A method for synthesizing n-phenylmaleimide

Abstract

The application discloses a kind of synthesis methods of N-phenyl maleimide, belong to N-phenyl maleimide synthesis technical field.The synthesis method includes the following steps: aniline is reacted with maleic anhydride solution, and N-phenyl maleimide acid is obtained;Under the condition that air is isolated and the vacuum degree is-0.01MPa to-0.07MPa, N-phenyl maleimide acid is subjected to dehydration cyclization reaction, and N-phenyl maleimide reaction solution is obtained.The synthesis method has short reaction time, simple operation, and the reaction process does not need to use polymerization inhibitor, the production cost is low, the yield and purity of the obtained product are higher and the quality is stable.

Description

Technical Field

[0001] This invention relates to the field of N-phenylmaleimide synthesis technology, and more specifically, to a method for synthesizing N-phenylmaleimide. Background Technology

[0002] N-Phenylated maleimide (N-PMI) possesses an α-β-unsaturated imide five-membered ring structure. Its insertion into polymer chains increases the internal gyration resistance, thereby raising the glass transition temperature of the polymer and imparting higher heat resistance to the resin. It can be used as a heat-resistant modifier in ABS, PVC, PMMA resins, and photosensitive materials to improve the resin's heat resistance, impact resistance, hot melt properties, and processability. Simultaneously, N-PMI can also be used as a vulcanizing crosslinking agent in natural and synthetic rubber; it can also be used as a resin intermediate in the manufacture of heat-resistant polymers, plant growth promoters, and other agricultural chemicals; furthermore, N-PMI exhibits certain antibacterial activity and can be used as a fungicide.

[0003] Currently, domestically produced N-phenylmaleimide is still inferior to imported products in terms of purity and color. The main reason is that the production process is complicated, which not only increases production costs but also leads to more by-products, posing a great challenge to subsequent processing.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing N-phenylmaleimide to solve or improve the above-mentioned technical problems.

[0006] This invention can be implemented as follows:

[0007] In a first aspect, the present invention provides a method for synthesizing N-phenylmaleimide, comprising the following steps:

[0008] Aniline was reacted with maleic anhydride solution to give N-phenylmaleamic acid;

[0009] Under conditions of air isolation and a vacuum of -0.01 MPa to -0.07 MPa, N-phenylmaleimide is subjected to a dehydration cyclization reaction to obtain an N-phenylmaleimide reaction solution.

[0010] In an optional embodiment, aniline is completely added to the maleic anhydride solution within 2 hours while the temperature is controlled at 10°C to 100°C. After the addition is complete, the temperature is maintained and the reaction continues for no more than 2 hours.

[0011] In an optional embodiment, the aniline is added for 0.5 h to 1 h.

[0012] In an optional implementation, the temperature is controlled to be between 20°C and 80°C.

[0013] In an optional implementation, the temperature is maintained for a reaction time of 0.5 h to 1 h.

[0014] In an optional embodiment, the maleic anhydride solution includes maleic anhydride, benzene-based solvents, and co-solvents.

[0015] In an optional embodiment, the molar ratio of maleic anhydride to aniline is 1:1 to 1.4:1.

[0016] In an optional embodiment, the molar ratio of maleic anhydride to aniline is 1.1:1 to 1.3:1.

[0017] In an optional embodiment, the mass ratio of benzene solvent to maleic anhydride is 1:1 to 15:1.

[0018] In an optional embodiment, the mass ratio of benzene solvent to maleic anhydride is 1:1 to 6:1.

[0019] In an optional embodiment, the volume ratio of benzene-based solvent to co-solvent is 1:1 to 20:1.

[0020] In an optional embodiment, the volume ratio of benzene-based solvent to co-solvent is 5:1 to 10:1.

[0021] In optional embodiments, the benzene solvent includes at least one of toluene, p-xylene, o-xylene, m-xylene, chlorobenzene, and 1,2,3-trimethylbenzene.

[0022] In an optional embodiment, the co-solvent includes at least one selected from dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, tetrahydrofuran, and N-methylpyrrolidone.

[0023] In an optional embodiment, the dehydration cyclization reaction step includes: heating N-phenylmaleimide to 50°C to 180°C, adding a catalyst, reducing the vacuum to -0.01 MPa to -0.07 MPa and refluxing the solvent to remove the water generated during the reaction, and performing vacuum distillation on the reaction solution obtained from the cyclization reaction to obtain the N-phenylmaleimide reaction solution.

