A method for preparing high-purity 1,1-difluoro-2-iodoethylene

Abstract

This invention belongs to the field of fine chemical engineering and organic synthesis technology, and relates to a method for preparing high-purity 1,1-difluoro-2-iodoethylene. The method includes: firstly, in an aprotic organic solvent, under controlled low-temperature conditions, allowing vinylidene fluoride to undergo an addition reaction with iodine monochloride to obtain the intermediate 1-chloro-1,1-difluoro-2-iodoethane; subsequently, the intermediate undergoes a controlled elimination reaction in an alkaline aqueous solution, and the product is immediately removed by reactive distillation, finally purified by distillation to obtain the target product. This invention effectively controls the thermal effect of the addition reaction by introducing a specific solvent, suppressing side reactions such as iodine radical coupling, and eliminating the need for expensive metal catalysts or phase transfer catalysts. The process is simple and safe to operate, with an intermediate separation yield of over 95%, high overall yield, and high product purity, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical and organic synthesis technology, and relates to a method for preparing high-purity 1,1-difluoro-2-iodoethylene. Background Technology

[0002] Fluoropolymers occupy an irreplaceable position in many industrial fields due to their excellent thermal stability, chemical and weather resistance, unique electrical properties, and self-lubricating and non-sticking characteristics. However, traditional long-chain perfluoroalkyl (-C) fluoropolymers... n F 2n+1 Polymers with n≥8 have been proven to be environmentally hazardous and bioaccumulative, a problem that has fueled a surge in global research interest in environmentally friendly short-chain fluoropolymers (carbon chain length C≤6). Among these, environmentally friendly fluorinated vulcanizing point monomers show broad market prospects in polymer modification. By introducing these monomers into the polymer molecular chain, the distribution of vulcanization sites can be precisely controlled, thereby improving the mechanical processing properties of fluoroelastomers. 1,1-Difluoro-2-iodoethylene (DFIE), as a key short-chain vulcanizing point monomer, has extremely high application potential in the preparation of fluoroelastomers, drug molecule synthesis, and the development of novel functional materials.

[0003] In the field of fluorine-containing molecule synthesis, DFIE can serve as a core intermediate in reactions such as Suzuki coupling, Stille coupling, and Sonogashira coupling to construct more complex fluorine-containing polymer monomers. These fluorine-containing derivatives, due to their unique chemical stability and biological activity, have important application value in drug development and pesticide creation. For example, in the preparation of fluorinated pyridine fungicides, DFIE can serve as a key intermediate. Through the directional introduction of fluorine atoms, the biological activity, metabolic stability, and in vivo transport properties of the molecule can be significantly optimized, thereby improving the control efficacy of the fungicide and reducing the field dosage. In the rubber industry, DFIE is mainly used as a comonomer in the preparation of high-performance fluororubber. Because its molecular structure contains active iodine atoms, this group can serve as a crosslinking point or active site during subsequent vulcanization, enabling precise control of the properties of fluororubber. Fluororubber itself already possesses excellent high-temperature resistance, chemical corrosion resistance, oil resistance, and weather resistance, making it widely suitable for demanding applications such as aerospace, automotive manufacturing, chemical production, and semiconductor processing. The introduction of DFIE can further improve the crosslinking efficiency of fluororubber, enhance its mechanical properties, and optimize its processing technology, expanding its application boundaries in high-end industrial fields.

[0004] Currently, the mainstream synthesis method for DFIE is a two-step process, mainly consisting of two core steps: halogenation addition and dehydrohalogenation. The dehydrohalogenation reaction usually involves eliminating hydrogen chloride, hydrogen fluoride, and other hydrogen halide molecules from structurally similar fluoroethanes to form carbon-carbon double bonds. However, the disclosed related technical solutions have many shortcomings. For example, patent CN112062651A uses vinylidene fluoride to add iodine monochloride and then performs gas-phase cracking under the action of a metal catalyst to prepare DFIE; patent CN118108569A proposes a three-step process, which reduces byproducts by adding a distillation step and adding a copper inhibitor, but the overall operation process is cumbersome; patent CN113307720B uses chlorine as a raw material and completes the preparation through multiple reactions and relies on a magnetic catalyst. In summary, existing DFIE synthesis processes generally suffer from the following common defects: First, they rely on expensive and complex metal catalysts, increasing production costs; second, the reaction conditions are harsh, requiring extremely high performance in terms of corrosion resistance and pressure resistance of production equipment; and third, the heat generated during the reaction process is difficult to control precisely, making large-scale continuous production impossible and posing significant safety hazards for industrial scale-up. Therefore, developing a new, efficient, safe, and easily scaled-up DFIE synthesis method has important industrial value and scientific research significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing high-purity 1,1-difluoro-2-iodoethylene.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing high-purity 1,1-difluoro-2-iodoethylene includes the following steps: S1. Addition reaction: In the presence of a nonprotic organic solvent, vinylidene fluoride (VDF) is introduced into a reaction system containing iodine monochloride (ICl) to carry out the reaction. After the reaction is completed, the product is quenched and the solvent is separated to obtain the intermediate product 1-chloro-1,1-difluoro-2-iodoethane. S2, Elimination reaction: The 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 is mixed with an alkaline aqueous solution and subjected to a dehydrohalogenation elimination reaction under heating conditions. The gaseous product generated by the reaction is extracted and condensed to obtain crude 1,1-difluoro-2-iodoethylene. S3. Refining and purification: The crude 1,1-difluoro-2-iodide obtained in step S2 is subjected to alkali washing, drying and distillation in sequence to obtain high-purity 1,1-difluoro-2-iodide product.

