Synthesis method of 2, 3, 3 ', 4'-diphenyl ether tetracarboxylic dianhydride and 6-(2, 3-dicarboxyphenoxy) phthalide

Abstract

The invention relates to the technical field of organic synthesis, and particularly discloses a synthesis method of 2, 3, 3 ', 4'-diphenyl ether tetracarboxylic dianhydride. The invention relates to a synthetic method of 2, 3, 3 ', 4'-diphenyl ether tetracarboxylic dianhydride, which comprises the following steps: firstly carrying out nucleophilic reaction on methyl 3-hydroxybenzoate and 3-nitro-N-methylphthalimide in a base catalyst, then hydrolyzing under an alkaline condition, and finally carrying out cyclization reaction with paraformaldehyde under an acidic condition to obtain 6-(2, 3-dicarboxyl phenoxy) phthalide, the preparation method comprises the following steps: oxidizing 6-(2, 3-dicarboxyphenoxy) phthalide into acid, and then forming anhydride, thereby obtaining the 2, 3, 3 ', 4'-diphenyl ether tetracarboxylic dianhydride. According to the synthesis method, the low-toxicity methyl 3-hydroxybenzoate is adopted as the raw material to synthesize the target product, so that the synthesis cost of the 2, 3, 3 ', 4'-diphenyl ether tetracarboxylic dianhydride is effectively reduced.

Description

Technical Field

[0001] This application relates to the technical field of organic synthesis, and more specifically, it relates to a method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride and 6-(2,3-dicarboxyphenoxy) phthalide. Background Art

[0002] Polyimide (PI) is a high-performance polymer material with excellent heat resistance, good mechanical properties, and excellent electrical insulation properties, etc. Therefore, it has applications in many fields such as aerospace, automotive, machinery, and electronic and electrical. However, due to the insoluble and infusible characteristics of polyimide, it is difficult to process, which limits its uses. To improve the processing performance of polyimide, many scholars have conducted extensive research. A relatively convenient method is to use isomeric monomers to synthesize isomerized polyimide.

[0003] 2,3,3',4'-Diphenylether tetracarboxylic dianhydride (α-ODPA) and 3,3',4,4'-diphenylether tetracarboxylic dianhydride (ODPA) are isomeric monomers commonly used in the synthesis of polyimide, and can synthesize polyimide with various diamines. Compared with 3,3',4,4'-diphenylether tetracarboxylic dianhydride, the polyimide resin synthesized using 2,3,3',4'-diphenylether tetracarboxylic dianhydride, due to its good solubility, can be made into a film with better transparency, and the temperature for processing into a film or plastic part can be reduced by about 100 °C. Therefore, the polyimide film synthesized using 2,3,3',4'-diphenylether tetracarboxylic dianhydride can be applied to special requirement fields such as insulating materials and flexible printed circuit boards (FCB), and has a broader application market.

[0004] Currently, the general method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride is: after oxidizing the prepared 4-(2,3-dimethylphenoxy) phthalic acid to synthesize 2,3,3',4'-diphenylether tetracarboxylic acid, then performing high-temperature dehydration on 2,3,3',4'-diphenylether tetracarboxylic acid, and 2,3,3',4'-diphenylether tetracarboxylic dianhydride can be obtained. Among them, the preparation of 4-(2,3-dimethylphenoxy) phthalic acid is an important step in the synthesis of 2,3,3',4'-diphenylether tetracarboxylic dianhydride.

[0005] In related technologies, 4-(2,3-dimethylphenoxy) phthalic acid usually uses phthalic anhydride as the starting material, first undergoes a ring-opening reaction with 2,3-dimethylphenol under alkaline conditions to generate the corresponding sodium salt, and then is obtained through acidification treatment. However, because 2,3-dimethylphenol is highly toxic and special experimental equipment is required to protect the health of experimental personnel and reduce environmental pollution, the synthesis cost of 2,3,3',4'-diphenylether tetracarboxylic dianhydride is increased. Summary of the Invention

[0006] In order to reduce the synthesis cost of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, the present application provides a synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride and 6-(2,3-dicarboxyphenoxy)phthalide.

