JPH06184101A - Production of n-substituted maleimides - Google Patents

Abstract

PURPOSE:To obtain N-substituted maleimides in high reaction yield by using a solvent capable of readily carrying out separation and recovery of maleimides and an inexpensive acid catalyst. CONSTITUTION:In producing an N-substituted maleimide of formula II by subjected an N-substituted maleamic acid of formula I (R<1> is substitutive 1-12C alkyl or substitutive 3-12C cycloalkl) obtained from maleic anhydride and a primary amine to ring closure and imidation reaction in an organic solvent azeotropic with water in the presence of an acid catalyst, an aprotic polar solvent and a polymerization inhibitor while carrying out azeropic removal of produced water out of the system, dehydrocyclization and imidation reactions are carried out in homogeneous state without separation of an acid catalyst phase by using a sulfuric acid which is previously subjected to azeotropic dehydration with the organic solvent or a sulfonic acid as an acid catalyst, and after the reaction, the solvent is distilled away and the N-substituted maleimide produced by distillation purification is separated and recovered, and the acid catalyst phase after the distillation purification is recovered to re-utilize for imidation reaction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing N-substituted maleimides. N-substituted maleimides include ABS,
It is a compound useful as a heat resistance improver for resins such as PMMA and PVC and as an intermediate for pharmaceuticals and agricultural chemicals.

[0002]

2. Description of the Related Art Various methods for producing maleimides have long been studied. Among them, the most general method is a method for producing maleimides by subjecting maleamic acid to a dehydration ring closure using a dehydrating agent such as acetic anhydride. (U.S. Pat. No. 2,444,536). In this method, maleic anhydride and an amine compound are reacted with each other, and the maleamic acid produced is subjected to ring-closure imidization in the presence of acetic anhydride and sodium acetate.

However, this method requires expensive acetic anhydride in an equivalent amount or more with respect to maleamic acid in the imidization reaction. Furthermore, after the imidization reaction, a large amount of water is used for separation and recovery of maleimide, so that a large amount of acetic acid-containing wastewater is generated, and it requires a great deal of cost to render this wastewater harmless. For this reason, this method is industrially disadvantageous.

Further, in Japanese Patent Publication No. Sho 51-40078, solvents such as toluene, xylene and chlorobenzene having a boiling point of 80 ° C. or higher and chlorosulfonic acid,
A method is disclosed in which heat dehydration ring closure is performed with a catalyst such as p-toluenesulfonic acid, benzenesulfonic acid, orthophosphoric acid, pyrophosphoric acid, and phosphorous acid, and water generated at this time is distilled out of the system by azeotropic distillation with a solvent. ing. This method is superior to the above-mentioned method in that the produced maleimide can be easily separated and recovered. However, although this method uses a relatively large amount of expensive acid catalyst such as chlorosulfonic acid, the yield of maleimides is low, and it is not economically satisfactory as an industrial production method.

On the other hand, in the method of carrying out the reaction in the coexistence of an aprotic polar solvent, for example, in JP-A-53-68770, maleic anhydride and a maleamic acid obtained from primary amines are used as an acid catalyst and an acid catalyst. A method for producing maleimides by reacting in a water-immiscible solvent at high temperature in the presence of an aprotic polar solvent such as dimethylacetamide is disclosed. Further, JP-A No. 63-122666 discloses a temperature range of 5 to 200 ° C. in an aromatic organic solvent containing an aprotic polar solvent such as dimethyl sulfoxide in the presence or absence of maleic anhydride in the presence or absence of an acid catalyst. Discloses a method for producing maleimides by reacting with primary amines. However, according to these methods,
Since the acid catalyst and the aprotic polar solvent used in the reaction are not recovered but become a large amount of industrial waste, there is an environmental problem.

[0006]

The object of the present invention is to reduce the waste and improve the economical efficiency by separating and recovering the acid catalyst and the aprotic polar solvent and using them repeatedly, and further to produce the maleimide. N-substituted maleimides are synthesized with a high reaction yield using a solvent that is easy to separate and recover, and an inexpensive acid catalyst, and easily produce highly pure N-substituted maleimides with little coloration by a simple purification process. To provide a method.

