A kind of preparation method of pentafluoropropionyl fluoride

Abstract

The present invention relates to a preparation method of pentafluoropropionyl fluoride; the first step is to carry out fluorine bromination reaction of acrylate with triethylamine trihydrofluoride complex and N-bromosuccinimide in dichloromethane, and separate the organic layer after diluting the product obtained by the reaction with water; the solvent in the organic layer is evaporated to obtain a propionate substituted with fluorine bromine; the obtained fluorine bromine propionate is added to a fluorination electrolyzer for electrolytic fluorination, and the gaseous products generated during the electrolysis process are collected, and the target product pentafluoropropionyl fluoride is obtained after separation. The electrolysis process of the present invention is carried out at normal pressure, and it is not necessary to use a higher electrolysis temperature to make the generated product quickly separate from the electrolyzer, so it can be electrolyzed under milder conditions, avoiding the formation of transitional electrolysis products, and improving the yield of the target product pentafluoropropionyl fluoride. Compared with the original electrolysis process, the yield of pentafluoropropionyl fluoride can reach more than 70%, which greatly reduces the production cost of pentafluoropropionyl fluoride.

Description

Technical Field

[0001] The invention relates to a method for preparing pentafluoropropionyl fluoride, and belongs to the field of fluorine-containing fine chemicals. Background Art

[0002] Pentafluoropropionyl fluoride is an important chemical synthesis intermediate. This compound can undergo addition, decomposition, hydrolysis, aminolysis, alcoholysis and other reactions to obtain a wide range of derivative compounds, such as perfluoropropionic acid, perfluoroalkoxy acyl fluoride, perfluorohexanone and other high value-added fluorine-containing fine chemicals, which are widely used in fluorine-containing medicines, fluorine-containing pesticides, electronics and precision instruments. Therefore, it is very necessary to develop a low-cost, easy-to-mass-produce process route.

[0003] According to literature reports, the current preparation methods of pentafluoropropionyl fluoride mainly include hexafluoropropylene oxide isomerization method, electrolysis method, perfluoromethyl vinyl ether isomerization method, tetrafluoroethylene and fluorophosgene polymerization method, etc. Among them, electrolysis method and hexafluoropropylene oxide isomerization method are the main synthetic routes for preparing pentafluoropropionyl fluoride on an industrial scale. US4729856 reported that under the catalysis of a catalyst, hexafluoropropylene oxide can be isomerized to pentafluoropropionyl fluoride under a certain pressure with DMF or ethers as the volume; US5684193 reported that liquid hydrogen fluoride and amine complexes are used as catalysts, and perfluoropropylene oxide is isomerized to pentafluoropropionyl fluoride at a certain temperature. In CN103145544, organic amine compounds, five-membered or six-membered nitrogen-containing heterocyclic compounds or six-membered condensed ring aromatic compounds and alkali metal fluoride salts are combined into catalysts in a certain proportion, and isomerization reactions can be carried out under milder process conditions. CN105541606 reports that alkali metal fluoride is loaded on activated carbon as a catalyst, and reacts at normal pressure in a chromatography column, and the process yield can reach 90%. CN105315150 reports that alkali metal fluoride is used as a catalyst, ether is a solvent, reacts at 90-200 degrees, collects gas phase products to obtain pentafluoropropionyl fluoride, and the yield can reach more than 90%. Although some of the above methods can obtain pentafluoropropionyl fluoride, all of these methods require hexafluoropropylene oxide as a raw material for isomerization reaction, and hexafluoropropylene oxide needs to be prepared by epoxidation from hexafluoropropylene. At present, the yield of hexafluoropropylene oxide prepared by epoxidation of hexafluoropropylene is low, and the price of hexafluoropropylene is higher, so the cost of preparing pentafluoropropionyl fluoride remains high.

