JPH0482875A - Production of 2-ethyl-4-methylimidazole-containing composition excellent in stability - Google Patents

Abstract

PURPOSE:To obtain the subject substance excellent in stability without requiring any specific stabilizer and solidifying even in the winter season in good yield by reacting ammonia with propionaldehyde and methylglyoxal under specified conditions. CONSTITUTION:Ammonia is reacted with propionaldehyde and methylglyoxal in the presence of at least one aldehyde selected from formaldehyde and acetaldehyde in an aqueous medium at 0-45 deg.C for 0.5-1.0 hr to afford the objective substance. The reaction ratios of the ammonia, propionaldehyde and methylglyoxal are (2.0-3.0):(0.5-1.5):1.0 and the aldehyde is added in a molar amount of 0.3-0.7 based on the methylglyoxal. The above-mentioned objective substance is useful as a coating for various substrates such as glass or metal and a curing accelerator for adhesive epoxy resins.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a 2-ethyl-4-methylimidazole-containing composition with excellent stability. More specifically, it is a 2-ethyl-4-methylimidazole-containing composition that is widely used industrially as a curing accelerator for epoxy resins used as paints and adhesives for various base materials such as glass and metals. Regarding manufacturing methods.

[Prior art] 2-ethyl-4-methylimidazole (hereinafter referred to as 2E4M
(abbreviated as 1) has a melting point of 47 to 48°C, and is a crystalline substance at room temperature, but is prone to supercooling, so industrially produced 2E4M I often takes on a liquid state. Liquid 2E4MI has better compatibility with liquid epoxy resin than crystalline 2E4MI, so its commercial value is higher; however, this supercooling phenomenon is destroyed by the slightest stimulus, resulting in less assimilation. However, there is a drawback that storage stability is poor due to precipitation of crystals in low-temperature atmospheres such as winter. As such measures, 2 E 4
．． 4゜4'-medylene-pis (2-ethyl-
5-methylimidazole) (Japanese Patent Application Laid-open No. 1983-
252422), and are currently stored in the form of solutions diluted with various solvents such as ethyl-nonglycol, N,N-trimethylformamide, and methyl cellosolve.

[Problems to be Solved by the Invention] However, the method of blending 2E4MI with 4,4'-methylene-bis(2-ethyl-5-methylimidazole) to prevent crystallization requires separately manufacturing the blend. It takes time and effort. In addition, the use of a solvent may require an extremely large amount of 2E4MI solution in situations where a high concentration of curing agent is required, and depending on the type of solvent, it may have an adverse effect on the epoxy resin, so neither of these is advantageous. I can not say. Therefore, it has excellent stability and does not cause crystallization even under slight stimulation or low temperature conditions, even without the use of solvents.
If E4MI can be easily produced industrially, it will be extremely useful industrially.

Therefore, the present inventor first reacted ammonia, propionaldehyde, and methylglyoxal based on the knowledge that 2 E 4 M I is difficult to assimilate if it contains other components. When producing MI, a 2E4MI-containing composition with excellent stability can be obtained by containing 30% by weight or more and 70% by weight or less of 2,4-dimethylimidazole and/or 4-methylimidazole in the product liquid system. He discovered this and applied for a patent.

However, further study by the present inventor revealed that the yield of the target 2E4M T-containing composition was 5.
It has become clear that practical problems remain at around 0%, and that ingenuity is required to improve the yield.

[Means for Solving the Problems] However, as a result of extensive research in order to solve the above problems, the present inventors reacted ammonia, propionaldehyde, and methylglyoxal to form 2,4-dimethylimidazole and/or 4-dimethylimidazole. When producing a 2E4MI-containing composition in which the content of methylimidazole is 30% by weight or more and 70% by weight or less, at least one aldehyde selected from formaldehyde and acetaldehyde is allowed to coexist during the reaction. The present invention was completed by discovering that the yield of Mr-containing compositions is significantly improved.

In the present invention, as described in 2, at least one aldehyde selected from formaldehyde and acetaldehyde is allowed to coexist when ammonia, propionaldehyde, and methylglyoxal are reacted. The ratio is 2.0~3.0 + 0.5~15・
1.0, preferably 2.0-2.5: 1.0-1.
3: 1.0.

Further, the amount of at least one aldehyde selected from formaldehyde and acetaldehyde added is 0.3 to 0.7 times mole relative to methylglyoxal. The mixing ratio of formaldehyde and acetaldehyde is arbitrary;
The effects of the present application can be obtained as long as at least one of them coexists in the reaction system.

By employing such a reaction ratio, there is no need to newly add a specific stabilizer, and a 2E4-M I-containing composition with excellent stability that does not solidify even in winter can be produced in an extremely good yield <2E4. Since it can be obtained all at once from the MI manufacturing process, it is extremely industrially advantageous.