[0024] In an optional embodiment, the cyclization reaction takes 2 to 10 hours.

[0025] In an optional embodiment, the cyclization reaction takes 2 to 5 hours.

[0026] In an optional embodiment, N-phenylmaleamic acid is heated to 80°C to 140°C before adding the catalyst.

[0027] In an optional embodiment, the vacuum level is reduced to -0.02 MPa to -0.06 MPa after the addition of the catalyst.

[0028] In optional embodiments, the catalyst includes at least one selected from phosphoric acid, sulfuric acid, p-toluenesulfonic acid, perfluorosulfonic acid, dodecylbenzenesulfonic acid, phosphoric acid support, anhydrous sodium acetate, and anhydrous zinc acetate.

[0029] In an optional embodiment, the mass ratio of catalyst to raw material is 1:5 to 1:100, wherein the raw material is aniline and maleic anhydride.

[0030] In an optional embodiment, the mass ratio of catalyst to feedstock is 1:10 to 1:50.

[0031] In an optional embodiment, the synthesis method further includes washing and drying the N-phenylmaleimide reaction solution to obtain N-phenylmaleimide.

[0032] In an optional embodiment, the washing includes an initial alkaline wash followed by a water wash, wherein the alkaline solution used for the alkaline wash includes at least one of sodium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, and potassium bicarbonate solution.

[0033] In an optional embodiment, the mass concentration of the alkali solution is 1% to 10%.

[0034] In an optional embodiment, the mass concentration of the alkaline solution is 4% to 8%.

[0035] In an optional implementation, the amount of alkali solution used is 1 to 20 times the theoretical product mass.

[0036] In an optional implementation, the amount of alkali solution used is 5 to 10 times the theoretical product mass.

[0037] The beneficial effects of this invention include:

[0038] This application creatively proposes a dehydration cyclization reaction of N-phenylmaleimide under air-isolated and specific vacuum conditions. This method inhibits the oligomerization of N-phenylmaleimide, achieving the same effect as the addition of polymerization inhibitors in existing technologies. This method not only simplifies the operation steps but also significantly reduces production costs and the difficulty of subsequent wastewater treatment. Furthermore, the use of reduced pressure reflux during the cyclization dehydration process not only accelerates the reaction rate and reduces reaction time but also minimizes side reactions, further reducing the difficulty of subsequent treatment, simplifying the reaction process, and lowering production costs.

[0039] The synthesis method of N-phenylmaleimide provided by this invention has a short reaction time, is simple to operate, does not require the use of polymerization inhibitors, nor does it require the addition of clay or acid coating agents, resulting in low production costs and high product yield, purity, and stable quality. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0041] The synthesis method of N-phenylmaleimide provided by the present invention will be described in detail below.

[0042] This invention provides a method for synthesizing N-phenylmaleimide, comprising the following steps:

[0043] S1: Aniline is reacted with maleic anhydride solution to obtain N-phenylmaleamic acid.

[0044] In an optional embodiment, aniline is completely added to the maleic anhydride solution within 2 hours while the temperature is controlled at 10°C to 100°C. After the addition is complete, the temperature is maintained and the reaction continues for no more than 2 hours.

[0045] In some optional embodiments, the addition time of aniline can be 0.1h, 0.2h, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, or 2h, or other values ​​not exceeding 2h but greater than 0h. In some more typical embodiments, the addition time of aniline is 0.5h to 1h.

[0046] For example, aniline can be added dropwise. Adding aniline dropwise helps to control the reaction rate and reduce the formation of byproducts.

[0047] In some optional embodiments, the temperature is controlled at 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C during the addition of aniline to the maleic anhydride solution, or other values ​​within the range of 10°C to 100°C. In some more typical embodiments, the temperature is controlled at 20°C to 80°C during the addition of aniline to the maleic anhydride solution.

[0048] In some optional embodiments, the reaction time can be maintained at the temperature for 0.1h, 0.2h, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, or 2h, or other values ​​not exceeding 2h but greater than 0h. In some more typical embodiments, the reaction time is maintained at the temperature for 0.5h to 1h. By maintaining the temperature for the reaction, the complete reaction of aniline and maleic anhydride can be ensured.

[0049] In some alternative embodiments, the maleic anhydride solution includes maleic anhydride, a benzene-based solvent, and a co-solvent. The maleic anhydride solution can be prepared by sequentially adding maleic anhydride, a benzene-based solvent, and a co-solvent to a reaction vessel, allowing the maleic anhydride to completely dissolve.

