JPH03120251A - Production of maleimides - Google Patents

Abstract

PURPOSE:To obtain the subject compound by heating maleamic acids in a specific solvent using an acid catalyst incompatible with the solvent, carrying out cyclizing imidation reaction, adding a specified amount of water thereto, removing water-insoluble substances, then removing the added water and reusing the resultant acid catalyst. CONSTITUTION:Maleamic acids, such as N-cyclohexylmaleamic acid, are heated in a nonpolar organic solvent, such as xylene, capable of forming an azeotropic mixture with water in the presence of an acid catalyst, such as phosphoric acid, substantially incompatible with the aforementioned solvent to carry out cyclizing imidation reaction. Water in an amount of at least 30wt.% based on the separated and recovered acid catalyst is then added to remove deposited water-insoluble substances. The above-mentioned added water is subsequently removed to afford the acid catalyst with deteriorated activity. The obtained acid catalyst is effectively activated to reuse the activated catalyst for the aforementioned cyclizing imidation reaction. Thereby, the objective compound useful as a heat resistance improver for thermoplastic resins, such as polyvinyl chloride, polystyrene or ABS, and a raw material, etc., for heat-resistant resins is readily obtained in high yield and quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrially advantageous method for producing maleimides.

Maleimides include polyvinyl chloride, polystyrene, AB
It is a compound useful as a heat resistance improver for thermoplastic resins such as S and as a raw material for heat-resistant resins.

Conventional Techniques and Their Problems The present inventors first developed a technique in which an acid catalyst and a specific organic amine, which are incompatible with the solvent, coexist in a solvent mainly consisting of a non-polar organic solvent that is azeotropic with water. We proposed an industrial method for producing maleimides characterized by the reaction under heating and reflux while supplying maleamic acid (Japanese Patent Application Laid-Open No. 63-19656).
No. 0).

According to this method, highly pure maleimide with a good hue can be obtained in high yield, and the produced maleimide can be easily separated and recovered. However, on the other hand,
Since a relatively large amount of acid catalyst is required, it is desirable to use the recovered acid catalyst repeatedly from the viewpoint of reducing waste and improving economic efficiency.

In subsequent studies, it was found that although the acid catalyst could indeed be reused multiple times without any treatment, the catalytic activity suddenly decreased at a certain stage.

The present inventors have conducted extensive studies on a method for easily activating the deactivated acid catalyst used in the method for producing maleimide by ring-closing imidization, and have found that the cause of catalyst deactivation is found to be present in the acid catalyst. The present inventors have discovered that it is a water-insoluble side reaction product, and have completed the present invention based on this finding.

That is, the present invention proposes a method for easily activating an acid catalyst that has been deactivated by being reused, and further aims to provide an industrial method for producing maleimides with improved economic efficiency. do.

The method for producing maleimides according to the present invention involves heating maleamic acids in a nonpolar organic solvent that is azeotropic with water in the presence of an acid catalyst that is substantially incompatible with the solvent. In a method for producing maleimides by ring-closing imidization, (1) adding at least 30% by weight of water to the acid catalyst subjected to the ring-closing imidization reaction and quickly separated and recovered; and (2) precipitating. After removing water-insoluble substances, (3) (
The method is characterized in that the acid catalyst obtained by removing the water added in step 1) is used again as a catalyst for the ring-closing imidization reaction.

The maleamic acids according to the present invention are compounds derived from maleic anhydride and primary amines.

The above-mentioned primary amine may be aliphatic, alicyclic, or aromatic, and includes not only monoamines but also diamines and polyamines. Specifically, monoamines represented by the general formula (A), diamines represented by the general formula (B), and polyamines represented by the general formulas (C) and (D) are exemplified.

