JPH0441477A - Production of 2-ethyl-4-methylimidazole-containing composition having excellent stability - Google Patents

Abstract

PURPOSE:To industrially and advantageously obtain the title compound useful as a promoter for curing of epoxy resin, having improved stability, by reacting NH3 with propionaldehyde and methylglyoxal. CONSTITUTION:Ammonia is reacted with propionaldehyde and methylglyoxal to give a reaction product solution of 2-ethyl-4-methylimidazole base containing <=30 wt.% to <=70wt.% content of 2,4-dimethylimidazole and/or 4-methylimi- dazole. The reaction ratio of NH3, etc., by the method is (2.0-3.0):(1.0-1.5):(1.0), preferably (2.0-3.5):(1.0-1.2):(1.0). A composition not solidifying even in winter is obtained by the method.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for improving the stability of 2-ethyl-4-methylimidazole, which is widely used as a curing accelerator for epoxy resins. .

[Prior art 1 2-ethyl-4-methylimidazole (hereinafter referred to as 2E4M
(abbreviated as +) is an epoxy resin used as paint and adhesive for various base materials such as glass and metal.
= It is a useful compound that is widely used industrially as a W conversion accelerator. 2E4MI has a melting point of 47-48°C
Industrially produced 2E4MI is often in a liquid state because it is a crystalline substance or prone to supercooling at room temperature. 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 stimulation and solidification is prevented. It also has the disadvantage of poor storage stability, such as precipitation of crystals and layer separation in low-temperature atmospheres such as in winter. As a countermeasure against this, 4,4'-methylene-bis(2ethyl-5-methylimidazole) is added to 2E4MI (
Currently, they are stored in the form of solutions diluted with various solvents such as ethylene glycol, N,N-dimethylformamide, 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 manufactured industrially, it can be said to be extremely useful industrially.

[Means for Solving the Problems] Based on the knowledge that 2E4MI is less likely to solidify when it contains other components, the present inventor has worked diligently to develop a method for producing a 2E4MI-containing composition with excellent stability. As a result of repeated research, it was found that when producing 2E4MI by reacting ammonia, propionaldehyde, and methylglyoxal, 2,4-dimethylimidazole and/or 4
- It has been discovered that a 2E4MI-containing composition with excellent stability can be obtained by containing 30% by weight or more and 70% by weight or less of methylimidazole, and the present invention has been completed.

As described above, in the present invention, ammonia, propionaldehyde, and methylglyoxal are reacted, and the desirable reaction ratio is 2.0-3.0:1.0-
15.1. O1 preferably 2.0-3.5: LO-
1.2:I.

It is 0. By adopting such a reaction ratio, 2,4
2E4MI containing 30% by weight or more and 70% by weight or less of dimethylimidazole and/or 4-methylimidazole
2E4 is a highly stable 2E4MI-containing composition that does not solidify even in winter.
Since it can be obtained all at once from the MI manufacturing process, it is extremely industrially advantageous.

Since 4-methylimidazole and 2,4-dimethylimidazole have similar structures to 2E4MI, they do not affect the curing accelerating effect of 2E4MI on epoxy resins within the range of 30 to 70% by weight. That is, when 4-methylimidazole and/or 2.4-dimethylimidazole is 30% by weight or less, the probability of crystal precipitation of 2E4MI increases; The above cases have drawbacks such as a decrease in the purity of 2E4MI.

Further, the mixing ratio of 4-methylimidazole and 24-dimethylimidazole is arbitrary, and at least one of 30
The effect of the present application can be obtained if the amount is present at ~70% by weight, but it is usually desirable for both to coexist, and the weight ratio is 1O:
A ratio of 1.0 to 1.0:3.0 is advantageous.

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, first, ammonia and propionaldehyde are supplied into an aqueous medium, and ammonia is charged in order to cause the two to react, and then propionaldehyde is added dropwise or in bulk. The reaction temperature during such reaction is suitably 15 to 40°C, preferably 20 to 30°C. The reaction time is preferably about 0.5 to 11.0 hours.

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 40 to 70°C, preferably 50 to 60°C. A practical reaction time is about 0.5 to 20 hours.

The reaction is completed by aging for about 0.5 to 1.0 hours after the completion of the preparation.

The reaction product liquid contains 2E4MI as the 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-tmethylimidazofur was added.
A composition containing 2E4MI containing 70% by weight or less is produced. Note that the composition range targeted by the present application can be achieved by appropriately selecting the amount of collected distillate fraction.

The 2E4MI-containing composition thus obtained has excellent stability and is resistant to crystallization, and is thus useful as a curing accelerator for epoxy resins.

[Function] The 2-ethyl-4-methylimidazole-containing composition obtained in the present invention does not precipitate crystals even at low temperatures, has excellent stability, and is useful as a curing accelerator for epoxy resins.

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

Example 1 238 g (1.75 mol) of 12.5% aqueous ammonia was supplied to an IQ volume separable flask, and 40.69 (0.7 mol) of propionaldehyde was added while keeping the temperature below 50°C.
was dripped. Subsequently, 126 g (0.7 mol) of a 40% aqueous methylglyoxal solution was added dropwise over 2 hours. After the addition was completed, the mixture was aged for 0.5 hours at the same temperature. The obtained product liquid was subjected to vacuum distillation to obtain 4-methylimidazole 1
5%, 2.4-dimethylimidazole 15%, 2E4M
A composition containing 70% of 2E4MI was obtained. Even when this composition was stored at 0 to 2°C for 30 days, no crystals were deposited at all.

Example 2 In Example 1, 25% ammonia water, 1009 (1
, 47 mol), propionaldehyde 46.4 g (0,
8 mol), methylglyoxal aqueous solution 1269 (0,
An experiment was carried out according to the method of Example 1 except that 4-methylimidazole was used at 15% and 2.4 mol).
-dimethylimidazole 25%, 2E4MI 60%
A 2E4MI-containing composition was obtained.

Even when this composition was stored at 0 to 2°C for 45 days, no crystals were deposited at all.

Control Example 1 In Example 1, aqueous ammonia 12.5%, 160°89 (1,33 mo/l), propionaldehyde 52
．． 87 (0.91 mol) and methylglyoxal aqueous solution 1269 (0.7 mol) according to the method of Example I. As a result, 4-methylimidazole 2.
5%, 2.4-dimethylimidazole 2.5%, 2E4
A composition containing 2E4MI with an MI of 95% was obtained.

When this composition was stored at 0 to 2°C for 2 days, crystals precipitated and the entire system took on a solid state.

[Effect] In the present invention, the content of 2゜4-dimethylimidazole and/or 4-methylimidazole obtained by reacting ammonia, propionaldehyde, and methylglyoxal is 30% by weight or more and 70% by weight or less. The 2-ethyl-4-methylimidazole-containing composition does not solidify even in winter and has excellent stability.

July 6, 1990

Claims (1)

[Claims] Ammonia, propionaldehyde, and methylglyoxal are reacted to produce a 2-ethyl-4-methylimidazole-based reaction with a content of 2,4-dimethylimidazole and/or 4-methylimidazole of 30% by weight or more and 70% by weight or less. A method for producing a highly stable 2-ethyl-4-methylimidazole-containing composition, characterized by obtaining a liquid.