JPH0372060B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is to obtain imidazole with few impurities. Imidazole is a fungicide and other agricultural chemicals. It is useful as a raw material for medicines, etc. It has been widely known that this compound can be obtained by reacting glyoxal, formalin, and ammonia, and when carried out on an industrial scale, it is necessary to use the imidazole-containing compound obtained after the completion of the reaction. The aqueous solution was concentrated and then reduced under reduced pressure. The imidazole that is distilled off is condensed. A method of crystallization is performed. Furthermore, the desired product is usually obtained by dissolving the crystals in an appropriate amount of water and recrystallizing them. However, the present inventors have investigated that even if operations such as distillation and recrystallization are carried out, trace amounts of impurities are still mixed into the product, causing problems with the product's storage stability. It has been discovered that if it is stored for a long time or transported for a long time, it may change over time and become discolored, which reduces the value of the product. However, as a result of extensive research in order to solve the above problem, the present inventors found that in obtaining imidazole crystals from an imidazole-containing aqueous solution obtained by reacting glyoxal, formalin, and ammonia, The inventors have discovered that when the imidazole-containing aqueous solution is treated with an anion exchange resin and then subjected to crystallization, imidazole crystals with few impurities and little change over time can be obtained, which led them to complete the present invention. Ivy. The present invention will be explained in order below. In the present invention, the anion exchange resin is a styrenic resin having a quaternary ammonium base type, primary, secondary, or tertiary amine as an exchange group;
Commercially available exchange resins such as various amine condensation resins can be used arbitrarily. The main commercial product names of such anion exchange resins are Amberlite (Rohm
& HassCo), Diaion (Mitsubishi Chemical
Co., Ltd.), Dowex (manufactured by Dow Chemical Co.), Duolite
(manufactured by Chemical Process), Lewatit (manufactured by Bayer), etc. Among such resins, strong anion exchange resins, ie, those having a quaternary ammonium base type as an exchange group, are generally preferably used. The imidazole-containing aqueous solution to be purified in the present invention is reacted and produced by a conventionally known method. That is, the ammonia aqueous solution has a temperature of 70°C.
The reaction is carried out by dropping a mixture of glyoxal aqueous solution and formalin aqueous solution little by little while maintaining the temperature at -85°C, preferably 70-80°C. The optimum reaction molar ratio (in terms of solid content) is 0.7 to 1.2 mol of formalin and 0.7 to 1.2 mol of ammonia to 1 mol of glyoxal.
It is between 2.0 and 3.0. Since each raw material is generally commercially available as an aqueous solution, it is common to use it directly, but it may be diluted or concentrated as necessary. The preferred concentration range of the raw material is glyoxal aqueous solution of 10 to 80% by weight, more preferably 35% by weight.
~50% by weight, formalin aqueous solution 10-80% by weight,
More preferably 30 to 40% by weight, 5 to 40% by weight of ammonia aqueous solution, and more preferably 10 to 30% by weight. After the reaction is completed, the mixture is aged for 0.5 to 1 hour to obtain an imidazole-containing reaction solution. The imidazole-containing aqueous solution thus obtained contains imidazole as well as unreacted raw materials, water, and other by-products. In the present invention, such an imidazole-containing aqueous solution is treated with an anion exchange resin as it is or after adjusting the concentration appropriately, and the resulting treated solution is cooled to crystallize, thereby producing an imidazole with little change over time. is obtained. However, in practical terms, in order to obtain a product of even higher quality, the above-mentioned reaction-completed liquid is first concentrated, and then
It is effective to distill it and treat it with an anion exchange resin. Distillation itself does not require any special operations, but concentration and distillation are carried out by the method previously applied by the present applicant (Japanese Patent Application No. 133212/1982).
In this case, very favorable results are obtained. The most typical method for distillation is to distill an imidazole-containing aqueous concentrate under 20 torr, more preferably at 10 torr.
The following method of vacuum distillation at 190 to 210°C under reduced pressure is adopted. Since the imidazole obtained by distillation is condensed and crystallized, it is necessary to dissolve the crystals in an aqueous medium for treatment with an anion exchange resin. When treating such an aqueous solution with an anion exchange resin, there are no particular restrictions on the method, and the method may be a batch method in which an aqueous imidazole-containing solution and an anion exchange resin are mixed, or an anion exchange resin is added to a column, a packed tube, etc. Any method can be used, such as a continuous method in which the imidazole-containing aqueous solution is passed from the top, but the latter method is industrially practical. Furthermore, it is of course possible to treat the aqueous solution with an anion exchange resin membrane.
