Synthetic method of hexafluorodianhydride

Abstract

The invention discloses a synthesis method of hexafluorodianhydride, which belongs to the field of chemical synthesis, and specifically comprises the following steps: (1) bisphenol AF and an alkaline substance react under a heating condition; then carrying out Kolbe-Schmitt reaction on the reaction product I and carbon dioxide at high temperature and high pressure, and acidifying by adopting inorganic acid to obtain an intermediate I; (2) dissolving the intermediate I in a reaction solvent, adding inorganic alkali, transferring into a nitrogen atmosphere, adding a nickel catalyst, a ligand and metal manganese, transferring into a carbon dioxide atmosphere, carrying out carboxylation reaction, and sequentially quenching, extracting, drying, filtering and carrying out reduced pressure distillation on a reaction product II to obtain an intermediate II; and (3) carrying out heating reflux on the intermediate II and acetic anhydride, and carrying out a dehydration reaction to obtain hexafluorodianhydride. Through the limited three-step synthesis method, the synthesis route is simplified, the synthesis time is shortened, a large amount of waste generated in the synthesis process is avoided, and the yield of hexafluorodianhydride is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and more particularly to a method for synthesizing hexafluorodiacid anhydride. Background Art

[0002] At present, with the rapid development of fields such as microelectronics, displays, and solar materials, fluorine-containing polyimide materials have also been widely used. Currently, fluorine-containing polyimide materials are mainly used in optical communication, transparent flexible circuit boards, solar cells, flexible transparent conductive films, and other applications.

[0003] Hexafluorodiacid anhydride (6FDA) is one of the six most widely used dianhydride monomers. It has the largest usage amount in colorless transparent polyimides and is also one of the dianhydride monomers with the highest degree of industrialization. The polyimide material synthesized from hexafluorodiacid anhydride usually has a glass transition temperature above 300 °C, and its mechanical properties and electrical properties are well balanced. So far, it is still the most representative fluorine-containing polyimide material. Therefore, the market demand for hexafluorodiacid anhydride has been continuously expanding with the rapid growth of fluorine-containing polyimides.

[0004] Currently, the method for synthesizing hexafluorodiacid anhydride usually uses hexafluoroacetone and o-xylene as starting materials, uses hydrogen fluoride as a catalyst, and completes the first fluorination reaction under high temperature and high pressure conditions. Then, an oxidation reaction is carried out under the action of an oxidant (oxygen, nitric acid, potassium permanganate, etc.). Finally, hexafluorodiacid anhydride is obtained through an acid anhydride dehydration reaction. In this method, the reaction conditions in the first and second steps are severe, the requirements for equipment are high, and the operation is more difficult, which is not conducive to industrialization and environmental protection production.

[0005] Patent CN104529965 uses hexafluorotetracid as a raw material, heats and refluxes in acetic anhydride for the first ring-closing dehydration reaction, and then heats and refluxes in trifluoroacetic anhydride for the second ring-closing dehydration reaction to obtain the hexafluorodiacid anhydride product. Although the hexafluorodiacid anhydride synthesized by this method has a purity as high as 99.8%, the reaction conversion rate is too low (about 55%).

[0006] Patent CN109678826 uses phthalonitrile and hexafluoroacetone trihydrate as raw materials, synthesizes hexafluorophthalonitrile at high temperature under the action of a catalyst, then hydrolyzes it under alkaline conditions to generate hexafluorotetracid, and then adds toluene and acetic anhydride and refluxes at high temperature to generate hexafluorodiacid anhydride. This method has a complex synthesis route, a long reaction time, and requires multiple post-treatment purifications. Moreover, a large amount of strong acid and strong base are used in the reaction, generating a large amount of wastewater, which is not conducive to green environmental protection.