[0007] The present application provides a synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, adopting the following technical solution: A synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, the synthesis route is as follows: ; The above synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: Methyl 3-hydroxybenzoate and 3-nitro-N-methylphthalimide are subjected to a nucleophilic reaction under an alkali catalyst to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide is hydrolyzed under alkaline conditions to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Cyclization reaction: 3-(3-methoxycarbonylphenoxy)phthalic acid and paraformaldehyde are subjected to a cyclization reaction under acidic conditions to obtain 6-(2,3-dicarboxyphenoxy)phthalide; (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: 6-(2,3-dicarboxyphenoxy)phthalide and an oxidant are subjected to an oxidation reaction to obtain 2,3,3',4'-diphenylether tetracarboxylic acid; (3) Preparation of the target product: 2,3,3',4'-diphenylether tetracarboxylic acid is subjected to an anhydride formation reaction to obtain 2,3,3',4'-diphenylether tetracarboxylic dianhydride.

[0008] Preferably, the preparation of (1) 6-(2,3-dicarboxyphenoxy)phthalide includes the following steps: 1.1 Nucleophilic reaction: Methyl 3-hydroxybenzoate and N,N-dimethylformamide are mixed to obtain a mixed solution; Potassium tert-butoxide is added to the mixed solution at 0-5°C, first stirred and reacted at 25-30°C for 0.3-0.5 h, then 3-nitro-N-methylphthalimide is added, and stirred and reacted for 1.5-2.5 h to obtain a reaction solution; The reaction solution is distilled under reduced pressure to remove N,N-dimethylformamide, water is added to precipitate a solid, filtered, and washed to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide and an aqueous solution of caustic alkali were mixed and stirred at 100 °C for 5.0 h to obtain a reaction solution; the reaction solution was cooled to 80 °C, and then the pH value of the reaction solution was adjusted to 2-3 to precipitate a solid, which was filtered and washed to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Cyclization reaction: 3-(3-methoxycarbonylphenoxy)phthalic acid and concentrated sulfuric acid were stirred and mixed to obtain a mixed solution; paraformaldehyde was added to the mixed solution at 25-50 °C, and the mixture was stirred and reacted for 5.0-5.5 h to obtain a reaction solution; the reaction solution was poured into ice water to precipitate a solid, which was filtered and washed to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

[0009] Preferably, in the 1.1 nucleophilic reaction, the molar ratio of methyl 3-hydroxybenzoate to 3-nitro-N-methylphthalimide is 1:1.

[0010] Preferably, in the 1.1 nucleophilic reaction, the mass ratio of methyl 3-hydroxybenzoate to N,N-dimethylformamide is 1:(3.7-4.1).

[0011] Preferably, in the 1.1 nucleophilic reaction, the molar ratio of methyl 3-hydroxybenzoate to potassium tert-butoxide is 1:(1.05-1.08).

[0012] Preferably, in the 1.2 hydrolysis reaction, the caustic alkali is sodium hydroxide, and the mass ratio of 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide to sodium hydroxide is 1:3.

[0013] Preferably, in the 1.3 cyclization reaction, the molar ratio of 3-(3-methoxycarbonylphenoxy)phthalic acid to paraformaldehyde is 1:(1.50-1.55).

[0014] Preferably, the preparation of (2) 2,3,3',4'-diphenylether tetracarboxylic acid includes the following steps: 6-(2,3-Dicarboxyphenoxy)phthalide and water were stirred and mixed to obtain an aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide; dilute nitric acid was added to the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide at 0-30 °C, and the mixture was stirred and reacted at 100 °C for 8.0-9.0 h to obtain a reaction solution; the pH of the reaction solution was adjusted to 2-3, the solid was collected, filtered, washed, and dried to obtain 2,3,3',4'-diphenylether tetracarboxylic acid.

[0015] Preferably, in the preparation of (2) 2,3,3',4'-diphenylether tetracarboxylic acid, the molar ratio of 6-(2,3-dicarboxyphenoxy)phthalide to dilute nitric acid is 1:(1.0-1.04).

