A continuous process for the preparation of diiodoperfluoroalkanes

Abstract

The application discloses a continuous preparation method of diiodoperfluoroalkane. Tetrafluoroethylene and iodine are continuously introduced into a reactor after preheating in a nitrogen atmosphere, and a gas phase reaction is carried out under the action of a catalyst. The molar ratio of the tetrafluoroethylene and the iodine is 1-8:1, the reaction temperature is 200-400 DEG C, the pressure is 0.1-1.0 MPa, the residence time is 5-50 s, and the reaction product is collected to obtain diiodoperfluoroalkane product. The application has the advantages of simple process, large operation flexibility, high reaction efficiency and safety controllability.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis, specifically relating to a continuous preparation method of diiodoperfluoroalkane. Background Technology

[0002] Because the CI bonds in diiodoperfluoroalkanes are easily broken, they can undergo free radical addition, telomerization, and polymerization reactions. Therefore, diiodoperfluoroalkanes are widely used in the synthesis of long-chain, branched perfluorinated or polyfluorinated compounds, serving as a very important intermediate. For example, diiodoperfluoroalkanes can undergo addition reactions with many substances containing both functional groups and double bonds. The resulting diadditions can then be reacted by eliminating the HI group to yield fluorinated epoxides, fluorinated diacetylenes, and branched fluorinated diols. These substances can be copolymerized with other compounds to obtain various fluorinated polymers such as fluorinated polyesters, fluorinated polyepoxy resins, and fluorinated polyacrylates.

[0003]

[0004] Diiodoperfluoroalkanes can also undergo an addition reaction with ethylene in the presence of a catalyst to generate diiodoperfluoroalkanes diethylene addition products. These diaddition products are very important intermediates, as they can convert the iodine at both ends into other functional groups through functional group conversion, thereby synthesizing various fluorinated compounds. For example, they can react with sodium azide to generate fluorinated diamines, which can be used to synthesize fluorinated polyimide esters, fluorinated polyamide esters, etc. Further oxidation of these diamines yields fluorinated diisocyanates, from which fluorinated polyisocyanates can be synthesized.

[0005]

[0006]

[0007] It can also be converted into adducts such as fluorinated diols and fluorinated diacids, and through these products, fluorinated polyamide esters, fluorinated polyesters, fluorinated polyimide esters, etc. can be obtained.

[0008]

[0009]

[0010] Some of the aforementioned polymers are good elastomers, while others are excellent adhesives, and they are widely used in the manufacturing processes of metals, glass, and polytetrafluoroethylene materials.

[0011] There are three main routes for the preparation of diiodoperfluoroalkanes:

[0012] (1) Synthesis of other bifunctional perfluoroalkanes via chemical transformation

[0013] In 1951, Hauptschein et al. prepared perfluorinated diiodides by reacting perfluorinated dicarboxylates with iodine at 200°C.

[0014]

[0015] In addition, perfluorodicarboxylic acids, perfluorodiacyl chlorides, perfluorodiesters, and perfluorodiacyl fluorides can all be used as raw materials for the Hunsdiecher reaction. During this reaction, the iodizing agent must be in large excess; otherwise, incomplete reaction products (products with one end iodized) will occur, leading to a significant decrease in yield. Due to its high cost, this method has been gradually phased out.

[0016] (2) Synthesized via perfluoroolefin telomerization reaction

[0017] Patent GB1301617A discloses a method for preparing α,ω-diiodoperfluoroalkanes. Using 1,2-diiodoethane as a raw material, it reacts with 4.25 times its volume of tetrafluoroethylene at 80°C and 650 psi for more than 26 hours under benzoyl peroxide catalysis to obtain a mixture of perfluoroalkyl diiodides. The contents of I(C2F4)nI (n = 1, 2, 3, 4) are 62.9%, 17.6%, 11.5%, and 2.5%, respectively, and the conversion rate of 1,2-diiodoethane is 35%.

