A method for preparing trifluoroacetic acid by electrolytic fluorination using acetyl chloride as raw material

Abstract

The application discloses a method for preparing trifluoroacetic acid by electrolytic fluorination with acetyl chloride as raw material. The method uses anhydrous acetyl chloride as raw material, anhydrous hydrogen fluoride as fluorine source, and anhydrous potassium fluoride and metal chloride as co-electrolyte. The electrolysis is carried out in a nickel electrode electrolytic cell at a constant voltage of 0-10V and 5-7V. The gaseous fluorine-containing intermediate generated in the electrolysis is subjected to condensation and impurity removal, then is introduced into an alkali solution for absorption, and then is subjected to alkaline hydrolysis and fluorine removal by adding hydroxide of an alkali metal and oxide / hydroxide of an alkaline earth metal in sequence. After filtration, the refined potassium trifluoroacetate is obtained through vacuum rotary evaporation, hot ethanol extraction and drying. The high-purity trifluoroacetic acid is obtained through acidification by concentrated sulfuric acid and distillation. The method is mild and safe, has good electrode stability and high selectivity, does not need complex chromatographic separation, can obtain trifluoroacetic acid with a purity of greater than or equal to 99%, has a simple process flow and low cost, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the fields of organofluorine chemistry and electrochemical synthesis technology, specifically to a method for preparing high-purity trifluoroacetic acid by electrolytic fluorination under mild conditions using acetyl chloride as a raw material. Background Technology

[0002] Trifluoroacetic acid (TFA) is a colorless, pungent liquid that is hygroscopic, volatile, and fuming. It is a perfluorinated derivative of acetic acid and is used in fluorinated pharmaceuticals, pesticides, and dyes. Its potassium salt (potassium trifluoroacetate) is also a key fluorinated synthon. In synthetic chemistry, besides being a basic raw material for introducing trifluoromethyl structures, trifluoroacetic acid is also used as a catalyst and solvent. Due to its low nucleophilicity and the chemical inertness of the trifluoromethyl group, trifluoroacetic acid is an excellent solvent for fluorination, nitration, and halogenation reactions, and is used in fundamental research on solvents. Using trifluoroacetic acid as a catalyst is beneficial for many reactions, such as the alkylation and acylation of aromatic compounds, the polymerization and telomerization of olefins, and the Beckmann rearrangement from oxime to amide.

[0003] Currently, the main industrial methods for preparing trifluoroacetic acid include: direct fluorination of trichloroacetic acid, oxidation of 1,1,1-trifluoro-2,3-epoxypropane, and oxidation of tetrafluoroethylene. These methods generally suffer from problems such as harsh conditions (high temperature and high pressure), the need for highly toxic fluorine gas or expensive fluorinating reagents, severe equipment corrosion, difficulty in product separation, or low overall yield.

[0004] Electrochemical fluorination (ECF) is an environmentally friendly and mild fluorination technology that utilizes electrons as a clean "reagent" to introduce fluoride ions into organic molecules under an electric field. This ensures the stable conversion of intermediates into fluorinated products and greatly expands the tolerance of functional groups and chemoselectivity. Internationally, electrochemical fluorination technology is relatively mature. For example, US Patent 02717871 discloses a method for producing trifluoroacetic acid and its derivatives by electrolytic fluorination of acetic acid or acetic anhydride in anhydrous hydrogen fluoride. This route utilizes electrochemical means to avoid the use of hazardous reagents such as fluorine gas in traditional chemical fluorination, providing a relatively safe alternative. However, existing electrofluorination techniques for preparing trifluoroacetic acid or its derivatives often suffer from drawbacks such as low current efficiency, poor selectivity, numerous side reactions, easy electrode poisoning and deactivation, and cumbersome subsequent purification steps leading to low product purity.

[0005] Therefore, developing an electrochemical synthesis method that features mild reaction conditions, readily available raw materials, high selectivity, simple operation, and the ability to directly obtain high-purity trifluoroacetic acid has significant industrial application value.