[0007]

The inventors of the present invention have made extensive studies in view of these problems, and as a result, a solvent and an inexpensive acid catalyst which facilitate separation and recovery of maleimides are used, and a high reaction yield is obtained. The inventors have found that an N-substituted maleimide can be obtained, and completed the present invention.

That is, the present invention provides the following general formula (1) obtained from maleic anhydride and primary amines.

[0009]

[Chemical 3]

(In the formula, R ¹ represents an unsubstituted or substituted alkyl group having 1 to 12 carbon atoms or an unsubstituted or substituted cycloalkyl group having 3 to 12 carbon atoms)
The N-substituted maleamic acid represented by the formula (I) is subjected to cyclization by azeotropic removal of water generated in the presence of an acid catalyst, an aprotic polar solvent and a polymerization inhibitor in an organic solvent capable of azeotropic distillation with water to the outside of the system by azeotropic removal. The following general formula (2) is obtained by imidization.

[0011]

[Chemical 4]

In producing the N-substituted maleimides represented by the formula (1), sulfuric acid is previously azeotropically dehydrated with an organic solvent or sulfonic acid is used as an acid catalyst,
A step of synthesizing N-substituted maleimides by dehydration ring-closure imidization reaction of N-substituted maleamic acid while the acid catalyst phase is not separated and homogeneous, and the solvent is distilled off from the reaction solution, followed by distillation purification. The present invention relates to a method for producing N-substituted maleimides, which includes a step of separating and recovering the N-substituted maleimides produced by the above, a step of recovering an acid catalyst phase after distillation and purification, and reusing it in the imidization reaction.

The present invention will be described in detail below.

In the present invention, sulfuric acid means one containing H ₂ SO ₄ , and specifically, for example, concentrated sulfuric acid, diluted sulfuric acid,
Fuming sulfuric acid and the like can be mentioned, and it is preferable to use concentrated sulfuric acid because it is easy to handle. In place of the dehydrated sulfuric acid, for example, p-toluenesulfonic acid, xylenesulfonic acid, mesitylenesulfonic acid, chlorobenzenesulfonic acid, fluorobenzenesulfonic acid, which are prepared in advance,
Sulfonic acids such as nitrobenzenesulfonic acid, naphthalenesulfonic acid, trifluoromethanesulfonic acid, ethylbenzenesulfonic acid, methanesulfonic acid, benzenesulfonic acid, ethanesulfonic acid and octanesulfonic acid may be used.

On the other hand, the aromatic organic solvent may be any aromatic solvent which is inert to the N-substituted maleimides and is immiscible with water. For example, benzene, toluene, xylene, cumene, ethylbenzene, chlorobenzene, fluorobenzene, nitrobenzene, anisole and the like can be mentioned, and it is preferable to use toluene and xylene from the viewpoint of reaction temperature control and ease of solvent removal.

In the above azeotropic dehydration, for example, when concentrated sulfuric acid is used as sulfuric acid, it is about 0.4 with respect to 1 mol of concentrated sulfuric acid.
It is suitable to distill off the mole of water to 1.1 mole, preferably 0.6 mole to 1.1 mole of water from the viewpoint of increasing the yield of maleimide in the subsequent ring-closing imidization reaction.

Azeotropic dehydration is carried out, for example, at 70 to 180 ° C., preferably 80 to 160 ° C. for 10 to 90 minutes, preferably 1
It can be carried out by heating for 5 to 60 minutes, and can be carried out at any of normal pressure, pressurization and reduced pressure.