[0018] Bedford and Baum (J. Org. Chem. 1980(45):347) et al. synthesized 1,2-diiodotetrafluoroethane and its telomerization reaction with tetrafluoroethylene in a single step using iodine as the starting material in an autoclave. They added iodine and excess tetrafluoroethylene to the autoclave and reacted it at 200-220°C for 22 hours. After cooling, the gas in the autoclave was replaced with 45 ml of fresh tetrafluoroethylene, and the reaction was continued at the same temperature for 18 hours. The resulting product was extracted, washed, dried, and analyzed. The product contained 22.7% 1,2-diiodotetrafluoroethane, 20.9% 1,4-diiodooctafluorobutane, 11.2% 1,6-diiodoperfluorohexane, and 6.4% 1,8-diiodoperfluorooctane.

[0019] (3) Synthesis by thermal decomposition reaction

[0020] Suzuki, Kaichiro (JP1978144507A), and others proposed the preparation of α,ω-diiodoperfluoroalkanes by heating and deiodizing 1,2-diiodoperfluoroethane. The reaction principle is as follows:

[0021] ICF2CF2I→I(C2F4) n I+(n-1)I2

[0022] At 250 °C, a deiodination polymerization reaction was carried out using 1,2-diiodoperfluoroethane. The conversion rate of 1,2-diiodoperfluoroethane was 70.0%, and the selectivity for I(C₂F₄)nI (n = 2, 3, 4) was 56.7%, 13.8%, and 1.06%, respectively, with an overall selectivity of 71.6% and a total yield of 50.1%. However, a large amount of elemental iodine was generated after the reaction, causing equipment blockage. Moreover, the generated products mixed with iodine, which brought great difficulties to the post-processing of the products. Although iodine could be recovered from the reaction mixture by filtration or reduction, this increased the complexity of the operation and the loss of iodine.

[0023] In summary, telomerization has attracted much attention due to its high single-pass conversion rate and selectivity of diiodoperfluoroalkanes. However, it requires the addition of a large amount of excess tetrafluoroethylene gas, resulting in high reaction pressure, long reaction time, and is a strongly exothermic reaction with high risks. Furthermore, during the closed-system reaction, some tetrafluoroethylene gas dimerizes into octafluorocyclobutane, which remains in the reaction system. Octafluorocyclobutane is a free radical scavenger, and the accumulation of octafluorocyclobutane in the reaction system as the reaction proceeds can lead to a decrease in the reaction rate or even termination of the reaction. Therefore, after a certain period of telomerization, the tetrafluoroethylene gas in the reactor needs to be replaced before continuing the reaction. This reaction method undoubtedly affects its industrial application prospects. In addition, most of the reported telomerization reactions are currently batch reactor reactions, which are cumbersome to operate and have low reaction efficiency. Summary of the Invention

[0024] The purpose of this invention is to address the shortcomings of existing technologies by providing a continuous method for preparing diiodoperfluoroalkanes that is simple in process, highly flexible in operation, highly efficient in reaction, safe and controllable, and easy to industrialize.

[0025] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: a continuous preparation method of diiodoperfluoroalkane, wherein tetrafluoroethylene and iodine are preheated and continuously introduced into a reactor in a nitrogen atmosphere, and a gas-phase reaction is carried out under the action of a catalyst, wherein the molar ratio of tetrafluoroethylene to iodine is 1 to 8:1, the reaction temperature is 200 to 400°C, the pressure is 0.1 to 1.0 MPa, the residence time is 5 to 50 s, and the reaction products are collected to obtain diiodoperfluoroalkane product.

[0026] Preferably, the catalyst is one of copper or copper-zinc alloy.

[0027] Preferably, the molar ratio of tetrafluoroethylene to iodine is 1 to 4:1.

[0028] Preferably, the preheating temperature is 100–150°C.

[0029] Preferably, the reaction temperature is 220–320°C.

[0030] Preferably, the reaction pressure is 0.1 to 0.5 MPa.

[0031] Preferably, the dwell time is 10 to 30 seconds.

[0032] Preferably, the reactor is a fixed-bed reactor.