[0050] The molar ratio of maleic anhydride to aniline can be from 1:1 to 1.4:1, such as 1:1, 1.1:1, 1.2:1, 1.3:1, or 1.4:1, or other values ​​within the range of 1:1 to 1.4:1. In some typical embodiments, the molar ratio of maleic anhydride to aniline is from 1.1:1 to 1.3:1.

[0051] At the above molar ratio, a slight excess of maleic anhydride has the following two advantages: (1) it can reduce the reaction between the carbon-carbon double bonds of aniline and N-phenylmaleimide, thereby reducing the generation of by-products and improving the purity of the product; (2) it can avoid the problem of reduced N-phenylmaleimide yield due to partial hydrolysis of maleic anhydride during the reaction.

[0052] The mass ratio of benzene solvent to maleic anhydride can be from 1:1 to 15:1, such as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1, or other values ​​within the range of 1:1 to 15:1. In some typical embodiments, the mass ratio of benzene solvent to maleic anhydride is from 1:1 to 6:1.

[0053] The volume ratio of benzene solvent to co-solvent can be from 1:1 to 20:1, such as 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, or 20:1, or other values ​​within the range of 1:1 to 20:1. In some typical embodiments, the volume ratio of benzene solvent to co-solvent is from 5:1 to 10:1.

[0054] The benzene solvent may, by way of example but not by way of limitation, include at least one of toluene, p-xylene, o-xylene, m-xylene, chlorobenzene and 1,2,3-trimethylbenzene.

[0055] The cosolvent may, by way of example but not limitation, include at least one of dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, tetrahydrofuran, and N-methylpyrrolidone.

[0056] S2: Under conditions of air isolation and a vacuum of -0.01 MPa to -0.07 MPa, N-phenylmaleimide undergoes a dehydration cyclization reaction to obtain an N-phenylmaleimide reaction solution.

[0057] In some optional embodiments, the dehydration cyclization reaction step includes: heating N-phenylmaleimide to 50°C to 180°C, adding a catalyst, reducing the vacuum to -0.01 MPa to -0.07 MPa and refluxing the solvent to remove water generated during the reaction, and distilling the reaction solution obtained from the cyclization reaction under reduced pressure to obtain an N-phenylmaleimide reaction solution.

[0058] In some alternative embodiments, before adding the catalyst, N-phenylmaleamic acid can be heated to 50°C, 80°C, 100°C, 120°C, 150°C, or 180°C, or other values ​​within the range of 50°C to 180°C. In some more typical embodiments, before adding the catalyst, N-phenylmaleamic acid is heated to 80°C to 140°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C.

[0059] In some alternative embodiments, the catalyst may, by way of example but not by way of limitation, include at least one of phosphoric acid, sulfuric acid, p-toluenesulfonic acid, perfluorosulfonic acid, dodecylbenzenesulfonic acid, phosphoric acid support, anhydrous sodium acetate, and anhydrous zinc acetate.

[0060] In some optional embodiments, the mass ratio of catalyst to reactants can be from 1:5 to 1:100, such as 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1:100, or other values ​​within the range of 1:5 to 1:100. The reactants are aniline and maleic anhydride. In some more typical embodiments, the mass ratio of catalyst to reactants is from 1:10 to 1:50, such as 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50. Insufficient catalyst will prolong the reaction time.

[0061] In some alternative embodiments, the addition of a catalyst can reduce the vacuum level to -0.01 MPa, -0.02 MPa, -0.03 MPa, -0.04 MPa, -0.05 MPa, -0.06 MPa, or -0.07 MPa, or other values ​​within the range of -0.01 MPa to -0.07 MPa. In some more typical embodiments, the addition of a catalyst can reduce the vacuum level to -0.02 MPa to -0.06 MPa.

[0062] If the vacuum is too low, the dehydration effect will be poor and there will be more side reactions; if the vacuum is too high, the system temperature will be low, the reaction time will be long, more solvent will be evaporated, and more solvent will need to be added.