[0007] Further, in step (1), the aprotic organic solvent is selected from one or more of dichloromethane, 1,1,2,2-tetrachloroethane, and cyclopentyl methyl ether; the volume ratio of the aprotic organic solvent to iodine monochloride is 1:0.5 to 1:3.

[0008] Further, in step S1, the equivalence ratio of iodine monochloride to vinylidene fluoride is 1:1 to 1:2; the introduction rate of vinylidene fluoride is 200 to 1000 g / min; the aprotic organic solvent can be used to absorb the heat generated by the reaction, thus a larger introduction rate of vinylidene fluoride can be used; the reaction conditions are: reaction temperature 20 to 30 °C, reaction time 2 to 4 h, and stirring speed 200 to 400 rpm during the reaction.

[0009] Further, in step S1, the quenching is performed by adding a mixed solution containing a weak alkali and a weak reducing agent; the solvent separation temperature is 50~100 ℃.

[0010] Furthermore, in the mixed solution containing a weak base and a weak reducing agent, the total mass fraction of the weak base and the weak reducing agent is 5-15%; the solvent of the mixed solution is selected from water or ether. The weak base is selected from one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. The weak reducing agent is selected from one or more of sodium sulfite, sodium dithionite, sodium bisulfite, and sodium thiosulfate.

[0011] Further, in step S2, the alkaline aqueous solution is one or a mixture of sodium hydroxide solution and potassium hydroxide solution; the concentration of the alkaline aqueous solution is 5~15 wt.%; and the molar ratio of 1-chloro-1,1-difluoro-2-iodoethane to the alkali is 1:1~1:3.

[0012] Furthermore, in step S2, the elimination reaction is carried out at a temperature of 50~100 °C.

[0013] Further, in step S3, the alkaline washing is performed by using a weak alkaline solution to remove acidic impurities such as HCl contained in the crude product; the drying is performed using anhydrous calcium carbonate or molecular sieves; the distillation conditions are: distillation column bottom temperature 20~100 ℃, distillation pressure 0~0.1 MPa, and polymerization inhibitors are added during the distillation process.

[0014] Furthermore, the weak alkaline solution is selected from one or two of sodium bicarbonate solution and sodium carbonate solution; the mass fraction of the weak alkaline solution is 15-20%.

[0015] Furthermore, the GC (gas chromatography) purity of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane is ≥99%, and the separation yield is ≥95%; the GC purity of the target product 1,1-difluoro-2-iodoethylene is ≥99.99%, and the total yield is ≥80%.

[0016] The reaction mechanism is as follows: The preparation of 1,1-difluoro-2-iodoethylene (CHI=CF2) according to this invention consists of two core reactions, with the specific general formula as follows: CH2=CF2 + ICl → CClF2CH2I (1), CClF2CH2I → CHI=CF2+ HCl (2); Among them, reaction (1) is an addition reaction, that is, vinylidene fluoride (VDF, CH2=CF2) undergoes electrophilic addition with iodine monochloride (ICl) to generate the intermediate product 1-chloro-1,1-difluoro-2-iodoethane (CClF2CH2I); reaction (2) is an elimination reaction, that is, the intermediate product 1-chloro-1,1-difluoro-2-iodoethane is dehydrochlorinated (HCl) under specific conditions to form the target product 1,1-difluoro-2-iodoethylene.

[0017] Regarding reaction (1), from the perspective of reaction thermodynamics, reaction (1) is an endothermic reaction, but this addition process is actually divided into two steps: Step 1: I + (From the dissociation of ICl) acts as an electrophile to attack the carbon-carbon double bond (CH2=CF2) of VDF, generating the iodonium cation intermediate ([CH2=CF ... + -CF2-I] + This step is accompanied by intense heat release, and the instantaneous release of a large amount of heat is the core cause of the side reactions. Step 2: Cl- produced by the dissociation of ICl - The iodonium cation is attacked, completing the addition ring closure and generating the stable intermediate 1-chloro-1,1-difluoro-2-iodoethane. This step is an endothermic reaction.

[0018] Based on the absorption and release of heat, reaction (1) is generally endothermic.