[0007] Therefore, to address the drawbacks in existing preparation methods, such as complex preparation steps, long reaction times, cumbersome post-treatment, low reaction conversion rates, and the generation of a large amount of waste during synthesis that pollutes the environment, it is an urgent problem for those skilled in the art to provide a simple, easy-to-operate, environmentally friendly, and pollution-free synthesis method with high yield for preparing hexafluorodiacid anhydride. Summary of the Invention

[0008] In view of this, to solve the above-mentioned existing technical problems, the present invention provides a synthesis method for hexafluorodiacid anhydride. Through a three-step synthesis process, on the basis of simplifying the synthesis route and shortening the synthesis time, the yield of hexafluorodiacid anhydride is also increased.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A synthesis method for hexafluorodiacid anhydride specifically includes the following steps:

[0011] (1) Dissolve and mix bisphenol AF with solvent A to obtain mixture one; dissolve and mix the alkaline substance with solvent B to obtain mixture two; dropwise add mixture one into mixture two for reaction. After the reaction ends, remove solvent A and solvent B to obtain reaction product I, which is a mixture of sodium hexafluorobisphenolate and the alkaline substance;

[0012] Place reaction product I in an autoclave, introduce carbon dioxide, and carry out the Kolbe-Schmitt reaction under high temperature and high pressure conditions, and then acidify with inorganic acid to obtain intermediate I;

[0013] (2) Dissolve intermediate I in the reaction solvent, add inorganic base, then transfer it to a nitrogen atmosphere, add a nickel-based catalyst, ligand, and metallic manganese, transfer it to a carbon dioxide atmosphere for carboxylation reaction, and subject reaction product II to quenching, extraction, drying, filtration, and vacuum distillation in sequence to obtain intermediate II;

[0014] (3) Heat intermediate II and acetic anhydride under reflux for dehydration reaction to obtain hexafluorodiacid anhydride.

[0015] The beneficial effects achieved by the above technical solutions are as follows: The present invention first conducts the Kolbe-Schmitt reaction of bisphenol AF with carbon dioxide under alkaline and pressure conditions, then conducts the carboxylation reaction under the action of a catalyst, and finally obtains hexafluorodiacid anhydride through dehydration reaction; the specific reaction synthesis route is as follows:

[0016]

[0017] Through the above three-step synthesis method, the synthesis route and time can be shortened, which is easy to operate and suitable for industrial production. Among them, in step (1), a mixed solution of a solid reactant and a solvent is used as the reaction component, and the two are slowly added dropwise for reaction, which not only increases the contact area between the two to make them react more fully, but also dilutes the reactant concentration to avoid danger caused by violent reaction; in step (2), carbon dioxide, a non-toxic, low-cost and renewable gas, is used as the reactant, and the carboxylation reaction is carried out by a one-step method catalyzed by nickel. The whole reaction conditions are mild, the operation is simple, and the yield is high.

[0018] Preferably, the alkaline substance in step (1): bisphenol AF = (1 - 5): 1.

[0019] Preferably, the alkaline substance is sodium hydroxide or sodium alkoxide.

[0020] The sodium alkoxide is any one of sodium methoxide, sodium ethoxide, sodium n-propoxide, sodium isopropoxide, sodium n-butoxide or sodium tert-butoxide;

[0021] The solvent A is any one of ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, diethyl ether;

[0022] The solvent B is any one of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, toluene, xylene.

[0023] Preferably, when the alkaline substance is sodium alkoxide, the preparation method of the second mixture is as follows:

[0024] The sodium alkoxide is added to the solvent B, and at room temperature to the reflux temperature of the solvent B, the sodium alkoxide is completely dissolved.

[0025] Among them, the sodium alkoxide can be appropriately heated to dissolve, but the temperature cannot be higher than the reflux temperature of the solvent B, that is, it cannot boil, and it can also be expressed as the temperature needs to be lower than the boiling point of the solvent.

[0026] Preferably, the inorganic acid is sulfuric acid, hydrochloric acid or phosphoric acid; the pH value after acidification is 1 - 2.

[0027] Preferably, the nickel-based catalyst is nickel bis(triphenylphosphine) dichloride, and its molar ratio to intermediate I is (1% - 10%): 1.

[0028] Furthermore, the molar ratio of nickel bis(triphenylphosphine) dichloride to intermediate I is (5% - 10%): 1.

[0029] The beneficial effects achieved by the above technical solutions are as follows: The present invention uses a nickel-based catalyst to catalyze the carboxylation reaction and realizes it by a one-step reaction, which saves costs and also saves the post-treatment process, avoiding quality loss of the product caused by multiple operations.

