Process for the production of hexafluorobenzene by decarboxylative fluorination of pentafluorobenzoic acid

Abstract

This invention discloses a method for preparing hexafluorobenzene from pentafluorobenzoic acid through decarboxylation and fluorination, belonging to the field of fine chemicals. Pentafluorobenzoic acid is mixed with dichloromethane, and triphenylphosphine, iodine, and an activating reagent are added. Finally, triethylamine is added, and the mixture is reacted at a certain temperature to obtain an active ester of pentafluorobenzoic acid. Then, the active ester of pentafluorobenzoic acid is dissolved in an organic solvent, and under copper catalyst illumination, a tetrabutylammonium fluoride tetra-tert-butanol complex is used as a fluorine source for decarboxylation and fluorination to prepare hexafluorobenzene. The synthesis method described in this invention not only reduces production costs but also improves product yield and quality.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals, and more specifically, it relates to a method for producing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid. Background Technology

[0002] Hexafluorobenzene (C6F6), also known as perfluorobenzene, is a colorless, odorless, and non-corrosive liquid compound with high stability and excellent chemical inertness. As a crucial raw material in the fluorochemical industry, hexafluorobenzene is widely used in various high-tech industries, including semiconductor manufacturing, pharmaceutical intermediate synthesis, and specialty polymer production. In semiconductor manufacturing, hexafluorobenzene is used as an etchant and cleaning agent, particularly in advanced process nodes (such as 7nm and below). It is also used in the research and development and production of various novel drugs. Specialty materials, including high-performance plastics, rubber, and coating materials, are another important market for hexafluorobenzene. With the rapid development of the global semiconductor industry and the continuous deepening of new material research, the market demand for hexafluorobenzene continues to grow, becoming a major driving force for the industry's development. Existing methods for producing hexafluorobenzene include: 1. Halogen Exchange Method: In 1963, Vorozhtsov NN, Platonov VE, and Yakobson GG proposed in the Russian Chemical Bulletin the preparation of hexafluorobenzene by replacing the chlorine atom on hexachlorobenzene with anhydrous KF. This reaction was carried out in an autoclave at 450-500℃, ultimately yielding hexafluorobenzene in 20% yield, with the remainder being incompletely fluorinated chlorofluorobenzenes. Patent application publication number CN103360202A discloses a method for preparing hexafluorobenzene and monochloropentafluorobenzene, characterized by using hexachlorobenzene and potassium fluoride as raw materials, and preparing hexafluorobenzene and monochloropentafluorobenzene in a solvent under the action of a phase transfer catalyst in a high-pressure reactor. This method achieves a single-pass yield of over 60%, with a reaction temperature of 580-630℃ and a reaction pressure of 8.0-9.0 MPa. Patent application publication number CN111116306A discloses a method for the direct reaction of hexachlorobenzene and fluorine gas to prepare hexafluorobenzene. Hexachlorobenzene (HCB) is a persistent organic pollutant (POP) characterized by its toxicity, poor degradation, and tendency to accumulate in organisms. Its use is strictly restricted under the Stockholm Convention and relevant Chinese regulations. According to an announcement by the former State Environmental Protection Administration and other departments, my country has imposed a complete ban on hexachlorobenzene since May 17, 2009.

[0003] 2. Defluorination method: Godsell, Stacey, and Tatlow proposed in Nature in 1956 that nonafluorocyclohexane could be defluorinated with hydrogen fluoride in an alkaline solution to obtain hexafluorobenzene. However, nonafluorocyclohexane requires a reaction between benzene vapor and cobalt trifluoride at 150°C, and its low conversion rate limits its application.

[0004] 3. High-temperature pyrolysis method: In 1955, Arkad Roy Berg proposed the high-temperature pyrolysis of tribromofluoromethane in a platinum tube to prepare hexafluorobenzene, with a yield of 45% based on tribromofluoromethane. In addition to hexafluorobenzene, pentafluorobromobenzene and difluorotetrabromoethane were also isolated.

[0005] The above-mentioned traditional methods for synthesizing hexafluorobenzene all have drawbacks such as high raw material prices, raw materials that do not comply with national regulations, demanding reaction conditions, and low product yields. Summary of the Invention

[0006] To address the deficiencies and shortcomings of existing technologies, the present invention aims to provide a method for the decarboxylation and fluorination of pentafluorobenzoic acid to prepare hexafluorobenzene. Pentafluorobenzoic acid is mixed with dichloromethane, and triphenylphosphine, iodine, and an activating reagent are added. Finally, triethylamine is added to react and yield an active ester of pentafluorobenzoic acid. Then, the active ester of pentafluorobenzoic acid is dissolved in an organic solvent and, under copper catalyst illumination, a tetrabutylammonium fluoride tetra-tert-butanol complex is used as a fluorine source for decarboxylation and fluorination to prepare hexafluorobenzene. The synthesis method described in this invention not only reduces production costs but also improves the yield and quality of the product.

