JPH01242568A - Production of maleimides - Google Patents

Abstract

PURPOSE:To improve the yield of the subject substance useful as a raw material for resins, etc., from meleinamidic acids, without causing the formation of im purity by-product and the loss of catalyst, by adding primary amines at the former half stage of the reaction having low reaction temperature and adding maleic anhydride at the latter half stage of the reaction having high reaction temperature. CONSTITUTION:Primary amines are added to an organic solvent solution of maleic anhydride and reacted at <=150 deg.C to obtain maleinamidic acid. The molar ratio of maleic anhydride to the primary amines is preferably 1:1-1.3. An acid catalyst is added to the maleinamidic acid. In the above procedure, free primary amines are added to the solution when the amount of the primary amines is smaller than the maleic anhydride. The reaction is carried out at 100-250 deg.C and the produced water is distilled out of the system as a mixture with the solvent. When 40-99% of water is distilled based on the theoretical amount of water to be produced, the reaction is regarded to reach the end point. Thereafter, additional maleic anhydride is added to the system and the mixture is heated while the produced water is distilled out from the system to obtain the objective compound.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing maleimides.

Maleimide compounds are useful compounds as raw materials for resins, pharmaceuticals and agricultural chemicals, and the present invention provides an advantageous method for producing them.

(Prior Art) Methods for producing maleimides have been studied for a long time.

The most common method is to cyclodehydrate maleamic acid using a dehydrating agent such as acetic anhydride to convert maleimide into TIJ 3i.
It is also disclosed in the specification of No. 444536.

That is, it is a method in which maleic anhydride and an amine compound are reacted, and the resulting maleamic acid is dehydrated and ring-closing imidized in the presence of acetic anhydride and sodium acetate. This method requires more than the equivalent amount of expensive acetic anhydride to maleamic acid in the imidization reaction, and also requires a large amount of water to separate and recover the maleimide produced from the liquid after the imidization reaction. As a result, a large amount of wastewater containing acetic acid is generated, which has the disadvantage of requiring a large amount of cost to detoxify it. For these reasons, this method is too expensive (if
I have to say it's a fi-like method.

In addition, as disclosed in JP-A No. 53-68770, maleic anhydride and an amine compound are reacted in an organic solvent, and the resulting maleamic acid is not isolated, but non-containing substances such as dimethylformamide and dimethyl sulfoxide are used. There is also a method of carrying out a dehydration ring closure reaction in the coexistence of a protic polar solvent and an acid catalyst. However, this method uses a large amount of expensive and toxic aprotic polar solvents such as dimethylformamide, which increases the production cost of maleimide. There are problems such as increased loss due to deterioration of the solvent, and furthermore, it is difficult to remove these aprotic polar solvents from the product maleimide due to their high boiling points. Therefore, it cannot be said that it is an excellent method.

Furthermore, as disclosed in Equity IIF (51-40078@publication specification), solvents such as toluene, xylene, and chlorobenzene having a boiling point of 80°C or higher as diluents, and chlorosulfonic acid, p-toluenesulfonic acid,
Benzene sulfonic acid, orthophosphoric acid.

There is also a method of carrying out thermal dehydration ring closure together with an acid catalyst such as pyrophosphoric acid or phosphorous acid, and distilling the water produced at this time out of the yarn by azeotropy with a solvent. This method is superior to the above two methods in that it not only does not require a large amount of an expensive dehydrating agent such as acetic anhydride, but also that the maleimide produced is easy to separate and recover.

However, in this method, chlorsulfone M,
A relatively large amount of expensive acid catalysts such as p-toluenesulfonic acid, benzenesulfonic acid, orthophosphoric acid, pyrophosphoric acid, phosphorous acid, etc. are used, and the yield of maleimides is low, making it economical as an industrial production method. It is not completely satisfying.

As described above, the conventionally proposed methods for producing maleimides have many problems and are not satisfactory for industrial implementation.

(Problems to be Solved by the Invention) The present inventors have long continued research on the synthesis reaction of maleimides. In particular, we have intensively investigated the reaction conditions for the ring-closing imidization reaction of maleamic acid in a water-insoluble or water-immiscible inert organic solvent using an acid catalyst.

Maleamic acid is present in the organic solvent layer, and an acid catalyst is added to this organic solvent layer when performing the imidization reaction. The catalyst is insoluble in the solvent and forms another liquid phase in the reactor that is different from the organic solvent layer.

