JPH01216969A - Purification of n-substituted maleimides - Google Patents

Abstract

PURPOSE:To sufficiently remove impurities, prevent the simultaneous polymerization of a reaction mixture when distilled and thereby provide the subject compound having a high purity in a high yield, by washing the reaction mixture containing an N-substituted maleimide with a diluted alkali aqueous solution, rewashing the washed mixture with a diluted acid aqueous solution and subsequently distilling the rewashed mixture. CONSTITUTION:Maleic anhydride is reacted with an aromatic or aliphatic primary amine. The reaction mixture containing the obtained N-substituted maleimide is washed with a diluted alkali aqueous solution (e.g., NaOH) and the organic layer obtained from the washed mixture is again washed with a diluted acid aqueous solution (e.g., sulfuric acid or phosphoric acid), followed by distilling the rewashed mixture to provide the N-substituted maleimide (e.g., N-phenylmaleimide). The method can highly improve the yield of the distillation, prevent the simultaneous polymerization of the mixture during the distillation and greatly reduce the amount of distillation residues after the distillation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for purifying N-substituted maleimides. More specifically, the present invention relates to a reaction mixture containing an N-substituted maleimide obtained by dehydration ring-closing imidization of maleic anhydride and amines, or maleic acid monoamides obtained therefrom in an organic solvent in the presence of a catalyst. It relates to a method for purifying by washing and distillation.

N-substituted maleimides are compounds that have an extremely wide range of applications as medicines, agricultural chemicals, dyes, polymer raw materials, or intermediates thereof.

[Prior art]

Conventionally, the method for purifying N-substituted maleimides is to inject the reaction solution into a large amount of cold water, separate the precipitated crystals in a furnace, and wash these crystals with a large amount of water or organic solvent (Org.
anic 5ynthesis Co11. V944(
(1973)), a method in which the organic layer is separated after neutralization and washing with a dilute aqueous sodium carbonate solution, and the solvent is distilled off (
Japanese Patent Publication No. 55-46394), a method in which acid treatment is performed with a strong acid such as reactive sulfuric acid, the by-product is converted into a resin, separated, and then washed with water (Japanese Patent Application Laid-open No. 61-22065 and 1988)
JP-A-204166), a method of washing with a dilute aqueous alkali solution, washing again with water, distilling off the solvent, and recrystallizing from an alcoholic solvent (JP-A-60-100554) has been proposed. However, in the above-mentioned method, the by-products generated in the dehydration ring-closing imidization step are insoluble in water and cannot be sufficiently removed during washing, making it difficult to obtain highly pure N-substituted maleimides. Recrystallization from alcohols also causes side reactions with the recrystallization solvent and polymerization, making it difficult to obtain high-purity products in high yields.

On the other hand, as a purification method for N-substituted maleimides, a purification method by distillation has also been carried out (JP-A-60-112758 and JP-A-60-112759). Because it has a double bond, it tends to polymerize when heated during distillation, and therefore the distillation yield also decreases. In order to prevent such a decrease in yield due to polymerization during distillation, distillation in the coexistence of a stabilizer (JP-A-61-2
29862) and a method of neutralizing with an alkaline earth metal compound and then distilling (Japanese Patent Application Laid-Open No. 138468/1982), but it is still not possible to completely prevent polymerization.

As described above, conventional purification techniques are not sufficient in removing impurities such as by-products or preventing polymerization during distillation, and have problems in terms of yield and product purity, and are still not suitable for industrial implementation. It is insufficient.

[Problem to be solved by the invention]

The present invention was made to solve the problems in conventional methods, and its purpose is to provide a method for purifying N-substituted maleimides that can be carried out industrially advantageously.
More specifically, we are developing N-substituted maleimides that can sufficiently remove impurities such as by-products, prevent polymerization during distillation, and obtain high-purity N-substituted maleimides in high yields. A purification method is provided.

(Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventors found that N.
- It has been discovered that highly pure N-substituted maleimides can be obtained in high yield by washing the reaction mixture containing substituted maleimides with a dilute aqueous alkali solution, then washing again with a dilute aqueous acid solution, and then distilling the mixture. invention has been achieved.

The gist of the present invention is to prepare a reaction mixture containing an N-substituted maleimide by reacting maleic anhydride with an aromatic or aliphatic primary amine.
This is a method for purifying N-substituted maleimide, which is characterized in that the organic layer obtained after washing with a dilute aqueous alkaline solution is washed again with a dilute aqueous acid solution and then distilled.

Embodiments of the present invention will be described below.

Maleic anhydride, which is the starting material of the present invention, may be obtained from any source, and it is convenient to use an appropriately selected maleic anhydride from commercially available maleic anhydride. Further, even if maleic acid is used, the reaction and purification proceed in the same manner, but this is not considered a good idea due to reactivity and economic efficiency.

Examples of aromatic primary amines that are the other raw material include aniline, naphthylamine, toluidine, dimethylaniline, chloroaniline, dichloroaniline, nitroaniline, and phenylenediamine, and examples of aliphatic primary amines such as , methylamine, ethylamine, propylamine, butylamine, benzylamine,
Examples include cyclohexylamine, allylamine, and ethylenediamine.