[0033] This invention relates to the preparation of diiodoperfluoroalkanes via a continuous gas-phase reaction of iodine with tetrafluoroethylene. The process is simple, highly flexible, safe, efficient, and easily industrialized. The products of this invention can be obtained as single-component products—diiodoperfluoroethane, diiodoperfluorobutane, diiodoperfluorohexane, and diiodoperfluoroethane-octane—through conventional distillation. The reaction formulas of this invention are shown below:

[0034]

[0035] The catalyst described in this invention can be a transition metal or its alloy, preferably copper or copper-zinc alloy catalyst. The catalyst can be in various suitable forms, such as copper powder or copper-zinc alloy powder of 100-300 mesh. Without a catalyst, the reaction temperature of iodine and tetrafluoroethylene is high and the reaction rate is slow, and oligomers of tetrafluoroethylene are formed, affecting subsequent separation. The copper and copper-zinc alloy catalysts in this invention can significantly accelerate the reaction rate and reduce the reaction temperature.

[0036] In this invention, the molar ratio of tetrafluoroethylene to iodine has a significant impact on the reaction efficiency. If the molar ratio is too low, the iodine conversion rate is low, the reaction is incomplete, and excess iodine affects separation; if the molar ratio is too high, more high-boiling byproducts are generated, reducing selectivity. Therefore, in this invention, the molar ratio of tetrafluoroethylene to iodine is 1–8:1, preferably 1–4:1.

[0037] In this invention, reaction temperature and pressure affect the reaction effect. If the reaction temperature is too high, the reaction process is difficult to control, and more high-boiling byproducts are generated, reducing selectivity and making distillation purification difficult. If the reaction temperature is too low, iodine cannot be vaporized, easily clogging pipelines and slowing the reaction rate. If the reaction pressure is too low, the reaction rate is slow and the conversion rate is low; if the reaction pressure is too high, tetrafluoroethylene easily self-polymerizes, generating byproducts and reducing selectivity. Therefore, in this invention, the reaction temperature is 200–400℃, preferably 220–320℃; the reaction pressure is 0.1–1.0 MPa, preferably 0.1–0.5 MPa.

[0038] In this invention, the residence time of the reaction also affects the reaction effect. If the residence time is too short, the reaction is incomplete and the conversion rate is low; if the residence time is too long, by-products are easily generated, reducing selectivity and making distillation purification more difficult. Therefore, the residence time of the reaction in this invention is 5 to 50 seconds, preferably 10 to 30 seconds.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] 1. High reaction efficiency: This invention optimizes the reaction process by adopting a fixed-bed continuous gas-phase reaction method, which shortens the reaction time between raw materials and tetrafluoroethylene, thereby reducing the re-reaction of the generated products with tetrafluoroethylene and thus reducing the formation of high-boiling byproducts. At the same time, it avoids the situation where the reaction rate decreases or even the reaction terminates due to the dimerization of tetrafluoroethylene gas into octafluorocyclobutane, thus improving the conversion rate of raw materials and the selectivity of the target product. The conversion rate based on iodine is 100%; the total selectivity of the target product is 100%.

[0041] 2. Safe and controllable: This invention adds a catalyst to the existing gas-phase reaction method. The copper and copper-zinc alloy catalysts used can significantly accelerate the reaction rate, reduce the reaction pressure, shorten the reaction time, and make the reaction conditions mild and easy to control, thus effectively improving the safety of the reaction process.

[0042] 3. The process is simple and the operation is flexible. The equipment of this invention is simple and easy to operate, and it realizes continuous production. One set of equipment can simultaneously produce four products: diiodoperfluoroethane, diiodoperfluorobutane, diiodoperfluorohexane and diiodoperfluoroethane octane. The product ratio can be flexibly adjusted according to market conditions, which makes it easy to achieve industrialization. Detailed Implementation

[0043] The present invention will be described in more detail below through embodiments, but the present invention is not limited to the embodiments described.

[0044] The raw materials and equipment used in the embodiments of this invention are all commercially available. Some of the equipment is described below:

[0045] Fixed-bed reactor: manufactured by Tianjin Pengxiang Technology Co., Ltd., model PX081.