However, in the conventional reaction method, after the completion of the imidization reaction, a large amount of by-product insoluble impurities accumulates at the boundary between the acid catalyst Is layer and the organic solvent layer, resulting in a large amount of M1 accumulated at the boundary between these two liquid layers. was unclear. Therefore, when the acid catalyst layer is separated from the organic solvent layer and reused, there is a problem that the catalyst and the organic solvent layer cannot be separated well and a large amount of expensive catalyst is lost.

In addition, when the catalyst is separated and reused, a large amount of impurities accumulates in the recycled catalyst, causing drastic changes in the physical properties of the acid catalyst, such as an increase in the viscosity of the acid catalyst. Along with this, there was a problem in that the dispersion state of the catalyst deteriorated and the reaction yield significantly decreased.

As described above, the by-product of insoluble impurities such as those deposited at the interface between the acid catalyst layer and the organic solvent layer has been a major problem in industrially producing maleimides efficiently and inexpensively.

(Means for Solving the Problems) Therefore, the present inventors have intensively studied reaction conditions that can suppress side reactions that produce insoluble impurities in the organic soluble tJiN layer. As a result, the main component of the insoluble impurity is fumaric acid, and this fumaric acid is produced when maleic acid generated as a result of acid-catalyzed hydrolysis of maleamic acid is further converted to fumaric acid by heat. It has been found. Furthermore, primary amines, which are another component of maleamic acid when producing fumaric acid, react with maleimides produced by imidization and dehydration reaction, and produce 2-amino-N-substituted succinimides as a by-product. It comes alive. It was found that, for this reason, the selectivity for maleimide production was extremely low.

In addition, a more detailed study of fumaric acid production during the imidization dehydration reaction revealed that in the latter half of the maleamic acid dehydration reaction, where a large amount of reaction product water is generated, the reaction temperature is relatively low and the amount of water in the acid catalyst is low. Since the amount is also high, the hydrolysis reaction is noticeable.

On the other hand, in the latter half of the dehydration reaction, the amount of reaction product water produced was small, the internal temperature of the reaction solution was also relatively high, and the water content in the acid catalyst was low, making it difficult for the hydrolysis reaction to occur.

However, it has been discovered that if primary amines, which are one of the reaction raw materials, are allowed to coexist in the low-temperature part of the first half of the reaction, the hydrolysis reaction is significantly suppressed, and therefore fumaric acid production is hardly observed. It was.

Furthermore, although it was completely unexpected, by coexisting maleic anhydride in the second half of the high temperature section, 2-amino-N-substituted succinimide, which was once produced by the DI reaction in the first half of the reaction, was They also discovered that they could be efficiently decomposed and converted back into maleimides, leading to the completion of the present invention.

That is, the present invention involves heating maleamidic acids obtained from maleic anhydride and primary amines in the presence of an acid catalyst in a water-insoluble or water-immiscible inert organic solvent, and converting the resulting water into the organic When producing maleimides by ring-closing imidization while distilling them out of the system as a mixture with a solvent, the amount of water is 40 to 99% based on the theoretical amount of water produced from the start of the reaction.
Maleamidic acids characterized in that the reaction is carried out in the presence of a primary amine until the produced water is distilled off, then maleic anhydride is added, and the reaction is carried out in the presence of the acid. This is a method for producing maleimides from.

Another feature of the present invention is that when producing maleimides from maleamic acids, primary amines are added in the first half of the imidization and dehydration reaction, where the reaction temperature is low, to remove the primary amines in the reaction system. The production of fumaric acid is suppressed by making it in excess of maleic anhydride, and then in the second half of the imidization and dehydration reaction where the reaction temperature is high, maleic anhydride is added to make it in excess of the primary amines in the reaction system. In other words, the purpose is to efficiently decompose impurities produced as by-products in the presence of maleic anhydride to generate maleimides.

According to the present invention having the above-described configuration, the catalyst can be efficiently separated and recovered, and maleimides can be obtained in high yield.

The present invention will be explained in detail below.

The maleamic acid used in the present invention is usually easily obtained by the reaction of maleic anhydride and primary amines, and is represented by the following formula.

CI-(-C-0)-1 CH-C-N)-1-R (wherein, R is an alkyl group having 1 to 20 carbon atoms, a phenyl group, a benzyl group, a cyclohexyl group, a pyridyl group,
Quinolyl group and these groups substituted with halogen or carboxyl group.