[0016] Second aspect, the present application provides a 6-(2,3-dicarboxyphenoxy)phthalide, adopting the following technical solution: A 6-(2,3-dicarboxyphenoxy)phthalide, the structural formula is as follows: ; The synthesis route of the above 6-(2,3-dicarboxyphenoxy)phthalide is as follows: ; The synthesis method of the above 6-(2,3-dicarboxyphenoxy)phthalide includes the following steps: 1.1 Nucleophilic reaction: Mix methyl 3-hydroxybenzoate and N,N-dimethylformamide to obtain a mixed solution; add potassium tert-butoxide to the mixed solution at 0-5 °C, first stir and react at 25-30 °C for 0.3-0.5 h, then add 3-nitro-N-methylphthalimide, stir and react for 1.5-2.5 h to obtain a reaction solution; distill the reaction solution under reduced pressure to remove N,N-dimethylformamide, add water to precipitate a solid, filter and wash to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: Mix 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide and an aqueous solution of caustic alkali, stir and react at 100 °C for 5.0 h to obtain a reaction solution; cool the reaction solution to 80 °C, then adjust the pH value of the reaction solution to 2-3, precipitate a solid, filter and wash to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Cyclization reaction: Stir and mix 3-(3-methoxycarbonylphenoxy)phthalic acid and concentrated sulfuric acid to obtain a mixed solution; add paraformaldehyde to the mixed solution at 25-50 °C, stir and react for 5.0-5.5 h to obtain a reaction solution; pour the reaction solution into ice water, precipitate a solid, filter and wash to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

[0017] In summary, the present application has the following beneficial effects: The present application uses methyl 3-hydroxybenzoate as a raw material, and after nucleophilic reaction, hydrolysis reaction and cyclization reaction with 3-nitro-N-methylphthalimide, 6-(2,3-dicarboxyphenoxy)phthalide is synthesized. Then 6-(2,3-dicarboxyphenoxy)phthalide is oxidized to synthesize 2,3,3',4'-diphenylether tetracarboxylic acid, and finally 2,3,3',4'-diphenylether tetracarboxylic dianhydride is obtained through anhydride formation. Since methyl 3-hydroxybenzoate has low toxicity, the synthesis cost of 2,3,3',4'-diphenylether tetracarboxylic dianhydride is reduced, and the application range of 2,3,3',4'-diphenylether tetracarboxylic dianhydride is increased. Description of the Drawings

[0018] Figure 1It is the hydrogen nuclear magnetic spectrum of 2,3,3',4'-diphenylether tetracarboxylic dianhydride in Example 1 of this application. Detailed implementation mode

[0019] The following further elaborates on this application in conjunction with the attached drawings and examples.

[0020] Except for the following special instructions, other raw materials used in the examples of this application are all commercially available.

[0021] Paraformaldehyde, CAS number is 30525-89-4. Example Example 1

[0022] A synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, and the synthesis route is as follows: 。

[0023] The above synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: Add N,N-dimethylformamide (60 ml, 57 g) and methyl 3-hydroxybenzoate (15.2 g, 100 mmol) to a four-necked flask under nitrogen protection, stir and mix to obtain a mixed solution; cool the mixed solution to 0-5 °C in an ice-water bath, and then dropwise add potassium tert-butoxide (15.2 g, 100 mmol), controlling the temperature not to exceed 20 °C during the dropping process. After adding, first stir and react at 30 °C for 0.5 h, then add 3-nitro-N-methylphthalimide (20.6 g, 100 mmol), and stir and react for 2 h to obtain a reaction solution.

[0024] First, distill off N,N-dimethylformamide from the reaction solution under reduced pressure, then add water (60 ml), precipitate a pale yellow solid, cool to room temperature, filter, and wash the filter cake once with pure water to obtain a pale yellow solid (42 g).

[0025] After detection, the pale yellow solid is 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide.

[0026] 1.2 Hydrolysis reaction: Add pure water (100 ml) and sodium hydroxide (14 g, 350 mmol) to a four-necked flask, and under nitrogen protection, then add 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide (42 g) prepared in step 1.1 of the nucleophilic reaction, and stir and reflux at 100 °C for 5 h to obtain a reaction solution.