[0063] It should be noted that common N-phenylmaleimide is produced by heating and refluxing the reaction solution of N-phenylmaleimic acid with the addition of a catalyst and the polymerization inhibitor hydroquinone. After the reaction, the product is obtained by cooling and crystallizing with the addition of bleaching clay and an acid-coating agent. The entire process is carried out under normal pressure. The above-mentioned process of adding a polymerization inhibitor introduces impurities, increases production costs, and complicates wastewater treatment. Furthermore, the addition of bleaching clay and an acid-coating agent during cooling crystallization also increases production costs and makes the operation cumbersome. This application creatively proposes a dehydration cyclization reaction under air-isolated and specific vacuum conditions. This method can inhibit the oligomerization of N-phenylmaleimide, achieving the same effect as the addition of a polymerization inhibitor in existing technologies. This method not only simplifies the operation steps but also significantly reduces production costs and the difficulty of subsequent wastewater treatment. In addition, the use of reduced pressure reflux in the cyclization dehydration process can not only accelerate the reaction rate and reduce the reaction time, but also reduce the occurrence of side reactions, further reducing the difficulty of subsequent processing, simplifying the reaction process and reducing production costs.

[0064] In some optional embodiments, the cyclization reaction time can be 2h to 10h, such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or other values ​​within the range of 2h to 10h. In some more typical embodiments, the cyclization reaction time is 2h to 5h.

[0065] After the dehydration and cyclization reaction is completed, the reaction solution is subjected to vacuum distillation to remove benzene solvents as needed, yielding N-phenylmaleimide reaction solution.

[0066] Furthermore, the above synthesis method also includes washing and drying the N-phenylmaleimide reaction solution to obtain N-phenylmaleimide.

[0067] The washing process includes an initial alkaline wash followed by a water wash.

[0068] The alkaline solution used for alkaline washing may, by way of example but not by way of limitation, include at least one of sodium carbonate solution, sodium bicarbonate solution, potassium carbonate solution and potassium bicarbonate solution.

[0069] In some optional embodiments, the mass concentration of the alkali solution can be 1% to 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or other values ​​within the range of 1% to 10%. In some more typical embodiments, the mass concentration of the alkali solution is 4% to 8%.

[0070] In some optional embodiments, the amount of alkali solution used can be 1 to 20 times the theoretical product mass, such as 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, or 20 times, or other values ​​within the range of 1 to 20 times. In some more typical embodiments, the amount of alkali solution used is 5 to 10 times the theoretical product mass, such as 5, 6, 7, 8, 9, or 10 times, etc. Here, "theoretical product mass" refers to the theoretical production of N-phenylmaleimide based on a relatively small number of moles of raw materials. In specific embodiments, the mass of N-phenylmaleimide theoretically produced corresponds to the relatively smaller molar number of maleic anhydride and aniline.

[0071] In conclusion, the synthesis method of N-phenylmaleimide provided by this invention has a short reaction time, is simple to operate, does not require the use of polymerization inhibitors, nor does it require the addition of clay or acid coating agents, resulting in low production costs and high product yield and purity with stable quality.

[0072] In some typical embodiments, the N-phenylmaleimide synthesized by the synthesis method provided by the present invention can achieve a purity of 99% or higher and a yield of 90% or higher.

[0073] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0074] Example 1

[0075] This embodiment provides a method for synthesizing N-phenylmaleimide, including the following steps:

[0076] S1: Amide synthesis.

[0077] At room temperature, 68.28 g of maleic anhydride, 450 mL of toluene (mass ratio of toluene to maleic anhydride is 5.75:1) and 45 mL of N,N-dimethylformamide (volume ratio of toluene to N,N-dimethylformamide is 10:1) are added to a 2 L reactor equipped with a stirrer, a constant pressure dropping funnel and a thermometer. The mixture is stirred thoroughly until the maleic anhydride is completely dissolved to obtain a maleic anhydride solution.

[0078] Take 55.95g of aniline (the molar ratio of maleic anhydride to aniline is 1.1:1) and add it to a constant pressure dropping funnel. Then slowly add it dropwise into a continuously stirred maleic anhydride solution. The reaction temperature is controlled at 60℃ and the aniline is added over 1 hour. After the addition is complete, maintain the temperature and continue the reaction for 0.5 hours to finally obtain N-phenylmaleamic acid.

[0079] S2: Dehydration cyclization.

[0080] 6g of p-toluenesulfonic acid (mass ratio of p-toluenesulfonic acid to raw material is 1:20.705) was dissolved in 30mL of toluene and added to a constant pressure dropping funnel. Air was evacuated from the reactor using a vacuum pump, and nitrogen was added. The reaction solution was heated to 125℃. The dropping funnel was opened, and after the catalyst was completely added, the vacuum degree of the reactor was reduced to -0.03MPa. The solvent was refluxed under this vacuum degree. The cyclization reaction time was 3h. After the reaction was completed, the reaction solution was subjected to vacuum distillation to remove toluene, and finally N-phenylmaleimide reaction solution was obtained.