It is selected from those with nitro group substitution.

) In particular, the following primary amines are suitable as raw materials for the maleamic acid used in the present invention.

Methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine.

5ec-butylamine, tert-butylamine, n
-hexylamine, n-dodecylamine, allylamine, benzylamine, cyclohexylamine, aniline,
nitroaniline, amine phenol, aminobenzoic acid,
Anisidine, ethoxyphenylamine, monochloroaniline, dichloroaniline.

Toluidine, xylidine, ethylaniline, etc.

Furthermore, the organic solvent used in the present invention is preferably a solvent that is insoluble or immiscible in water, inert, and does not participate in the reaction, such as benzene.

Toluene, petroleum fractions with a boiling point of 50 to 120°C, xylenes, ethylbenzene, isopropylbenzene, cumene, mesitylene, tert-butylbenzene, pseudocumene, trimethylhexane, octane, tetrachloroethane, nonane, chlorobenzene, ethylcyclohexane,
Petroleum fraction with a boiling point of 120 to 170°C, ■-dichlorobenzene, 5ec-butylbenzene, p-dichlorobenzene, decane, p-cymene.

0-dichlorobenzene, butylbenzene, decahydronaphthalene, tetrahydronaphthalene.

Dodecane, naphthalene, cyclohexylbenzene.

There are petroleum fractions with a boiling point of 170 to 250°C. The amount of this solvent to be used is 0.5 to 20 times the amount of maleamic acid in order to perform the reaction smoothly and satisfy economic conditions.
(capacity), preferably 1 to 7 times.

Furthermore, a compound having a boiling point suitable for the reaction conditions is selected while taking into account the solubility, price, handling, size, etc. of the maleimide. Furthermore, when considering the separation of the maleimides from the solvent after the reaction is completed, it may be advantageous to use a low boiling point solvent and carry out the reaction under pressure F.

Sulfuric acid, orthophosphoric acid, and metaphosphoric acid are used as catalysts.

An amine salt obtained by neutralizing a monobasic acid such as pyrophosphoric acid or a polysalt MW and/or an amine, which is a raw material for producing maleimides, is used.

Further, these catalysts may be supported on a solid carrier.

　　.

Solid carriers include natural minerals, such as kaolins, clays, talc, chalk, quartz, bentonite, montmorillonite, diatomaceous earth, etc., di-synthetic minerals such as highly dispersed silicic acid, alumina, silicates, activated carbon, gypsum, red iron, oxides, etc. Titanium, silica, silica-alumina, zirconium oxide, etc.: Natural rocks such as calcite, marble, pumice, sepiolite, dolomite, etc. are used.

These inorganic carriers are powdered or granulated.

It is used in the form of granules or honeycombs obtained by classification.

It is also possible to use organic carriers, and particulate carriers such as polyfluorocarbon, polystyrene, and phenolic resins can also be used.

Particularly good results can be obtained when the carrier is porous, such as diatomaceous earth, silica gel, etc. For example, examples of commercially available diatomaceous earth include Radiolite (manufactured by Showa Kagaku Kogyo Co., Ltd.), and examples of silica gel include Caract, Cyroid, Microbead Silica Gel (manufactured by Fuji Davison Chemical Co., Ltd.), and Wakogel (manufactured by Wako Pure Chemical Industries, Ltd.). , etc. can be given.

The amount of these catalysts used is 2 to 400 mol%, preferably 20 to 2 mol%, based on the maleamic acid contained in the acid content.
The range is 0.00 mol%. Further, part or all of the acid serving as a catalyst may be neutralized with an amine.

Further, depending on the case, a metal-containing compound or a stabilizer may be allowed to coexist in the reaction system for the reaction. The metal-containing compounds used at this time include zinc and chromium.

At least one metal oxide selected from the group consisting of palladium, cobalt, nickel, iron and aluminum,
Acetate, maleate, succinate.

It is selected from nitrates, phosphates, chlorides and sulfates, among which zinc acetate is particularly effective. These usage amounts are based on 1 mole of maleamic acid.
The content of the metal is 0.005 to 0.5 mol%, preferably 0.01 to 0.1 mol%.