[0027] Cool the reaction solution to 80 °C, then add dropwise HCl (30% concentration) to adjust the pH value of the reaction solution to 2, precipitate white solid, filter while it is hot, wash the filter cake once with pure water, and dry the obtained wet product at 100 °C to obtain white solid (26.5 g, 87.7 mmol).

[0028] Upon detection, the white solid is 3-(3-methoxycarbonylphenoxy)phthalic acid, and the two-step yields of 1.1 nucleophilic reaction and 1.2 hydrolysis reaction are 87.7% (the theoretical value is 100 mmol).

[0029] 1.3 Cyclization reaction: Add concentrated H2SO4 (90 ml, 98% concentration) to a three-necked flask, start stirring, and add 3-(3-methoxycarbonylphenoxy)phthalic acid (26.5 g, 87.7 mmol) to obtain a mixed solution; within 2 h, add paraformaldehyde (3.95 g, 132 mmol) in batches to the mixed solution at 50 °C, stir and react for 5 h to obtain a reaction solution; Pour the reaction solution into ice water (200 ml), precipitate white solid, filter, wash the filter cake with pure water to obtain a filter cake (36 g). Add the filter cake (36 g) to methanol (100 ml) and slurry for 0.5 h, filter and dry to obtain white solid (22.6 g, 72 mmol).

[0030] Upon detection, the white solid is 6-(2,3-dicarboxyphenoxy)phthalide, and the yield is 82% (the theoretical value is 87.7 mmol).

[0031] (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: Add 6-(2,3-dicarboxyphenoxy)phthalide (22.6 g, 72 mmol) to water (300 ml), stir and mix to obtain an aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide; add 15% concentration nitric acid (30.6 g, 73.0 mmol) dropwise to the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide, control the temperature of the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide not to exceed 30 °C during the dropwise addition, and after the dropwise addition, reflux and stir at 100 °C for 8 h to obtain a reaction solution.

[0032] After filtering the reaction solution to remove insoluble substances, add HCl (30% concentration) to the aqueous phase, adjust the pH value of the aqueous phase to 2, precipitate white solid, filter, wash the filter cake with pure water, and dry to obtain white solid (20.2 g, 58.4 mmol).

[0033] Upon detection, the white solid is 2,3,3',4'-diphenylether tetracarboxylic acid, and the yield is 81% (the theoretical value is 72 mmol).

[0034] (3) Preparation of the target product: 2,3,3',4'-diphenylether tetracarboxylic acid (20.2 g, 58.4 mmol) was dehydrated at 260 °C for 15 h, cooled to room temperature, and pulverized to obtain a white powder (17.0 g, 54.8 mmol).

[0035] Refer to Figure 1 , and the white powder was 2,3,3',4'-diphenylether tetracarboxylic dianhydride, with a yield of 93.8% (the theoretical value was 58.4 mmol), a purity of 99.2%, and a melting point of 182.6 °C. Example 2

[0036] A synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, which is different from Example 1, includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: N,N-dimethylformamide (65 ml, 62 g) and methyl 3-hydroxybenzoate (15.2 g, 100 mmol) were added to a four-necked flask protected by nitrogen, stirred and mixed to obtain a mixed solution; the mixed solution was cooled to 0-5 °C by an ice-water bath, and then potassium tert-butoxide (11.8 g, 105 mmol) was added dropwise, and the temperature was controlled not to exceed 20 °C during the dropping process. After the addition, the mixture was stirred and reacted at 30 °C for 0.5 h, and then 3-nitro-N-methylphthalimide (20.6 g, 100 mmol) was added, and the mixture was stirred and reacted for 2.5 h to obtain a reaction solution.

[0037] First, the reaction solution was distilled under reduced pressure to remove N,N-dimethylformamide, then water (60 ml) was added, a pale yellow solid was precipitated, cooled to room temperature, filtered, and the filter cake was washed once with pure water to obtain a pale yellow solid (43 g).

[0038] After detection, the pale yellow solid was 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide.

[0039] 1.2 Hydrolysis reaction: The same as the steps in Example 1 to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid.

