JPH0369342B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for purifying maleimides. Maleimides are compounds useful as raw materials for resin raw materials, medicines, agricultural chemicals, etc., and the present invention provides a purification method for obtaining high-purity maleimides in good yields. <Prior Art> Methods for producing maleimides have been studied for a long time, and numerous documents can be found. That is, a method of isolating maleamic acid produced by reacting maleic anhydride and an amine compound in an organic solvent, and imidizing the isolated maleamic acid using a dehydrating agent such as acetic anhydride (U.S. Patent No.
2444536 specification); A method in which isolated maleamide acids are imidized by heating in the presence of an acid catalyst using an organic solvent such as toluene, xylene, or chlorobenzene as a diluent; A method of imidizing acids by directly heating them in the presence of an acid catalyst (Japanese Patent Application Laid-open No. 47-27974); adding an acid catalyst to the reaction mixture without isolating the maleamidic acids produced from the organic solvent. Method of imidization by adding
No. 40078, JP-A-53-68770, JP-A-57-42043
A number of manufacturing methods are known. However, there are problems with any of the methods for producing maleimides, as a non-negligible amount of by-products are produced during the imidization reaction, and purification is required if high-purity maleimides are to be obtained. Conventionally, methods for purifying maleimides include injecting the reaction solution into a large amount of cold water, separating the precipitated crystals, and washing the crystals with an even larger amount of water, or using dilute aqueous sodium carbonate or caustic soda solutions. method of cleaning and drying (U.S. Patent No.
244536, Japanese Patent Application Laid-open No. 149253 (1983)) and a method in which a reaction solution of an organic solvent containing maleimide is neutralized with a dilute weak alkali aqueous solution, washed with water, and the organic solvent is separated (Japanese Patent Laid-Open No. 53 −68770 publication specification)
is proposed. <Problems to be Solved by the Invention> However, in the above method, the by-products generated in the imidization step are resin-like substances and substances insoluble in water like maleimides, so it is difficult to obtain high-purity substances. It is difficult to obtain maleimides. Furthermore, since a large amount of water is used, including its treatment, it is extremely impractical and is industrially disadvantageous. <Means for Solving the Problems> In view of the current situation, the present inventors have conducted intensive research on purification methods for obtaining high-purity maleimides. The present inventors have discovered that highly pure maleimides can be obtained by carrying out a ring-closing reaction and treating the resulting reaction mixture with acid under specific conditions, thereby completing the present invention. That is, the present invention is specified as follows. (1) General formula

[Formula] In the formula, R is an alkyl group having 1 to 20 carbon atoms, a phenyl group, a benzyl group, a cyclohexyl group, a pyridyl group, a quinolyl group, and those in which these groups are substituted with halogen, carboxyl group, or nitro group. It can be obtained from The maleamic acid represented by is subjected to an imidization ring-closing reaction in the presence of an acid catalyst in an organic solvent, and the resulting reaction mixture contains at least 1% by weight of an organic or inorganic acid (with the exception of sulfuric acid) based on the starting maleamic acid. ) is added, excluding the use of alone.
A method for purifying maleimides, which comprises processing at a temperature range of 5 to 100°C, and then washing the obtained organic layer with water to remove water-soluble contaminants. (2) After the imidization ring-closing reaction, the acid catalyst layer is separated and removed, and the resulting organic layer is treated by adding an organic acid or an inorganic acid (excluding the use of sulfuric acid alone). The method described in (1) above. (3) The method according to (2) above, wherein the separation and removal operation of the acid catalyst layer is carried out at a temperature range of 50 to 140°C. Hereinafter, specific embodiments of the present invention will be explained. Crude maleimides to which the purification method of the present invention can be applied can be obtained by conventionally known production methods. That is, the above-mentioned raw material maleamic acids are usually easily obtained by the reaction of maleic anhydride and amines, and the imidization ring-closing reaction of these is carried out in the presence of an acid catalyst using toluene, xylene, chlorobenzene, dimethylformamide, This is done by heating and dehydrating in a solvent such as dimethyl sulfoxide. For the reaction mixture obtained in this way, it is preferable to first separate and remove the acid catalyst from this mixture at a temperature range of 50 to 140°C, and then add at least 1% by weight of acid to the maleamic acid used as the raw material. After 5 to 60 minutes, acid treatment is carried out under stirring at a temperature range of 5 to 100°C. Inorganic acids or organic acids are effective as acids used in this acid treatment, such as orisophosphoric acid, pyrophosphoric acid, sulfuric acid, sulfuric anhydride, fuming sulfuric acid, methanesulfonic acid, chlorosulfonic acid, chloromaleic acid, paratoluenesulfonic acid, Examples include fluoroacetic acid, and sulfonic acids are preferred. These acids can be used alone or in mixtures. The amount of acid to be used is appropriately determined taking into consideration the amount of impurities in the crude maleimides, the desired product purity, purification yield, work efficiency, economic efficiency, etc., and this amount is the amount used in the present invention. It does not affect the However, when ordinary crude maleimides are purified according to the present invention, the treatment effect can be obtained if the amount used is at least 1% by weight based on the raw maleamic acid. The upper limit can essentially take any value, but if we take into account purification yield, work efficiency, economic efficiency, etc.