[0006] Currently, Chinese patent CN119080604A discloses a method for preparing trifluoroacetic acid. This method uses 2-chloro-1,1,1-trifluoroethane, a Freon waste gas, as a raw material. Under visible light irradiation, sodium hypochlorite pentahydrate and sulfuric acid solution are used to oxidize 2-chloro-1,1,1-trifluoroethane. The hypochlorite reacts rapidly with the acid solution to generate the corresponding metal salt and hypochlorous acid, releasing heat. Hypochlorous acid is unstable and undergoes a disproportionation reaction to generate hydrogen chloride and chloric acid. Chloric acid can then decompose to generate chlorine, perchloric acid, oxygen, and water. Chlorine is converted into chlorine free radicals under light irradiation. These chlorine free radicals react with 2-chloro-1,1,1-trifluoroethane through a free radical chlorination process to generate trifluorotrichloroethane. Trifluorotrichloroethane is then oxidized by an in-situ generated oxidant to produce trifluoroacetic acid, where the oxide may be oxygen, chlorine, hypochlorous acid, chloric acid, or perchloric acid. However, this method relies on visible light initiation, and the reaction conditions are greatly affected by light intensity. Although the free radicals are highly reactive, they have poor selectivity, are difficult to control, and are prone to chain termination or side reactions. The reaction process involves hazardous intermediates such as chlorine free radicals and chlorine gas, requiring high equipment safety standards. Furthermore, the separation steps between the product and by-product salts can be complex, with high energy consumption and limited product purity. Chinese patent CN111763146A discloses a method for preparing trifluoroacetic acid by hydrolysis of trifluoroacetyl chloride. This method uses trifluoroacetyl chloride as a raw material and directly obtains trifluoroacetic acid through efficient hydrolysis and membrane separation purification steps. This technology optimizes the hydrolysis and post-processing, providing a feasible solution for the preparation of trifluoroacetic acid. However, the core raw material of this method, trifluoroacetyl chloride, is itself a high-value-added fluorinated fine chemical. Its industrial production usually requires tetrachloroethylene as a raw material and involves complex processes such as multi-step fluorination and disproportionation. The economics and efficiency of the entire industrial chain are highly dependent on the synthesis cost and supply of trifluoroacetyl chloride.

[0007] Research on the electro-fluorination synthesis of trifluoroacetic acid is still in its early stages both domestically and internationally. Existing literature describes complex synthesis processes for trifluoroacetic acid and its derivatives, typically using acetyl fluoride, acetyl chloride, acetic anhydride, and acetic acid as starting materials. Because trifluoroacetyl fluoride often undergoes co-hydrolysis with a small amount of anhydrous hydrogen fluoride during the absorption process, potassium fluoride impurities are introduced into the potassium trifluoroacetate formed during the alkaline hydrolysis reaction. These impurities are difficult to remove using conventional separation methods, leading to two major hazards in the acidification process: firstly, the release of corrosive and toxic hydrogen fluoride gas during acidification, damaging reaction equipment; and secondly, an increase in the fluoride ion concentration in the product trifluoroacetic acid, negatively impacting product quality. Current domestic electrolytic fluorination processes largely rely on or borrow from European, American, and Japanese companies (such as Simons' electrolytic fluorination technology), with limited domestically developed low-energy electrolysis devices and highly selective catalysts. Existing processes using only single impurity removal methods are insufficient to completely remove fluorine impurities, failing to simultaneously achieve both impurity removal efficiency and product purity. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for synthesizing trifluoroacetic acid from acetyl chloride via electrolytic fluorination. This method is simple, operates under mild conditions, has a high yield, and is environmentally friendly, making it more suitable for industrial production.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing trifluoroacetic acid from acetyl chloride via electrolytic fluorination includes the following steps:

[0011] (1) Electrolytic fluorination: In a closed electrolytic reactor, anhydrous acetyl chloride, anhydrous potassium fluoride and anhydrous chloride are mixed evenly, and liquid anhydrous hydrogen fluoride is introduced. Constant voltage electrolysis is performed with nickel sheet as cathode and anode. The gaseous mixture containing trifluoroacetyl fluoride generated during the electrolysis process is discharged from the reactor.

[0012] (2) Absorption and alkaline conversion: After the gaseous mixture derived in step (1) is condensed and separated to remove the entrained hydrogen fluoride, it is passed into an alkaline solution for complete absorption to obtain trifluoroacetyl fluoride absorption solution; alkali metal hydroxides are first added to the obtained trifluoroacetyl fluoride absorption solution to adjust the pH value to strong alkalinity so that the trifluoroacetyl fluoride is completely alkalinely decomposed, and then alkaline earth metal oxides or hydroxides are added to make the residual fluoride ions in the system generate fluoride precipitates. After filtration, the filtrate is collected to obtain the first filtrate.