If the amounts of sulfuric acid and sulfonic acids used are too small, the acid catalyst phase and the solvent phase are separated in the subsequent imidization reaction, the reaction does not proceed sufficiently, the reaction time becomes long, and the catalyst phase Decomposition of amic acid and maleimide may occur, leading to a decrease in selectivity. On the contrary, if the amount of the acid catalyst is too large, a large amount of by-products due to hydrolysis and polymerization reaction tend to be produced. Therefore, the amount is 20 to 90 mol, preferably 3 to 100 mol of the N-substituted maleamic acid.
It is suitable to use 0 to 70 mol.

The amount of the aromatic organic solvent used is 1 to 7 times, preferably 1 to the weight of the N-substituted maleamic acid, in order to carry out the reaction smoothly and to satisfy the economical conditions.
It is suitable to make it 3 times.

Specific examples of the N-substituted maleamic acid represented by the general formula (1) include N-methylmaleamic acid, N-ethylmaleamic acid, N- (n-propyl) maleamic acid, N- Isopropylmaleamic acid, N- (n-butyl) maleamic acid, N- (s
ec-Butyl) maleamic acid, N-isobutylmaleamic acid, N- (tert-butyl) maleamic acid, N- (n-hexyl) maleamic acid, N-cyclohexylmaleamic acid, N- (n-octyl) )
Maleamic acid, N- (n-decyl) maleamic acid, N- (n-dodecyl) maleamic acid, N- (n
-Octadodecyl) maleamic acid, N- (2-methyl-cyclohexyl) maleamic acid, N- (4-methyl-cyclohexyl) maleamic acid, N-allylmaleamic acid and the like can be mentioned.

The maleamic acid of the general formula (1) is obtained by mixing primary amines 0.90 to 1.
Almost quantitatively obtained by reacting 10 mol, preferably 0.95 mol to 1.05 mol, at 50 to 70 ° C. under normal pressure. Further, it is desirable to carry out the reaction in an inert gas atmosphere, for example, a nitrogen atmosphere. In the reaction, it may be previously charged with maleic anhydride primary amines from the beginning, but it is preferable to add a small amount at a time either for exothermic. More preferably, the primary amines are added to maleic anhydride completely dissolved in a solvent in the above temperature range for 5 to 180 minutes, preferably 1 to facilitate operation.
It is preferable to add it dropwise over 5 to 60 minutes. The reaction time of the amidation reaction is 0.5 to 10 hours after the addition of amines is completed,
It is preferably 2 to 5 hours. As the solvent, any solvent may be used as long as it is inert to maleic anhydride and amines, but toluene and xylene are preferably used in consideration of the imidization reaction that follows.

Examples of the primary amines include methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, sec-butylamine, isobutylamine, tert-butylamine, n-hexylamine, n-octylamine, n. -Decylamine, n
-Dodecylamine, n-octadodecylamine, cyclohexylamine, 2-methyl-cyclohexylamine,
4-methyl-cyclohexylamine, allylamine, etc. can be mentioned.

The solution containing maleamic acid thus obtained can be used as it is for the imidization reaction, or can be used for the imidization reaction after isolation as crystals.

In the method of the present invention, the N-substituted maleamic acid represented by the general formula (1) can be azeotroped with water in a mixture of the azeotropically dehydrated sulfuric acid or sulfonic acids and the aromatic solvent. By heating in a group organic solvent in the presence of an acid catalyst to remove produced water out of the system and ring-closing imidization, N-substituted maleimides represented by the general formula (2) are obtained. Regarding the reaction conditions, the reaction temperature is, for example, 30 to 180 ° C., preferably 40 to 160 ° C., and the reaction time is, for example, 1 to 8 hours, preferably 1 to 4 hours, although it depends on the reaction temperature and the like. . Further, the present reaction can be carried out not only under normal pressure but also under pressure or under reduced pressure within the above reaction temperature range. It is also possible to continuously raise the reaction temperature within the above temperature range and reaction time.