Amounts up to 30% by weight may be used. Acid treatment is carried out at a temperature range of 5 to 100°C.
If the treatment is carried out at a temperature exceeding 100°C, polymerization of maleimides and the like will occur as well as treatment of by-products, which will substantially reduce the yield, which is undesirable. In addition, if the treatment is performed at a temperature below 5℃, the treatment effect may not be sufficient.
The maleimides in the reaction solution are also precipitated and removed at the same time as the by-products, which is undesirable because the purity and yield of the maleimides obtained decreases. As described above, by carrying out the acid treatment specified in the present invention, substantially all of the byproducts during the imidization ring-closing reaction contained in the reaction mixture are precipitated as a viscous resinous substance. This made it possible to precipitate it. This precipitate can then be easily separated from the reaction mixture by conventional means such as filtration or decantation, yielding an organic layer containing substantially only maleimides. Furthermore, even if the acid treatment is carried out directly from the reaction mixture without separating and removing the acid catalyst used in the imidization ring-closing reaction, the same effect as in the case where the acid catalyst is separated and removed can be obtained. Subsequently, water was added in an amount of 1 to 5 times the weight of maleamic acid to the organic layer obtained after the acid treatment, and the organic layer was washed at a temperature of 10 to 50°C. Remove trace amounts of acid and by-products remaining in the tank. The water used for this washing process is pure water,
It is possible to use not only industrial water, tap water, etc., but also weakly alkaline or slightly acidic water. Through this water washing treatment, the acid content in the organic layer is reduced to 0.5% by weight or less.
The content should preferably be 0.1% by weight or less. Thereafter, the organic solvent is removed from the organic layer by evaporation, thereby safely obtaining highly pure maleimide containing substantially no impurities. The water washing treatment in this step removes a small amount of impurities that could not be completely removed by the acid treatment, and also removes the remaining acid at the same time. In addition,
In the step of evaporating and separating the organic solvent from the reaction solution after acid treatment, if acid remains in the reaction solution, a polymerization reaction of maleimides will occur, which will not only cause a decrease in the purity of the maleimide obtained, but also increase the heat of polymerization. Problems caused by this are also predicted, and the safety situation has been found to be unfavorable. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 Ortho-xylene was added to a flask equipped with a thermometer, a condenser with a water separator, a dropping funnel and a stirrer.
100 g of maleic anhydride was added thereto, and the temperature inside the flask was raised to 70° C. to dissolve the maleic anhydride. Next, a solution of 90 g of aniline dissolved in 630 g of ortho-xylene was added dropwise to the N-
An ortho-xylene slurry of phenylmaleamide acid was synthesized. When the aniline ortho-xylene solution was added dropwise, heat was generated at the same time, so the solution temperature was adjusted to 70°C by cooling. Next, 20 g of orthophosphoric acid (85% by weight aqueous solution), 0.06 g of zinc acetate, and 0.2 g of paramethoxyphenol were added to the above slurry liquid, and heated to 140 g with stirring.
The reaction was carried out for 3 hours while maintaining the temperature at 0.degree. C. and removing water produced by the reaction by azeotropy with ortho-xylene.
After the reaction was completed, the temperature of the reaction solution was lowered to 100° C., and the acid catalyst layer separated from the reaction solution as a lower layer was separated and removed. Subsequently, the temperature of the reaction solution was lowered to 70° C., 30 g of pyrophosphoric acid (98% by weight or less) was added, and the mixture was stirred for 60 minutes. After separating the resinous substances that precipitate from the reaction solution by acid treatment, add 200% to the reaction solution.
g of water was added, and the mixture was stirred and washed with water for 15 minutes, and the aqueous layer was separated. Finally, ortho-xylene was distilled off from the organic layer under reduced pressure of 15 mmHg to obtain 142 g of yellow crystals of N-phenylmaleimide. This is analyzed by high performance liquid chromatography.