The molar ratio of the primary amines to maleic anhydride is 1:0.8-1.5, preferably 1:0.9-1.
Used in a range of 2.

The N-substituted maleimide reaction mixture used in the present invention is obtained by dehydrating and ring-closing imidization of the above maleic anhydride and the above primary amines, or the maleic acid monoamides obtained by reacting them in an organic solvent in the presence of a catalyst. can be obtained.

At this time, the catalysts used are sulfuric acid, sulfurous acid, sulfuric anhydride, phosphoric acid, sonic acid, and polyphosphoric acid.

Inorganic acids such as benzenesulfonic acid, toluenesulfonic acid, benzenephosphonic acid, trichloroacetic acid.

Organic acids such as trifluoroacetic acid, organic bases such as triethylamine, pyridine, dimethylaniline, sodium acetate, and strongly acidic ion exchange resins.

Weakly acidic ion exchange resin 1 Examples include ion exchange resin catalysts such as weakly basic ion exchange resins, but sulfuric acid, phosphoric acid, and benzenesulfonic acid are preferred.

These include toluenesulfonic acid and ion exchange resins.

Any reaction solvent may be used as long as it dissolves the N-substituted maleimides, forms an azeotrope with water, is inert, and does not participate in the reaction, but preferably benzene, toluene, xylene, ethylbenzene, and chloride. Examples include benzene. There is no particular limit to the amount of organic solvent used, but considering operability and economic efficiency, the concentration of the product should be 10 to 6.
It is preferable to use it so that it is about 0%.

Further, as the organic solvent, an aprotic polar solvent may be mixed with the water azeotropic solvent and used. The aprotic polar solvents used are formamide,
N-methylformamide.

Dimethylformamide, dimethylacetamide.

Examples include dimethyl sulfoxide, sulfolane, T-butyrolactone, and hexamethylphosphoramide. The amount of the aprotic polar solvent to be used is arbitrary, but it is usually preferably about 2 to 30% of the total amount of solvent.

The reaction temperature is usually in the range of 50 to 200°C, preferably 70°C.
~160°C.

In addition, when synthesizing these N-substituted maleimides,
Hydroquinone, methoxyphenol.

Dobutylcatechol, phenothiazine, thiourea.

There is no problem in using polymerization inhibitors such as hydroxyquinoline, cuperone, and N-nitron diphenylamine in combination.

In addition, when performing the aforementioned dehydration ring-closing imidization reaction on maleic acid monoamides obtained by reacting maleic anhydride with aromatic or aliphatic primary amines, the maleic acid monoamides are isolated from the reaction product. Dehydration and ring closure treatment can be performed without separation. This synthesis reaction of maleic acid monoamides is preferably carried out in an organic solvent.
As the organic solvent, those mentioned above are used. This reaction easily proceeds at a reaction temperature of about 150°C or lower without using any particular catalyst.The reaction temperature ranges from room temperature to 100°C.
up to is appropriate.

The reaction mixture containing the N-substituted maleimide thus obtained is first washed with a dilute aqueous alkali solution, and then the resulting organic layer is washed again with a dilute aqueous acid solution.

Sodium for cleaning with dilute aqueous alkaline solutions.

Potassium or ammonium salt hydroxide, carbonate or hydrogen carbonate, or an aqueous solution of calcium, barium or magnesium hydroxide can be used, but sodium or potassium hydroxide is preferred from the viewpoint of cleaning effect and operability. thing.

It is preferable to use carbonate or hydrogen carbonate.The concentration of the dilute alkali aqueous solution is 1 to 20%, and the pH of the aqueous layer after washing is in the range of 3 to 8, preferably 4 to 7. There is no particular restriction on the amount of the dilute alkali aqueous solution used, but it is recommended to wash the solution so that the
%, and the washing temperature is 20 to 90°C, preferably 30 to 70°C.

In addition, for re-cleaning with a dilute acid aqueous solution, an aqueous solution of an inorganic acid such as sulfuric acid, sulfurous acid, phosphoric acid, arsenic acid, or hydrochloric acid, or an organic acid such as benzenesulfonic acid or toluenesulfonic acid can be used. From the viewpoint of cleaning effect and economy, it is preferable to use sulfuric acid or phosphoric acid.The concentration of the dilute acid aqueous solution is preferably in the pH range of 0.1 to 5, and the pi of the aqueous layer after rewashing is 0.1. Washing should be carried out so that the ratio is preferably in the range of 1 to 4.The amount of dilute acid aqueous solution used is not particularly limited, but is 10 to 100% of the reaction mixture liquid volume.
The cleaning temperature is preferably 20-90°C, preferably 30-70°C. Furthermore, by washing with a dilute aqueous alkali solution, washing with water once or more, and then washing with a dilute acid aqueous solution, a higher purity N-substituted maleimide can be obtained.

The organic layer obtained by such a washing operation is then subjected to a distillation operation to remove the organic solvent. Distillation is carried out under normal pressure or reduced pressure.Since imides in N-substituted polymers have polymerizability, distillation is preferably carried out at as low a temperature as possible.For this reason, usually 2
Distillation is preferably carried out under reduced pressure of 0 mHg or less, preferably 10 ml or less.