[0007] The objective of this invention is achieved through the following technical solution: This invention provides a method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid, comprising the following steps:

[0008] Step 1: Using pentafluorobenzoic acid and activating reagent as raw materials, react in the presence of triphenylphosphine and iodine to obtain the active ester of pentafluorobenzoic acid.

[0009] Furthermore, in the above technical solution, the activating agent is selected from N-hydroxysuccinimide, N-hydroxyphthalimide, hexafluoro-2-propanol or N-hydroxybenzotriazole, and the molar ratio of pentafluorobenzoic acid to the activating agent is 1:1.5-3.

[0010] Furthermore, in the above technical solution, the molar ratio of pentafluorobenzoic acid, triphenylphosphine, and iodine is 1:1-2:1-2.

[0011] Furthermore, in the above technical solution, the reaction temperature is 10-40℃ and the reaction time is 2-5h.

[0012] Step 2: Using pentafluorobenzoic acid active ester and tetrabutylammonium fluoride-tetratert-butanol complex as raw materials, hexafluorobenzene is obtained by catalytic decarboxylation and fluorination in an organic solvent in the presence of copper catalyst and visible light.

[0013] Furthermore, in the above technical solution, the organic solvent is selected from at least one of nitrile solvents, C1-C4 alcohols, tetrahydrofuran, 2-methyltetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetone, butanone, methyl isobutyl ketone, dichloromethane, ethyl acetate, and water.

[0014] Furthermore, in the above technical solution, the tetrabutylammonium fluoride tetratert-butanol complex serves as a fluorine source, acting as both a nucleophilic fluorinating agent and a phase transfer catalyst to accelerate the reaction rate. The molar ratio of the active pentafluorobenzoic acid ester to the fluorine source is 1:1-8.

[0015] Furthermore, in the above technical solution, the copper catalyst is selected from at least one of CuBr, Cu(OTf)2, Cu(MeCN)4PF6, Cu(MeCN)4BF4, CuTc, CuI, CuCl, Cu(OAc)2, CuBr2, CuCl2 or Cu(acac)2.

[0016] In the most preferred embodiment, the copper catalyst is a combination of Cu(OTf)2 and Cu(MeCN)4BF4; the molar ratio of methyl pentafluorobenzoate, Cu(OTf)2 and Cu(MeCN)4BF4 is 1: 0.1-0.5: 0.1-0.5.

[0017] Furthermore, in the above technical solution, the visible light wavelength is 370-550nm.

[0018] Furthermore, in the above technical solution, the photocatalytic reaction temperature is 0-70℃ and the reaction time is 3-10 hours.

[0019] The synthesis method of the present invention has the following advantages: 1. The photocatalytic reaction used in this invention has the advantages of low cost, easy availability, no environmental pollution, and few by-products.

[0020] 2. The method of the present invention has simple reaction conditions, low raw material cost, mild and easy-to-control reaction, low operation requirements, and high product yield.

[0021] 3. The decarboxylation and fluorination method of the present invention uses traditional bulk chemicals as catalysts, which are low in cost, easy to obtain, and can be reused after recovery. Detailed Implementation

[0022] The technical solution of the present invention will be described below with reference to embodiments, but the present invention is not limited to the following embodiments. In order to enable those skilled in the art to better understand the technical solution of the present invention and to implement it, the present invention will be further described below with reference to specific embodiments, but the embodiments are not intended to limit the present invention. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially. Example 1

[0023] 120 mL of dichloromethane was added to the reaction vessel, followed by 22.5 g (0.106 mol) of pentafluorobenzoic acid, which was stirred and dissolved. Then, 41.7 g (0.16 mol) of triphenylphosphine and 40.4 g (0.16 mol) of iodine were added. After 3 hours, 24.4 g (0.21 mol) of N-hydroxysuccinimide was added, while maintaining the vessel temperature at 20-25 °C. After the addition was complete, 32 g (0.32 mol) of triethylamine was added dropwise. After the addition was complete, the vessel temperature was maintained at 20-25 °C for 3 hours. Anhydrous zinc chloride was added, and the byproducts were removed by filtration. The solvent was then concentrated under reduced pressure to obtain a white solid, which was N-succinimide pentafluorobenzoic acid ester with a yield of 94.3% and a purity of 99.4%.