[0081] S3: Wash and dry.

[0082] The reaction solution was washed with a 6% sodium carbonate solution (600 ml) for 15 min, filtered, washed with water, and the resulting filter cake was dried.

[0083] In this example, 98.04 g of N-phenylmaleimide was obtained, with a yield of 94.2%, and the purity was 99.1% as determined by high performance liquid chromatography.

[0084] Example 2

[0085] This embodiment provides a method for synthesizing N-phenylmaleimide, including the following steps:

[0086] S1: Amide synthesis.

[0087] At room temperature, 70.75 g of maleic anhydride, 350 mL of toluene (mass ratio of toluene to maleic anhydride is 4.31:1), and 60 mL of N,N-dimethylformamide (volume ratio of toluene to N,N-dimethylformamide is 5.83:1) are added to a 2 L reactor equipped with a stirrer, a constant pressure dropping funnel, and a thermometer. The mixture is stirred thoroughly until the maleic anhydride is completely dissolved to obtain a maleic anhydride solution.

[0088] Take 55.95g of aniline (the molar ratio of maleic anhydride to aniline is 1.2:1) and add it to a constant pressure dropping funnel. Then slowly add it dropwise into a continuously stirred maleic anhydride solution. The reaction temperature is controlled at 40℃ and the aniline is added over 1 hour. After the addition is complete, maintain the temperature and continue the reaction for another hour to finally obtain N-phenylmaleamic acid.

[0089] S2: Dehydration cyclization.

[0090] 6g of dodecylbenzenesulfonic acid (mass ratio of dodecylbenzenesulfonic acid to raw material is 1:21.117) was dissolved in 30mL of toluene and added to a constant pressure dropping funnel. Air was evacuated from the reactor using a vacuum pump, and nitrogen was added. The reaction solution was heated to 110℃. The dropping funnel was opened, and after the catalyst was completely added, the vacuum degree of the reactor was reduced to -0.05MPa. The solvent was refluxed under this vacuum degree. The cyclization reaction time was 5h. After the reaction was completed, the reaction solution was subjected to vacuum distillation to remove toluene, and finally N-phenylmaleimide reaction solution was obtained.

[0091] S3: Same as Example 1.

[0092] In this example, 97.63 g of N-phenylmaleimide was obtained, with a yield of 93.8%, and the purity was 98.9% as determined by high performance liquid chromatography.

[0093] Example 3

[0094] This embodiment provides a method for synthesizing N-phenylmaleimide, including the following steps:

[0095] S1: Amide synthesis (the difference from Example 1 is that the amount of N,N-dimethylformamide used is reduced).

[0096] At room temperature, 68.28 g of maleic anhydride, 450 mL of toluene (mass ratio of toluene to maleic anhydride is 5.75:1) and 25 mL of N,N-dimethylformamide (volume ratio of toluene to N,N-dimethylformamide is 18:1) are added to a 2 L reaction vessel equipped with a stirrer, a constant pressure dropping funnel and a thermometer. The mixture is stirred thoroughly until the maleic anhydride is completely dissolved to obtain a maleic anhydride solution.

[0097] Take 55.95g of aniline (the molar ratio of maleic anhydride to aniline is 1.1:1) and add it to a constant pressure dropping funnel. Then slowly add it dropwise into a continuously stirred maleic anhydride solution. The reaction temperature is controlled at 60℃ and the aniline is added over 1 hour. After the addition is complete, maintain the temperature and continue the reaction for 0.5 hours to finally obtain N-phenylmaleamic acid.

[0098] S2: Dehydration cyclization (the difference from Example 1 lies in the cyclization time).

[0099] 6g of p-toluenesulfonic acid (mass ratio of p-toluenesulfonic acid to raw material is 1:20.705) was dissolved in 30mL of toluene and added to a constant pressure dropping funnel. Air was evacuated from the reactor using a vacuum pump, and nitrogen was added. The reaction solution was heated to 125℃. The dropping funnel was opened, and after the catalyst was completely added, the vacuum degree of the reactor was reduced to -0.03MPa. The solvent was refluxed under this vacuum degree. The cyclization reaction time was 6h. After the reaction was completed, the reaction solution was subjected to vacuum distillation to remove toluene, and finally N-phenylmaleimide reaction solution was obtained.