[0030] Preferably, the high temperature and high pressure in step (1) are specifically: the pressure is 0.1 to 3 MPa; the temperature is 70 to 140 °C.

[0031] Preferably, the ligand in step (2) is any one of 2,9-dimethyl-1,10-phenanthroline, tricyclohexylphosphine, triphenylphosphine, 1,1'-binaphthalene-2,2'-bis(diphenylphosphine), and dipyridine, preferably any one of 2,9-dimethyl-1,10-phenanthroline, dipyridine, and triphenylphosphine;

[0032] The molar ratio of it to the catalyst is (1 to 10):1.

[0033] Furthermore, the molar ratio of the ligand to the catalyst is (2 to 3):1.

[0034] Preferably, the inorganic base in step (2) is any one of sodium hydride, lithium hydride, and potassium hydride,

[0035] The molar ratio of it to intermediate I is (0.5 to 10):1.

[0036] Furthermore, the molar ratio of the inorganic base to intermediate I is (1 to 2):1.

[0037] Preferably, the molar ratio of manganese metal to intermediate I in step (2) is (1 to 10):1.

[0038] Furthermore, the molar ratio of manganese metal to intermediate I is (3 to 5):1.

[0039] Preferably, the reaction solvent in step (2) is any one of dichloromethane, dichloroethane, carbon tetrachloride, tetrahydrofuran, toluene, xylene, dimethylformamide, and dimethylacetamide.

[0040] Furthermore, the reaction solvent is dichloroethane or dimethylformamide.

[0041] Preferably, the carboxylation reaction temperature in step (2) is 10 to 150 °C.

[0042] Furthermore, the carboxylation reaction temperature is preferably 20 to 70 °C.

[0043] Preferably, the carboxylation reaction time in step (2) is 0.5 to 36 h.

[0044] Furthermore, the carboxylation reaction time is preferably 12 to 24 h.

[0045] Preferably, the pressure under the carbon dioxide atmosphere in step (2) is 0.1 - 5 MPa.

[0046] Preferably, the molar ratio of intermediate II to acetic anhydride in step (3) is 1:(5 - 10).

[0047] Preferably, the heating reflux time in step (3) is 6 - 12 h.

[0048] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method for synthesizing hexafluorodiacid anhydride, having the following technical effects:

[0049] The present invention uses bisphenol AF as a raw material and adopts a three-step synthesis process to prepare hexafluorodiacid anhydride, improving the yield of hexafluorodiacid anhydride. Moreover, the synthesis route is short, the time consumption is less, it is easy to operate, and it is suitable for industrial production. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0051] Figure 1 It is the nuclear magnetic resonance hydrogen spectrum of the product obtained in Example 1. Detailed Embodiments

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0053] Example 1

[0054] A method for synthesizing hexafluorodiacid anhydride, which successively performs the following steps:

[0055] 1) After adding 50 g of ethanol to a flask equipped with a stirring device, a thermometer, and a condensation reflux device, add 10.2 g (0.15 mol) of sodium ethoxide. After heating (not higher than the reflux temperature of ethanol) to dissolve sodium ethoxide, dropwise add a solution of 33.6 g of bisphenol AF (0.1 mol) dissolved in 200 g of ethanol. The dropping is completed in about 15 min. Keep warm and continue stirring for 1 h, and then stop.

[0056] 2) The reaction solution obtained in 1) was transferred to an autoclave, sealed, heated to 100°C, and then carbon dioxide was introduced. While the inlet valve was kept open, the exhaust valve was slowly opened to control the pressure to 0.1MPa, and the solvent ethanol began to be evaporated. After no ethanol was evaporated, the exhaust valve was closed. The pressure was raised to 0.5MPa, and the reaction was maintained at 100°C for 2h, and then the heating was stopped. After cooling, 1000g of cold water was added and stirred for 20min. The mixed solution was taken out, cooled to room temperature, and 50% sulfuric acid was slowly added dropwise. During the addition, more carbon dioxide was released. After the pH was adjusted to 1-2, a large amount of white solid precipitated. After cooling with ice water for 15min, 38.1g of white solid intermediate I was obtained by filtration, washing, and drying, with a yield of 89.9%.