[0024] N-succinimide pentafluorobenzoate was dissolved in propionitrile, and 139.5 g (0.25 mol) of TBAF·(tBuOH)4 was added as a fluorinating agent. The temperature was controlled at 30 °C, and the mixture was stirred (200 rpm) until the system became clear. Then, 3.62 g (0.01 mol) of Cu(OTf)2 and 3.15 g (0.01 mol) of Cu(MeCN)4BF4 were added. Under nitrogen protection, the photocatalytic reaction was carried out at room temperature under 440 nm light for 5 hours. The reaction was stirred during the process, and HPLC was used to detect the complete reaction until N-succinimide pentafluorobenzoate ≤0.1%, during which carbon dioxide gas was released. Then, the product hexafluorobenzene was distilled off at 80-90 °C under normal pressure, with a purity of 99.6% and a yield of 95.2%. Example 2

[0025] 120 mL of dichloromethane was added to the reaction vessel, followed by 22.5 g (0.106 mol) of pentafluorobenzoic acid, which was stirred and dissolved. Then, 41.7 g (0.16 mol) of triphenylphosphine and 40.4 g (0.16 mol) of iodine were added. After 3 hours, 34.2 g (0.21 mol) of N-hydroxyphthalimide was added, while maintaining the vessel temperature at 25-30 °C. After the addition was complete, 32 g (0.32 mol) of triethylamine was added dropwise. After the addition was complete, the vessel temperature was maintained at 25-30 °C for 3 hours. Anhydrous zinc chloride was added, and the byproducts were removed by filtration. The solvent was then concentrated under reduced pressure to obtain a white solid, which was N-hydroxyphthalimide pentafluorobenzoic acid ester, with a yield of 82% and a purity of 98.1%.

[0026] N-hydroxyphthalimide pentafluorobenzoate was dissolved in methanol, and 121.4 g (0.22 mol) of TBAF·(tBuOH)4 was added as a fluorinating agent. The temperature was controlled at 30℃, and the mixture was stirred (200 rpm) until the system was clear. Then, 3.15 g (0.0087 mol) of Cu(OTf)2 and 2.74 g (0.0087 mol) of Cu(MeCN)4BF4 were added. Under nitrogen protection, the photocatalytic reaction was carried out at room temperature under 400 nm light for 6 hours. The reaction was stirred during the process. HPLC monitoring showed that the N-hydroxyphthalimide pentafluorobenzoate was ≤0.1% and the reaction was complete, with carbon dioxide gas released during the process. Methanol was first distilled off under normal pressure, and then the product hexafluorobenzene was distilled off at 80-90℃ under normal pressure. The purity was 99.2% and the yield was 93.6%. Example 3

[0027] 120 mL of dichloromethane was added to a reaction vessel at room temperature, followed by 22.5 g (0.106 mol) of pentafluorobenzoic acid, which was stirred and dissolved. Then, 41.7 g (0.16 mol) of triphenylphosphine and 40.4 g (0.16 mol) of iodine were added. After 3 hours, 35.2 g (0.21 mol) of hexafluoro-2-propanol was added while maintaining the vessel temperature at 25-30°C. After the addition was complete, 32 g (0.32 mol) of triethylamine was added dropwise. After the addition was complete, the vessel temperature was maintained at 25-30°C for 3 hours. Anhydrous zinc chloride was added, and the byproducts were removed by filtration. The solvent was then concentrated under reduced pressure to obtain a white solid, which was hexafluoro-2-propanol pentafluorobenzoate, with a yield of 90% and a purity of 99.1%.

[0028] Hexafluoro-2-propanol pentafluorobenzoate was dissolved in tert-butanol, and 133.1 g (0.24 mol) of TBAF·(tBuOH)4 was added as a fluorinating agent. The temperature was controlled at 30 °C, and the mixture was stirred (200 rpm) until the system became clear. Then, 3.44 g (0.0095 mol) of Cu(OTf)2 and 3.0 g (0.0095 mol) of Cu(MeCN)4BF4 were added. Under nitrogen protection, the photocatalytic reaction was carried out at room temperature under 460 nm light for 8 hours. The reaction was stirred during the process, and HPLC was used to detect the complete reaction until hexafluoro-2-propanol pentafluorobenzoate ≤0.1%, during which carbon dioxide gas was released. Then, the product hexafluorobenzene was distilled off at 80-90 °C under normal pressure, with a purity of 99.8% and a yield of 96.1%. Example 4

[0029] 120 mL of dichloromethane was added to a reaction vessel at room temperature, followed by 22.5 g (0.106 mol) of pentafluorobenzoic acid, which was stirred and dissolved. Then, 41.7 g (0.16 mol) of triphenylphosphine and 40.4 g (0.16 mol) of iodine were added. After 3 hours, 28.4 g (0.21 mol) of N-hydroxybenzotriazole was added, while maintaining the vessel temperature at 25-30 °C. After the addition was complete, 32 g (0.32 mol) of triethylamine was added dropwise. After the addition was complete, the vessel temperature was maintained at 25-30 °C for 3 hours. Anhydrous zinc chloride was added, and the byproducts were removed by filtration. The solvent was then concentrated under reduced pressure to obtain a white solid, which was N-hydroxybenzotriazole pentafluorobenzoic acid ester, with a yield of 68% and a purity of 96.1%.