4-Methylimidazole and 2.4-dimethylimidazole have similar structures to 2E4MI, so within the range of 30 to 70% by weight, 2E4.
It does not adversely affect the curing accelerating effect of MI. i.e. 4
- If methylimidazole and/or 24-dimethylimidazole is 30% by weight or less, the probability of crystal precipitation of 2E4MI increases, and if 4-medylimidazole and/or 24-dimethylimidazole is 70% by weight or more, 2E4MI It has disadvantages such as low purity.

Further, the mixing ratio of 4-methylimidazole and 24-dimethylimidazole is arbitrary, and at least one is 30
The stability of the 2E4MI content composition is maintained when present at ~70% by weight.

Although this reaction is carried out in an aqueous medium, it is possible to use small amounts of organic solvents if necessary.

In carrying out the reaction, ammonia is first introduced into an aqueous medium, followed by propionaldehyde and formaldehyde.The appropriate reaction temperature during the reaction is 0 to 45°C, preferably 15 to 30°C, and the reaction time is 0.゜5
About 1.0 hours is preferable.

Subsequently, methylglyoxal is charged into the system and the reaction is continued. As for the preparation method, either batch preparation or dropwise preparation is possible, but dropwise preparation is preferable.

The reaction temperature is preferably 10 to 70°C, particularly 25 to 35°C. A practical reaction time is about 1.0 to 5.0 hours.

The reaction is completed by aging for about 0.5 to 0 hours after the completion of the preparation.

The reaction product liquid contains 2g4MI as a main component, 4-methylimidazole and/or 2,4-dimethylimidazole,
Contains other by-products and water. By subjecting this product liquid to vacuum distillation, 30% by weight of 4-methylimidazole and/or 24-dimethylimidazole was added.
2E containing 70% by weight or more 4. The MI-containing composition is produced in good yield. Note that the composition range targeted by the present application can be achieved by appropriately selecting the amount of collected distillate fraction.

The 2g4MI-containing composition thus obtained has excellent stability and is resistant to crystallization, so it is useful as a curing accelerator for epoxy resins.

[Function] The present invention does not require the operation of newly adding a specific stabilizer, and the 2g4MI has excellent stability and does not solidify even in winter.
The containing composition can be manufactured all at once from a manufacturing process with an extremely good yield of <2g4MI.

[Example] Next, the method of the present invention will be explained in more detail with reference to Examples. "%" is based on weight.

Example 1 30% of 25% ammonia water in a 1ρ volume separable flask
After cooling with water, 98.6 g (1.7 mol) of propionaldehyde and 26.49 (0.6 mol) acetaldehyde were added dropwise over 30 minutes. Then, after heating the above mixture to an internal temperature of 50°C, 4.0%
Medylglyoxal 3609 (2.0 mol) was added dropwise over 90 minutes. After completion of the dropwise addition, the resulting product solution was aged for 0.5 hours at the same temperature and distilled under reduced pressure to obtain 50% 4-methylimidazole, 3
0%, 2g4M1 A composition containing 65% of 2E4-MI was obtained. Even when this composition was stored at 0 to 2°C for 30 days, no crystals were precipitated at all, and when this 2g4MI-containing composition was analyzed by gas chromatography, the yield (total yield of the composition, hereinafter referred to as the total yield of the composition) relative to the raw material methylglyoxal was found to be (similar) was 73.10%.

Example 2 The reaction was carried out in the same manner as in Example 1, except that acetaldehyde was changed to formaldehyde. 4-methylimidazole 35%, 2.4-dimethylimidazole 4
%, 2g4MI 61% of 2 E4. An MI-containing composition was obtained, and no crystals were deposited even after storage at 0-2°C for 30 days. The yield of this 2g4MI-containing composition based on the raw material methylglyoxal was 75.2%.

Example 3 In Example 1, only acetaldehyde 13.2 @ (0.3 mol) was allowed to coexist in the reaction system, but acetaldehyde 13.29 C0.3 mol) and formaldehyde 37%, 24. ．． When the reaction was carried out according to the same procedure except that 3gC0.3mol) was used in combination, 4-methylimidazole! 6
%, 24-dimethylimidazole 15%, 2g4M1
A composition containing 69% of 2g4MI was obtained, with a
Even after storage for 0 days, no crystals were deposited at all. This 2
The yield of the E 4 M I-containing composition based on the raw material methylglyoxal was 76%.

Comparative Example 1 In Example 1, when the reaction was carried out without acetaldehyde coexisting in the reaction system, the yield based on the raw material methylglyoxal decreased to 50%.

[Effects] The present invention does not require the operation of newly adding a specific stabilizer, and has excellent stability that does not solidify even in winter.
．． It is industrially very advantageous because the M2-containing composition can be produced all at once from a manufacturing process of <2g4MI in extremely good yield.

Claims (1)

[Claims] A 2-ethyl-4-methylimidazole-containing composition in which the content of 2,4-dimethylimidazole and/or 4-methylimidazole is 30% by weight or more and 70% by weight or less by reacting ammonia, propionaldehyde, and methylglyoxal. A method for producing a 2-ethyl-4-methylimidazole-containing composition with excellent stability, characterized in that at least one aldehyde selected from formaldehyde and acetaldehyde is allowed to coexist during the reaction.