[0040] 1.3 Cyclization reaction: The same as the steps in Example 1 to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

[0041] (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: The same as the steps in Example 1 to obtain 2,3,3',4'-diphenylether tetracarboxylic acid.

[0042] (3)Preparation of the target product: The same steps as in Example 1 were followed to obtain 2,3,3',4'-diphenylether tetracarboxylic dianhydride (17.1 g, 55.0 mmol), with a yield of 94.2%, a purity of 99.0%, and a melting point of 182.3 °C. Example 3

[0043] A method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride, which is different from Example 1, includes the following steps: (1)Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: N,N-dimethylformamide (60 ml, 57 g) and methyl 3-hydroxybenzoate (15.2 g, 100 mmol) were added to a four-necked flask under nitrogen protection, stirred and mixed to obtain a mixed solution; the mixed solution was cooled to 0-5 °C in an ice-water bath, and then potassium tert-butoxide (12.1 g, 108 mmol) was added dropwise, controlling the temperature not to exceed 20 °C during the dropping process. After the addition, the mixture was stirred and reacted at 30 °C for 0.5 h, and then 3-nitro-N-methylphthalimide (20.6 g, 100 mmol) was added, and the mixture was stirred and reacted for 1.5 h to obtain a reaction solution.

[0044] First, the reaction solution was distilled under reduced pressure to remove N,N-dimethylformamide, then water (60 ml) was added, a pale yellow solid was precipitated, cooled to room temperature, filtered, and the filter cake was washed once with pure water to obtain a pale yellow solid (42.5 g).

[0045] After detection, the pale yellow solid was 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide.

[0046] 1.2 Hydrolysis reaction: The same steps as in Example 1 were followed to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid.

[0047] 1.3 Cyclization reaction: The same steps as in Example 1 were followed to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

[0048] (2)Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: The same steps as in Example 1 were followed to obtain 2,3,3',4'-diphenylether tetracarboxylic acid.

[0049] (3)Preparation of the target product: The same steps as in Example 1 were followed to obtain 2,3,3',4'-diphenylether tetracarboxylic dianhydride (17.3 g, 55.8 mmol), with a yield of 95.6%, a purity of 99.3%, and a melting point of 182.8 °C.

[0050] In Examples 1-3 of this application, in the 1.1 nucleophilic reaction step and the (3) preparation step of the target product, the synthesized compounds, their weights and yields are shown in the following table.

[0051]

[0052] By analyzing the data in the above table, it can be seen that for the 2,3,3',4'-diphenylether tetracarboxylic dianhydride prepared by the synthesis methods of Examples 1 to 3, the yield is as high as 93.8 to 95.6%, and the purity is over 99.0%. This shows that in the nucleophilic reaction step 1.1 of the synthesis method of this application, when the molar ratio of methyl 3-hydroxybenzoate to 3-nitro-N-methylphthalimide is 1:1, the mass ratio of methyl 3-hydroxybenzoate to N,N-dimethylformamide is 1:(3.7 to 4.1), and the molar ratio of methyl 3-hydroxybenzoate to potassium tert-butoxide is 1:(1.05 to 1.08), 2,3,3',4'-diphenylether tetracarboxylic dianhydride with high purity and high yield can be synthesized, which has high economic benefits and is suitable for large-scale production. Example 4

[0053] A synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, which is different from that of Example 1, includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: The same as the step of Example 1, to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide.

[0054] 1.2 Hydrolysis reaction: The same as the step of Example 1, to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid.

[0055] 1.3 Cyclization reaction: Add concentrated H2SO4 (90 ml) with a concentration of 98% to a three-necked flask, start stirring, and add 3-(3-methoxycarbonylphenoxy)phthalic acid (26.5 g, 87.7 mmol) to obtain a mixed solution; within 2 h, add paraformaldehyde (3.95 g, 132 mmol) to the mixed solution at 50 °C in batches, stir and react for 5.5 h to obtain a reaction solution; Pour the reaction solution into ice water (200 ml), white solid precipitates, filter, wash the filter cake with pure water to obtain a filter cake (36 g). Add the filter cake (36 g) to methanol (100 ml) and slurry for XX h, filter and dry to obtain a white solid (23.1 g, 74 mmol).