[0013] This step employs a two-stage defluorination process: low-temperature condensation and alkaline earth metal precipitation. Low-temperature condensation removes most of the hydrogen fluoride entrained in the gaseous products, reducing the formation of soluble potassium fluoride at the source. Alkaline earth metal precipitation further removes trace amounts of residual fluoride ions from the system. Through the synergistic effect of these two stages, efficient removal of fluorine impurities is achieved.

[0014] (3) Refining and purification: The first filtrate obtained in step (2) is mixed with an alcohol solvent, and the solvent is removed by rotary evaporation under reduced pressure to obtain crude potassium trifluoroacetate; the crude potassium trifluoroacetate is subjected to thermal extraction with an alcohol solvent; after the thermal extraction is completed, it is filtered while hot and the filtrate is collected to obtain the second filtrate; the solvent is removed by rotary evaporation under reduced pressure and the filtrate is dried under vacuum to obtain refined potassium trifluoroacetate;

[0015] (4) Acidification distillation: The refined potassium trifluoroacetate obtained in step (3) is acidified with an inorganic strong acid under ice-water bath and stirring conditions; the acidified mixture is distilled under normal pressure, and the fraction with a boiling range of 70~75℃ is collected to obtain high-purity trifluoroacetic acid.

[0016] In step (1), the molar ratio of anhydrous acetyl chloride, anhydrous potassium fluoride, anhydrous chloride and liquid anhydrous hydrogen fluoride is 1:1.2~4.0:0.8~1.2:70~75; the anhydrous chloride is anhydrous nickel dichloride or anhydrous cobalt dichloride.

[0017] In step (1), the electrolysis temperature is 0~10℃; the electrolysis voltage is 5~7V.

[0018] In step (2), the temperature of the condensation separation is -10~-5℃.

[0019] In step (2), the alkaline solution is a 20wt% aqueous solution of potassium hydroxide; the alkali metal is potassium or sodium; and the alkaline earth metal is calcium or magnesium.

[0020] In step (3), the alcohol solvent is anhydrous ethanol or anhydrous methanol; the temperature of the hot extraction is 50~60℃, the solid-liquid ratio is controlled at 1g:4mL~1g:6mL during the hot extraction, and the hot extraction is performed 1~3 times, each time for 30 minutes.

[0021] In step (4), the amount of inorganic strong acid added is based on adjusting the pH value of the system to 2.0±0.2.

[0022] In step (4), the inorganic strong acid is concentrated sulfuric acid of 95wt%~98wt%.

[0023] The above method is applied in the preparation of trifluoroacetic acid.

[0024] In this invention, the theoretical charge is calculated based on the complete fluorination of the acetyl groups in the substrate, requiring 6 faradaic charges per mole of acetyl group. For example, acetyl chloride (containing 1 acetyl group) requires 6 F per mole, and acetic anhydride (containing 2 acetyl groups) requires 12 F per mole.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) Low raw material cost and high selectivity: Acetyl chloride, which is cheap and readily available, is used as raw material. Its acyl chloride group has high reactivity and a clear pathway. In the system of this invention, it exhibits the highest fluorination selectivity and yield compared with other carboxylic acid substrates such as acetic acid and acetic anhydride.

[0027] (2) Mild and efficient reaction conditions: By constructing a transition metal chloride composite electrolyte system, the problem of poor electrolyte conductivity under low voltage is solved, and efficient and stable electrolysis is achieved at 6V voltage and low temperature and normal pressure, with low energy consumption and small electrode loss.

[0028] (3) The purification process is simple and efficient: The innovative "hot ethanol extraction" step utilizes the significant difference in solubility between potassium trifluoroacetate and inorganic salts in ethanol to achieve efficient purification of intermediates, laying the foundation for obtaining high-purity final products.

[0029] (4) Further catalytic enhancement: Introducing nickel dichloride or cobalt dichloride as a coelectrolyte can further reduce the reaction activation energy, increase the current density and final yield, and provide a clear direction for process optimization. Attached Figure Description

[0030] Figure 1 This is a simplified reaction flow diagram of the present invention.