[0046] Example 1

[0047] 150 ml of copper powder catalyst (average particle size 200 mesh) was loaded into a fixed-bed reactor. The reactor was purged three times with high-purity nitrogen. The temperature was raised to 220 °C under a nitrogen atmosphere. Iodine and tetrafluoroethylene were preheated to 110 °C and then continuously added to the fixed-bed reactor via metering pumps. The molar ratio of tetrafluoroethylene to iodine was controlled at 1:1, the reaction pressure at 0.1 MPa, and the reaction residence time at 10 s. The reaction solution was condensed and collected for chromatographic analysis. The conversion rate, calculated as iodine, was 100%. The composition of the reaction solution is shown in Table 1.

[0048] Table 1. Composition of the reaction solution products in Example 1

[0049]

[0050] Example 2

[0051] 150 ml of copper-zinc alloy powder catalyst (average particle size 240 mesh, copper to zinc mass ratio 3:2) was loaded into a fixed-bed reactor. The reactor was purged three times with high-purity nitrogen. The temperature was raised to 320 °C under a nitrogen atmosphere. Iodine and tetrafluoroethylene were preheated to 110 °C and then continuously added to the gas-phase reactor via metering pumps. The molar ratio of tetrafluoroethylene to iodine was controlled at 4:1, the reaction pressure at 0.5 MPa, and the reaction residence time at 30 s. The reaction solution was condensed and collected for chromatographic analysis. The conversion rate, calculated as iodine, was 100%. The composition of the reaction solution is shown in Table 2.

[0052] Table 2 Composition of the reaction liquid product in Example 2

[0053]

[0054]

[0055] Example 3

[0056] 150 ml of copper powder catalyst (average particle size 260 mesh) was loaded into a fixed-bed reactor. The reactor was purged three times with high-purity nitrogen. The temperature was raised to 300 °C under a nitrogen atmosphere. Iodine and tetrafluoroethylene were preheated to 120 °C and then continuously added to the gas-phase reactor via metering pumps. The molar ratio of tetrafluoroethylene to iodine was controlled at 2:1, the reaction pressure at 0.3 MPa, and the reaction residence time at 20 s. The reaction solution was condensed and collected for chromatographic analysis. The conversion rate, calculated as iodine, was 100%. The composition of the reaction solution is shown in Table 3.

[0057] Table 3 Composition of the reaction liquid product in Example 3

[0058]

[0059] Example 4

[0060] 150 ml of copper-zinc alloy powder catalyst (average particle size 300 mesh, copper to zinc mass ratio 7:3) was loaded into a fixed-bed reactor. The reactor was purged three times with high-purity nitrogen. The temperature was raised to 250 °C under a nitrogen atmosphere. Iodine and tetrafluoroethylene were preheated to 130 °C and then continuously added to the gas-phase reactor via metering pumps. The molar ratio of tetrafluoroethylene to iodine was controlled at 3:1, the reaction pressure at 0.4 MPa, and the reaction residence time at 25 s. The reaction solution was condensed and collected for chromatographic analysis. The conversion rate, calculated as iodine, was 100%. The composition of the reaction solution is shown in Table 4.

[0061] Table 4 Composition of the reaction solution products in Example 4

[0062]

[0063] .

Claims

1. A continuous preparation method for diiodoperfluoroalkanes, characterized in that, In a nitrogen atmosphere, tetrafluoroethylene and iodine are preheated and continuously fed into a fixed-bed reactor for a gas-phase reaction under the action of a catalyst. The molar ratio of tetrafluoroethylene to iodine is 1–8:1, the reaction temperature is 200–400°C, the pressure is 0.1–1.0 MPa, and the residence time is 5–50 s. The reaction products are collected to obtain diiodoperfluoroalkane products. The catalyst is copper or a copper-zinc alloy.

2. The continuous preparation method of diiodoperfluoroalkane according to claim 1, characterized in that, The molar ratio of tetrafluoroethylene to iodine is 1 to 4:

1.

3. The continuous preparation method of diiodoperfluoroalkane according to claim 1, characterized in that, The preheating temperature is 100-150℃.

4. The continuous preparation method of diiodoperfluoroalkane according to claim 1, characterized in that, The reaction temperature is 220–320°C.

5. The continuous preparation method of diiodoperfluoroalkane according to claim 1, characterized in that, The reaction pressure is 0.1–0.5 MPa.

6. The continuous preparation method of diiodoperfluoroalkane according to claim 1, characterized in that, The dwell time is 10 to 30 seconds.

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