Additionally, methoxybenzoquinone is used as a stabilizer.

p-methoxyphenol, phenothiazine, hydroquinone, alkylated diphenylamines, methylene blue
, tert-butylcatechol, tert-butylhydroquinone, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionic acid esters,
Mercaptobenzimidazole, triphenyl phosphite, alkylphenols, alkylbisphenols, etc. are used.

The effects of these stabilizers play a role in allowing the maleimide produced by the imidization reaction to exist stably without deterioration even under the high temperature of the imidization reaction.

Regarding the amount added, adding a trace amount will reduce the effect, and conversely, adding an excessive amount is not desirable because it may cause a problem of mixing into the product. Therefore, when these are used, o, ooi to 0.5 mol% per mol of maleamic acid.
It is.

The method of carrying out the present invention is to first add primary amines to a solution of maleic anhydride in an organic solvent, and react at 150°C or lower, preferably at 30-120°C, for 15-120 minutes to convert maleamic acid. I can do it. In this case, the molar ratio of maleic anhydride to primary amines is 1:1 to 2 mol, preferably 1:1 to 1.3 mol.

Next, the above catalyst is added without isolating maleamic acid, but if the amount of primary amines is less than maleic anhydride during the synthesis of maleamic acid, free primary amines will be present again. Additional amounts are added to The presence ω of free primary amines in the system is 0.01 to 1.0 times, preferably 0.1 to 0.5 times, molar ratio to maleamic acid. Further, depending on the case, a metal compound I and/or a stabilizer may be added.

Thus 100-250°C, preferably 110-22
The first stage reaction is carried out while the water produced at a temperature of 0°C is distilled out of the system as a mixture with a solvent. The first stage reaction is completed when 40 to 99 mol %, preferably 60 to 90 mol % of water has been distilled out based on the theoretical amount of water to be produced.

Next, after the first stage reaction is completed, maleic anhydride is newly added without lowering the reaction temperature, and the reaction is carried out in the coexistence of maleic anhydride to complete the reaction. In this case, the amount of maleic anhydride added is such that the ratio of primary amine residue to maleimide acid group is 1:1 to 1.5 (mole ratio). Here, the primary amine residue refers to the primary amine skeleton that constitutes maleamic acid and the primary amines added during the first reaction, and the maleic acid residue refers to the primary amine skeleton that constitutes maleamic acid. The maleic acid skeleton and the maleic anhydride added during the second stage reaction are shown.

Thus, from the point of addition of maleic anhydride, 1 hour to 30
Maleimides can be produced in high yield by heating the water produced over time while distilling it out of the system as a mixture with a solvent.

(Effects of the Invention) The present invention has been described above, and the effects obtained by the present invention are as follows.

(1) Since the generation of insoluble side reaction products in the organic solvent layer is extremely small, separation of the catalyst layer and the organic solvent layer is extremely easy, and there is almost no catalyst loss.

(2) There is almost no accumulation of impurities in the catalyst, and the properties of the catalyst are stable. Therefore, even if the catalyst is used repeatedly, the dispersion performance of the catalyst does not change, so a stable yield can be obtained repeatedly.

(3) By adding maleic anhydride, the by-product impurities can be decomposed into maleimide once again, so
The desired product can be obtained with high selectivity and high yield.

(4) Due to the reaction with high selectivity, highly pure maleimides can be obtained and purification is extremely easy.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Anhydrous malein in a flask equipped with a thermometer, a condenser with a water separator, a dropping funnel and a stirrer! A solution prepared by dissolving 47g of 100g in 200g of ortho-xylene was charged.

Next, the temperature inside the flask was adjusted to 80° C., and aniline 50Q was added little by little over 30 minutes to synthesize a yellow-white ortho-xylene slurry of N-phenylmaleamic acid.

Then, add 20g of orthophosphoric acid to the slurry liquid.
(containing 3 g of water) was added, and the reaction was carried out at 133° C. for 2 hours while distilling the water produced by the reaction out of the system together with ortho-xylene. After 2 hours, the amount of water produced is 10
．． 7! :l, which corresponds to 89% of the amount of water that should theoretically be released when all of the added maleic acid is converted to maleimide.

An additional 11 g of maleic anhydride was then added and the reaction continued for 4 hours. After 4 hours of reaction, the stirrer was stopped and the catalytic layer and ortho-xylene layer were separated.
The mixture was completely separated into two layers, and no insoluble by-products were observed at the interface between the two phases.