[0019] The core drawback of existing technologies lies in the fact that when ICl is used directly as the reaction medium (solvent-free system), ICl dissociation is difficult, and there is a lack of effective temperature control and a mechanism for stabilizing intermediates. Furthermore, the large amount of heat released in the first step cannot be removed in time, easily triggering ICl dissociation. + Homolytic cleavage generates iodine radicals (I·), which further couple to form elemental iodine (I2). This not only consumes the raw material ICl, but also leads to side reactions such as multiple additions, ultimately reducing the reaction selectivity and conversion rate (as reported in patent CN118108569A, the highest GC yield in a solvent-free system is only 90%).

[0020] The inventive improvement of this invention lies in the introduction of a specific aprotic solvent. This solvent forms a weak interaction with ICl through electron-donating, thereby promoting the uniform dissociation and dispersion of ICl and stabilizing the key electrophilic reaction component I. +Intermediates should be avoided to prevent side reactions such as recombination and disproportionation due to their high activity, ensuring I... + It can continuously and efficiently undergo electrophilic addition reactions with VDF (vinylidene fluoride), improving the selectivity and conversion rate of the reaction from the source. On the other hand, it utilizes the heat capacity of the solvent to efficiently absorb the heat released in the first step of the reaction, avoiding local overheating of the system. Through these dual effects, side reactions such as the generation of iodine radicals and multiple additions are significantly suppressed, increasing the yield of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane to over 95%, providing a high-purity raw material basis for subsequent elimination reactions.

[0021] Regarding reaction (2), the intermediate product 1-chloro-1,1-difluoro-2-iodoethane (CClF2CH2I) contains an iodine group (-I) that is easy to leave, and a hydrogen atom (β-H) is attached to the carbon adjacent to the iodine group. It has the structural basis to undergo dehydrohalogenation (HCl) elimination reaction. However, in the existing technology, a high concentration of inorganic base with a mass fraction of 40~60% is generally used as the elimination condition. The high leaving activity of the iodine group is very easy to trigger substitution side reactions in the high concentration of inorganic base environment, which leads to a significant decrease in the selectivity of the target product. To address this issue, on the one hand, this invention precisely adjusts the type and concentration of the alkali used for elimination, reducing the alkali concentration to weaken the kinetic advantage of the substitution reaction, while simultaneously screening suitable alkali reagent types. This effectively suppresses the substitution side reactions initiated by the iodine group while ensuring the elimination reaction rate. On the other hand, this invention fully utilizes the physical properties of the target product and, combined with precise control of the reaction temperature, constructs a highly efficient elimination reaction system: First, the reactor temperature is uniformly raised to a preset reaction temperature (usually higher than the boiling point of the target product), providing sufficient motive force for the dehydrochlorination (HCl) elimination reaction of the substrate 1-chloro-1,1-difluoro-2-iodoethane, promoting its efficient formation of the volatile target product 1,1-difluoro-2-iodoethylene (CF2=CHI); Second, the boiling point of the target product 1,1-difluoro-2-iodoethylene is only 40℃, significantly lower than the system temperature of the elimination reaction. Therefore, the product can immediately volatilize and separate from the reaction system after formation, forming a dynamic irreversible equilibrium of "formation-deactivation". This characteristic not only promotes the forward reaction of elimination and improves the reaction conversion rate, but also reduces the residence time of the target product in the reaction system from the source, avoiding secondary side reactions and further enhancing the reaction selectivity.

[0022] Through the synergistic effect of "alkali concentration and type regulation + precise reaction temperature control + immediate product volatilization and separation", this invention effectively solves the problem of low selectivity caused by high concentration of inorganic alkali in the prior art, and achieves efficient preparation of the target product.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) In view of the pain points in the existing technology of 1,1-difluoro-2-iodide (DFIE) synthesis, such as the difficulty in controlling the heat effect of addition reaction, many side reactions, low selectivity of elimination reaction, insufficient product yield and purity, and difficulty in scaling up the process to industrial production, this invention provides an efficient and safe DFIE preparation process by creatively improving the two core steps of addition reaction and elimination reaction, and finally achieves the goal of high-efficiency and high-purity preparation at the hundred-kilogram level.

[0024] (2) This invention creatively introduces a specific aprotic organic solvent into the addition reaction system. On the one hand, the solvent's heat capacity characteristics efficiently absorb the large amount of heat generated by the reaction, avoiding local overheating that could trigger side reactions such as iodine radical coupling and multiple additions. This increases the separation yield of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane to over 95%, with a gas chromatography (GC) purity of not less than 99%. On the other hand, the introduction of the solvent optimizes the mass and heat transfer efficiency of the reaction system, allowing for a higher vinylidene fluoride (VDF) influent rate. This overcomes the technical bottleneck of scaling up solvent-free systems, making the process more suitable for large-scale industrial production. Furthermore, this process eliminates the need for expensive metal catalysts, effectively reducing production costs.