[0057] 3) Dissolve 42.4g of intermediate I (0.1mol) obtained from 2) in a flask containing 250g of dichloroethane, add 2.4g of sodium hydride (0.1mol), stir at room temperature for 30min, and transfer to a glove box filled with nitrogen. Then add 3.3g of dichlorobistriphenylphosphine nickel (5mmol), 0.1g of 2,9-dimethyl-o-phenanthroline (10mmol), and 16.5g of manganese powder (0.3mol), and transfer to a three-necked flask filled with carbon dioxide, keep the carbon dioxide pressure at 1MPa, and stir at 20°C for 24h. After the reaction is completed, the mixed solution is quenched with 6M hydrochloric acid, extracted 3 times with 500mL of ethyl acetate, and the organic layer is collected, dried with anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain 38.8g of intermediate II with a yield of 80.8%.

[0058] 4) Add intermediate II obtained in 3) into a flask, then add 300 mL of acetic anhydride, stir evenly and heat under reflux for 10 h, then slowly evaporate the acetic anhydride to obtain 34.1 g of hexafluorodianhydride product, with a yield of 95.0%.

[0059] The hydrogen nuclear magnetic resonance spectrum of the product prepared in Example 1 is shown in Figure 1 Through analysis, it can be known that the peaks at chemical shifts 7.8-7.9, 8.0, and 8.1 are all hydrogen atoms on the benzene ring, with a total of 6 hydrogen atoms, corresponding to hydrogen at three different positions on the benzene ring, so the relative peak area of ​​the hydrogen spectrum is 1. This value is completely consistent with the hydrogen atom group and number in the structure of the product hexafluorodianhydride, indicating that hexafluorodianhydride is successfully prepared through the synthesis scheme of this embodiment.

[0060] Example 2

[0061] A method for synthesizing hexafluorodianhydride comprises the following steps:

[0062] 1) After adding 100 g of propanol to a flask equipped with a stirring device, a thermometer, and a condensation reflux device, 16.4 g (0.2 mol) of sodium propoxide was added. After heating (not exceeding the reflux temperature of propanol) to dissolve sodium propoxide, a solution of 33.6 g of bisphenol AF (0.1 mol) dissolved in 200 g of propanol was added dropwise. The addition was completed in about 15 min, and the reaction was continued with stirring for 1.5 h at a constant temperature and then stopped.

[0063] 2) The reaction solution obtained from 1) was transferred to an autoclave. After sealing, the temperature was raised to 110 °C, and then carbon dioxide was introduced. With the inlet valve kept open, the exhaust valve was slowly opened, and the pressure was controlled at 0.1 MPa. The solvent propanol was distilled out. After no more propanol was distilled out, the exhaust valve was closed. The pressure was increased to 0.8 MPa, and the reaction was carried out at 110 °C for 3 h. Then, the heating was stopped. After cooling, 1000 g of cold water was added and stirred for 20 min. The mixture was taken out. After cooling to room temperature, concentrated hydrochloric acid was slowly added dropwise. A large amount of carbon dioxide was released during the addition process. After continuing to adjust the pH to 1 - 2, a large amount of white solid precipitated. After cooling with ice water for 15 min, it was filtered, washed, and dried to obtain 39.5 g of white solid intermediate I, with a yield of 93.2%.

[0064] 3) 42.4 g of intermediate I (0.1 mol) obtained from 2) was dissolved in a flask containing 250 g of dimethylformamide. 1.6 g of lithium hydride (0.2 mol) was added, and after stirring at room temperature for 30 min, it was transferred to a glove box filled with nitrogen. Then, 5.2 g of dichlorobis(triphenylphosphine)nickel (8 mmol), 3.1 g of dipyridine (20 mmol), and 22.0 g of manganese powder (0.4 mol) were added, and then it was transferred to a three-necked flask filled with carbon dioxide. With the carbon dioxide pressure maintained at 1 MPa, the reaction was carried out with stirring at 50 °C for 16 h. After the reaction was completed, the mixture was quenched with 6 M hydrochloric acid and extracted 3 times with 500 mL of ethyl acetate. The organic layer was collected, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain 37.9 g of intermediate II, with a yield of 78.9%.