[0056] After detection, the white solid is 6-(2,3-dicarboxyphenoxy)phthalide, and the yield is 84% (the theoretical value is 87.7 mmol).

[0057] (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: The same as the step of Example 1, to obtain 2,3,3',4'-diphenylether tetracarboxylic acid.

[0058] (3) Preparation of the target product: Following the same steps as in Example 1, 2,3,3',4'-diphenylether tetracarboxylic dianhydride (17.2 g, 55.5 mmol) was obtained, with a yield of 95.0% and a purity of 99.1%, and a melting point of 182.5 °C.

[0059] In Examples 1 and 4 of this application, in the 1.3 ring-forming reaction and the (3) preparation step of the target product, the synthesized compounds, their weights and yields are shown in the following table.

[0060]

[0061] By analyzing the data in the above table, it can be seen that compared with Example 1, the yield and purity of 2,3,3',4'-diphenylether tetracarboxylic dianhydride synthesized in Example 4 are higher. This shows that in the synthesis method of this application, by controlling the molar ratio of 3-(3-methoxycarbonylphenoxy)phthalic acid to paraformaldehyde to be 1:1.5 in the 1.3 ring-forming reaction step, the purity and yield of the target product can be improved. Example 5

[0062] A method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride, which is different from Example 1 in that it includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: Following the same steps as in Example 1, 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide was obtained.

[0063] 1.2 Hydrolysis reaction: Following the same steps as in Example 1, 3-(3-methoxycarbonylphenoxy)phthalic acid was obtained.

[0064] 1.3 Ring-forming reaction: Following the same steps as in Example 1, 6-(2,3-dicarboxyphenoxy)phthalide was obtained.

[0065] (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: 6-(2,3-dicarboxyphenoxy)phthalide (22.6 g, 72 mmol) was added to water (300 ml), stirred and mixed to obtain an aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide; 15% concentrated nitric acid (31.3 g, 74.8 mmol) was added dropwise to the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide, and the temperature of the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide was controlled not to exceed 30 °C during the dropwise addition. After the dropwise addition, the mixture was refluxed and stirred at 100 °C for 9 h to obtain a reaction solution.

[0066] After filtering the reaction solution to remove insoluble substances, HCl (30% concentration) was added to the aqueous phase to adjust the pH value of the aqueous phase to 2, and a white solid was precipitated. The solid was filtered, and the filter cake was washed with pure water and dried at 100 °C to obtain a white solid (20.4 g, 59.0 mmol).

[0067] After testing, the white solid was 2,3,3',4'-diphenylether tetracarboxylic acid, and the yield was 82% (the theoretical value was 72 mmol).

[0068] (3)Preparation of the target product: The same steps as in Example 1 were carried out to obtain 2,3,3',4'-diphenylether tetracarboxylic dianhydride (16.9 g, 54.5 mmol), with a yield of 93.3%, a purity of 99.1%, and a melting point of 182.4 °C. Example 6

[0069] A synthetic method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride, which is different from that of Example 5, includes the following steps: (1)Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: The same steps as in Example 1 were carried out to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide.

[0070] 1.2 Hydrolysis reaction: The same steps as in Example 1 were carried out to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid.

[0071] 1.3 Cyclization reaction: The same steps as in Example 1 were carried out to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

[0072] (2)Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: Sodium hydroxide (8.64 g, 216 mmol) was added to pure water (300 ml), and after stirring and mixing, 6-(2,3-dicarboxyphenoxy)phthalide (22.6 g, 72 mmol) was added to obtain a mixed solution; potassium permanganate (11.5 g, 72.8 mmol) was added dropwise to the mixed solution, and the temperature of the mixed solution was controlled not to exceed 20 °C during the addition. After the addition, the mixture was refluxed and stirred at XX °C for 8 h to obtain a reaction solution.

[0073] After filtering the reaction solution to remove insoluble substances, HCl (30% concentration) was added to the aqueous phase to adjust the pH value of the aqueous phase to 2, and a white solid was precipitated. The solid was filtered, and the filter cake was washed with pure water and dried at 100 °C to obtain a white solid (18.9 g, 54.6 mmol).