[0025] (3) This invention abandons the complex system that relies on high concentrations of inorganic base and phase transfer catalyst in the prior art. By precisely controlling the concentration of the base solution and the reaction temperature, the elimination reaction can be carried out efficiently without adding a phase transfer catalyst. At the same time, it creatively combines reactive distillation technology and takes advantage of the physical property that the target product DFIE has a boiling point of only 40 °C to immediately export and condense the generated gaseous product, forming a dynamic irreversible equilibrium of "generation-desorption". This not only promotes the elimination reaction to proceed in the forward direction, but also reduces the residence time of the target product in the system from the source, avoiding the occurrence of secondary side reactions.

[0026] (4) The preparation process of the present invention is simple, mild and easy to operate. Neither the addition nor the elimination reaction requires special or complex equipment. Subsequent purification only requires alkali washing, drying and distillation to obtain high-purity products. The GC purity of the final DFIE product is higher than 99.99%, and the total yield can reach more than 80%. In addition, the entire process does not require the use of expensive catalysts or special additives, which greatly reduces production and material costs. Moreover, the product separation and post-processing process is simple and suitable for large-scale industrial application. Attached Figure Description

[0027] Figure 1 The GC chromatogram of 1-chloro-1,1-difluoro-2-iodoethane from Example 1 of this invention is shown below. Figure 2 1-Chloro-1,1-difluoro-2-iodoethane as described in Example 1 of this invention 1H-NMR spectrum; Figure 3 This is a GC diagram of the refined product 1,1-difluoro-2-iodoethylene of Example 1 of the present invention; Figure 4 The refined product 1,1-difluoro-2-iodine of Example 1 of this invention 19 F-NMR spectrum; Figure 5 The refined product 1,1-difluoro-2-iodine of Example 1 of this invention 1 H-NMR spectrum. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified in the embodiments, all procedures shall be performed in accordance with conventional methods in the field, technical solutions described in relevant literature, or operational requirements specified in the product manual; reagents and instruments whose manufacturers are not indicated are all general-purpose products that can be purchased through formal commercial channels.

[0030] Example 1 A high-purity 1,1-difluoro-2-iodoethylene is prepared by the following steps: S1. In a 5 L 316L reactor with a water content <50 ppm and equipped with -15 ℃ cooling water, first add 500 mL of dichloromethane and 1497.3 g of iodine monochloride. Close the reactor, first evacuate the air from the system, then purge with nitrogen for replacement, and repeat this process until the oxygen content in the reactor is ≤50 ppm. Then start stirring (300 rpm) and heat the system to 25 ℃. Subsequently, introduce VDF at a flow rate of 200 g / min, stop the aeration after 3 min, and continue the reaction at this temperature for 2 hours. After the reaction is complete, first vent the gas from the system, then add 1 L of a 10% (w / w) mixed aqueous solution of sodium bicarbonate and sodium sulfite (mass ratio of sodium bicarbonate to sodium sulfite is 1:1) to the system for quenching, with a quenching time of 60 min. After standing, the organic phase was collected by separation and the solvent was removed by rotary evaporation at 50 °C on a 5 L rotary evaporator to obtain 1999.4 g of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane, with a yield of 95.1%.

[0031] like Figure 1 As shown, the gas chromatographic (GC) purity of 1-chloro-1,1-difluoro-2-iodoethane reached 99.99%, and the reaction yield was 95.1%. Figure 2It is 1-chloro-1,1-difluoro-2-iodoethane. 1 The H-NMR spectrum shows that the chemical environment of the hydrogen atoms in this product perfectly matches that of 1-chloro-1,1-difluoro-2-iodoethane (CClF2CH2I): a single peak appears at a chemical shift δ≈3.8-4.0 ppm, corresponding to the two equivalent hydrogen atoms on the -CH2-I group in the molecule. This peak is sharp and free of interference from other peaks, indicating that there are no hydrogen-containing impurities remaining in the product. Since the -CClF2- group in the molecule does not contain hydrogen atoms, there are no other hydrogen signal peaks in the spectrum. Combined with... Figure 1 The GC purity data fully confirms that the prepared intermediate product is high-purity 1-chloro-1,1-difluoro-2-iodoethane.

[0032] S2. Add 1.61 kg of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 to a 5 L reactor connected to a gas outlet pipe. Heat the reactor to 70 °C, and add a 10% (w / w) NaOH aqueous solution through a liquid feeder at a rate of 200 mL / min. This rate effectively avoids temperature runaway due to violent exothermic reactions during the feeding process. Complete the feeding of all the alkali solution within 15 min. Simultaneously, collect the gaseous product exiting the gas outlet pipe using a condenser during the feeding process. After the alkali solution feeding is complete, continue the reaction at the specified temperature for 2 h, and terminate the reaction when no liquid distills out of the condenser. Finally, collect 1.28 kg of crude 1,1-difluoro-2-iodoethane at the condenser end. The yield of this step is 94.8%, and the GC purity of the crude product is 99.0%.

