Method for purifying n-phenylmaleimide

Abstract

To provide a method for purifying N-phenylmaleimide (PMI) that allows reduction of hydrolysis, polymerization, thermal decomposition, and discoloration of N-phenylmaleimide, and enables removal of an impurity, N-phenylmaleamic acid (PMA).SOLUTION: A method for purifying N-phenylmaleimide (PMI) comprises filtering and purifying a solution comprising crude N-phenylmaleimide (PMI) dissolved in an organic solvent through a filter, wherein the mass ratio of N-phenylmaleamic acid (PMA) to PMI in the solution is a predetermined value or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for purifying N-phenylmaleimide.

Background Art

[0002] Maleimide compounds are compounds useful as raw materials for resins, raw materials for pharmaceuticals, agricultural chemicals, etc. In particular, styrene resins such as ABS resin, AS resin, AB resin, ACS resin, AES resin, AAS resin, and polyvinyl chloride resin, polymethyl methacrylate resin, phenol resin, etc. are widely used as one of the copolymerization components to improve heat resistance. Among them, N-phenylmaleimide (hereinafter also referred to as PMI) is particularly widely used because of its excellent reactivity and heat resistance.

[0003] Regarding the production method of maleimide compounds, there are many conventionally known methods such as a method obtained by subjecting maleic anhydride and primary amines to a dehydration reaction in one step, a method of generating maleamic acids from maleic anhydride and primary amines and obtaining them by the dehydration ring-closure imidization reaction of these maleamic acids, and a method obtained by the ring-closure imidization reaction of corresponding maleamic acid monoesters. Among these methods, in the method obtained in one step from maleic anhydride and primary amines, there is a problem that the productivity is poor because the yield is still low, and in the method obtained from maleamic acid monoesters, there is a problem that the alcohol generated by the ring-closure imidization reaction remains and mixes into the product. Therefore, industrially, generally, a method obtained by the dehydration ring-closure imidization reaction of maleamic acids is used. The primary amines when producing N-phenylmaleimide are aniline, and the maleamic acids are N-phenylmaleamic acid.

[0004] By the way, in the production of N-phenylmaleimide by the above method, the formation of N-phenylmaleamic acid (hereinafter also referred to as PMA) will be involved as an intermediate. When this PMA undergoes hydrolysis or thermal decomposition, aniline and maleic acid are generated, and the generated (or derived from the raw material) aniline is known to react with the target product PMI to produce 2-anilino-N-phenylsuccinimide. When PMI containing these intermediates and by-products as impurities is used as one of the copolymerization components for obtaining the resin product as described above, problems such as the resulting copolymer being colored or discolored, or the quality (heat resistance, strength) of the copolymer being reduced will occur. Therefore, in the production of PMI by the above method, in addition to purification to remove dehydrating agents and catalysts, etc., a purification operation to remove the impurity PMA is necessary.

[0005] Many purification methods of N-phenylmaleimide have been known conventionally. For example, methods of washing a reaction mixture containing N-substituted maleimides with water at 60°C or higher, or acid-base aqueous solutions such as sulfuric acid, sodium carbonate, and ammonia (for example, Patent Documents 1 to 8) are disclosed. Further, after washing a reaction mixture containing N-substituted maleimides with an aqueous solution, a purification method of distilling the obtained organic layer in the coexistence of phosphoric oxygen acids (for example, Patent Documents 9 and 10), and a purification method of maleimides in which only maleimide is separated and recovered by bringing supercritical carbon dioxide into contact with a maleimide compound containing impurities (for example, Patent Document 11) are also disclosed.