The appropriate concentration of the treatment liquid is about 60 to 75% by weight.
Imidazole crystals are obtained from the imidazole-containing aqueous solution thus obtained. If necessary, concentrate the solution to bring the imidazole concentration to 75-80% by weight.
After preparing to a degree, the temperature is 10-25℃, preferably 15
Crystallize by cooling to ~20°C. The precipitated crystals are separated from the mother liquor using an appropriate method such as centrifugation or suction, washed with cold water as appropriate, and then dried at a temperature of 75 to 80°C. The mother liquor obtained at this time contains a considerable amount of imidazo.
This can be reused as an aqueous medium by mixing it with the imidazole-containing aqueous solution to be treated, or by dissolving the imidazole condensed and crystallized by the distillation into the mother liquor. That is advantageous. That is, the mother liquor is used as part of the water used as the aqueous medium during the crystallization described above. Normally, when the recovered mother liquor is reused, the more times it is reused, the more impurities will be included in the crystals, and the tendency to change over time will become even stronger, resulting in an undesirable product. However, the present invention is characterized by the fact that there is no such concern since the anion exchange resin treatment is performed. Anion exchange resins that have been used once are usually
After being regenerated with an alkaline aqueous solution having a concentration of about 50 to 10% by weight and further washed with an appropriate amount of water, it is subjected to the next treatment with an imidazole-containing aqueous solution. As the alkaline aqueous solution, a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution are used. The purified imidazole crystals obtained in this way are always of high purity, and show almost no change over time even when exposed to light, and are therefore of very high industrial value. 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: Into a 20% ammonia aqueous solution kept at 80℃,
A mixture of 5 moles of 40% glyoxal aqueous solution and 5 moles of 37% formalin aqueous solution was added dropwise over 2 hours.
After completion of the dropwise addition, the mixture was further aged for 30 minutes to carry out the reaction. The liquid was concentrated at 130°C and normal pressure, and then further concentrated at 210°C.
Imidazole crystals were obtained by vacuum distillation at 5 torr. Add 125 g of water to 375 g of the crystals, dissolve the imidazole by heating at 30°C, and add Diaion SA-20A (SV
= 2.0 to 3.0, a column filled with 75 ml of anion exchange resin manufactured by Mitsubishi Chemical Industries, Ltd. (size: 100 to 150)
ml), and after passing, 220 g of water was further passed through the column. Approximately 720 g of the obtained liquid was concentrated at 100 torr and 100°C, and after cooling, crystallization was performed at 15 to 18°C. The obtained crystals were separated by centrifugation and dried at 75°C for 2 hours. The crystal is A. Separately, 140 g of the imidazole crystals after the distillation and 16.5 g of the imidal saturated solution were added to 343.5 g of the mother liquor obtained by centrifugation and uniformly dissolved at a temperature of 30 DEG C. in the same manner as above. 200 ml of a 5% alkaline aqueous solution and 500 ml of water were poured into the solution in advance, and the solution was passed through the regenerated anion exchange resin, followed by crystallization in the same manner.
Obtained crystals. This crystal is designated as B. Thereafter, the above-described operations were repeated by successively reusing the obtained mother liquors, and crystallization was performed three times in total to obtain imidazole crystals. These crystals are designated as C, D, and E in the order of crystallization. Melting points of purified crystals of A to E,
The purity and APHA of the crystals were determined. The results are shown in Table 1. Control Example The mother liquor was recycled and crystallization was performed 5 times in the same manner as in Example except that activated carbon (granular, SV=2.5) was used instead of the anion exchange resin. The order of crystallization of these crystals is A′, B′, C′, D′,
Let it be E′. Each crystal was analyzed and measured in the same manner as in the example. The results are also shown in Table 1. 【table】

Claims (1)

[Claims] 1. In obtaining imidazole crystals from an imidazole-containing aqueous solution obtained by reacting glyoxal, formalin, and ammonia, the imidazole-containing aqueous solution is treated with an anion exchange resin. 1. A method for purifying imidazole, which comprises performing crystallization. 2. The purification method according to claim 1, wherein the recrystallization, particularly the obtained mother liquor, is reused as a medium for the aqueous solution.