[0033] S3. The crude product obtained in step S2, weighing 1.28 kg, is first washed with a 15 wt% sodium bicarbonate solution to remove impurities, and then dried using a molecular sieve. The dried material is then transferred to a glass distillation vessel containing 100 ppm 2,6-di-tert-butyl-p-cresol (BHT). After deoxygenation treatment of the system (nitrogen purging to ensure the oxygen content in the column is below 10 ppm), distillation is started under slightly positive pressure. During distillation, the column top temperature is maintained at 20 °C (operating pressure 0.06 MPa), and a reflux ratio of 5:1 is maintained to collect the main fraction. Simultaneously, the column bottom temperature must be strictly controlled to not exceed 40 °C, and the column liquid must be protected from light to inhibit thermal decomposition and polymerization side reactions. When the column bottom temperature rises sharply, heating is stopped to terminate distillation. A final purified product of 1.258 kg is collected, with a distillation yield of 98.3% and a GC purity ≥99.99%.

[0034] The refined 1,1-difluoro-2-iodide product should be stored in a cool, dark, and sealed environment.

[0035] The GC chromatogram of the refined product 1,1-difluoro-2-iodoethylene in this embodiment is shown below. Figure 3 As shown, 19 F-NMR spectrum as shown Figure 4 As shown, 1 H-NMR spectrum as shown Figure 5 As shown. The purity of the product in GC is 99.99%. 19 F-NMR and 1 The integral, chemical shift, and coupling constant of the H-NMR spectrum are in perfect agreement with the target structure of 1,1-difluoro-2-iodoethylene, with no obvious impurity peaks, confirming that the prepared product is the high-purity target compound 1,1-difluoro-2-iodoethylene.

[0036] Example 2 A high-purity 1,1-difluoro-2-iodoethylene is prepared by the following steps: S1. In a 5L 316L reactor with a water content <50 ppm and equipped with -15 ℃ cooling water, first add 500 mL of 1,1,2,2-tetrachloroethane and 1495.3 g of iodine monochloride. Close the reactor, first evacuate the system of air, then purge with nitrogen for replacement, and repeat this process until the oxygen content in the reactor is ≤50 ppm. Then start stirring (300 rpm) and heat the system to 25 ℃. Subsequently, introduce VDF at a flow rate of 200 g / min, stop the aeration after 3 min, and continue the reaction at this temperature for 2 hours. After the reaction is complete, first vent the gas from the system, then add 1 L of a 10% (w / w) mixed aqueous solution of sodium bicarbonate and sodium sulfite (mass ratio of sodium bicarbonate to sodium sulfite is 1:1) to the system for quenching for 60 min. After standing, the organic phase was collected by separation and the solvent was removed by rotary evaporation at 70 °C on a 5 L rotary evaporator to obtain 2001.2 g of intermediate product 1-chloro-1,1-difluoro-2-iodoethane, with a gas chromatography (GC) purity of 99.99% and a reaction yield of 96.0%.

[0037] S2. Add 1.59 kg of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 to a 5 L reactor connected to a gas outlet pipe. Heat the reactor to 70 °C, and add a 10% (w / w) KOH aqueous solution through a liquid feeder at a rate of 200 mL / min. This rate effectively avoids temperature runaway due to violent exothermic reactions during the feeding process. Complete the feeding of all the alkali solution within 20 min. Simultaneously, collect the gaseous product exiting the gas outlet pipe using a condenser during the feeding process. After the alkali solution feeding is complete, continue the reaction at the specified temperature for 2 h, and terminate the reaction when no liquid distills out of the condenser. Finally, collect 1.25 kg of crude 1,1-difluoro-2-iodoethane at the condenser end. The yield of this step is 92.5%, and the GC purity of the crude product is 98.8%.

[0038] S3. 1.25 kg of the crude product obtained in step S2 is first washed with a 15 wt.% sodium bicarbonate solution to remove impurities, and then dried using a molecular sieve. The dried material is then transferred to a glass distillation vessel containing 100 ppm BHT. The system is deoxygenated (nitrogen purging to ensure the oxygen content in the column is below 10 ppm), and distillation is started under slightly positive pressure. During distillation, the column top temperature is maintained at 20 ℃ (operating pressure 0.06 MPa), and the main fraction is collected at a reflux ratio of 5:1. Simultaneously, the column bottom temperature must be strictly controlled to not exceed 40 ℃, and the column liquid must be protected from light to inhibit thermal decomposition and polymerization side reactions. When the column bottom temperature rises sharply, heating is stopped and distillation is terminated. A final purified product of 1.229 kg is collected, with a distillation yield of 98.3% and a GC purity ≥99.99%.

[0039] The refined 1,1-difluoro-2-iodide product should be stored in a cool, dark, and sealed environment.