[In the formula, R1 is a carbon number 1 which may have a substituent such as a halogen atom, an alkoxy group, or a hydroxyl group.
~20 alkyl, cycloalkyl, phenyl or naphthyl groups. ]H2NR-R-NH2(B) [In the formula, R2 represents a divalent organic group having 2 to 20 carbon atoms. ] NH2NH2NH2 [In the formula, R3 is a hydrogen atom, a halogen atom, and a carbon number of 1 to 8
alkyl group, alkoxy group, hydroxyl group, n is 1
Indicates an integer between ~10. ] NH2N tj2 NH,
2 [wherein R3 and n are the same as in general formula C]. ] Among these primary amines, the effect is particularly remarkable when the R1 group in general formula (A) is an alkyl group or a cycloalkyl group.

Specifically, aliphatic or alicyclic primary amines include ethylamine, n-butylamine, n-octylamine,
2-ethylhexylamine, n-decylamine, n-dodecylamine, n-octadecylamine, cyclohexylamine, 2-methylcyclohexylamine, 4-methylcyclohexylamine, 4,4-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, 1
゜3-diaminocyclohexane, 1,4-butanediamine, 1,6-hexanediamine, 1,8-octanediamine, bis(3-aminopropyl)ethylene glycol ether, bis(3-aminopropyl)diethylene glycol ether, α, ω-bis(3-aminopropyl)
Examples include polyethylene glycol ether, bis(3-aminopropyl)tetrahydrofuran, α,ω-bis(3-aminopropyl)polytetrahydrofuran, and nuclear hydrides of aniline and formaldehyde condensates.

Further, as aromatic primary amines, aniline, 〇-toluidine, p-toluidine, xylidine, p-edylaniline, p-isopropylaniline, p-dodecylaniline, p-chloroaniline, 2゜4-dichloroaniline,
Anisidine, phenetidine, p-aminobenzoic acid, nitroaniline, aminephenol, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminophenylmethane, 2,2-bis(4-aminophenyl)p[] bread, 4,4-diaminophenyl oxide, 4.
4--Diaminodiphenylsulfone, bis(4-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, m-xylene diamine, 4,4-diaminobenzophenone, bis( 4-aminophenyl)phenylmethane, 1,1bis(4-aminophenyl)cyclohexane,
Examples include a condensate of aniline and formaldehyde, and a condensate of 0-toluidine and formaldehyde.

Examples of acid catalysts used in the present invention include inorganic acids such as phosphoric acid, phosphorous acid, hypophosphorous acid, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and sulfuric acid, and the amount used is usually , 10-200 for maleamic acid
It is about % by weight.

The solvent applied during the ring-closing imidization reaction is preferably a nonpolar organic solvent having a boiling point range of 60 to 200°C and capable of azeotropically distilling off the produced water, and is substantially miscible with the acid catalyst. First, any material that forms a two-liquid phase after the ring-closing imidization reaction may be used. Specifically, toluene, xylene, ethylbenzene, cumene, hexane, octane, decane, cyclohexane, methylcyclohexane, ethylcyclohexane, light oil, light oil Hydrocarbons such as hydrides, halogen-containing hydrocarbons such as chlorobenzene, dichloroethane, trichloroethane, perchloroethylene, and the like are exemplified, and may be used alone or in a mixture of two or more of them.

Furthermore, an aprotic polar organic solvent can also be used together with the above-mentioned non-polar organic solvent.

Such aprotic polar organic solvents include N.

N-dimethylformamide, N,N-diethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, hexamethylene phosphoramide, γ-butyrolactam, tetramethylurea, 1°3-dimethyl-2-imidazolidine, diglyme , dioxane, etc.

In this case, the amount of the aprotic polar solvent to be used in combination is within a range in which such a mixed solvent is not substantially compatible with the acid catalyst, and is generally within 50% by weight based on the non-polar organic solvent. be.

The amount of these reaction solvents used is generally about 1 to 20 times the weight of maleamic acid.

Further, in order to prevent coloring of the reactants and obtain high quality maleimide, it is preferable to carry out the reaction in the presence of a stabilizer. Suitable stabilizers include hydroquinone, methoxybenzoquinone, phenothiazine, tert-butylcatechol,
Examples include dimethyldithiocarbamic acid, and the amount added is generally preferably about 0.001 to 1% by weight in the reaction system.