[0006] However, in the case of the method of washing and purifying using water at 60°C or higher, acidic and basic aqueous solutions, especially when using a high-temperature aqueous solution, hydrolysis of maleimides occurs concomitantly. For example, in the case of N-phenylmaleimide, there is a problem that N-phenylmaleamic acid (PMA) is by-produced. In addition, in purification by distillation or supercritical carbon dioxide, since a high-temperature and high-pressure process is required, there is a problem that the purification method of N-phenylmaleimide has a high hurdle in terms of equipment and cost. Therefore, in order to produce N-phenylmaleimide that can suppress the deterioration of the quality (appearance, heat resistance, strength) of the copolymer described above, a purification method of PMI is required that can remove the impurity N-phenylmaleamic acid (PMA) without requiring drastic conditions such as high temperature and high pressure and while suppressing the hydrolysis of N-phenylmaleimide.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] An object of the present invention is to provide a method for purifying N-phenylmaleimide that reduces hydrolysis, polymerization, thermal decomposition, and coloring of N-phenylmaleimide (PMI) and enables removal of N-phenylmaleamic acid (PMA) which is an impurity.

MEANS FOR SOLVING THE PROBLEMS

[0009] As a result of intensive studies to solve the above-described problems of the prior art, the present inventors have found that when crude N-phenylmaleimide (PMI) is dissolved in a specific organic solvent, the solubility of PMI and PMA which is its impurity is greatly different, and by controlling the temperature and concentration, filtering the mixed solution of PMI and PMA dissolved in the organic solvent through a filter to reduce the PMA content in PMI, it has been clarified that the above problems can be solved.

[0010] That is, the present invention is as follows. [1] A method for purifying PMI, comprising filtering and purifying a solution obtained by dissolving crude N-phenylmaleimide (PMI) in an organic solvent, wherein the mass ratio of N-phenylmaleamic acid (PMA) to PMI contained in the solution is PMA / PMI = 6×10 -5 The following is a method for purifying PMI. [2] The purification method according to [1], wherein the PMA content of the purified PMI is 0.1% by mass or less. [3] The purification method according to [1] or [2], wherein the pore diameter of the filter used for filtration is 1 μm or less. [4] The purification method according to any one of [1] to [3], wherein the filtration temperature is 25°C or lower. [5] The purification method according to any one of [1] to [4], wherein the organic solvent is an aromatic compound.

Advantages of the Invention

[0011] According to the present invention, the co-occurrence of hydrolysis can be reduced to obtain high-purity N-phenylmaleimide. Further, since a distillation step is not required, the heat cost can be reduced, and since an aqueous solution washing step is not required, wastewater can be reduced.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. However, the present invention is not limited to the following description and can be variously modified and implemented within the scope of the gist.

[0013] (N-phenylmaleimide, N-phenylmaleamic acid) N-phenylmaleimide (PMI), which is one of N-substituted maleimide compounds, can be produced by the methods described in the above-mentioned prior art documents and the like. Specifically, (a) a method obtained by subjecting maleic anhydride and primary amines to a dehydration reaction in one step; (b) a method obtained by generating maleamic acids from maleic anhydride and primary amines and subjecting the maleamic acids to a dehydration cyclization imidization reaction; (c) a method obtained by subjecting corresponding maleamic acid monoesters to a cyclization imidization reaction, and the like. Further, it is known that N-phenylmaleamic acid (PMA) is by-produced as an impurity of N-phenylmaleimide (PMI) in the process of producing N-phenylmaleimide (PMI) by the above-mentioned method, and it is necessary to reduce PMA in order to suppress a decrease in quality (appearance, heat resistance, strength), as described in the above-mentioned background art.

[0014] Here, N-phenylmaleimide (PMI) referred to in the present invention is a compound having a chemical structure represented by the following formula.

[0015]

Chemical Formula

[0016] In addition, the N-phenylmaleamic acid (PMA) referred to in the present invention is a compound having a chemical structure represented by the following formula.

[0017] [Chemical formula]

[0018] (Purification method by filtration) The purification method of N-phenylmaleimide according to the present invention is a purification method for reducing the content of N-phenylmaleamic acid (PMA) contained as an impurity in crude N-phenylmaleimide (PMI) by dissolving the crude N-phenylmaleimide (PMI) in a specific organic solvent to form a mixture and then performing a filter filtration step.