[0100] S3: Same as Example 1.

[0101] In this example, 94.19 g of N-phenylmaleimide was obtained, with a yield of 90.5%, and the purity was 98.5% as determined by high performance liquid chromatography.

[0102] Example 4

[0103] This embodiment provides a method for synthesizing N-phenylmaleimide, including the following steps:

[0104] S1: Same as Example 2.

[0105] S2: Dehydration cyclization (The difference from Example 2 is the different amount of catalyst and the different cyclization reaction time).

[0106] 2g of dodecylbenzenesulfonic acid (mass ratio of dodecylbenzenesulfonic acid to raw material is 1:63.35) was added to a constant pressure dropping funnel. Air was evacuated from the reactor using a vacuum pump, and nitrogen was added. The reaction solution was heated to 125℃. The dropping funnel was opened, and after the catalyst was completely added, the vacuum degree of the reactor was reduced to -0.05MPa. The solvent was refluxed under this vacuum degree. The cyclization reaction time was 10h. After the reaction was completed, the reaction solution was subjected to reduced pressure distillation to remove toluene, and finally N-phenylmaleimide reaction solution was obtained.

[0107] S3: Same as Example 2.

[0108] In this example, 95.02 g of N-phenylmaleimide was obtained, with a yield of 91.3%, and the purity was 98.7% as determined by high performance liquid chromatography.

[0109] Example 5

[0110] This embodiment provides a method for synthesizing N-phenylmaleimide, including the following steps:

[0111] S1: Amide synthesis. (The difference from Example 1 is that the amount of maleic anhydride used is reduced).

[0112] At room temperature, 58.96 g of maleic anhydride, 450 mL of toluene (mass ratio of toluene to maleic anhydride is 6.66:1) and 45 mL of N,N-dimethylformamide (volume ratio of toluene to N,N-dimethylformamide is 10:1) were added to a 2 L reactor equipped with a stirrer, a constant pressure dropping funnel and a thermometer. The mixture was stirred thoroughly until the maleic anhydride was completely dissolved to obtain a maleic anhydride solution.

[0113] Take 55.95g of aniline (the molar ratio of maleic anhydride to aniline is 1:1) and add it to a constant pressure dropping funnel. Then slowly add it dropwise into a continuously stirred maleic anhydride solution. The reaction temperature is controlled at 60℃ and the aniline is added over 1 hour. After the addition is complete, maintain the temperature and continue the reaction for 0.5 hours to finally obtain N-phenylmaleamic acid.

[0114] S2: Same as Example 1.

[0115] S3: Same as Example 1.

[0116] In this example, 91.79 g of N-phenylmaleimide was obtained, with a yield of 88.2%, and the purity was 98.2% as determined by high performance liquid chromatography.

[0117] Comparative Example 1

[0118] The difference between this comparative example and Example 1 is that in S2, the dehydration cyclization reaction is carried out under normal pressure nitrogen conditions, and the dehydration cyclization reaction time is 8 hours.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that in S2, the dehydration cyclization reaction is carried out under normal air pressure, and the dehydration cyclization reaction time is 10 hours.

[0121] Comparative Example 3

[0122] The difference between this comparative example and Example 1 is that in S1, the molar ratio of maleic anhydride to aniline is 0.8:1 during the amidation synthesis process.

[0123] The reaction time, yield, and purity of the N-phenylmaleimide obtained in Examples 1-5 and Comparative Examples 1-3 are summarized in Table 1.

[0124] Table 1. Results of cyclization reaction time, yield, and purity.

[0125] Cyclization reaction time (h) Yield (%) purity(%) Example 1 3 94.2 99.1 Example 2 5 93.8 98.9 Example 3 6 90.5 98.5 Example 4 10 91.3 98.7 Example 5 3 88.2 98.2 Comparative Example 1 8 85.3 98.1 Comparative Example 2 10 83.5 91.3 Comparative Example 3 3 78.1 94.5

[0126] As can be seen from Table 1, the synthesis method provided by the present invention can obtain N-phenylmaleimide with short cyclization reaction time, high yield and high purity.