[0074] After testing, the white solid was 2,3,3',4'-diphenylether tetracarboxylic acid, and the yield was 76% (the theoretical value was 72 mmol).

[0075] In Examples 1, 5, and 6 of this application, the preparation steps of (2) 2,3,3',4'-diphenylether tetracarboxylic acid and (3) the target product, the synthesized compounds, their weights, and yields are as shown in the following table.

[0076]

[0077] By analyzing the data in the above table, it can be seen that the yield of 2,3,3',4'-diphenylether tetracarboxylic dianhydride synthesized by the synthesis methods of Examples 1 and 5 is as high as 93.2 - 93.8%, and the purity is above 99.1%. This shows that in the preparation step of (2) 2,3,3',4'-diphenylether tetracarboxylic acid in the synthesis method of this application, when the molar ratio of 6-(2,3-dicarboxyphenoxy)phthalide to nitric acid is 1:(1.0 - 1.04) and the stirring reaction time is 8 - 9 h, 2,3,3',4'-diphenylether tetracarboxylic dianhydride with a high yield can be synthesized.

[0078] Compared with Examples 1 and 5, the yield of 2,3,3',4'-diphenylether tetracarboxylic acid synthesized in Example 6 is significantly reduced. This shows that in the synthesis method of this application, in the preparation step of (2) 2,3,3',4'-diphenylether tetracarboxylic acid, using dilute nitric acid as the oxidant can increase the yield of 2,3,3',4'-diphenylether tetracarboxylic acid. At the same time, in Example 6, potassium permanganate is used as the oxidant, and the manganese-containing wastewater generated is difficult to treat, and the environmental friendliness is poor.

[0079] This specific embodiment is only an explanation of this application, and it is not a limitation of this application. After reading this specification, those skilled in the art can make modifications without creative contributions to this embodiment as needed, but as long as it is within the scope of the claims of this application, it is protected by the patent law.

Claims

1. A method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride, characterized in that the synthesis route is as follows: ; The above method for synthesizing 2,3,3',4'-diphenylether tetracarboxylic dianhydride includes the following steps: (1) Preparation of 6-(2,3-dicarboxyphenoxy)phthalide: 1.1 Nucleophilic reaction: Methyl 3-hydroxybenzoate and 3-nitro-N-methylphthalimide are subjected to a nucleophilic reaction under an alkali catalyst to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide is hydrolyzed under alkaline conditions to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Cyclization reaction: 3-(3-methoxycarbonylphenoxy)phthalic acid and paraformaldehyde are subjected to a cyclization reaction under acidic conditions to obtain 6-(2,3-dicarboxyphenoxy)phthalide; (2) Preparation of 2,3,3',4'-diphenylether tetracarboxylic acid: After 6-(2,3-dicarboxyphenoxy)phthalide and an oxidant are subjected to an oxidation reaction, 2,3,3',4'-diphenylether tetracarboxylic acid is obtained; (3) Preparation of the target product: 2,3,3',4'-diphenylether tetracarboxylic acid is subjected to an anhydride formation reaction to obtain 2,3,3',4'-diphenylether tetracarboxylic dianhydride.

2. The synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride according to claim 1, characterized in that, The preparation of the said (1) 6-(2,3-dicarboxyphenoxy)phthalide includes the following steps: 1.1 Nucleophilic reaction: Methyl 3-hydroxybenzoate and N,N-dimethylformamide are mixed to obtain a mixed solution; Potassium tert-butoxide is added to the mixed solution at 0-5°C, stirred and reacted at 25-30°C for 0.3-0.5 h, then 3-nitro-N-methylphthalimide is added, and stirred and reacted for 1.5-2.5 h to obtain a reaction solution; The reaction solution is distilled under reduced pressure to remove N,N-dimethylformamide, water is added to precipitate a solid, filtered, and washed to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide and an aqueous solution of caustic alkali are mixed, stirred and reacted at 100°C for 5.0 h to obtain a reaction solution; The reaction solution is cooled to 80°C, and then the pH value of the reaction solution is adjusted to 2-3 to precipitate a solid, filtered, and washed to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Cyclization reaction: 3-(3-methoxycarbonylphenoxy)phthalic acid and concentrated sulfuric acid are stirred and mixed to obtain a mixed solution; Paraformaldehyde is added to the mixed solution at 25-50°C, stirred and reacted for 5.0-5.5 h to obtain a reaction solution; The reaction solution is poured into ice water to precipitate a solid, filtered, and washed to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

3. The synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride according to claim 2, characterized in that, In the said 1.1 nucleophilic reaction, the molar ratio of methyl 3-hydroxybenzoate to 3-nitro-N-methylphthalimide is 1:

1.