[0065] 4) Intermediate II prepared in 3) was added to a flask, and then 300 mL of acetic anhydride was added. After stirring evenly, it was heated under reflux for 10 h, and then the acetic anhydride was slowly evaporated to dryness to obtain 33.4 g of hexafluorodiacid anhydride product, with a yield of 95.3%.

[0066] Example 3

[0067] A method for synthesizing hexafluorodiacid anhydride, which successively carries out the following steps:

[0068] 1) After adding 150 g of tert-butanol to a flask equipped with a stirring device, a thermometer, and a reflux condenser, 24.0 g (0.25 mol) of sodium tert-butoxide was added. After heating (not exceeding the reflux temperature of tert-butanol) to dissolve sodium tert-butoxide, a solution of 33.6 g of bisphenol AF (0.1 mol) dissolved in 200 g of tert-butanol was added dropwise. The addition was completed in about 15 min, and the mixture was kept warm and stirred for 2 h before stopping.

[0069] 2) The reaction solution obtained from 1) was transferred to an autoclave. After sealing, the temperature was raised to 120 °C, and then carbon dioxide was introduced. With the inlet valve kept open, the exhaust valve was slowly opened to control the pressure at 0.15 MPa, and the solvent tert-butanol was distilled out. After no more tert-butanol was distilled out, the exhaust valve was closed. The pressure was increased to 1.0 MPa, and the reaction was maintained at 120 °C for 5 h. Then, heating was stopped. After cooling, 1000 g of cold water was added and stirred for 20 min. The mixture was taken out, cooled to room temperature, and 80% phosphoric acid was slowly added dropwise. A large amount of carbon dioxide was released during the addition. After continuing to adjust the pH to 1 - 2, a large amount of white solid precipitated. After cooling with ice water for 15 min, it was filtered, washed, and dried to obtain 38.8 g of white solid intermediate I, with a yield of 91.5%.

[0070] 3) 42.4 g of intermediate I (0.1 mol) obtained from 2) was dissolved in a flask containing 250 g of dimethylformamide. 4.0 g of potassium hydride (0.1 mol) was added, and the mixture was stirred at room temperature for 30 min, then transferred to a glove box filled with nitrogen. Then, 6.5 g of dichlorobis(triphenylphosphine)nickel (10 mmol), 7.8 g of triphenylphosphine (30 mmol), and 27.4 g of manganese powder (0.5 mol) were added. It was then transferred to a three-necked flask filled with carbon dioxide, and the carbon dioxide pressure was maintained at 1 MPa. The reaction was stirred at 70 °C for 12 h. After the reaction was completed, the mixture was quenched with 6 M hydrochloric acid and extracted 3 times with 500 mL of ethyl acetate. The organic layer was collected, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain 38.2 g of intermediate II, with a yield of 79.5%.

[0071] 4) Intermediate II prepared in 3) was added to a flask, and then 300 mL of acetic anhydride was added. After stirring evenly, the mixture was heated under reflux for 10 h, and then acetic anhydride was slowly evaporated to obtain 33.5 g of hexafluorodiacid anhydride product, with a yield of 94.8%.

[0072] Comparative Example 1

[0073] The same reaction apparatus and reaction conditions as in Example 1 were selected, where: in 1), "10.2 g (0.15 mol) of sodium ethoxide" was changed to "3.4 g (0.05 mol) of sodium ethoxide"; in 2), "reaction temperature 100 °C" was changed to "reaction temperature 50 °C", and other conditions remained unchanged. Finally, 21.1 g of hexafluorodiacid anhydride product was obtained, with a yield of 47.5%.

[0074] Comparative Example 2

[0075] The same reaction apparatus and reaction conditions as in Example 1 were selected, wherein: in 3), "2.4 g of sodium hydride (0.1 mol)" was changed to "0.24 g of sodium hydride (0.01 mol)", and other conditions remained unchanged. Finally, 17.6 g of hexafluorodiacid anhydride finished product was obtained, and the yield was 39.6%.

[0076] Comparative Example 3

[0077] The same reaction apparatus and reaction conditions as in Example 1 were selected, wherein: in 3), "3.3 g of nickel dichloride bis(triphenylphosphine) (5 mmol)" was changed to "0.066 g of nickel dichloride bis(triphenylphosphine) (0.1 mmol)", and "0.1 g of 2,9-dimethyl-1,10-phenanthroline (10 mmol)" was changed to "0.01 g of 2,9-dimethyl-1,10-phenanthroline (1 mmol)", and other conditions remained unchanged. Finally, 16.8 g of hexafluorodiacid anhydride finished product was obtained, and the yield was 37.8%.