In the method of the present invention, an aprotic polar solvent is added to the mixture of the azeotropically dehydrated sulfuric acid and the aromatic organic solvent. Examples of the aprotic polar solvent that can be added to this reaction system include N-methyl-2-pyrrolidone and N-
Examples thereof include ethyl-2-pyrrolidone, N- (n-butyl) -2-pyrrolidone, dimethyl sulfoxide and dimethylformamide. The amount of these aprotic polar solvents added is 10% by weight of N-substituted maleamic acid.
It is suitable that the amount is 1 to 80 mol, preferably 5 to 70 mol, relative to 0 mol. The effect of adding the aprotic polar solvent is that the reaction rate is accelerated and the hydrolysis reaction is suppressed.

The polymerization inhibitor used in the present invention is, for example, phenol, methoxyphenol or t.
ert-butylcatechol, 2,4-dinitrophenol, hydroquinone, tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol,
2,2'-methylene-bis- (4-methyl-6-ter
t-butylphenol), 2,2'-methylene-bis-
(4-ethyl-6-tert-butylphenol),
Alkylmonophenyls and alkylbisphenyls having a phenyl skeleton such as 4,4′-thiobis- (3-methyl-6-tert-butylphenol), dilauryl thiodipropionate, distearyl thiodipropionate, thiodipropione Thiodipropionic acid diesters such as acid dododecyl, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, di-n-
Sodium butyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate,
Dithiocarbamate salts such as zinc di-n-butyldithiocarbamate, nickel dimethyldithiocarbamate, nickel diethyldithiocarbamate, nickel di-n-butyldithiocarbamate, sodium salicylate, phenyl salicylate, salicylate-p-tert-butylphenyl, salicylate-p- Salicylates and salicylates such as octylphenyl, phenothiazine,
Phenothiazines such as methylene blue, 1,6-hexanediol-bis- [3- (3,5-di-t-butyl-
4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,
2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, etc. Hindered phenols, 2-mercaptobenzimidazoles, 2-mercaptobenzimidazole zinc salts, 2-mercaptomethylbenzimidazoles and other mercaptoimidazoles,
Trialkyl phosphites such as triphenyl phosphite and diphenyl isodecyl phosphite, copper sulfate, copper (I) chloride, copper (II) chloride, copper nitrate, copper acetate, copper carbonate, and other inorganic salts of copper. be able to.

The amount of the polymerization inhibitor used is N-
It is 0.001 to 5% by weight, preferably 0.002 to 1% by weight, based on the substituted maleamic acid. If the amount of the polymerization inhibitor used is small, the effect is not sufficient, and there is a risk that the reaction yield may decrease due to the polymerization reaction. On the other hand, if it is used in excess, it is uneconomical.

The general formula (2) obtained by the method of the present invention
Examples of N-substituted maleimides represented by
Methyl maleimide, N-ethyl maleimide, N- (n-
Propyl) maleimide, N-isopropylmaleimide,
N- (n-butyl) maleimide, N- (sec-butyl) maleimide, N-isobutylmaleimide, N- (t
ert-butyl) maleimide, N- (n-hexyl) maleimide, N- (n-octyl) maleimide, N- (n
-Decyl) maleimide, N- (n-dodecyl) maleimide, N- (n-octadodecyl) maleimide, N-cyclohexylmaleimide, N- (2-methyl-cyclohexyl) maleimide, N- (4-methyl-cyclohexyl) maleimide , N-allyl maleimide and the like.

The reaction solution containing the N-substituted maleimides obtained by the above-mentioned reaction procedure is subjected to solvent removal under reduced pressure of 20 to 200 mmHg, and then 0.1 to 20 mmHg.
High-purity N-substituted maleimides having no coloration can be obtained by distillation and purification under reduced pressure. Further, the residue after distillation and purification can be repeatedly used as an acid catalyst in the imidization reaction. Further, water may be added to the residue to form an aqueous solution, insoluble matter may be removed, and then dehydrated and concentrated for use.

