtained in this way contains unreacted raw materials and trace amounts of formic acid, formic acid amide, etc. in addition to water, so post-treatments such as concentration and distillation are usually performed to remove these impurities. is necessary. Concentration is usually carried out once or multiple times at 110-150°C under normal pressure or reduced pressure. In distillation, preferably the pre-concentrated reaction solution is heated to 20 torr or less, more preferably
Vacuum distillation is employed at 190-210°C under reduced pressure below 10 torr. Through such distillation, imidazole is distilled out, and by condensing it, imidazole crystals are obtained. In addition to such concentration and distillation, the post-treatment may be performed using an ion exchange resin or the like. In such cases, imidazole is obtained as an aqueous solution, and the desired product is obtained from it by crystallization. The crude imidazole crystals after impurities have been removed as described above are further recrystallized if necessary to obtain purified crystals. Recrystallization is performed by dissolving imidazole in water to a concentration of 75 to 80% by weight, and then heating at a temperature of 10 to 25%.
Crystallization is carried out by cooling to 15-20°C, preferably 15-20°C. The precipitated crystals are separated from the mother liquor using an appropriate method such as centrifugation or suction filtration, washed with cold water as appropriate, and then dried at a temperature of 75 to 80°C to obtain the desired imidazole. [Effect of the invention] As mentioned above, in the present invention, compared to the conventional method, formalin is not used as a raw material, so there is no concern about the reaction between imidazole and residual formalin or imidazole and urotropin during the imidazole production process or post-treatment process. imidazole can be obtained in good yield. Furthermore, since glyoxylic acid is used, which is easier to handle from a safety standpoint than formalin, it is particularly advantageous in industrial implementation. [Example] The present invention will be explained in more detail with reference to Examples below. However, "%" in the examples is based on weight unless otherwise specified. Example 1 While stirring 426.0 g of 10% ammonia aqueous solution kept at 70°C, 40% glyoxal aqueous solution was added to it.
A mixture of 144.4 g and 147.0 g of 50% glyoxylic acid aqueous solution was added dropwise over about 2 hours (final molar ratio of
Glyoxal/glyoxyl/ammonia=
1/1/2.5), and after the completion of the dropwise addition, the reaction was further aged for 30 minutes to obtain a reaction solution. This reaction solution was concentrated at 130°C and normal pressure to 20 torr, and further vacuum distilled at 210°C and 5 torr to obtain 51.0 g of distillate. The final yield of imidazole was about 82.0 mol% (based on glyoxal charged). Control example 144.1 g of 40% glyoxalic acid was added to 426.0 g of 10% ammonia aqueous solution kept at 70°C with stirring.
g and 81.2 g of 37% formalin aqueous solution.
Dropwise over 1.5 hours (Final molar ratio of glyoxal/formalin/ammonia = 1/1/
2.5) After completion of the dropwise addition, the mixture was further aged for 30 minutes to carry out the reaction, and a reaction solution was obtained. The reaction solution was concentrated and distilled in the same manner as in Example 1 to obtain 42.9 g of distillate. The final yield rate of imidazole was approximately 72.0 mol% (to glyoxal charged). From the above results, it is understood that the method of the present invention significantly reduces the yield of imidazole compared to the conventional method. Examples 2 to 4 The same reaction, concentration, and distillation as in Example 1 were carried out, except that the raw material charging ratio was changed as shown in Table 1, and the reaction conditions were appropriately changed, and the yield of imidazole was examined. The results are shown in Table 1.

[Table] (Note) All imidazole yields are based on the charged glyoxal.

Claims (1)

[Claims] 1. A method for producing imidazole, which comprises reacting glyoxal, glyoxylic acid, and ammonia.