A method for preparing perfluoroacyl fluoride by electrochemical method

Abstract

The present invention relates to a method for preparing perfluoroacyl fluoride by electrochemical method, wherein fatty acid ester is added with alkyl acyl chloride, and is put into an electrolytic cell containing anhydrous hydrogen fluoride, and electrolysis is performed at 4-20°C to prepare perfluoroacyl fluoride; the perfluoroacyl fluoride includes perfluoroacetyl fluoride, perfluoropropionyl fluoride or perfluorobutyryl fluoride; the electrolysis product is collected and distilled to obtain a high-purity perfluoroacyl fluoride product. The present invention uses the method of adding an initiator to initiate the electrolysis process, and the electrolysis process is relatively mild; as the electrolysis process proceeds, the insoluble ester product undergoes a fluorine substitution reaction or dissociation to form a substance soluble in hydrogen fluoride, so that the material between the plates can be maintained at a certain concentration, and the occurrence of a transitional electrolysis process can be avoided. The yield of the target product obtained by the electrolysis method is above 80%, which is much higher than the existing literature value of 65-70%, greatly reducing the cost of the product.

Description

Technical Field

[0001] The invention relates to a method for preparing perfluoroacyl fluoride by electrochemical method, belonging to the field of fluorine-containing fine chemicals. Background Art

[0002] Perfluoroacyl 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 perfluorooctanoic acid, perfluorobutyric acid, perfluoropropionic acid, perfluoroalkoxyacyl fluoride and other high value-added fluorine-containing fine chemicals, which are widely used in fluorine-containing medicines, fluorine-containing pesticides, electronics and precision instruments.

[0003] According to literature reports, the current preparation methods of perfluoropropionyl fluoride mainly include electrolysis, perfluoromethyl vinyl ether isomerization, tetrafluoroethylene and fluorophosgene telomerization, etc. Among them, electrolysis and propylene oxide isomerization are the main synthetic routes for preparing perfluoroacyl fluoride on an industrial scale. Patents US4729856, US5684193, CN103145544, CN105541606 and CN105315150 all report the preparation of pentafluoropropionyl fluoride by isomerization reaction with hexafluoropropylene oxide, 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. The yield of preparing hexafluoropropylene oxide by hexafluoropropylene epoxidation is currently low, and the price of hexafluoropropylene is high, which leads to the high cost of preparing pentafluoropropionyl fluoride.

[0004] A variety of organic products can be prepared by electrolysis, but the yield is very low. When electrolysis is performed using acyl fluoride or ester raw materials, sodium fluoride additives need to be added to improve the conductivity of the electrolyte to increase the electrolysis efficiency.

[0005] Patents US2717871 and GB735730 mention the preparation of perfluorocarboxylic acid products through electrolysis. The yield of preparing perfluoroacetic acid by electrolysis of acetyl fluoride can reach 70%, and the yield will drop significantly when preparing perfluoroacyl fluoride with a higher carbon number. The above research also caused salt pollution problems due to the addition of third substances such as sodium fluoride.

[0006] Compared with the propylene oxide isomerization method, the electrolysis method uses industrial bulk products as raw materials with a wide source, and compared with hexafluoropropylene as a raw material, the price of non-fluorinated organic compound raw materials is cheaper. 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

[0007] The purpose of the present invention is to provide a new electrolysis process route for the current situation that the yield of perfluoroacyl fluoride is low (65-70%) in the process of preparing perfluoroacyl fluoride by electrolysis. The electrolysis is carried out under milder electrolysis conditions, which can significantly improve the yield of the electrolysis process, thereby reducing the production cost of perfluoroacyl fluoride and reducing the environmental pressure of the production process. In the process of preparing perfluoroacyl fluoride by using acyl fluoride or ester compound, adding a certain amount of acyl halide to the electrolyte can greatly improve the conductivity of the electrolyte, thereby improving the yield of the electrolysis product of fatty acid ester.

[0008] The present invention provides a method for preparing perfluoroacyl fluoride by electrochemical method, which mainly comprises the following steps:

[0009] (1) adding fatty acid ester and alkyl acyl chloride, putting into an electrolytic cell containing anhydrous hydrogen fluoride, and performing electrolysis at 4-20° C. to prepare perfluorinated acyl fluoride;

[0010] (2) The electrolytic products are collected and distilled to obtain high-purity perfluorinated acyl fluoride products

[0011] Furthermore, the perfluorinated acyl fluoride described in (1) above has the following structural formula:

[0012]

[0013] Where R is a perfluorinated aliphatic group containing 1 to 3 carbon atoms.

[0014] Such as perfluoroacetyl fluoride CF3-COF

[0015] Perfluoropropionyl fluoride CF3CF2-COF

[0016] Perfluorobutyryl fluoride CF3CF2CF2-COF

[0017] Furthermore, the electrolysis raw material fatty acid ester described in (1) above has the following structure:

[0018]

[0019] Where R is an aliphatic hydrogenated alkyl group containing 1 to 3 carbon atoms, and R1 is the number of carbon atoms corresponding to R plus one hydrogenated carbon atom.

[0020] Aliphatic groups such as ethyl acetate, propyl propionate and butyl butyrate.

[0021] Furthermore, the additive alkyl acyl halide described in (1) above has the following structural formula:

[0022]

[0023] Where R is an aliphatic group containing 1 to 3 Cs, and Z is a halogen element

[0024] Furthermore, the fatty acid ester described in (1) above accounts for 1 to 15% by mass of HF, preferably 4 to 10% by mass.

[0025] Furthermore, the alkyl acyl chloride described in (1) above accounts for 0.1 to 15% by mass of HF, preferably 1 to 3% by mass of HF.

[0026] Furthermore, the voltage of the electrolytic fluorination described in (1) above is 5.0V-7.0V.

[0027] Furthermore, the current density of the electrolytic fluorination described in (1) above is 1.2-1.5 A / dm 2 .

[0028] Furthermore, the electrolysis temperature of the electrolytic fluorination process described in (1) above is 4-20°C.

[0029] Furthermore, the distillation tower used for product separation described in (2) above can be a packed tower or a plate tower.

[0030] Furthermore, the reflux ratio of the distillation tower used in (2) is 10:1 to 1:5, preferably 10:1 to 1:3.

[0031] Furthermore, the number of theoretical plates of the distillation tower used in (2) above is 20 to 50.

[0032] Furthermore, the operating pressure of the distillation tower used in (2) above is: normal pressure to positive pressure 8kg / cm 2 , preferably at normal pressure to 2kg / cm 2

[0033] The electrolysis process mainly relies on the raw materials to dissolve in anhydrous hydrogen fluoride for electrical conduction. The reason for the low yield of the electrolysis method is that the solubility of the raw materials in anhydrous hydrogen fluoride is low, so the current will be unevenly distributed on the electrode during the electrolysis process, causing excessive local current and thus excessive electrolysis. On the other hand, when the first hydrogen atom in the molecule is replaced by a fluorine atom, the electron cloud of the entire molecule will produce a large polarization. When the local current is too large, it will cause the CC bond to break, thereby generating small molecular products.

[0034] In the traditional electrolysis process, for raw materials insoluble in hydrogen fluoride, a large amount of sodium fluoride conductive agent is added to hydrogen fluoride to promote electrolysis. Although the electrolysis process can be carried out, the material concentration between the plates is low. At the same time, due to the presence of the conductive agent, the current is large, so the local content of fluoride ions between the plates is too high, which leads to the occurrence of material transition electrolysis process and low yield of electrolysis products. The present invention uses the method of adding an initiator to initiate the electrolysis process, and the electrolysis process is relatively mild; as the electrolysis process proceeds, the insoluble ester products will undergo fluorine substitution reaction or dissociation to form substances soluble in hydrogen fluoride, so that the material between the plates can be maintained at a certain concentration, avoiding the occurrence of transition electrolysis process, and obtaining a higher yield of electrolysis products. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with specific embodiments:

[0036] Example 1 Preparation of perfluoroacetyl fluoride

[0037] In an electrolytic cell equipped with a thermometer, a tube condenser, four nickel anode plates and four stainless steel cathode plates with a total plate area of ​​20.8 dm2, 7500 kg of anhydrous hydrogen fluoride is added, and then 75 g of acetyl chloride and 370 g of ethyl acetate are mixed and added to the electrolytic cell. The electrolysis is carried out at an electrolytic cell temperature of 4 to 6°C, an average voltage of 4 to 6.0 V, and an average current of 32 A. The electrolysis is continued for 72 hours. After the electrolytic gas is cooled by a low-temperature condenser, the hydrogen fluoride liquid is returned to the electrolytic cell, and the gas containing perfluoroacetyl fluoride (CF3-COF) is further cooled and collected in a low-temperature cold trap receiving tank.

[0038] The material in the low temperature cold trap receiving tank is put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 22 pieces), at a reflux ratio of 5:1 and a gauge pressure of 2kg / cm 2 The fractions at -32 to -34°C were collected to obtain more than 99% of the perfluoroacetyl fluoride product, and the yield of perfluoroacetyl fluoride based on the feed ethyl acetate was 86.1%. In order to maintain the initial raw material concentration during the electrolysis process, ethyl acetate and anhydrous HF needed to be continuously supplemented.

[0039] Example 2 Preparation of perfluoroacetyl fluoride

[0040] Using the same electrolytic cell as in Example 1, 8000 g of anhydrous hydrogen fluoride was added to the electrolytic cell, and then 80 g of acetyl chloride and 800 g of ethyl acetate were mixed and added to the electrolytic cell. Electrolysis was performed at an electrolytic cell temperature of 6 to 8° C., an average voltage of 5 to 6.0 V, and an average current of 32 A. The electrolysis was continued for 72 hours. After the electrolytic gas was cooled by a low-temperature condenser, the hydrogen fluoride liquid returned to the electrolytic cell, and the gas containing perfluoroacetyl fluoride was further cooled and collected in a low-temperature cold trap receiving tank.

[0041] The material in the low temperature cold trap receiving tank is put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 30 pieces), at a reflux ratio of 5:1 and a gauge pressure of 2kg / cm 2 The fractions at -32 to -34 °C were collected to obtain more than 99.5% of the perfluoroacetyl fluoride product, and the yield of perfluoroacetyl fluoride based on the feed ethyl acetate was 85.3%.

[0042] Example 3 Preparation of perfluoropropionyl fluoride

[0043] Using the same electrolytic cell as in Example 1, 8000 g of anhydrous hydrogen fluoride was added to the electrolytic cell, and then 220 g of propionyl chloride and 320 g of propyl propionate were mixed and added to the electrolytic cell. Electrolysis was performed at an electrolytic cell temperature of 4 to 6° C., an average voltage of 6.0 to 7.0 V, and an average current of 32 A. The electrolysis was continued for 72 hours. After the electrolytic gas was cooled by a low-temperature condenser, the hydrogen fluoride liquid returned to the electrolytic cell, and the gas containing perfluoropropionyl fluoride (CF3CF2-COF) was further cooled and collected in a low-temperature cold trap receiving tank.

[0044] The material of the low temperature cold trap receiving tank is put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 20), and the fraction of -29.5 to -30.5°C is collected at a reflux ratio of 3:1 under normal pressure to obtain a perfluoropropionyl fluoride product of more than 99.1%, and the yield of perfluoropropionyl fluoride based on the feed propyl propionate is: 85.9%

[0045] Example 4 Preparation of perfluoropropionyl fluoride

[0046] Using the same electrolytic cell as in Example 1, 8000 g of anhydrous hydrogen fluoride was added to the electrolytic cell, and then 80 g of propionyl chloride and 650 g of propyl propionate were mixed and added to the electrolytic cell. The electrolysis was carried out at an electrolytic cell temperature of 4 to 6° C., an average voltage of 5 to 6.0 V, and an average current of 28 A. The electrolysis was continued for 72 hours. After the electrolytic gas was cooled by a low-temperature condenser, the hydrogen fluoride liquid returned to the electrolytic cell, and the gas containing perfluoropropionyl fluoride was further cooled and collected in a low-temperature cold trap receiving tank.

[0047] The material of the low temperature cold trap receiving tank was put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 35), and the fraction of -29.5 to -30.5°C was collected at a reflux ratio of 4:1 under normal pressure to obtain more than 99% perfluoropropionyl fluoride product, and the yield of perfluoropropionyl fluoride based on the feed propyl propionate was: 87.2%

[0048] Example 5 Preparation of perfluorobutyryl fluoride

[0049] Using the same electrolytic cell as in Example 1, 7600 g of anhydrous hydrogen fluoride was added to the electrolytic cell, and then 80 g of butyryl chloride and 380 g of butyl butyrate were mixed and added to the electrolytic cell. Electrolysis was carried out at an electrolytic cell temperature of 18 to 20° C., an average voltage of 6.0 to 7 V, and an average current of 25 A. The electrolysis was continued for 72 hours. After the electrolytic gas was cooled by a low-temperature condenser, the hydrogen fluoride liquid returned to the electrolytic cell, and the gas containing perfluorobutyryl fluoride (CF3CF2CF2-COF) was further cooled and collected in a low-temperature cold trap receiving tank.

[0050] The material of the low temperature cold trap receiving tank is put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 40), and the fraction of 7 to -9 ° C is collected at a reflux ratio of 3:1 under normal pressure to obtain more than 99% butyryl fluoride product, and the yield of perfluorobutyryl fluoride based on the feed butyl butyrate is: 82.6%

[0051] Example 6 Preparation of perfluorobutyryl fluoride

[0052] Using the same electrolytic cell as in Example 1, 8000 g of anhydrous hydrogen fluoride was added to the electrolytic cell, and then 100 g of butyryl chloride and 480 g of butyl butyrate were mixed and added to the electrolytic cell. The electrolysis was carried out at an electrolytic cell temperature of 20° C., an average voltage of 6.0 to 7 V, and an average current of 32 A. The electrolysis was continued for 72 hours. After the electrolytic gas was cooled by a low-temperature condenser, the hydrogen fluoride liquid was returned to the electrolytic cell, and the gas containing perfluorobutyryl fluoride was further cooled and collected in a low-temperature cold trap receiving tank.

[0053] The material of the low temperature cold trap receiving tank is put into a tower containing stainless steel wire mesh packing (theoretical plate number is about 45), and the fraction of 8-9°C is collected at a reflux ratio of 10:1 under normal pressure to obtain a perfluorobutyryl fluoride product of more than 99.3%, and the yield of perfluorobutyryl fluoride based on the feed butyl butyrate is: 83.6%

[0054] The yield of the target product obtained by the electrolysis method of this patent is above 80%, which is much higher than the existing literature value of 65-70%, greatly reducing the cost of the product.

[0055] 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 perfluoroacyl fluoride by electrochemical method, characterized in that: The steps include: (1) Adding an alkyl acyl chloride to a fatty acid ester, placing the mixture in an electrolytic cell containing anhydrous hydrogen fluoride, and performing electrolysis at 4 to 20° C. to prepare perfluorinated acyl fluoride; the voltage of the electrolytic fluorination is 5.0 V to 7.0 V; and the current density is 1.2 to 1.5 A / dm2; (2) collecting the electrolytic products and obtaining a high-purity perfluorinated acyl fluoride product by distillation; The electrolysis raw material fatty acid ester has the following structure: Wherein R is a hydrogenated alkyl group of a fatty acid containing 1 to 3 carbon atoms, and R1 is a hydrogenated aliphatic group with one carbon atom added to the carbon number corresponding to R, including ethyl acetate, propyl propionate and butyl butyrate; Alkyl acyl halides have the following structural formula: Wherein R is an aliphatic group containing 1 to 3 Cs, and Z is a halogen element.

2. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: Perfluorinated acyl fluorides include perfluoroacetyl fluoride, perfluoropropionyl fluoride or perfluorobutyryl fluoride.

3. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: The fatty acid ester described in step (1) accounts for 1-15% of HF by mass; the alkyl acyl chloride accounts for 0.1-15% of HF by mass.

4. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: The fatty acid ester described in step (1) accounts for 4-10% of HF by mass; the alkyl acyl chloride accounts for 1-3% of HF by mass.

5. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: The distillation tower used for product separation in step (2) is a packed tower and a plate tower.

6. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: The operating reflux ratio of the distillation tower used for the distillation in step (2) is 10:1 to 1:5; the number of theoretical plates of the distillation tower is 10 to 50; the operating pressure of the distillation tower is normal pressure to positive pressure 8 kg / cm 2 .

7. The method for preparing perfluoroacyl fluoride by electrochemical method according to claim 1, characterized in that: The operating reflux ratio of the distillation tower used in the distillation in step (2) is 10:1 to 1:3; the number of theoretical plates of the distillation tower is 20 to 50; the operating pressure of the distillation tower is normal pressure to positive pressure 2kg / cm 2 .

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