[0004] Compared with the propylene oxide isomerization method, the electrolysis method uses industrial bulk products as raw materials with a wide range of sources, and compared with hexafluoropropylene as a raw material, the price of non-fluorinated organic compound raw materials is cheaper, but the electrolysis method often has a low yield, generally around 30%-40%. If the yield of the electrolysis process can be better improved, the process route of preparing pentafluoropropionyl fluoride by electrolytic fluorination will be more suitable for large-scale industrial production. Summary of the invention

[0005] The purpose of the present invention is to provide a new synthesis process route for the current situation that the yield of pentafluoropropionyl fluoride is low in the process of preparing pentafluoropropionyl fluoride by electrolysis, which can significantly improve the yield of the electrolysis process and reduce the generation of transition electrolysis by-products, thereby reducing the production cost of pentafluoropropionyl fluoride and alleviating the environmental pressure of the production process.

[0006] In order to solve the above problems, the specific technical solution adopted by the present invention is:

[0007] A method for preparing pentafluoropropionyl fluoride; comprising the following steps:

[0008] In the first step, acrylate is subjected to a fluorination reaction with triethylamine trihydrogen fluoride complex (Et3N-3HF) and N-bromosuccinimide (NBS) in dichloromethane, and the product obtained by the reaction is diluted with water and an organic layer is separated; the solvent in the organic layer is evaporated to obtain a fluorine-bromine substituted propionic acid ester;

[0009] In the second step, the obtained fluorobromopropionate is added into a fluorination electrolytic cell for electrolytic fluorination, and the gas products generated during the electrolysis are collected and separated to obtain the target product pentafluoropropionyl fluoride.

[0010]

[0011] Furthermore, the raw material for the first step of the fluorination and chlorination reaction is ethyl acrylate, propyl acrylate or butyl acrylate, among which propyl acrylate is the most preferred.

[0012] Furthermore, the molar ratio of acrylic acid to Et3N-3HF and NBS in the first step of the fluorination and bromination reaction is 1:2:1.

[0013] Furthermore, the first step fluorination bromination reaction temperature is -10°C to 0°C.

[0014] Furthermore, the voltage of the second step electrolytic fluorination process is 5.0V-6.0V.

[0015] Furthermore, the current density of the second step electrolytic fluorination process is 1.5-2.0A / dm 2 .

[0016] Furthermore, the average electrolysis temperature of the second step electrolytic fluorination process is 4-6°C.

[0017] The electrolytic fluorination process mainly relies on the raw materials to dissolve in anhydrous hydrogen fluoride for electrical conduction. If the solubility of the raw materials in anhydrous hydrogen fluoride is low, the current will be unevenly distributed on the electrode during the electrolysis process, resulting in excessive local current and excessive electrolysis of the product. In addition, when the first hydrogen atom in the raw material molecule is replaced by a fluorine atom, the entire molecule is polarized, resulting in an imbalance in the electron cloud within the molecule. At this time, if the current is too large, the CC bond will break, thereby generating small molecular products.

[0018] The raw material acrylate used in the present invention is a bulk industrial product, low in price, and easily available in the market. Using acrylate as a raw material can greatly reduce the raw material cost of pentafluoropropionyl fluoride. The acrylate is subjected to a fluorine-bromine reaction, and the obtained fluorine-bromine-substituted propionate can be better dissolved in anhydrous hydrogen fluoride due to the presence of fluorine atoms in the molecule, making the electrolysis process more uniform and reducing the occurrence of excessive electrolysis. At the same time, the fluorine atoms and bromine atoms introduced after substitution in the molecule change the polarity and electron cloud density of the molecule, thereby avoiding the breakage of the CC bond caused by the sharp change of the electron cloud density during the electrolysis process, thereby reducing the generation of small molecule products.

[0019] The electrolysis process of the present invention is carried out under normal pressure, and there is no need to use a high electrolysis temperature to allow the generated product to quickly leave the electrolytic cell. Therefore, the electrolysis can be carried out under milder conditions, avoiding the formation of transitional electrolysis products, and improving the yield of the target product pentafluoropropionyl fluoride. Compared with the original electrolysis process, the yield of pentafluoropropionyl fluoride can reach more than 70%, greatly reducing the production cost of pentafluoropropionyl fluoride. DETAILED DESCRIPTION

[0020] Example 1

[0021] Fluorobromination reaction:

[0022] After adding 1000g of ethyl acrylate and 2000ml of dichloromethane to a 10-liter reactor equipped with a stirrer and a constant pressure feeder, the temperature in the reactor was lowered to -10°C, and then 1780g of N-bromosuccinimide (NBS) was added, and then a solution obtained by dissolving 3220g of Et3N-3HF in 600ml of dichloromethane was added dropwise under strong stirring. The temperature in the reactor was kept at -10°C throughout the entire dropping process, and then stirred overnight at this temperature. The obtained product was diluted with 5000ml of water and the organic layer was separated. The aqueous layer was extracted three times with 3000ml of dichloromethane. All the organic layers were combined and washed with water, dried with Na2SO4, and the solvent was evaporated. 1596.8g of a fluorinated bromination mixed product was obtained in the reactor, which could be directly used for the next step of electrolysis.

[0023] electrolysis:

[0024] The internal volume of the electrolytic cell is 10 liters, equipped with a liquid level gauge, a tube condenser, and a lower vent valve. There are four nickel anode plates and four stainless steel cathode plates in the electrolytic cell. The plate size is 400mm×130mm×3mm, and the total plate area is 20.8dm 2 7.4 kg of anhydrous hydrogen fluoride and 370 g of ethyl acrylate fluoride bromination product were added to the electrolytic cell and allowed to stand for 10 hours. Then, the electrolytic cell was heated at 4 °C, 6.0 V, 32 A (current density 1.53 A / dm 2 ) and the gas escaping from the tube condenser was received in a receiving tank cooled with -80°C ethanol. After 36 hours of electrolysis, when the concentration of the raw material in the electrolytic cell began to decrease, the voltage rose to 6.2V, the electrolysis was stopped, the receiving tank was heated to -10°C, the gas in the receiving tank was introduced into the product tank after adsorbing residual HF through a NaF absorption tube, and a total of 423g of product was obtained. According to gas chromatography analysis, the trifluoroacetyl fluoride content was 41.76%, the pentafluoropropionyl fluoride content was 56.16%, and the pentafluoropropionyl fluoride molar yield was 77.02%.

[0025] Example 2

[0026] Fluorobromination reaction:

[0027] 1140 g of propyl acrylate and 2000 ml of dichloromethane were added to a 10-liter reactor equipped with a stirrer and a constant pressure feeder, and then the temperature in the reactor was lowered to -5°C, and then 1780 g of N-bromosuccinimide (NBS) was added, and then a solution obtained by dissolving 3220 g of Et3N-3HF in 600 ml of dichloromethane was added dropwise under strong stirring. The temperature in the reactor was always kept at -5°C during the addition, and then stirred overnight at this temperature. The obtained product was diluted with 5000 ml of water and the organic layer was separated. The water layer was extracted three times with 3000 ml of dichloromethane. All the organic layers were combined and washed with water, dried with Na2SO4, and the solvent was evaporated. 1746.6 g of a fluorinated bromination mixed product was obtained in the reactor, which could be directly used for the next step of electrolysis.

[0028] electrolysis:

[0029] The internal volume of the electrolytic cell is 10 liters, equipped with a liquid level gauge, a tube condenser, and a lower vent valve. There are four nickel anode plates and four stainless steel cathode plates in the electrolytic cell. The plate size is 400mm×130mm×3mm, and the total plate area is 20.8dm 2 7.4 kg of anhydrous hydrogen fluoride and 370 g of propyl acrylate fluorinated product were added to the electrolytic cell and allowed to stand for 10 hours. Then, the electrolytic cell was heated to 5 °C, 5.5 V, 35 A (current density 1.68 A / dm 2) and the gas escaping from the tube condenser was received in a receiving tank cooled with -80°C ethanol. After 30 hours of electrolysis, when the concentration of the raw material in the electrolytic cell began to decrease, the voltage rose to 6.0V, the electrolysis was stopped, the receiving tank was heated to -10°C, and the gas in the receiving tank was introduced into the product tank after adsorbing residual HF through a NaF absorption tube, and a total of 484.9g of product was obtained. According to gas chromatography analysis, the trifluoroacetyl fluoride content was 4.21%, the pentafluoropropionyl fluoride content was 87.05%, and the pentafluoropropionyl fluoride molar yield was 73.19%.

[0030] Example 3

[0031] Fluorobromination reaction:

[0032] 1280 g of butyl acrylate and 2000 ml of dichloromethane were added to a 10-liter reactor equipped with a stirrer and a constant pressure feeder, and then the temperature in the reactor was lowered to 0°C, and then 1780 g of N-bromosuccinimide (NBS) was added, and then a solution obtained by dissolving 3220 g of Et3N-3HF in 600 ml of dichloromethane was added dropwise under strong stirring. During the dropping process, the temperature in the reactor was always kept at 0°C, and then stirred overnight at this temperature. The obtained product was diluted with 1000 ml of water and the organic layer was separated. The water layer was extracted three times with 3000 ml of dichloromethane. All the organic layers were combined and washed with water, dried with Na2SO4, and the solvent was evaporated. 1770.6 g of a fluorinated bromination mixed product was obtained in the reactor, which could be directly used for the next step of electrolysis.

[0033] electrolysis:

[0034] The internal volume of the electrolytic cell is 10 liters, equipped with a liquid level gauge, a tube condenser, and a lower vent valve. There are four nickel anode plates and four stainless steel cathode plates in the electrolytic cell. The plate size is 400mm×130mm×3mm, and the plate area is 20.8dm 2 7.4 kg of anhydrous hydrogen fluoride and 370 g of butyl acrylate fluoride bromination product were added to the electrolytic cell and allowed to stand for 10 hours. Then, the electrolytic cell was heated at 6 °C, 5.0 V, 42 A (current density 2.02 A / dm 2) and the gas escaping from the tube condenser was received by a receiving tank cooled with -80°C ethanol. After 38 hours of electrolysis, when the concentration of the raw material in the electrolytic cell began to decrease, the voltage rose to 5.5V, the electrolysis was stopped, the temperature of the electrolytic cell was raised to 15°C, and after all the perfluorobutyryl fluoride in the electrolytic cell entered the receiving tank, the receiving tank was heated to 15°C, and the gas in the receiving tank was introduced into the product tank after adsorbing residual HF through a NaF absorption tube, and a total of 467.2g of product was obtained. According to gas chromatography analysis, the trifluoroacetyl fluoride content was 7.46%, the pentafluoropropionyl fluoride content was 48.06%, the perfluorobutyryl fluoride content was 39.94%, the pentafluoropropionyl fluoride molar yield was 82.98%, and the perfluorobutyryl fluoride molar yield was 53.00%.

[0035] The technical solutions disclosed and proposed by the present invention can be realized by those skilled in the art by referring to the contents of this article and appropriately changing the conditions, routes and other links. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, relevant technicians can obviously modify or re-combine the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to realize the final preparation technology. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims

1. A method for preparing pentafluoropropionyl fluoride; characterized in that: The steps include: In the first step, acrylate is subjected to fluorination and bromination reaction with triethylamine trihydrogen fluoride complex and N-bromosuccinimide in dichloromethane, the product obtained by the reaction is diluted with water and the organic layer is separated; the solvent in the organic layer is evaporated to obtain fluorinated and brominated propionic acid ester; The second step is to add the obtained fluorobromopropionate into a fluorination electrolytic cell for electrofluorination, collect the gas products generated during the electrolysis process, and obtain the target product pentafluoropropionyl fluoride after separation; The acrylate includes ethyl acrylate, propyl acrylate or butyl acrylate; the molar ratio of the acrylate to the triethylamine trihydrogen fluoride complex and N-bromosuccinimide is 1:2:

1.

2. The method according to claim 1, characterized in that: The first step acrylate is propyl acrylate.

3. The method according to claim 1, characterized in that: The temperature of the first step fluorine bromination reaction is -10°C to 0°C.

4. The method according to claim 1, characterized in that: The voltage of the second step electrolytic fluorination process is 5.0V-6.0V.

5. The method according to claim 1, characterized in that: The current density of the second step electrolytic fluorination process is 1.5-2.0A / dm 2 .

6. The method according to claim 1, characterized in that: The average electrolysis temperature of the second step electrolytic fluorination process is 4-6°C.

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