[0031] Figure 2 This is a synthetic route diagram of the present invention.

[0032] Figure 3 This is the specific reaction formula of the present invention.

[0033] Figure 4 For example, trifluoroacetic acid in Example 5 19 F NMR spectrum (DMSO-d6, 565MHz). Detailed Implementation

[0034] In the following description, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Those skilled in the art should understand that the following embodiments are merely illustrative of the invention and should not be considered as specific limitations thereof. When terms used in the embodiments described below are specifically defined in this specification, those definitions shall be followed; and if no specific definition is provided, they shall be interpreted in the sense commonly understood by those skilled in the art.

[0035] The present invention will be further described below through specific embodiments.

[0036] The preparation method of trifluoroacetic acid of this invention, the reaction process of which is described in [reference needed]. Figure 1 Using acetyl chloride as raw material, gaseous trifluoroacetyl fluoride is generated through electrolytic fluorination. Then, crude potassium trifluoroacetate is obtained through alkaline absorption and alkaline hydrolysis. After refining and purification, refined potassium trifluoroacetate is obtained. Finally, high-purity trifluoroacetic acid is obtained through acidification and atmospheric distillation.

[0037] Figure 2 A schematic diagram of the synthetic route for producing trifluoroacetic acid according to the present invention is provided. It mainly includes a core electrolysis reaction unit, an absorption and conversion unit, a potassium trifluoroacetate purification unit, and an acidification distillation unit, which are fully corresponding to... Figure 1 The synthetic route.

[0038] The specific steps are as follows:

[0039] (1) Electrolytic fluorination reaction: In a closed reactor, anhydrous acetyl chloride, anhydrous potassium fluoride and supporting electrolyte (such as anhydrous nickel dichloride or anhydrous cobalt dichloride) are mixed evenly, and liquid anhydrous hydrogen fluoride is introduced. High-purity nickel sheets are used as the electrolytic cathode and anode respectively. Under continuous stirring, the temperature of the reaction system is controlled to be constant at 5°C. Constant voltage electrolysis mode is adopted, and the electrolysis voltage is set to 6V.

[0040] (2) Absorption and alkaline hydrolysis conversion: The gaseous mixture containing trifluoroacetyl fluoride generated by electrolysis in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride. It is then fully absorbed by a 20% potassium hydroxide aqueous solution to obtain a trifluoroacetyl fluoride absorbent. Potassium hydroxide is added to the trifluoroacetyl fluoride absorbent until the pH value is 11~12. Then calcium oxide is added to cause the residual fluoride ions in the system to form calcium fluoride precipitate. After the reaction is complete, the solid and liquid are separated to obtain the first filtrate.

[0041] (3) Purification of potassium trifluoroacetate: The first filtrate obtained in step (2) is mixed with anhydrous ethanol and the solvent is removed by rotary evaporation under reduced pressure to obtain crude potassium trifluoroacetate; the crude potassium trifluoroacetate is subjected to hot anhydrous ethanol at 50~60℃ for 1~3 hot extractions, and after solid-liquid separation, the second filtrate is obtained; the solvent is removed by rotary evaporation under reduced pressure and the filtrate is dried under vacuum to obtain purified potassium trifluoroacetate;

[0042] (4) Acidification distillation: The refined potassium trifluoroacetate obtained in step (3) is acidified with concentrated sulfuric acid, and then distilled at atmospheric pressure. The fraction at 70~75℃ is accurately collected to obtain high-purity trifluoroacetic acid.

[0043] Example 1:

[0044] A method for preparing trifluoroacetic acid from acetyl chloride via electrolytic fluorination includes the following steps:

[0045] (1) Electrolytic fluorination reaction

[0046] In a 50 mL closed electrolytic reactor resistant to fluorine corrosion (PEEK material), 3 mL of anhydrous acetyl chloride and 3 g of anhydrous potassium fluoride were mixed thoroughly, and then 20 mL of liquid anhydrous hydrogen fluoride was introduced. High-purity nickel sheets measuring 1 cm × 2 cm were used as the cathode and anode, respectively, with an electrode spacing of 1.5 cm. Under continuous stirring (600 rpm), the reaction system temperature was kept constant at 5 °C, and a constant voltage electrolysis mode was adopted, with the electrolysis voltage set to 6 V (at which point the initial current density was 5 mA / cm²). 2 The electrolysis reaction is initiated, and the cumulative charge is monitored in real time. Electrolysis is terminated when the cumulative charge reaches 10.8 kC (approximately 0.44 times the theoretical charge). A gaseous mixture containing trifluoroacetyl fluoride is generated during electrolysis and discharged from the reactor.