[0040] Example 3 A high-purity 1,1-difluoro-2-iodoethylene is prepared by the following steps: S1. In a 5L 316L reactor with a water content <50 ppm and equipped with -15 ℃ cooling water, first add 500 mL of cyclopentyl methyl ether and 1490.1 g of iodine monochloride. Close the reactor, first evacuate the system of air, then purge with nitrogen for replacement, and repeat this process until the oxygen content in the reactor is ≤50 ppm. Then start stirring (300 rpm) and heat the system to 25 ℃. Subsequently, introduce VDF at a flow rate of 200 g / min, stop the aeration after 3 min, and continue the reaction at this temperature for 2 hours. After the reaction is complete, first vent the gas from the system, then add 1 L of a 10% (w / w) mixed aqueous solution of sodium bicarbonate and sodium sulfite (mass ratio of sodium bicarbonate to sodium sulfite is 1:1) to the system for quenching for 60 min. After standing, the organic phase was collected by separation and the solvent was removed by rotary evaporation at 70 °C on a 5 L rotary evaporator to obtain 1997.2 g of intermediate product 1-chloro-1,1-difluoro-2-iodoethane, with a gas chromatography (GC) purity of 99.99% and a reaction yield of 96.1%.

[0041] S2. Add 1.60 kg of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 to a 5 L reactor connected to a gas outlet pipe. Heat the reactor to 60 °C, and add a 10% (w / w) NaOH aqueous solution through a liquid feeder at a rate of 400 mL / min. This rate effectively avoids temperature runaway due to violent exothermic reactions during the feeding process. Complete the feeding of all the alkali solution within 15 min. Simultaneously, collect the gaseous product exiting the gas outlet pipe using a condenser during the feeding process. After the alkali solution feeding is complete, continue the reaction at the specified temperature for 2 h, terminating the reaction when no liquid distills from the condenser. Finally, collect 1.23 kg of crude 1,1-difluoro-2-iodoethane at the condenser end. The yield of this step is 91.1%, and the GC purity of the crude product is 99.3%.

[0042] S3. The crude product obtained in step S2, weighing 1.23 kg, is first washed with a 15 wt.% sodium bicarbonate solution to remove impurities, and then dried using a molecular sieve. The dried material is then transferred to a glass distillation vessel containing 100 ppm BHT. The system is deoxygenated (nitrogen purging to ensure the oxygen content in the column is below 10 ppm), and distillation is started under slightly positive pressure. During distillation, the column top temperature is maintained at 20 °C (operating pressure 0.06 MPa), and a reflux ratio of 5:1 is maintained to collect the main fraction. Simultaneously, the column bottom temperature must be strictly controlled to not exceed 40 °C, and the column liquid must be protected from light to inhibit thermal decomposition and polymerization side reactions. When the column bottom temperature rises sharply, heating is stopped to terminate distillation. A final purified product of 1.209 kg is collected, with a distillation yield of 98.3% and a GC purity ≥99.99%.

[0043] The refined 1,1-difluoro-2-iodide product should be stored in a cool, dark, and sealed environment.

[0044] Example 4 A high-purity 1,1-difluoro-2-iodoethylene is prepared by the following steps: S1. In a 5L 316L reactor with a water content <50 ppm and equipped with -15 ℃ cooling water, first add 500 mL of dichloromethane and 1491.3 g of iodine monochloride. Close the reactor, first evacuate the air from the system, then purge with nitrogen for replacement, and repeat this process until the oxygen content in the reactor is ≤50 ppm. Then start stirring (300 rpm) and heat the system to 25 ℃. Subsequently, introduce VDF at a flow rate of 300 g / min, stop the aeration after 2 min, and continue the reaction at this temperature for 2 hours. After the reaction is complete, first vent the gas from the system, then add 1 L of a 10% (w / w) mixed aqueous solution of sodium bicarbonate and sodium sulfite (mass ratio of sodium bicarbonate to sodium sulfite is 1:1) to the system for quenching for 60 min. After standing, the organic phase was collected by separation and the solvent was removed by rotary evaporation at 50 °C on a 5 L rotary evaporator to obtain 2002.2 g of intermediate product 1-chloro-1,1-difluoro-2-iodoethane, with a gas chromatography (GC) purity of 99.99% and a reaction yield of 96.3%.

[0045] S2. Add 1.60 kg of the intermediate product 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 to a 5 L reactor connected to a gas outlet pipe. Heat the reactor to 70 °C, and add a 10% (w / w) NaOH aqueous solution through a liquid feeder at a rate of 300 mL / min. This rate effectively avoids temperature runaway due to violent exothermic reactions during the feeding process. Complete the feeding of all the alkali solution within 10 minutes. Simultaneously, collect the gaseous product exiting the gas outlet pipe using a condenser during the feeding process. After the alkali solution feeding is complete, continue the reaction at the specified temperature for 2 hours, terminating the reaction when no liquid distills from the condenser. Finally, collect 1.09 kg of crude 1,1-difluoro-2-iodoethane at the condenser end. The yield of this step is 81.2%, and the GC purity of the crude product is 98.2%.