[0019] The organic solvent for dissolving the crude N-phenylmaleimide (PMI) to form a solution is not particularly limited, but from the viewpoint of suppressing the hydrolysis of PMI, a solvent that is insoluble or immiscible with water and inert (not involved in the reaction) is preferred. Examples of such solvents include benzene, toluene, petroleum fractions having a boiling point of 50 to 120 °C, o-xylene, m-xylene, p-xylene, ethylbenzene, isopropylbenzene, cumene, mesitylene, tert-butylbenzene, methoxybenzene, chlorobenzene, pseudocumene, trimethylhexane, octane, tetrachloroethane, nonane, ethylcyclohexane, petroleum fractions having a boiling point of 120 to 170 °C, m-dichlorobenzene, sec-butylbenzene, p-dichlorobenzene, decane, p-cymene, o-dichlorobenzene, butylbenzene, decahydronaphthalene, tetrahydronaphthalene, dodecane, naphthalene, cyclohexylbenzene, petroleum fractions having a boiling point of 170 to 250 °C, and the like. The above organic solvents may be used alone or in the form of a mixture of two or more. Among the above organic solvents, toluene, o-xylene, m-xylene and p-xylene are more preferable because of the superiority of the solubility of N-phenylmaleamic acid (PMA) and the filtration efficiency. The amount of the above organic solvent used is not particularly limited, but those that can perform filtration smoothly and have a large difference between the solubility of PMI and the solubility of PMA are selected. Further, considering the separation of PMI and the solvent after the purification is completed, it may be advantageous to use a low-boiling solvent and perform the purification under pressure. Here, the concentration of PMI is not particularly limited as long as PMI can be dissolved. Specifically, it is preferable that 1 to 50 g, more preferably 5 to 30 g, and still more preferably 10 to 20 g of an organic solvent is added and dissolved per 1 g of PMI.

[0020] Also, the mass ratio of PMA dissolved in the organic solvent to PMI contained in the mixture of PMI and the organic solvent at the time of performing filter filtration is PMA / PMI = 6×10 -5 It is preferably as follows. Here, when the mass ratio of PMA to PMI is PMA / PMI = 6×10 -5 If it is larger, PMA will dissolve too much in the organic solvent and the PMA content in PMI cannot be sufficiently reduced. Also, from the viewpoint of improving the quality (heat resistance, strength) of the copolymer, the mass ratio of PMA to PMI is PMA / PMI = 4×10 -5 It is more preferably as follows, and particularly preferably PMA / PMI = 3×10 -5 It is particularly preferably as follows. PMA / PMI may be calculated and determined based on, for example, the solubilities of PMA and PMI at the temperature at which filter filtration is performed (filtration temperature), and the amounts of the crude PMI and the organic solvent used, or may be determined by measuring the dissolved amounts of PMA and PMI in the liquid phase of the organic solvent in which the crude PMI is dissolved by nuclear magnetic resonance (NMR).

[0021] The mixing time of the mixture of the crude PMI and the organic solvent is not particularly limited, but it is preferably 5 minutes or more, more preferably 10 minutes or more, and particularly preferably 15 minutes or more. When the mixing time is less than 5 minutes, the dissolution equilibrium cannot be reached, and the mass ratio PMA / PMI of PMA and PMI is not stable, so the PMA reduction efficiency deteriorates.

[0022] The temperature at which the filter filtration is carried out (filtration temperature) is not particularly limited, but it is preferably 60 ° C or lower, more preferably 40 ° C or lower, still more preferably 25 ° C or lower, and particularly preferably 20 ° C or lower. When the filter filtration is carried out at 60 ° C or higher, PMA dissolves too much, and the reduction effect of PMA by filtration becomes insufficient.

[0023] The pore size of the filter used for filtration is not particularly limited, but from the viewpoint of the efficiency of the filter capturing PMA, it is preferably 1 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less.

[0024] In order to obtain PMI from the mixture after filter filtration, it is necessary to distill off the solvent, but the temperature is not particularly limited as long as it is below the boiling point of PMI. From the viewpoint of suppressing the decomposition of PMI, it is preferably 30 ° C to 100 ° C, and particularly preferably 50 ° C to 80 ° C or lower. In addition, the distillation of the solvent can be carried out not only under normal pressure but also under reduced pressure.