After separating this ortho-xylene layer from the catalyst layer, the ortho-xylene was distilled off under reduced pressure to obtain a yellowish-brown solid with a particle size of 92σ. When this product was analyzed using liquid chromatography, it was found to have the following composition.

N-phenylmaleimide 93.3% by weight fumaric acid
0.2 weight ω% 2-anilino N-phene 0.1 weight % or less Nyl succinimide The yield of N-phenylmaleimide corresponds to 92.3 mol % based on the aniline charged in the reaction.

Comparative Example 1 The same reactor as used in Example 1 was used. Instead of dividing maleic anhydride into two portions as in Example 1, 58 g of maleic anhydride was added from the beginning to synthesize N-phenylmaleamic acid. Next, the same catalyst as the IC used in Example 1 was added, and the reaction was carried out for 6 hours under the same temperature conditions. After the reaction was completed, the stirring JT machine was stopped to separate the catalyst layer and the ortho-xylene layer, and a large amount of whitish-brown byproducts were deposited at the contact interface between the two phases. Therefore, it has been extremely difficult to separate the ortho-xylene layer and the catalyst layer. Therefore, the ortho-xylene layer and the catalyst layer were allowed to stand still in the flask for about 5 hours,
Thereafter, the ortho-xylene layer was slowly separated so as not to mix the catalyst into the ortho-xylene layer.

When ortho-xylene was distilled off from the separated ortho-xylene layer under reduced pressure, 90% of a yellow solid was obtained.
(+ was obtained.) When this was analyzed by liquid chromatography, it was found that it had the following composition.

N-phenylmaleimide 77.5 ffl ffi
% fumaric acid 4.6% by weight 2-anilino N-phene 12.3% by weight Nylsuccinimide The yield of N-phenylmaleimide calculated from this composition was 75.0 mol % based on the charged aniline.

Example 2 The same flask used in Example 1 was charged with a solution of 479 maleic anhydride dissolved in 300 ml of ortho-xylene.

Next, the temperature inside the flask was adjusted to 60°C, and the aniline 5
0 (l) was added little by little over 1 hour to synthesize an ortho-xylene slurry of N-phenylmaleamic acid.

To the slurry thus obtained, 0.19% of zinc acetate, 0.19% of dibutyldithiocarbamic acid, tflo, ol(1, phosphorus)
M20σ (adding 3q of water and distilling the water generated at an internal temperature of 135°C out of the system together with ortho-xylene).
Allowed time to react. At this time, the ω of the water being generated is 8.
5g, which is the theoretical amount of water that should come out when all the added maleic anhydride is converted to maleimide.
This corresponds to 4%. At this stage, an additional 8 g of maleic anhydride was added and the reaction continued for 3 hours.

After the reaction was completed, the stirrer was stopped, and the catalyst layer and ortho-xylene layer were easily separated, and no insoluble impurities were observed at the interface between the two.

Subsequently, the ortho-xylene layer was separated from the catalyst layer, and the ortho-xylene was distilled off under reduced pressure, resulting in a yellowish-brown solid 9.
3g was obtained. When the composition of this product was analyzed by liquid chromatography, it was found to have the following composition.

N-phenylmaleimide 97.8% by weight fumaric acid
0.1% by weight or less 2-anilino N
-Fe 0.1% by weight or less Nilsuccinimide The yield of N-7 enylmaleimide was 97.8 mol% based on the charged aniline.

Example 3 Into a flask equipped with a thermometer, a cooling tube equipped with a water separator, a dropping funnel and a stirrer, 60 g of Ortholin M (90 g of water) was added.
g) and 20 g of water were added. Subsequently, cyclohexylamine 37G was added dropwise to synthesize a mixture of orthophosphoric acid and cyclohexylamine salt of orthophosphoric acid. Subsequently, 60 g of a granular silica gel carrier (microbead silica gel manufactured by Fuji Davison Chemical Co., Ltd.) was added to this and stirred to support the acid on the carrier. Next, mesitylene 2009 was added and heated, and water 29(+) was distilled off together with mesitylene to remove water from the supported catalyst.

On the other hand, 100 g of mesitylene was charged into the same flask used for preparing the catalyst, 90 g of maleic anhydride was added thereto, and the temperature inside the flask was raised to 60° C. to dissolve the maleic anhydride.