[0030]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1 To a 5-liter three-neck separable flask equipped with a thermometer, an amine introduction tube and a stirrer was added 3.5 liters of toluene, and then 343 g (3.5 mo) of maleic anhydride was added.
1) was added and the temperature was raised to 60 ° C. After reaching 60 ° C., 109.0 g (3.5 mol) of methylamine gas was blown into the toluene solution of maleic anhydride over 1 hour, and after the blowing of methylamine was completed, stirring was continued for 3 hours to carry out the amidation reaction. went. After completion of the reaction, the crystals of methylmaleamic acid were filtered, and the crystals were washed with water and methanol. The washed crystals were dried under reduced pressure to obtain 406.4 g (90%) of white crystals of methylmaleamic acid.

In a 500 ml four-necked flask equipped with a thermometer, a condenser equipped with a water separator and a stirrer, xylene 45 was added.
ml and concentrated sulfuric acid 5.3 ml (50 mol% with respect to maleamic acid) were added, and the mixture was stirred and refluxed under normal pressure in the temperature range of 135 to 140 ° C. for 30 minutes to produce 1.6 ml of water (1 mol of the concentrated sulfuric acid added was 0. (Corresponding to 0.9 mol) was removed from the system by azeotropic distillation. After heating under reflux and completion of azeotropic dehydration, the mixture was allowed to cool to room temperature and 51.6 mg of pentaerythrityl [tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate]] as a polymerization inhibitor. (2000 ppm with respect to maleamic acid), N-methyl-2-pyrrolidone 4.8 m as aprotic polar solvent
1 (corresponding to 25 mol% relative to maleamic acid) was added, and then 25.8 g (0.2 mol) of N-methylmaleamic acid obtained above was added, and the mixture was heated to reflux to produce 1. While distilling off the water to be removed from the reaction system together with xylene, the temperature of 140 to 145 ° C.
The ring-closing imidization reaction was carried out for 5 hours. During this time, the reaction solution was always homogeneous.

After the reaction was completed, the reaction solution was analyzed by high performance liquid chromatography to find that 21.1 g of N-methylmaleimide was formed. This corresponds to 95.0 mol% with respect to the raw material N-methylmaleamic acid.

After completion of the reaction, xylene was removed at 50 ° C. and 40 mmHg, and then at 70 ° C. under reduced pressure of 10 mmHg.
The temperature was raised to ˜150 ° C. and N-methylmaleimide was distilled. The crystals obtained by distillation were 20.2 g, and when analyzed by high performance liquid chromatography, the purity of N-methylmaleimide in the crystals was 99% by weight, and 0.4% by weight of maleic anhydride was contained. . As a result of analysis by gas chromatography, N-methyl-2-pyrrolidone was not detected in the crystals at all. The crystals were white crystals, and the absorbance of 5% by weight of toluene and methanol solution in the visible region was substantially 0 in the ultraviolet spectroscopic analysis. On the other hand, 2 as a residue after distillation
3.5 g was obtained.

Example 2 23.5 g of the residue after distillation obtained in Example 1 was measured with a thermometer,
500 ml with condenser and stirrer with water separator
Add to 4-neck flask. 45 ml of xylene and 25.8 g of N-methylmaleamic acid (0.2 mo
l) was added and the temperature was raised until the mixture was refluxed, while the water formed was distilled off together with xylene out of the reaction system.
The ring-closing imidization reaction was carried out in the temperature range of 0 to 145 ° C. for 1.5 hours. During this time, the reaction solution was always homogeneous.

After the reaction was completed, the reaction solution was analyzed by high performance liquid chromatography to find that 21.5 g of N-methylmaleimide was formed. This corresponds to 96.9 mol% with respect to the raw material N-methylmaleamic acid.

After completion of the reaction, xylene was removed at 50 ° C. and 40 mmHg, and then at 70 ° C. under reduced pressure of 10 mmHg.
The temperature was raised to ˜150 ° C. and N-methylmaleimide was distilled. The crystals obtained by distillation were 19.7 g, and when analyzed by high performance liquid chromatography, the purity of N-methylmaleimide in these crystals was 99% by weight, and 0.4% by weight of maleic anhydride was contained. . As a result of analysis by gas chromatography, N-methyl-2-pyrrolidone was not detected in the crystals at all.