EXAMPLES Hereinafter, the structure and effects of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 107.8 g of maleic anhydride was placed in a reactor equipped with a reflux condenser with water separator, thermometer, stirrer and dropping funnel.
, xylene 400-2, dimethylformamide was added, heated and dissolved under stirring.Next, 93.1 g of aniline was added dropwise from the dropping funnel over 1 hour, and the reaction was then carried out under solvent reflux for 2 hours.The water produced during the reaction was After the reaction was completed, the reaction solution (yellow transparent liquid) was analyzed by gas chromatography, and it was confirmed that 166.5 g of N-phenylmaleimide was produced (reaction yield 96.1%). ).

Next, the reaction solution was cooled to 50° C., washed with 200 g of a 6% aqueous sodium carbonate solution, and the aqueous layer was separated. At this time, the pH of the aqueous layer was 6.8. The obtained organic layer was kept at 50°C and diluted with a dilute aqueous sulfuric acid solution adjusted to pH 2 at 150 °C.
g was added thereto and washed again, and the aqueous layer was separated.

The aqueous layer at this time had a pH of 2.9. Next, the organic layer thus obtained was mixed at a temperature of 60 to 110°C and a pressure of 130°C.
After distilling at ~20 msHg and removing the solvent, distillation was carried out for 3 hours at a bath temperature of 160°C and a reduced pressure of 9 degrees Hg.

As a result, 162.3 g of N-phenylmaleimide was obtained (yellow solid with melting point 89-90°C, yield 93.7
%, purity 99.8% by gas chromatography),
At this time, the remaining amount in the still was 4.8 g.

Comparative Example 1 The same procedure as in Example 1 was performed except that rewashing with dilute sulfuric acid was not performed, and 81.6 g of N-phenylmaleimide was obtained (melting point 88-90'C (7 ) Yellow solid, yield 47.1%, purity 98.6% as determined by gas chromatography), the amount remaining in the distillation pot at this time was 88.6 g.

Example 2 1O% potassium hydroxide aqueous solution 1 as dilute alkali aqueous solution
The same operation as in Example 1 was performed except that 300 g of a dilute phosphoric acid solution of PHL5 was used as the dilute aqueous solution, and 160.5 g of N-phenylmaleimide was obtained (melting point 88-90 °C @ Yellow solid, yield 92.7%,
Purity by gas chromatography: 99.5. %), and the remaining amount in the distillation pot at this time was 6.6 g.

Examples 3 to 4 The same operation as in Example 1 was performed except that 127.6 g of 0-chloroaniline or 107.2 g of 0-toluidine was used as the primary amine and the distillation pressure was changed.
I got the result of blowing.

Example 5 Maleic anhydride 107.8 was added to a reactor similar to Example 1.
g, ) toluene 400d, dimethylformamide 25
d1 and 50 g of ion exchange resin Amberlyst 15'' (manufactured by Rohm & Haas) were added and heated to dissolve with stirring.

Next, 73.1 g of n-butylamine was added dropwise from the dropping funnel over a period of 1 hour, and the reaction was then carried out under reflux of the solvent for 5 hours.The water produced during the reaction was removed from the water separator.After the reaction was completed, the temperature was raised to 60'C. After cooling, removing the catalyst and washing with toluene, the reaction solution (light brown liquid) was analyzed by gas chromatography, and it was confirmed that 120.1 g of N-n-butylmaleimide was produced (reaction yield). Rate 78.4%
).

Next, the reaction solution was kept at 60°C, washed with 250 g of a 6% aqueous sodium carbonate solution, and the aqueous layer was separated. At this time, the pH of the aqueous layer was 5.2. The obtained organic layer was kept at 60° C. and washed again by adding 100 g of a dilute aqueous phosphoric acid solution adjusted to pH 1.5, and the aqueous layer was separated. p of the water layer at this time
H was 2.0. Next, the organic layer thus obtained was heated at a temperature of 60 to 110°C and a pressure of 130 to 20 ssH.
After desolvation at 90°C bath temperature, pressure 6I111Hg
Distillation was carried out over a period of 3 hours at a reduced pressure of . As a result, 115.
6 g of N-n-butylmaleimide was obtained (boiling point 86
~89°C/11g of colorless transparent liquid, yield 75.5
%, purity 99.0% by gas chromatography),
The remaining amount in the distillation pot at this time was 8.6 g.

〔Effect of the invention〕

According to the method of the present invention, N-substituted maleimides having a purity of about 99% or more can be obtained with a purification yield of about 95% or more.The present invention also has the following advantages. .

i) The distillation yield is significantly improved.

ii) Polymerization during distillation can be prevented.

ii) The amount remaining in the pot after distillation can be significantly reduced.

iv) Product purity is improved.

Claims (1)

[Claims] A reaction mixture containing an N-substituted maleimide obtained by reacting maleic anhydride with an aromatic or aliphatic primary amine is washed with a dilute aqueous alkaline solution, and the resulting organic layer is washed again with a dilute aqueous acid solution. A method for purifying N-substituted maleimides, comprising the steps of: