Process for the preparation of alpha, omega-diiodoperfluoroalkanes

Abstract

The application provides a preparation method of alpha, omega-diiodo perfluoroalkane, taking dibromotetrafluoroethane and tetrafluoroethylene as raw materials, ultraviolet light as a catalyst, performing photocatalytic telomerization reaction to generate dibromoperfluoroalkane; in a polar aprotic solvent, the dibromoperfluoroalkane and sodium iodide or potassium iodide perform substitution reaction at 50-100 DEG C, and alpha, omega-diiodo perfluoroalkane is obtained through separation and purification. The reaction condition in the preparation process is mild, a high-temperature and high-pressure environment is not needed, safety is high, purification is easy, the purity and selectivity of the obtained alpha, omega-diiodo perfluoroalkane are high, and the problems of poor selectivity of the product, low raw material utilization rate and great environmental pollution caused by iodine in the preparation process of diiodoperfluoroalkane are solved.

Description

Technical Field

[0001] This application belongs to the technical field of fluorine-containing fine chemicals, specifically relating to a method for preparing α,ω-diiodoperfluoroalkanes. Background Technology

[0002] α,ω-Diiodoperfluoroalkanes (such as 1,4-diiodoperfluorobutane and 1,6-diiodoperfluorohexane) are an important class of fluorinated fine chemical intermediates. Their molecular structure contains two reactive iodine atoms, readily undergoing nucleophilic substitution and coupling reactions, and they are widely used in fluoropolymers, pharmaceuticals, electronic materials, and organic synthesis. For example, as crosslinking agents, they are used to prepare high-performance fluorinated elastomers, significantly improving their weather resistance, chemical corrosion resistance, and mechanical strength; as pharmaceutical intermediates, they are used to synthesize fluorinated anticancer and anti-inflammatory drugs, enhancing their bioavailability and metabolic stability; and as surface treatment agents for electronic materials, they can be used in etching processes during semiconductor manufacturing.

[0003] Currently, the main method for synthesizing α,ω-diiodoperfluoroalkanes is the free radical telomerization method. This method uses 1,2-diiodotetrafluoroethane as a telomerizing agent and tetrafluoroethylene as a monomer. The telomerization reaction occurs under the action of free radical initiators (such as azobisisobutyronitrile and benzoyl peroxide) to generate the target product. However, this method has significant technical drawbacks: First, the free radical reaction has poor selectivity, easily producing byproducts with a wide carbon chain distribution (such as diiodoperfluoroalkanes with C3, C8, and higher carbon chains). The selectivity of the target product is usually around 70%, making subsequent separation and purification difficult. Second, the reaction needs to be carried out under high temperature and high pressure conditions (usually 150~250℃ and 5~10MPa), resulting in high operational risks, high energy consumption, and stringent equipment requirements. Third, the free radical initiator is prone to decomposition, generating impurities and contaminating the product. Furthermore, the catalyst is difficult to recover, easily causing environmental pollution and resource waste. Fourth, cyclic byproducts such as octafluorocyclobutane are easily generated during the reaction, leading to reaction stagnation and reduced product yield.

[0004] To address the aforementioned issues, existing technologies have attempted to improve the synthesis process using other catalytic systems, such as Lewis acids like antimony pentafluoride and boron trifluoride. However, these catalysts are highly corrosive, easily damaging reaction equipment, and have low activity, making it difficult to significantly improve the selectivity of the target product. Other technologies employ supported palladium catalysts, which can improve selectivity to some extent, but these catalysts are expensive, prone to deactivation, and cannot be recycled, hindering industrial applications.

[0005] Chinese patent CN1267391C discloses a method for synthesizing α,ω-diiodoperfluoroalkanes, using elemental iodine as an initiator and carrying out a telomerization reaction at 180~220℃ and 6~8MPa. The product selectivity is only about 75%, and the yield is less than 85%, still suffering from the problems of harsh reaction conditions and poor selectivity. US patent US10011545 discloses a method for photocatalytic synthesis of diiodoperfluoroalkanes. Although it can lower the reaction temperature, it requires special photocatalytic equipment, which is costly and has low reaction efficiency, making it unsuitable for large-scale production.

[0006] Therefore, developing a method for synthesizing α,ω-diiodoperfluoroalkanes with mild reaction conditions, high selectivity for target products, environmental friendliness, and suitability for industrial production has become an urgent technical problem to be solved in the field of fluorine-containing fine chemicals. Summary of the Invention

[0007] To address the problems existing in the synthesis methods of α,ω-diiodoperfluoroalkanes, this application provides a method for preparing α,ω-diiodoperfluoroalkanes that features mild reaction conditions, high selectivity of the target product, environmental friendliness, and suitability for industrial production.

[0008] The purpose of this application is to achieve the following technical solution.

[0009] This application provides a method for preparing α,ω-diiodoperfluoroalkanes, comprising the following steps: 1) Using dibromotetrafluoroethane and tetrafluoroethylene as raw materials and ultraviolet light as a catalyst, a photocatalytic polymerization reaction is carried out to produce dibromoperfluoroalkanes; The molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:(1~3), the wavelength range of ultraviolet light is 200~400nm, the reaction temperature is 45~100℃, and the reaction pressure is 0.05~0.2MPa; 2) In a polar aprotic solvent, dibromoperfluoroalkanes undergo a substitution reaction with sodium iodide or potassium iodide at 50-100℃ to generate α,ω-diiodoperfluoroalkanes. 3) After the reaction is complete, filter the crude solution containing α,ω-diiodoperfluoroalkanes from step 2) to remove the solid precipitate. Wash the filtrate with sodium thiosulfate solution and then with deionized water to separate the organic phase. Dry, filter, and finally distill under reduced pressure to obtain α,ω-diiodoperfluoroalkanes.

[0010] Furthermore, in step 1), dibromotetrafluoroethane is added first, followed by the introduction of tetrafluoroethylene.

[0011] Furthermore, in step 1), before introducing tetrafluoroethylene, high-purity nitrogen is continuously purged to reduce the oxygen content in the reaction system to below 20 ppm. Tetrafluoroethylene is then introduced to replace the nitrogen in the reactor, the mixture is heated to the reaction temperature, the ultraviolet light source is turned on, and then tetrafluoroethylene is continuously introduced.

[0012] Furthermore, in step 2), the polar aprotic solvent is at least one of acetone, dimethyl sulfoxide, and N,N-dimethylformamide.

[0013] Furthermore, in step 2), the mass ratio of the dibromoperfluoroalkane to the polar aprotic solvent is 1:(1~3).

[0014] Furthermore, in step 2), the molar ratio of the dibromoperfluoroalkane to sodium iodide or potassium iodide is 1:(2~3).

[0015] Furthermore, in step 3), the crude solution containing α,ω-diiodoperfluoroalkane from step 2) is cooled to room temperature and then filtered.

[0016] Furthermore, in step 3), the sodium thiosulfate solution has a mass fraction of 5%.

[0017] Furthermore, in step 3), the drying process uses anhydrous sodium sulfate.

[0018] Furthermore, when the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:1, the final α,ω-diiodoperfluoroalkane is 1,4-diiodoperfluorobutane; when the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:2, the final α,ω-diiodoperfluoroalkane is 1,6-diiodoperfluorohexane; and when the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:3, the final α,ω-diiodoperfluoroalkane is 1,8-diiodoperfluorooctane.

[0019] Compared with the prior art, this application has the following advantages: This application primarily employs a two-step method to synthesize the target product. Using dibromotetrafluoroethane and tetrafluoroethylene as raw materials, a UV-catalyzed telomerization reaction is carried out to generate dibromoperfluoroalkanes, followed by a substitution reaction using sodium iodide or potassium iodide. This application avoids the use of elemental iodine, which is highly polluting to the environment, thus reducing the generation of environmental pollutants and improving the selectivity of the target product.

[0020] The preparation method described in this application can yield α,ω-diiodoperfluoroalkanes with a purity greater than 99.5% and a product selectivity exceeding 90%. It produces few byproducts, is easy to purify, and operates under mild reaction conditions, requiring no high-temperature or high-pressure environment, thus ensuring high safety. This application solves the problems of poor product selectivity, low raw material utilization, and significant environmental pollution caused by iodine in the preparation of diiodoperfluoroalkanes. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described herein are only a part of the embodiments of this application, not all of them, and are merely used to explain this application and are not intended to limit it. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the protection scope of this application.

[0022] This application provides a method for preparing α,ω-diiodoperfluoroalkanes, comprising the following steps: 1) Using dibromotetrafluoroethane and tetrafluoroethylene as raw materials, and ultraviolet light as a catalyst, a photocatalytic polymerization reaction is carried out to generate dibromoperfluoroalkane; the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:(1~3), the wavelength range of ultraviolet light is 200~400nm, the reaction temperature is 45~100℃, and the reaction pressure is 0.05~0.2MPa; 2) In a polar aprotic solvent, dibromoperfluoroalkanes undergo a substitution reaction with sodium iodide or potassium iodide at 50-100℃ to generate α,ω-diiodoperfluoroalkanes. 3) After the reaction is complete, filter the crude solution containing α,ω-diiodoperfluoroalkanes from step 2) to remove the solid precipitate. Wash the filtrate with sodium thiosulfate solution and then with deionized water to separate the organic phase. Dry, filter, and finally distill under reduced pressure to obtain α,ω-diiodoperfluoroalkanes.

[0023] In some specific embodiments, in step 1), dibromotetrafluoroethane is added first, followed by the introduction of tetrafluoroethylene. Because the reaction is a bubbling reaction, the liquid is added first, followed by the gas.

[0024] In some specific embodiments, in step 1), before introducing tetrafluoroethylene, high-purity nitrogen is continuously purged to reduce the oxygen content in the reaction system to below 20 ppm. Tetrafluoroethylene is then introduced to replace the nitrogen in the reactor, the mixture is heated to the reaction temperature, the ultraviolet light source is turned on, and then tetrafluoroethylene is continuously introduced.

[0025] In some specific embodiments, in step 2), the polar aprotic solvent is at least one of acetone, dimethyl sulfoxide, and N,N-dimethylformamide. These three polar aprotic solvents are ideal choices for halogen exchange and produce good reaction results.

[0026] In some specific embodiments, in step 2), the mass ratio of the dibromoperfluoroalkane to the polar aprotic solvent is 1:(1~3). A higher solvent content will accelerate the reaction rate, but too much solvent will result in less of the target product being generated; when the mass ratio is within the selected range, the reaction rate and the target product reach an optimal balance.

[0027] In some specific embodiments, in step 2), the molar ratio of the dibromoperfluoroalkane to sodium iodide or potassium iodide is 1:(2~3). Using this molar ratio, the bromine at both ends of the dibromoperfluoroalkane can be replaced as much as possible.

[0028] In some specific embodiments, in step 3), the crude solution containing α,ω-diiodoperfluoroalkane in step 2) is cooled to room temperature and then filtered.

[0029] In some specific embodiments, in step 3), the sodium thiosulfate solution has a mass fraction of 5%. Sodium thiosulfate has a good neutralizing effect on free iodine in the product, and a mass fraction of 5% is relatively economical and practical, as it does not consume too much sodium thiosulfate while effectively removing free iodine.

[0030] In some specific embodiments, in step 3), the drying is performed using anhydrous sodium sulfate.

[0031] In some specific embodiments, when the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:1, the final α,ω-diiodoperfluoroalkane is 1,4-diiodoperfluorobutane; when the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:2, the final α,ω-diiodoperfluoroalkane is 1,6-diiodoperfluorohexane. The molar ratio can be adjusted to control the final product, but if the molar percentage of tetrafluoroethylene is too high, it will lead to a higher reaction temperature requirement but lower selectivity.

[0032] The specific implementation methods of this application will be further explained and illustrated below through examples and comparative examples.

[0033] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art. Compounds conforming to this application are commercially available.

[0034] Example 1 This embodiment provides a method for preparing 1,4-diiodoperfluorobutane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 50℃. Turn on the ultraviolet light source with a wavelength of 300nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.08MPa. Control the reaction temperature between 45~55℃ and carry out the photocatalytic polymerization reaction for 3h to generate dibromoperfluoroalkane. During this process, a total of 250g (2.5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane to reduce the temperature. 2) Add 1500g of acetone and 850g (5.12mol) of potassium iodide to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath until acetone is under reflux, control the temperature at 55~60℃, and keep under reflux for 8 hours to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane. 3) After reflux, the crude solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, and potassium bromide precipitate was filtered off. The filtrate was washed once with 5% sodium thiosulfate solution, then once with deionized water. The organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,4-diiodoperfluorobutane. Gas chromatography analysis showed a product purity of 99.7% and a product selectivity of 91.7%.

[0035] Example 2 This embodiment provides a method for preparing 1,4-diiodoperfluorobutane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 60℃. Turn on the ultraviolet light source with a wavelength of 200nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.08MPa and the reaction temperature between 55~65℃. Carry out the photocatalytic polymerization reaction for 2.5h to generate dibromoperfluoroalkane. During this process, a total of 250g (2.5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane to reduce the temperature. 2) Add 1500g of N,N-dimethylformamide and 825g (5.5mol) of sodium iodide to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath at 70~80℃, and keep the reaction at this temperature for 10h to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane.

[0036] 3) After the heat treatment reaction was completed, the crude product solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, and sodium bromide precipitate was filtered off. The filtrate was washed once with 5% sodium thiosulfate solution, then washed once with deionized water. The organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,4-diiodoperfluorobutane. The purity of the product was determined to be 99.6% by gas chromatography, and the product selectivity reached 90.5%.

[0037] Example 3 This embodiment provides a method for preparing 1,6-diiodoperfluorohexane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 70℃. Turn on the ultraviolet light source with a wavelength of 200nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.10MPa and the reaction temperature between 65~75℃. Carry out the photocatalytic polymerization reaction for 5h to generate dibromoperfluoroalkane. During this process, a total of 500g (5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane to reduce the temperature. 2) Add 2000g of acetone and 1050g of potassium iodide (6.3mol) to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath until acetone is under reflux, control the temperature at 55~60℃, and keep under reflux for 8 hours to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane.

[0038] 3) After reflux, the crude solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, and potassium bromide precipitate was filtered off. The filtrate was washed once with 5% sodium thiosulfate solution, then once with deionized water. The organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,6-diiodoperfluorohexane. Gas chromatography analysis showed a product purity of 99.8% and a product selectivity of 92.7%.

[0039] Example 4 This embodiment provides a method for preparing 1,6-diiodoperfluorohexane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 80℃. Turn on the ultraviolet light source with a wavelength of 400nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.10MPa and the reaction temperature between 75~85℃. Perform photocatalytic polymerization for 6h to generate dibromoperfluoroalkane. During this process, a total of 500g (5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane.

[0040] 2) Add 2200g of N,N-dimethylformamide and 960g (6.4mol) of sodium iodide to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath at 75~85℃, and keep the reaction at this temperature for 12h to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane.

[0041] 3) After the heat treatment, the crude solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, and the sodium bromide precipitate was filtered off. The filtrate was washed once with a 5% sodium thiosulfate solution, then once with deionized water. The organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,6-diiodoperfluorohexane. Gas chromatography analysis showed a product purity of 99.5% and a product selectivity of 92.5%.

[0042] Example 5 This embodiment provides a method for preparing 1,8-diiodoperfluorooctane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 90℃. Turn on the ultraviolet light source with a wavelength of 250nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.15MPa and the reaction temperature between 85~95℃. Carry out the photocatalytic polymerization reaction for 8h to generate dibromoperfluoroalkane. During this process, a total of 750g (7.5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane to reduce the temperature. 2) Add 4000g of acetone and 1200g of potassium iodide (7.2mol) to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath until acetone is under reflux, control the temperature at 55~60℃, and keep under reflux for 10h to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane.

[0043] 3) After reflux, the crude solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, and potassium bromide precipitate was filtered off. The filtrate was washed once with 5% sodium thiosulfate solution, then once with deionized water. The organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,8-diiodoperfluorooctane. Gas chromatography analysis showed a product purity of 99.7% and a product selectivity of 90.8%.

[0044] Example 6 This embodiment provides a method for preparing 1,8-diiodoperfluorooctane: 1) In a glass reactor equipped with a bottom tube, jacket, ultraviolet light source, and temperature and pressure display instruments, add 650g (2.5mol) of dibromotetrafluoroethane. Continuously purge with high-purity nitrogen to keep the oxygen content in the reaction system below 20ppm. Replace the nitrogen in the reactor with tetrafluoroethylene and heat the material in the reactor to 95℃. Turn on the ultraviolet light source with a wavelength of 300nm and continuously purge tetrafluoroethylene gas into the reactor to maintain the pressure in the reactor at 0.15MPa and the reaction temperature between 90~100℃. Carry out the photocatalytic polymerization reaction for 10h to generate dibromoperfluoroalkane. During this process, a total of 750g (7.5mol) of tetrafluoroethylene is consumed. Cool the reaction material containing dibromoperfluoroalkane to reduce the temperature. 2) Add 4000g of N,N-dimethylformamide and 1100g of sodium iodide (7.3mol) to a three-necked flask and stir until completely dissolved. Add the reactants containing dibromoperfluoroalkane dropwise into the three-necked flask, connect a reflux condenser, heat in a water bath at 80~85℃, and keep the reaction at this temperature for 10h to carry out the substitution reaction and generate α,ω-diiodoperfluoroalkane.

[0045] 3) After the heat treatment reaction was completed, the crude product solution containing α,ω-diiodoperfluoroalkane was cooled to room temperature, potassium bromide precipitate was filtered off, the filtrate was washed once with 5% sodium thiosulfate solution, then washed once with deionized water, the organic phase was separated, dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,8-diiodoperfluorooctane. Gas chromatography analysis showed the product purity to be 99.6% and the product selectivity to be 91.2%.

[0046] Comparative Example 1 This comparative example provides a method for preparing 1,4-diiodoperfluorobutane: In a high-pressure reactor equipped with a stirrer, temperature and pressure display instruments, 700 g of 1,2-diiodotetrafluoroethane and 4 g of azobisisobutyronitrile (azobisisobutyronitrile) free radical initiator were added. The air inside the reactor was replaced with high-purity nitrogen to reduce the oxygen content in the reaction system to below 20 ppm. After the oxygen content met the requirements, the reactor was evacuated and purged with tetrafluoroethylene monomer. The temperature was raised to 200°C for the reaction, the reaction pressure was 1.5–1.8 MPa, and the reaction time was 12 h. A total of 300 g of tetrafluoroethylene was introduced. After the reaction was completed, the mixture was cooled to room temperature, discharged, and filtered. The filtrate was washed once with a 5% sodium thiosulfate solution, then washed once with deionized water to separate the organic phase. The filtrate was dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,4-diiodoperfluorohexane. Gas chromatography analysis showed a product purity of 99.5% and a product selectivity of 73%.

[0047] Comparative Example 2 This comparative example provides a method for preparing 1,6-diiodoperfluorohexane: In a high-pressure reactor equipped with a stirrer, temperature and pressure display instruments, 800 g of 1,2-diiodotetrafluoroethane and 4.5 g of azobisisobutyronitrile (azobisisobutyronitrile) free radical initiator were added. The air inside the reactor was replaced with high-purity nitrogen to reduce the oxygen content in the reaction system to below 20 ppm. After the oxygen content met the requirements, the reactor was evacuated and purged with tetrafluoroethylene monomer. The temperature was raised to 220°C for the reaction, the reaction pressure was 1.8–2.0 MPa, and the reaction time was 20 h. A total of 600 g of tetrafluoroethylene was introduced. After the reaction was completed, the mixture was cooled to room temperature, discharged, and filtered. The filtrate was washed once with a 5% sodium thiosulfate solution, then washed once with deionized water to separate the organic phase. The filtrate was dried with anhydrous sodium sulfate, filtered, and finally distilled under reduced pressure to obtain the product 1,6-diiodoperfluorohexane. Gas chromatography analysis showed a product purity of 99.3% and a product selectivity of 69%.

[0048] The purity and selectivity of the products obtained from the examples and comparative examples are summarized in Table 1.

[0049] As can be seen from Table 1, the selectivity of the target product prepared in this application is higher than that of the target product obtained by direct diiodotetrafluoroethane telomerization. Moreover, the reaction in the comparative example needs to be carried out under high temperature and high pressure, and octafluorocyclobutane will be generated during the reaction, affecting the reaction process and resulting in an excessively long reaction time. Furthermore, diiodotetrafluoroethane will undergo high-temperature bond breakage during the reaction, and elemental iodine will be released. The emission during vacuum replacement will lead to environmental pollution.

[0050] The present application has been further described above with reference to specific embodiments. However, it should be understood that the specific descriptions herein should not be construed as limiting the substance and scope of the present application. Various modifications made by those skilled in the art to the above embodiments after reading this specification are all within the scope of protection of the present application.

Claims

1. A method for preparing α,ω-diiodoperfluoroalkane, characterized in that, Includes the following steps: 1) Using dibromotetrafluoroethane and tetrafluoroethylene as raw materials and ultraviolet light as a catalyst, a photocatalytic polymerization reaction is carried out to produce dibromoperfluoroalkanes; The molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:(1~3), the wavelength range of ultraviolet light is 200~400nm, the reaction temperature is 45~100℃, and the reaction pressure is 0.05~0.2MPa; 2) In a polar aprotic solvent, dibromoperfluoroalkanes undergo a substitution reaction with sodium iodide or potassium iodide at 50-100℃ to generate α,ω-diiodoperfluoroalkanes. 3) After the reaction is complete, filter the crude solution containing α,ω-diiodoperfluoroalkane from step 2) to remove the solid precipitate. Wash the filtrate with sodium thiosulfate solution and then with deionized water to separate the organic phase. Dry, filter, and finally distill under reduced pressure to obtain α,ω-diiodoperfluoroalkane.

2. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 1), dibromotetrafluoroethane is added first, followed by the introduction of tetrafluoroethylene.

3. The method for preparing α,ω-diiodoperfluoroalkane according to claim 2, characterized in that, In step 1), before introducing tetrafluoroethylene, high-purity nitrogen is continuously purged to keep the oxygen content in the reaction system below 20 ppm. Tetrafluoroethylene is then introduced to replace the nitrogen in the reactor. The mixture is heated to the reaction temperature, the ultraviolet light source is turned on, and then tetrafluoroethylene is continuously introduced.

4. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 2), the polar aprotic solvent is at least one of acetone, dimethyl sulfoxide, and N,N-dimethylformamide.

5. The method for preparing α,ω-diiodoperfluoroalkane according to claim 4, characterized in that, In step 2), the mass ratio of the dibromoperfluoroalkane to the polar aprotic solvent is 1:(1~3).

6. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 2), the molar ratio of the dibromoperfluoroalkane to sodium iodide or potassium iodide is 1:(2~3).

7. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 3), the crude solution containing α,ω-diiodoperfluoroalkane from step 2) is cooled to room temperature and then filtered.

8. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 3), the sodium thiosulfate solution has a mass fraction of 5%.

9. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, In step 3), the drying process uses anhydrous sodium sulfate.

10. The method for preparing α,ω-diiodoperfluoroalkane according to claim 1, characterized in that, When the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:1, the final α,ω-diiodoperfluoroalkane obtained is 1,4-diiodoperfluorobutane. When the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:2, the final α,ω-diiodoperfluoroalkane obtained is 1,6-diiodoperfluorohexane. When the molar ratio of dibromotetrafluoroethane to tetrafluoroethylene is 1:3, the final α,ω-diiodoperfluoroalkane obtained is 1,8-diiodoperfluorooctane.

Images