The reaction is usually carried out under reflux conditions, specifically at about 100 to 200°C, preferably about 120 to 160°C.

Ring-closing imidization is usually completed in about 2 to 12 hours, and the desired maleimide can be obtained.

After the reaction is completed, the reactants can be separated by standing still and separated into an organic solvent layer and an acid catalyst layer at any temperature. The recovered acid catalyst can be used repeatedly as it is, but if the acid catalyst is used repeatedly, water-insoluble side reactants (structure unknown) will accumulate in the acid catalyst, and the subsequent reaction yield and selectivity will rapidly decrease due to the influence of this product. and it becomes practically difficult to use further catalysts. Although this phenomenon varies depending on the types of raw materials, acid catalysts, reaction solvents, etc. and reaction conditions, it is generally observed after reusing the product 3 to 8 times.

The acid catalyst thus deactivated can be easily activated by the following method. That is, (1) Add 30% by weight or more, preferably 50% by weight or more of water to the acid catalyst, and heat at about 10 to 100'C for 1 minute to
Stir for about 2 hours.

If the amount of water added is less than 30% by weight, the separation of by-products will be insufficient and the regeneration effect will be poor. Also, as long as the desired effect is achieved, there is no upper limit to the amount of water to be added; however, since water is distilled off in the shun process, it is not economically advisable to add a large amount of water, and usually up to about 500% by weight. used in

(2) By performing the above treatment, the side reaction products that had accumulated in the acid catalyst layer are precipitated in water and can be easily separated by commonly used solid-liquid separation means such as filtration and centrifugation. .

(3) Next, all or part of the water added in step (1) is distilled off under normal pressure or reduced pressure. Since water is also generated in the process of the ring-closing imidization reaction, it is not necessary to completely remove the water in the acid catalyst, but it is better to minimize the amount of water in the acid catalyst. This is preferable in terms of prompt progress.

Before or during the addition of water in step (1), the operation of extracting the acid catalyst layer with the non-polar organic solvent is performed as described above (
It is effective to use it together with the regeneration processing according to 1) to (3). By performing this operation, maleimides dissolved in the recovered acid catalyst layer can be recovered.

The non-polar solvent used in the extraction is usually about 10 to 500% by weight based on the acid catalyst layer.

Although the extraction temperature is not particularly limited, it is usually 10 to 1
A temperature of about 00°C is selected.

The acid catalyst thus regenerated is reused as a catalyst for the ring-closing imidization reaction according to the present invention.

``L-in-law'' The present invention will be described in detail below with reference to Examples.

In addition, the yield and selectivity of maleimide on each side are determined by HP
Measured by LC.

(Manufacturing example) 200 g of N-cyclohexyl maleamic acid, 79 g of cyclohexylamine, 400 g of xylene, and 157 g of 85% phosphoric acid were placed in a 21-piece fourth flask equipped with a cooling tube with a decanter, a thermometer, and a stirrer. , and heated to reflux temperature (150° C.) with stirring. The mixture was reacted for 6 hours while removing produced water from the system, and then left to cool.

Next, the lower catalyst layer was separated by liquid separation, and the upper layer (non-polar organic solvent layer) was washed with water. As a result of the measurement, N-cyclohexylmaleimide was contained in the upper layer at a yield of 77%. In addition, unreacted N-cyclohexyl maleamic acid and by-products were not detected.

The catalyst layer separated and recovered in the manufacturing process of Il and I contained 82 g of cyclohexylamine. N in this catalyst phase
- 1200 g of cyclohexyl maleamide and 4 xylene
00g was added and reacted for 6 hours under the same conditions as in the above production. The reaction product was separated and the upper layer was washed with water. As a result of the measurement, 88% of N-cyclohexylmaleimide was found in the upper layer.
% yield. In addition, unreacted N-cyclohexyl maleamic acid and by-products were not detected.