[0046] S3. The crude product obtained in step S2, weighing 1.09 kg, is first washed with a 15 wt.% sodium bicarbonate solution to remove impurities, and then dried using a molecular sieve. The dried material is then transferred to a glass distillation vessel containing 100 ppm BHT. The system is deoxygenated (nitrogen purging to ensure the oxygen content in the column is below 10 ppm), and distillation is started under slightly positive pressure. During distillation, the column top temperature is maintained at 20 ℃ (operating pressure 0.06 MPa), and a reflux ratio of 5:1 is maintained to collect the main fraction. Simultaneously, the column bottom temperature must be strictly controlled to not exceed 40 ℃, and the column liquid must be protected from light to inhibit thermal decomposition and polymerization side reactions. When the column bottom temperature rises sharply, heating is stopped to terminate distillation. A final purified product of 1.071 kg is collected, with a distillation yield of 98.3% and a GC purity ≥99.99%.

[0047] The refined 1,1-difluoro-2-iodide product should be stored in a cool, dark, and sealed environment.

[0048] Comparative Example 1 A method for preparing 1,1-difluoro-2-iodoethylene is basically the same as in Example 1, except that in step S1, dichloromethane is not added, and instead 1490.5 g of iodine chloride is directly added to a reactor of the same specifications. The reactor is closed, the air in the system is first evacuated, then nitrogen is introduced for replacement, and then evacuation is repeated until the oxygen content in the reactor is ≤50 ppm. Then, stirring is started (300 rpm) and the system is heated to 25 °C. VDF is then introduced at a flow rate of 200 g / min. After the aeration begins, the system temperature rapidly rises uncontrollably to 80 °C, forcing a reduction in the VDF flow rate to 20 g / min. After the temperature returns to normal, aeration is continued until a sufficient amount (600 g) is reached and then stopped. After quenching and solvent separation, 1873.8 g of the intermediate product 1-chloro-1,1-difluoro-2-iodoethylene is obtained, with a GC purity of 98.21% and a reaction yield of 90.1%.

[0049] Compared to Example 1 of this invention, this comparative example did not include dichloromethane. Due to the lack of dichloromethane, heat could not be rapidly dispersed during the reaction, leading to a sudden rise in local temperature and subsequently causing the entire reaction system to experience a runaway temperature increase to 80°C. To alleviate this temperature runaway problem, the feed rate of VDF (vinylidene fluoride) needed to be reduced. This not only weakened the temperature control effect of the system and reduced operational safety but also significantly prolonged the reaction time.

[0050] Comparative Example 2 A 1,1-difluoro-2-iodoethylene was prepared according to Example 1 of CN118108569A. 10 kg of distilled 1-chloro-1,1-difluoro-2-iodoethane was added to a 20 L distillation reactor equipped with a distillation apparatus. 50 g of tetrabutylammonium bromide and 5 g of copper powder were also added. The mixture was heated to 60 °C, and 12.39 kg of 20% NaOH solution was added to the reactor at a rate of 100 mL / min. After reacting for 30 min, 7446 g of 1,1-difluoro-2-iodoethylene was collected by reactive distillation. GC analysis showed its content to be 99.8%, and the reaction yield was 85.3%.

[0051] Compared to Example 1 of this invention, this comparative example requires the addition of two auxiliary agents: tetrabutylammonium bromide and copper powder, which increases both raw material costs and post-processing complexity. Furthermore, the product yield of this comparative example is lower than that of Example 1 of this invention, further impacting overall economic efficiency and production efficiency.

[0052] Comparative Example 3 A method for preparing 1,1-difluoro-2-iodine is basically the same as that in Example 1, except that in step S3, 1.28 kg of the crude product obtained in step S2 is first washed with a 15 wt.% sodium bicarbonate solution to remove impurities, and then dried using a molecular sieve. The dried material is then transferred to a glass distillation vessel, and the system is deoxygenated (nitrogen purging to ensure that the oxygen content in the column is below 10 ppm) before distillation is started under slightly positive pressure. During the distillation process, the top temperature of the column is controlled to be stable at 20°C (operating pressure 0.06 MPa). First, a low reflux ratio of 2:1 is used for pre-cutting to collect and separate low-boiling-point impurities. After the top temperature and pressure of the column stabilize, the reflux ratio is adjusted to 5:1, and the high-purity 1,1-difluoro-2-iodine main fraction is collected.

[0053] Throughout the distillation process, the reboiler temperature must be strictly controlled below 50 °C, and the reboiler liquid must be protected from light to inhibit thermal decomposition and polymerization side reactions. When the reboiler temperature rises sharply, heating is stopped and distillation is terminated. A final purified product of 1.216 kg was collected, with a distillation yield of 95.0% and a GC purity of 94.2%.

[0054] Compared with Example 1 of the present invention, this comparative example did not add BHT as a stabilizer, so some of the distillation products reacted with oxidizing substances, reducing the total purity of the product.