[0078] Comparative Example 4

[0079] The same reaction apparatus and reaction conditions as in Example 1 were selected, wherein: in 3), "16.5 g of manganese powder (0.3 mol)" was changed to "55 g of manganese powder (0.1 mol)", and other conditions remained unchanged. Finally, 11.2 g of hexafluorodiacid anhydride finished product was obtained, and the yield was 25.2%.

[0080] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple. For the relevant parts, refer to the description in the method section. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for synthesizing hexafluorodiacid anhydride, characterized in that, Specifically, it includes the following steps: (1) Bisphenol AF reacts with an alkaline substance under heating conditions; then the reaction product I undergoes a Kolbe-Schmitt reaction with carbon dioxide under high temperature and high pressure, and then is acidified with an inorganic acid to obtain intermediate I; (2) Dissolve the intermediate I in a reaction solvent, add an inorganic base, then transfer it to a nitrogen atmosphere, and then add a nickel-based catalyst, a ligand, and metallic manganese, and transfer it to a carbon dioxide atmosphere for a carboxylation reaction. The reaction product II is successively quenched, extracted, dried, filtered, and distilled under reduced pressure to obtain intermediate II; (3) The intermediate II is heated under reflux with acetic anhydride for a dehydration reaction to obtain hexafluorodiacid anhydride.

2. The synthesis method of hexafluorodiacid anhydride according to claim 1, characterized in that, Calculated by molar ratio, the alkaline substance: the bisphenol AF in step (1) = (1-5):

1.

3. The synthesis method of hexafluorodiacid anhydride according to claim 2, characterized in that, Before the reaction, the bisphenol AF and the alkaline substance need to be dissolved in solvent A and solvent B respectively; Among them, the alkaline substance is any one of sodium hydroxide, sodium methoxide, sodium ethoxide, sodium n-propoxide, sodium isopropoxide, sodium n-butoxide, and sodium tert-butoxide; The solvent A is any one of ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, and diethyl ether; The solvent B is any one of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, toluene, and xylene.

4. The synthesis method of hexafluorodiacid anhydride according to claim 1, characterized in that, The specific high temperature and high pressure conditions in step (1) are: the pressure is 0.1-3 MPa; the temperature is 70-140 °C.

5. A method for synthesizing hexafluorodiacid anhydride according to claim 1, characterized in that, Calculated by molar ratio, the intermediate I: the nickel-based catalyst: the inorganic base: the metallic manganese in step (2) = 1: (0.01-0.1): (0.5-10): (1-10); The ligand: the nickel-based catalyst = (1-10):

1.

6. A method for synthesizing hexafluorodiacid anhydride according to claim 5, characterized in that The nickel-based catalyst is nickel dichloride bis(triphenylphosphine); The ligand is any one of 2,9-dimethyl-1,10-phenanthroline, tricyclohexylphosphine, triphenylphosphine, 1,1'-binaphthalene-2,2'-bis(diphenylphosphine), and dipyridine; The inorganic base is any one of sodium hydride, lithium hydride, and potassium hydride.

7. A method for synthesizing hexafluorodiacid anhydride according to claim 1, characterized in that, The reaction solvent in step (2) is any one of dichloromethane, dichloroethane, carbon tetrachloride, tetrahydrofuran, toluene, xylene, dimethylformamide, and dimethylacetamide.

8. A method for synthesizing hexafluorodiacid anhydride according to claim 1, characterized in that, The carboxylation reaction conditions in step (2) are: The reaction temperature is 10-150 °C; the reaction time is 0.5-36 h; the pressure under the carbon dioxide atmosphere is 0.1-5 MPa.

9. A method for synthesizing hexafluorodiacid anhydride according to claim 1, characterized in that, The molar ratio of the intermediate II to the acetic anhydride in step (3) is 1: (5-10).

10. A method for synthesizing hexafluorodiacid anhydride according to claim 1, characterized in that, The heating reflux time in step (3) is 6-12 h.

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