Example 3 The reaction temperature after adding N-methylmaleamic acid was adjusted to 6
The temperature was raised from 0 ° C to 140 ° C over 0.5 hour. still,
During this period, the pressure was reduced to keep the solvent constantly refluxing, and the reaction was further performed at 140 ° C. for 1.5 hours. Other than that, the same operation as in Example 1 was repeated.

After the completion of the reaction, the reaction solution was analyzed by high performance liquid chromatography to find that 21.8 g of N-methylmaleimide was produced. This corresponds to 98.2 mol% with respect to the raw material N-methylmaleamic acid.

After completion of the reaction, xylene was removed at 50 ° C. and 40 mmHg, and then at 70 ° C. under reduced pressure of 10 mmHg.
The temperature was raised to ˜150 ° C. and N-methylmaleimide was distilled. The crystals obtained by distillation were 21.3 g, and when analyzed by high performance liquid chromatography, the purity of N-methylmaleimide in the crystals was 99% by weight, and 0.4% by weight of maleic anhydride was contained. . As a result of analysis by gas chromatography, N-methyl-2-pyrrolidone was not detected in the crystals at all. On the other hand, 23.8 g was obtained as a residue after distillation.

Example 4 23.8 g of the residue after distillation obtained in Example 3 was used in Example 2
After transferring the mixture to a four-necked flask and dehydrating it in the same manner as in the above operation, the same reaction operation as in Example 3 was performed.

After the reaction was completed, the reaction solution was analyzed by high performance liquid chromatography to find that 20.4 g of N-methylmaleimide was formed. This corresponds to 92.0 mol% with respect to the raw material N-methylmaleamic acid.

After the completion of the reaction, xylene was removed at 50 ° C. and 40 mmHg, and then at 70 ° C. under reduced pressure of 10 mmHg.
The temperature was raised to ˜150 ° C. and N-methylmaleimide was distilled. The crystals obtained by distillation were 20.0 g, and when analyzed by high performance liquid chromatography, the purity of N-methylmaleimide in the crystals was 99% by weight and contained 0.3% by weight of maleic anhydride. . As a result of analysis by gas chromatography, N-methyl-2-pyrrolidone was not detected in the crystals at all.

[0044]

EFFECTS OF THE INVENTION According to the method of the present invention, not only the maleimide can be easily separated and recovered, but also the acid catalyst can be repeatedly used, so that the environmental impact of waste water and the like is small, the economical efficiency is improved, and the yield is improved. It is possible to efficiently produce N-substituted maleimides.

Further, the method of the present invention is advantageous in that maleimides can be produced in a shorter step and the obtained N-substituted maleimides are less colored than the conventional method for producing maleimides.

Claims (1)

[Claims] 1. The following general formula (1) obtained from maleic anhydride and primary amines: (In the formula, R ¹ is an unsubstituted or substituted carbon atom 1
~ 12 alkyl groups, unsubstituted or substituted C3-12 cycloalkyl groups are shown)
-Substituted maleic amidates are subjected to ring-closing imidization by azeotropic removal of water generated in the presence of an acid catalyst, an aprotic polar solvent and a polymerization inhibitor in an organic solvent capable of azeotropic distillation with water to the outside of the system to effect cyclization imidization. General formula (2) In producing N-substituted maleimides represented by
As an acid catalyst, sulfuric acid is previously azeotropically dehydrated with an organic solvent, or sulfonic acid is used, and the dehydration ring-closure imidization reaction of the N-substituted maleamic acid is carried out while the acid catalyst phase is not separated, and N-substituted. The step of synthesizing maleimides, the solvent is distilled off from the reaction solution, and the N-substituted maleimides produced by distillation purification are separated,
A method for producing N-substituted maleimides, comprising a step of recovering, a step of recovering an acid catalyst phase after distillation purification, and reusing it in the imidization reaction.