[0055] Comparative Example 4 A 1,1-difluoro-2-iodide was prepared in a manner that was basically the same as in Example 1, except that in step S2, the mass fraction of the added NaOH aqueous solution was 40%; and finally, 0.58 kg of crude 1,1-difluoro-2-iodide was collected at the condenser end. The yield of this step was 45.0%, and the GC purity of the crude product was 84.8%.

[0056] Compared with Example 1 of the present invention, the comparative example used a high-concentration alkaline aqueous solution, which significantly aggravated the substitution side reaction of the iodine group, generating a large number of by-products and resulting in a significant decrease in the purity of the crude product; at the same time, the occurrence of the side reaction consumed a large number of intermediates, ultimately resulting in a significant decrease in yield.

[0057] Comparative Example 5 A method for preparing 1,1-difluoro-2-iodide is basically the same as that in Example 1, except that in step S2, the elimination reaction temperature is 30 °C, i.e., the temperature of the reaction vessel is raised to 30 °C. Finally, 0.12 kg of crude 1,1-difluoro-2-iodide was collected at the condenser end, with a yield of 9.3% and a GC purity of 60.1%.

[0058] Compared with Example 1 of the present invention, the reaction temperature of this comparative example is lower than the boiling point of the target product, which causes the generated 1,1-difluoro-2-iodoethylene to be unable to volatilize and separate from the system in time. A large amount of product remains in the reaction system and undergoes secondary side reactions (such as polymerization, deep substitution, etc.), which not only causes a sharp drop in yield, but also leads to a significant deterioration in the purity of crude product due to the accumulation of by-products.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity 1,1-difluoro-2-iodoethylene, characterized in that, Includes the following steps: S1. Addition reaction: In the presence of a nonprotic organic solvent, vinylidene fluoride is introduced into a reaction system containing iodine monochloride to carry out the reaction. After the reaction is completed, the intermediate product 1-chloro-1,1-difluoro-2-iodoethane is obtained by quenching and solvent separation. S2, Elimination reaction: The 1-chloro-1,1-difluoro-2-iodoethane obtained in step S1 is mixed with an alkaline aqueous solution and subjected to a dehydrohalogenation elimination reaction under heating conditions. The gaseous product generated by the reaction is extracted and condensed to obtain crude 1,1-difluoro-2-iodoethylene. S3. Refining and purification: The crude 1,1-difluoro-2-iodide obtained in step S2 is subjected to alkali washing, drying and distillation in sequence to obtain high-purity 1,1-difluoro-2-iodide product.

2. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S1, the aprotic organic solvent is selected from one or more of dichloromethane, 1,1,2,2-tetrachloroethane, and cyclopentyl methyl ether; the volume ratio of the aprotic organic solvent to iodine monochloride is 1:0.5 to 1:

3.

3. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S1, the equivalence ratio of iodine monochloride to vinylidene fluoride is 1:1 to 1:2; the reaction conditions are: reaction temperature 20 to 30 °C, reaction time 2 to 4 h.

4. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S1, the quenching is achieved by adding a mixed solution containing a weak alkali and a weak reducing agent; the solvent separation temperature is 50~100 ℃.

5. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 4, characterized in that, In the mixed solution containing a weak base and a weak reducing agent, the total mass fraction of the weak base and the weak reducing agent is 5-15%; the solvent of the mixed solution is selected from water or diethyl ether. The weak base is selected from one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. The weak reducing agent is selected from one or more of sodium sulfite, sodium dithionite, sodium bisulfite, and sodium thiosulfate.

6. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S2, the alkaline aqueous solution is one or both of sodium hydroxide solution and potassium hydroxide solution; the concentration of the alkaline aqueous solution is 5~15 wt.%; and the molar ratio of 1-chloro-1,1-difluoro-2-iodoethane to the alkali is 1:1~1:

3.

7. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S2, the elimination reaction is carried out at a temperature of 50~100 ℃.

8. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 1, characterized in that, In step S3, the alkaline washing involves using a weak alkaline solution to remove acidic impurities from the crude product; the drying process uses anhydrous calcium carbonate or molecular sieves; and the distillation conditions are: distillation column bottom temperature 20~100 ℃, distillation pressure 0~0.1 MPa, and polymerization inhibitors are added during the distillation process.

9. The method for preparing high-purity 1,1-difluoro-2-iodide according to claim 8, characterized in that, The weak alkaline solution is selected from one or two of sodium bicarbonate solution and sodium carbonate solution; the mass fraction of the weak alkaline solution is 15-20%.

10. The method for preparing high-purity 1,1-difluoro-2-iodide according to any one of claims 1 to 9, characterized in that, The intermediate product 1-chloro-1,1-difluoro-2-iodoethane had a GC purity of ≥99% and a separation yield of ≥95%; the target product 1,1-difluoro-2-iodoethylene had a GC purity of ≥99.99% and an overall yield of ≥80%.

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