[0127] By comparing Examples 1 to 5, it can be seen that Example 1 has the best effect, indicating that the corresponding synthesis conditions of this example are optimal. By comparing Example 1 and Comparative Examples 1 to 3, it can be seen that when the synthesis conditions are not set properly, the yield and purity of N-phenylmaleimide will decrease, or the reaction time will increase.

[0128] In summary, the synthesis method of N-phenylmaleimide provided by this invention has a short reaction time, is simple to operate, does not require the use of polymerization inhibitors, nor does it require the addition of clay or acid coating agents, resulting in low production costs and high product yield, purity, and stable quality.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing N-phenylmaleimide, characterized in that, Includes the following steps: Aniline was reacted with maleic anhydride solution to give N-phenylmaleamic acid; Under conditions of air isolation and a vacuum of -0.01 MPa to -0.07 MPa, N-phenylmaleimide is subjected to a dehydration cyclization reaction to obtain an N-phenylmaleimide reaction solution.

2. The synthesis method according to claim 1, characterized in that, Aniline was completely added to the maleic anhydride solution within 2 hours while the temperature was controlled at 10°C to 100°C. After the addition was complete, the temperature was maintained and the reaction continued for no more than 2 hours. Preferably, the aniline is added over a period of 0.5 h to 1 h; Preferably, the temperature is controlled between 20℃ and 80℃; Preferably, the temperature is maintained for 0.5 h to 1 h to continue the reaction.

3. The synthesis method according to claim 1 or 2, characterized in that, The maleic anhydride solution includes maleic anhydride, benzene-based solvents, and co-solvents; Preferably, the molar ratio of maleic anhydride to aniline is 1:1 to 1.4:1; more preferably, the molar ratio of maleic anhydride to aniline is 1.1:1 to 1.3:

1. Preferably, the mass ratio of the benzene solvent to the maleic anhydride is 1:1 to 15:1; more preferably, the mass ratio of the benzene solvent to the maleic anhydride is 1:1 to 6:

1. Preferably, the volume ratio of the benzene solvent to the co-solvent is 1:1 to 20:1; more preferably, the volume ratio of the benzene solvent to the co-solvent is 5:1 to 10:

1.

4. The synthesis method according to claim 3, characterized in that, The benzene solvents include at least one of toluene, p-xylene, o-xylene, m-xylene, chlorobenzene, and 1,2,3-trimethylbenzene; Alternatively, the co-solvent may include at least one of dichloromethane, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, tetrahydrofuran, and N-methylpyrrolidone.

5. The synthesis method according to claim 1, characterized in that, The dehydration cyclization reaction step includes: heating the N-phenylmaleimide to 50℃~180℃, adding a catalyst, reducing the vacuum to -0.01MPa to -0.07MPa and refluxing the solvent to remove the water generated during the reaction, and performing vacuum distillation on the reaction solution obtained from the cyclization reaction to obtain the N-phenylmaleimide reaction solution.

6. The synthesis method according to claim 5, characterized in that, The cyclization reaction takes 2 to 10 hours. Preferably, the cyclization reaction takes 2 to 5 hours.

7. The synthesis method according to claim 5, characterized in that, Before adding the catalyst, the N-phenylmaleamic acid is heated to 80°C to 140°C; Alternatively, by adding a catalyst, the vacuum level can be reduced to -0.02 MPa to -0.06 MPa.

8. The synthesis method according to claim 5, characterized in that, The catalyst comprises at least one of phosphoric acid, sulfuric acid, p-toluenesulfonic acid, perfluorosulfonic acid, dodecylbenzenesulfonic acid, phosphoric acid support, anhydrous sodium acetate, and anhydrous zinc acetate. Preferably, the mass ratio of the catalyst to the raw material is 1:5 to 1:100, wherein the raw material is aniline and maleic anhydride; More preferably, the mass ratio of the catalyst to the raw material is 1:10 to 1:

50.

9. The synthesis method according to claim 1, characterized in that, Also includes: The N-phenylmaleimide reaction solution was washed and dried to obtain N-phenylmaleimide.

10. The synthesis method according to claim 9, characterized in that, The washing process includes an initial alkaline wash followed by a water wash. The alkaline solution used for the alkaline wash includes at least one of sodium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, and potassium bicarbonate solution. Preferably, the mass concentration of the alkaline solution is 1% to 10%; more preferably, the mass concentration of the alkaline solution is 4% to 8%. Preferably, the amount of alkali solution used is 1 to 20 times the theoretical product mass; more preferably, the amount of alkali solution used is 5 to 10 times the theoretical product mass.