Next, add 10 cyclohexylamine to 300 Q of mesitylene.
A total of 5 drops of a solution containing 0g of N
- An ortho-xylene slurry of cyclohexyl maleamic acid was synthesized.

Next, the above-mentioned supported catalyst and 0.1 g of copper dibutyldithiocarbamate were added to this slurry liquid, heated and kept at 144°C with stirring, and the water produced by the reaction was distilled out of the system together with mesitylene. , and reacted for 5 hours.

The amount of water produced at this stage was 12 g, which corresponds to 73% of the amount of water that should theoretically come out if all the maleic anhydride added was converted to maleimide.

Next, 12 g of maleic anhydride was added and the reaction continued for 3.5 hours. After the reaction was completed, stirring was stopped, and the catalyst immediately precipitated and was separated into a mesitylene layer and a catalyst layer. Note that no insoluble impurities were observed at the interface between these two layers.

Next, the mesitylene layer was separated from the catalyst layer, and the yield was determined by analyzing the N-cyclohexylmaleimide content contained in the mesitylene layer. The yield was 98.5 mol based on the raw material cyclohexylamine. %Met.

Example 4 Ortholin M12+;+ (water 2
Then, 40 g of silica gel (Wako Glu C-100 manufactured by Wako Pure Chemical Industries, Ltd.) was added to support orthophosphoric acid on the silica gel.

Maleic anhydride 47 (
1 was dissolved in 250 g of xylene.

Next, adjust the temperature inside the flask to 80°C, and
A solution prepared by dissolving 0(+ in 150 g of xylene was added little by little over 30 minutes to synthesize an ortho-xylene slurry of N-phenylmaleamic acid.To this slurry of N-phenylmaleamic acid, The catalyst was added and the mixture was heated at 132° C. for 1 hour while the generated water was distilled out of the system as a mixture with ortho-xylene.

The amount of water produced at this time was 9.5 g, which corresponded to 87% of the water that would theoretically be produced if all the maleic anhydride added was converted to maleimide.

Maleic anhydride 13a was then added and the reaction continued for 2 hours. After the reaction was completed, the stirrer was stopped, and the supported catalyst rapidly settled at the bottom of the ortho-xylene layer and was separated into two layers.

At this time, no deposit of insoluble impurities was observed at the interface between the two layers. When ortho-xylene was distilled off from this ortho-xylene layer under reduced pressure, yellow crystals 97
I got a. When this product was analyzed by liquid chromatography, it had the following composition.

N-phenylmaleimide 93.9% by weight fumaric acid
0.1% by weight 2-anilino-N-phene 0.1[f1% or less Nilsuccinimide The yield of N-phenylmaleimide corresponds to 98.0 mol% based on the raw material aniline used in the reaction.

Comparative Example 2 A reaction was carried out for 3 hours in the same manner as in Example 4, except that the maleic anhydride was not added in two portions but was completely added from the beginning.

When the stirrer was stopped after the reaction, a large amount of yellowish-white impurities were present at the interface between the catalyst layer and the ortho-xylene layer, and the interface between the catalyst layer and the ortho-xylene layer was extremely unclear. Separation of the phases was not possible.

Example 5 The reaction was carried out under the same conditions as in Example 4 except that the solvent used in the reaction was toluene instead of ortho-xylene, the first reaction was carried out at 113°C for 7 hours, and the second reaction was carried out for 13 hours.

When the stirrer was stopped after the reaction was completed, the catalyst layer and the triene layer were clearly separated into two layers, and no insoluble impurities were observed. Further, when toluene was distilled off from the toluene group, yellow crystal 95() was obtained.When this crystal was analyzed by liquid chromatography, it had the following composition.

N-Phenylmaleimide 92.1fffffi% fumari! i0.1% by weight 2-anilino-N-phene 0.1% by weight or less Nil succinimide The yield of N-phenylmaleimide was 94.1 mol% based on the raw material aniline used in the reaction. .

Claims (1)

[Claims] (1) Maleamic acids obtained from maleic anhydride and primary amines are heated in a water-insoluble or water-immiscible inert organic solvent in the presence of an acid catalyst, and the resulting water is mixed with the organic solvent. When producing maleimides by ring-closing imidization while distilling the mixture out of the system, the primary amine is 1. A method for producing maleimides from maleamide acids, which comprises carrying out the reaction in the coexistence of maleamic acids, then adding maleic anhydride, and carrying out the reaction in the coexistence of the acid.