(2) The separated and recovered catalyst was used repeatedly in the same manner as (2). As a result, as the number of repetitions (N) increases, the yield of N-cyclohexylmaleimide increases to 85%.
(N=2>, 82% (N=3>, 67% (N=4>) and gradually decreased.

The acid catalyst layer (N=4> recovered through the above process is separated,
The organic solvent layer obtained by washing with water contained 2% of unreacted N-cyclohexyl maleamic acid and 3.5% of side reactants of unknown structure.
were included respectively.

Example 1 210 g of water was added to the acid catalyst (N=4) [phosphoric acid] recovered in the above production example (I [I>), stirred at room temperature for 30 minutes, and the precipitated insoluble substances were filtered out. Next, Under reduced pressure (300m
about 2,109 g of water was separated. Using the phosphoric acid thus obtained as a catalyst, N-cyclohexylmaleimide was prepared under the same conditions as in Production Example (I). As a result, the desired product was obtained with a yield of 87%. Obtained.

In addition, unreacted N-cyclohexyl maleamic acid and by-products were not detected.

As a result of repeatedly using the acid catalyst recovered through the above steps, the yield of the target products obtained was 83% (N=6>,
85% (N=7>), 62% (N=8>).

The organic solvent layer (N=8) contained 5% of unreacted N-cyclohexyl maleamic acid and 5% of a side reaction product of unknown structure.

Example 2 Water 2BS was added to the catalyst layer recovered in Example 1 (N=8>559)
After adding F and filtering off the precipitated insoluble matter, 27 g of water was distilled off under reduced pressure.

50 with cooling tube with decanter, thermometer and stirrer
50 N-hexyl maleamic acid in the fourth flask of 0d.
9. The above regenerated catalyst [phosphoric acid] 55 and xylene 15
0 g was added, and the mixture was reacted for 6 hours while stirring and refluxing while removing the generated water from the system, and then allowed to stand and cool. below,
8 N-cyclohexylmaleimide was prepared in the same manner as in the production example.
Obtained with a yield of 2%. Further, unreacted N-cyclohexylmaleamic acid and by-products were not detected.

Example 3 55 g of water was added to 55'g of the catalyst layer (N=8) recovered in Example 1.
After adding 559 g of xylene and filtering off the precipitated insoluble matter, water in 51 was distilled off under reduced pressure.

N-cyclohexylmaleimide was prepared according to Example 2 except that the thus obtained regenerated catalyst/xylene mixture was used, and as a result, the desired product was obtained with a yield of 90%. In addition, unreacted N-cyclohexyl maleamic acid and by-products were not detected.

Comparative Example 1 The catalyst (N=8) 559 recovered in Example 1 was used as a catalyst without any treatment, and the N
-As a result of preparing cyclohexylmaleimide, the yield of the target product was as low as 54%.

Comparative Example 2 119 g of water was added to the catalyst (N=8>55 g) recovered in Example 1 and stirred at room temperature, but no insoluble matter was precipitated. used as
Hereinafter, as a result of preparing N-cyclohexylmaleimide according to Example 2, the yield of the target product was as low as 52%.

Effects of the Invention By applying the treatment according to the present invention to an acid catalyst whose activity has decreased, it can be easily and effectively activated, and by repeatedly applying such a catalyst, an industrial advantage can be achieved. The desired maleimides can be produced.

Claims (1)

[Claims] 1. Maleimides can be converted into ring-closing imidization by heating maleamic acids in a non-polar organic solvent that is azeotropic with water in the presence of an acid catalyst that is substantially incompatible with the solvent. In the manufacturing method, (1) at least 30% by weight of water is added to the acid catalyst subjected to the ring-closing imidization reaction and then separated and recovered, (2) the precipitated water-insoluble substances are removed, and (3) ( 1
2. A method for producing maleimides, characterized in that the acid catalyst obtained by removing the water added in step ) is used again as a catalyst for the ring-closing imidization reaction.