[0025] In addition, the solid PMI remaining after the solvent distillation may be dried under reduced pressure. The temperature for drying is not particularly limited, but it is preferably below the boiling point of PMI. In particular, it is preferably 30 ° C to 100 ° C, and more preferably 50 ° C to 80 ° C. In addition, the drying of the solid PMI can be carried out not only under normal pressure but also under reduced pressure.

[0026] By the above method, hydrolysis, polymerization and thermal decomposition of N-phenylmaleimide (PMI) can be reduced, and the content of N-phenylmaleamic acid (PMA) is preferably reduced to 0.1% by mass or less, more preferably 0.06% by mass or less, and still more preferably 0.02% by mass or less, and an N-phenylmaleimide compound is obtained.

Examples

[0027] Hereinafter, the content of the present invention will be specifically described with reference to Examples and Comparative Examples. It should be noted that the present invention is not limited to the following Examples.

[0028] <1. Measurement of Impurity Content in PMI> The PMI in the Examples and Comparative Examples was dissolved in acetonitrile to prepare a 4% by mass solution, and measured under the following apparatus and conditions. · Measuring apparatus: High-performance liquid chromatography (LC Ultra3000 LTQ XL) manufactured by Thermо · Measurement conditions: Column: kinetex 2.6XB C-18 5.0×2.1 mm, Column temperature: 40 °C, flow rate: 0.2 mL / min, injection volume: 10 μL, Detector: UV detector (wavelength: 254 nm), Mobile phase: 0.1% by mass aqueous formic acid solution as A, 0.1% by mass formic acid acetonitrile solution as B, and the gradient conditions described in Table 1 below were used.

[0029]

Table 1

[0030] <2. Measurement of the Ratio of PMA to PMI (PMA / PMI) Contained in the Crude PMI Solution> The crude PMI in the Examples and Comparative Examples was dissolved in a filtering solvent and stirred for 10 minutes, and filtered using a 6 mL plastic syringe (product number: 2-4031-02, manufactured by AS ONE Corporation) equipped with a polytetrafluoroethylene (PTFE) syringe filter (13JP020AN, pore size 0.2 μm, manufactured by Advantec Toyo Co., Ltd.). 0.1 g of the filtered solution was diluted with 0.6 g of acetone-d6 (manufactured by Fujifilm Wako), and using an ECZ400S manufactured by JEOL Ltd. and a TFH probe, 1 1H-NMR was measured. The reference peak of the deuterated solvent was set at 2.05 ppm, and the measurement was performed with an integration number of 1024 times.

[0031] [Example 1] (Filtration and purification of PMI) To a 50 mL screw tube (manufactured by AS ONE Corporation, model number: No.7) equipped with a stir bar (manufactured by AS ONE Corporation, model number: C 5×15), 3.5 g of metaxylene (manufactured by Mitsubishi Gas Chemical Company, hereinafter referred to as mXy) and 0.30 g of N-phenylmaleimide (manufactured by Nippon Shokubai Co., Ltd., hereinafter referred to as PMI) were weighed and added. Stirring was carried out at 18 °C for 20 minutes (150 rpm) to dissolve PMI in mXy to obtain a PMI suspension solution. At this time, the ratio of PMA to PMI dissolved in metaxylene was PMA / PMI = 2.3×10 -5 It was as follows. Next, the PMI suspension solution was filtered at 18 °C using a 6 mL plastic syringe (manufactured by AS ONE Corporation, product number: 2-4031-02) equipped with a polytetrafluoroethylene (PTFE) syringe filter (manufactured by Advantec Toyo Kaisha, Ltd., 13JP020AN, pore size 0.2 μm) to obtain 3.8 g of a solution layer. From this solution layer, the temperature was raised to 60 °C under a reduced pressure of 4 kPa using an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd., model number: N-1300E) to distill off the mXy solvent. The remaining yellow solid was placed in a dryer (manufactured by AS ONE Corporation, model number: AVO-200SB-D), and vacuum drying was carried out at 60 °C for 2 hours. Finally, 0.29 g of purified PMI yellow solid was obtained. The PMA content contained in the obtained purified PMI was 120 ppm.