[0030] N-hydroxybenzotriazole pentafluorobenzoic acid was dissolved in methanol, and 0.6 g (0.18 mol) of TBAF·(tBuOH)4 was added as a fluorinating agent. The temperature was controlled at 30 °C, and the mixture was stirred (200 rpm) until the system was clear. Then, 2.61 g (0.0072 mol) of Cu(OTf)2 and 2.27 g (0.0072 mol) of Cu(MeCN)4BF4 were added. Under nitrogen protection, the photocatalytic reaction was carried out at room temperature under light at a wavelength of 400 nm for 6 hours. The reaction was stirred during the photocatalytic reaction. HPLC monitoring was performed until the N-hydroxybenzotriazole pentafluorobenzoic acid content was ≤0.1% and the reaction was complete, during which carbon dioxide gas was released. Methanol was first distilled off under normal pressure, and then the product hexafluorobenzene was distilled off under normal pressure at 80-90 °C with a purity of 99.2% and a yield of 94.6%. Comparative Example 1

[0031] 21.2 g (0.1 mol) of pentafluorobenzoic acid was dissolved in propionitrile at room temperature. 139.5 g (0.25 mol) of TBAF·(tBuOH)4 was added as a fluorinating agent. The temperature was controlled at 30 °C, and the mixture was stirred (200 rpm) until the system became clear. Then, 23.62 g (0.01 mol) of Cu(OTf)2 and 3.15 g (0.01 mol) of Cu(MeCN)4BF4 were added. Under nitrogen protection, the photocatalytic reaction was carried out at room temperature under 440 nm light for 5 hours. The reaction was stirred during the process, and HPLC analysis was performed until the pentafluorobenzoic acid content was ≤0.1%, indicating complete reaction. Carbon dioxide gas was released during the reaction. Then, the product hexafluorobenzene was distilled off at 80–90 °C under normal pressure. The purity was 66.4%, and the yield was 53.2%, containing 32% pentafluorobenzene.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid, characterized in that, Includes the following steps: ； Step 1: Using pentafluorobenzoic acid and activating reagent as raw materials, react in the presence of triphenylphosphine and iodine to obtain the active ester of pentafluorobenzoic acid; Step 2: Using pentafluorobenzoic acid active ester and tetrabutylammonium fluoride-tetratert-butanol complex as raw materials, hexafluorobenzene is obtained by catalytic decarboxylation and fluorination in an organic solvent in the presence of copper catalyst and visible light.

2. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: The first step involves selecting the activating agent from N-hydroxysuccinimide, N-hydroxyphthalimide, hexafluoro-2-propanol, or N-hydroxybenzotriazole, wherein the molar ratio of pentafluorobenzoic acid to the activating agent is 1:1.5-3.

3. The novel method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: In the first step, the molar ratio of pentafluorobenzoic acid, triphenylphosphine, and iodine is 1:1-2:1-2.

4. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: The first step involves a reaction temperature of 10-40℃ and a reaction time of 2-5 hours.

5. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: In the second step, the organic solvent is selected from at least one of nitrile solvents, C1-C4 alcohols, tetrahydrofuran, 2-methyltetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetone, butanone, methyl isobutyl ketone, dichloromethane, ethyl acetate, and water.

6. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: In the second step, the tetrabutylammonium fluoride tetratert-butanol complex is used as a fluorine source, which acts as both a nucleophilic fluorinating agent and a phase transfer catalyst to accelerate the reaction rate. The molar ratio of the active pentafluorobenzoic acid ester to the fluorine source is 1:1-8.

7. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: In the second step, the copper catalyst is selected from at least one of CuBr, Cu(OTf)2, Cu(MeCN)4PF6, Cu(MeCN)4BF4, CuTc, CuI, CuCl, Cu(OAc)2, CuBr2, CuCl2 or Cu(acac)2.

8. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 7, characterized in that: In the second step, the copper catalyst is a combination of Cu(OTf)2 and Cu(MeCN)4BF4; the molar ratio of methyl pentafluorobenzoate, Cu(OTf)2 and Cu(MeCN)4BF4 is 1: 0.1-0.5: 0.1-0.

5.

9. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: The second step is that the visible light wavelength is 370-550nm.

10. The method for preparing hexafluorobenzene by decarboxylation and fluorination of pentafluorobenzoic acid according to claim 1, characterized in that: The second step involves a photocatalytic reaction at a temperature of 0-70°C for 3-10 hours.

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