The purity is 96.7% by weight, and the standard yield of aniline is
It was 82.0 mol%. Comparative Example 1 In Example 1, the acid treatment was not performed, the reaction solution from which the acid catalyst layer was separated was washed with water as it was, and ortho-xylene was distilled off. The purity of N-phenylmaleimide was 90.0% by weight. It was hot. Example 2 The same procedure as in Example 1 was performed except that 10 g of methanesulfonic acid (98% by weight or more) was used instead of 30 g of pyrophosphoric acid in Example 1, and bright yellow N-phenyl was obtained. maleimide crystals
I gained 138g. The purity of this product was 98.7% by weight, and the yield based on aniline was 81.4% by mole. Example 3 The same procedure as in Example 1 was performed except that 10 g of chlorosulfonic acid (98% by weight or more) was used instead of 30 g of pyrophosphoric acid in Example 1, and a bright yellow N-phenyl was obtained. maleimide crystals
I gained 132g. The purity of this product was 98.2% by weight, and the yield based on aniline was 77.4% by mole. Example 4 Ortho-xylene was added to a flask equipped with a thermometer, a condenser with a water separator, a dropping funnel and a stirrer.
100 g of maleic anhydride was added thereto, and the temperature inside the flask was raised to 70° C. to dissolve the maleic anhydride. Then, a solution of 124 g of O-chloroaniline dissolved in 870 g of ortho-xylene was added dropwise over 30 minutes with stirring to synthesize a slurry of O-chlorophenylmaleamidic acid in ortho-xylene. Next, 20 g of orthophosphoric acid (85% by weight aqueous solution), 0.07 g of zinc acetate, and 0.2 g of para-methoxyphenol were added to the above slurry liquid, and the temperature was kept at 140°C while stirring, and the water produced by the reaction was azeotroped with ortho-xylene. The reaction was carried out for 3 hours while being removed by operation.
After the reaction was completed, the temperature of the reaction solution was lowered to 100° C., and the catalyst layer separated from the reaction solution as a lower layer was separated and removed. Subsequently, the temperature of the reaction solution was lowered to 30° C., 15% methanesulfonic acid (98% by weight) was added, and the mixture was stirred for 30 minutes. After separating the resinous substance precipitated from the reaction solution by acid treatment, 200 g of water was added to the reaction solution, and the mixture was stirred and washed with water at 30° C. for 15 minutes to separate the aqueous layer. The obtained organic layer was distilled off to remove ortho-xylene under reduced pressure of 30 mmHg to obtain N-(2-chlorophenyl).
I got maleimide. This is analyzed by high performance liquid chromatography.
The purity was 99.2% by weight, and the yield was 82.3% by mole based on the raw material O-chloroaniline. Comparative Example 2 N-(2-chlorophenyl) obtained by not performing acid treatment in Example 4 but washing the reaction solution from which the acid catalyst was separated with water and distilling off ortho-xylene.
The purity of maleimide was 88.3% by weight.

Claims (1)

[Claims] 1 General formula [Formula] In the formula, R is an alkyl group having 1 to 20 carbon atoms, a phenyl group, a benzyl group, a cyclohexyl group, a pyridyl group, a quinolyl group, and these groups are substituted with halogen or a carboxyl group. It is selected from those with substitution and nitro group substitution. The maleamic acid represented by is subjected to an imidization ring-closing reaction in the presence of an acid catalyst in an organic solvent, and the resulting reaction mixture contains at least 1% by weight of an organic or inorganic acid (with the exception of sulfuric acid) based on the starting maleamic acid. ) is added, and 5 to 100
1. A method for purifying maleimides, which comprises processing at a temperature range of °C, and then washing the obtained organic layer with water to remove water-soluble contaminants. 2. A patent characterized in that after the imidization ring-closing reaction, the acid catalyst layer is separated and removed, and the resulting organic layer is treated by adding an organic acid or an inorganic acid (excluding the use of sulfuric acid alone). The method according to claim 1. 3. The method according to claim 2, wherein the separation and removal operation of the acid catalyst layer is carried out at a temperature range of 50 to 140°C.