[0032] [Example 2] Using PMI (manufactured by Tokyo Chemical Industry Co., Ltd., Lot. I56CD-RQ), the filtration and purification operation of Example 1 was carried out. The ratio of PMA to PMI dissolved in metaxylene before filtration and purification was PMA / PMI = 2.3×10 -5 It was as follows. Other conditions were the same as those in Example 1, and the PMA content contained in the obtained purified PMI was 190 ppm.

[0033] [Comparative Example 1] The PMA content of the purchased PMI (manufactured by Nippon Shokubai Co., Ltd.) before the filtration and purification operation was 1140 ppm.

[0034] [Comparative Example 2] The purchased PMI (manufactured by Tokyo Chemical Industry Co., Ltd., Lot. I56CD-RQ) had a PMA content of 1020 ppm before the filtration and purification operation.

[0035] [Comparative Example 3] Using PMI (manufactured by Nippon Shokubai Co., Ltd.), the stirring temperature and filtration temperature of the PMI suspension solution were set to 80 °C, and the filtration and purification operation of Example 1 was carried out. The ratio of PMA to PMI dissolved in metaxylene before filtration and purification was PMA / PMI = 6.6×10 -5 . The other conditions were the same as those in Example 1, and the PMA content in the obtained purified PMI was 1110 ppm.

[0036] [Comparative Example 4] (Warm water washing of PMI) Weighed 0.62 g of toluene (manufactured by Fujifilm Wako Pure Chemical Corporation, Infinity Pure Grade) and 0.30 g of PMI (manufactured by Nippon Shokubai Co., Ltd.) and added them to a 50 mL screw tube (manufactured by AS ONE Corporation, model number: No. 7) equipped with a stirrer (manufactured by AS ONE Corporation, model number: C 5×15), stirred at 65 °C for 20 minutes (150 rpm) to obtain a PMI toluene solution. To this PMI toluene solution, 0.62 g of water was weighed and added, stirred at 65 °C for 30 minutes (150 rpm), the stirring was stopped and left to stand for 30 minutes, and then the aqueous layer was separated and only the organic layer was recovered. Next, the temperature of the recovered organic layer was raised to 60 °C under a reduced pressure of 4 kPa using an evaporator (manufactured by Tokyo Rikakikai Co., Ltd., model number: N-1300E) to distill off the toluene solvent, and the remaining yellow solid was put into a dryer (manufactured by AS ONE Corporation, model number: AVO-200SB-D) and dried under reduced pressure at 60 °C for 2 hours. Finally, 0.29 g of purified PMI yellow solid was obtained. The PMA content in the obtained purified PMI was 950 ppm.

[0037]

Table 2

Industrial Applicability

[0038] According to the method of the present invention, there can be provided a method for purifying N-phenylmaleimide, which can reduce hydrolysis, polymerization, thermal decomposition and coloring of N-phenylmaleimide (PMI) and remove N-phenylmaleamic acid (PMA) which is an impurity. In addition, since a distillation step is not required, the heat cost can be reduced, and since an aqueous solution washing step is not required, wastewater can be reduced, and a method for purifying PMI can be provided.

Claims

1. A method for purifying PMI, comprising filtering and purifying a solution obtained by dissolving crude N-phenylmaleimide (PMI) in an organic solvent, wherein the mass ratio of N-phenylmaleamic acid (PMA) to PMI contained in the solution is PMA / PMI = 6×10 －５ The following is a method for purifying PMI.

2. The purification method according to claim 1, wherein the content of N-phenylmaleamic acid (PMA) in the purified PMI is 0.1% by mass or less.

3. The purification method according to claim 1 or 2, wherein the pore diameter of the filter used for filtration is 1 μm or less.

4. The purification method according to claim 1 or 2, wherein the filtration temperature is 25°C or less.

5. The purification method according to claim 1 or 2, wherein the organic solvent is an aromatic compound.

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