4. The synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride according to claim 2, wherein In the said 1.1 nucleophilic reaction, the mass ratio of methyl 3-hydroxybenzoate to N,N-dimethylformamide is 1:(3.7-4.1).

5. The synthesis method of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride according to claim 2, characterized in that, In the said 1.1 nucleophilic reaction, the molar ratio of methyl 3-hydroxybenzoate to potassium tert-butoxide is 1:(1.05-1.08).

6. The synthesis method of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride according to claim 2, characterized in that, In the said 1.2 hydrolysis reaction, the caustic alkali is sodium hydroxide, and the mass ratio of 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide to sodium hydroxide is 1:

3.

7. The synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride according to claim 2, characterized in that, In the above 1.3 ring-forming reaction, the molar ratio of 3-(3-methoxycarbonylphenoxy)phthalic acid to paraformaldehyde is 1:(1.50 - 1.55).

8. The synthesis method of 2,3,3',4'-diphenylether tetracarboxylic dianhydride according to claim 2, characterized in that, The preparation of the above (2) 2,3,3',4'-diphenylether tetracarboxylic acid includes the following steps: 6-(2,3-dicarboxyphenoxy)phthalide and water are stirred and mixed to obtain an aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide; dilute nitric acid is added to the aqueous solution of 6-(2,3-dicarboxyphenoxy)phthalide at 0 - 30°C, and the mixture is stirred and reacted at 100°C for 8.0 - 9.0 h to obtain a reaction solution; the pH of the reaction solution is adjusted to 2 - 3, the solid is collected, filtered, washed, and dried to obtain 2,3,3',4'-diphenylether tetracarboxylic acid.

9. A 6-(2,3-dicarboxyphenoxy)phthalide, characterized in that, The structural formula is as follows: ； The synthesis route of the above 6-(2,3-dicarboxyphenoxy)phthalide is as follows: ； The synthesis method of the above 6-(2,3-dicarboxyphenoxy)phthalide includes the following steps: 1.1 Nucleophilic reaction: Methyl 3-hydroxybenzoate and N,N-dimethylformamide are mixed to obtain a mixed solution; potassium tert-butoxide is added to the mixed solution at 0 - 5°C, and the mixture is first stirred and reacted at 25 - 30°C for 0.3 - 0.5 h, then 3-nitro-N-methylphthalimide is added, and the mixture is stirred and reacted for 1.5 - 2.5 h to obtain a reaction solution; the reaction solution is distilled under reduced pressure to remove N,N-dimethylformamide, water is added to precipitate a solid, and the solid is filtered and washed to obtain 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide; 1.2 Hydrolysis reaction: 3-(3-methoxycarbonylphenoxy)-N-methylphthalimide and an aqueous solution of caustic alkali are mixed, and the mixture is stirred and reacted at 100°C for 5.0 h to obtain a reaction solution; the reaction solution is cooled to 80°C, and then the pH value of the reaction solution is adjusted to 2 - 3 to precipitate a solid, and the solid is filtered and washed to obtain 3-(3-methoxycarbonylphenoxy)phthalic acid; 1.3 Ring-forming reaction: 3-(3-methoxycarbonylphenoxy)phthalic acid and concentrated sulfuric acid are stirred and mixed to obtain a mixed solution; paraformaldehyde is added to the mixed solution at 25 - 50°C, and the mixture is stirred and reacted for 5.0 - 5.5 h to obtain a reaction solution; the reaction solution is poured into ice water to precipitate a solid, and the solid is filtered and washed to obtain 6-(2,3-dicarboxyphenoxy)phthalide.

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