[0047] (2) Absorption and alkaline hydrolysis transformation

[0048] The gaseous mixture extracted in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride, and then passed into 20mL of 20wt% potassium hydroxide aqueous solution for complete absorption, yielding a trifluoroacetyl fluoride absorbent. Potassium hydroxide is first added to the obtained trifluoroacetyl fluoride absorbent to adjust the pH to 11~12 to ensure complete alkaline hydrolysis of the trifluoroacetyl fluoride; then 2g of calcium oxide is added, and the mixture is stirred at room temperature for 30 minutes to allow residual fluoride ions in the system to precipitate as calcium fluoride. The mixture is then filtered, and the filtrate is collected to obtain the first filtrate.

[0049] (3) Refining and purification

[0050] The first filtrate obtained in step (2) was mixed with anhydrous ethanol at a volume ratio of 1:2. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 80-90°C to obtain crude potassium trifluoroacetate. Anhydrous ethanol preheated to 50-60°C was added to the obtained crude potassium trifluoroacetate, and the solid-liquid ratio (g:mL) was controlled at 1:6. A single hot extraction was performed by stirring continuously at 50-60°C for 30 minutes. After the hot extraction, the mixture was filtered while hot, and the filtrate was collected to obtain the second filtrate. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 70-80°C. The obtained solid was dried under vacuum at 50-60°C for 12 hours to obtain purified potassium trifluoroacetate (2.086g).

[0051] (4) Acidification distillation

[0052] The purified potassium trifluoroacetate obtained in step (3) was placed in a flask and acidified by slowly adding concentrated sulfuric acid (95wt%~98wt%) dropwise while cooling in an ice-water bath at 0~4℃ and stirring. The pH value of the system was monitored simultaneously, and the addition was stopped when the pH value stabilized at 2.0±0.2. The reaction equation is: 2CF3COOK+H2SO4→2CF3COOH+K2SO4. The acidified mixture was then distilled at atmospheric pressure, and the fraction distilled at 71~75℃ was accurately collected to obtain high-purity trifluoroacetic acid (1.50g, with a total yield of 31.2% based on anhydrous acetyl chloride). The purity of the product was determined by... 19 The purity of trifluoroacetic acid was determined by the F NMR peak area normalization method. 20 mg of the sample was dissolved in 0.5 mL of deuterated dimethyl sulfoxide (DMSO-d6), and the concentration was measured using a Bruker AVANCE NEO 600 NMR spectrometer. 19 F NMR spectrum, relaxation delay time 10 s, 64 scans. Only the characteristic fluorine peak of trifluoroacetic acid (δ-76.5 ppm) was observed in the spectrum, and no other fluorine signals were detected. Three parallel determinations were performed, and the average value was taken. The results showed that the purity of the obtained trifluoroacetic acid was 99.5% (relative standard deviation <0.5%).

[0053] Example 2:

[0054] A method for preparing trifluoroacetic acid from acetic anhydride via electrolytic fluorination includes the following steps:

[0055] (1) Electrolytic fluorination reaction

[0056] In a 50 mL closed electrolytic reactor resistant to fluorine corrosion (PEEK material), 3 mL of anhydrous acetic anhydride and 3 g of anhydrous potassium fluoride were mixed thoroughly, and then 20 mL of liquid anhydrous hydrogen fluoride was introduced. High-purity nickel sheets measuring 1 cm × 2 cm were used as the cathode and anode, respectively, with an electrode spacing of 1.5 cm. Under continuous stirring (600 rpm), the reaction system temperature was kept constant at 5 °C, and a constant voltage electrolysis mode was adopted, with the electrolysis voltage set to 6 V (at which point the initial current density was 5 mA / cm²). 2 The electrolysis reaction is initiated, and the cumulative charge is monitored in real time. Electrolysis is terminated when the cumulative charge reaches 12.8 kC (approximately 0.35 times the theoretical charge). A gaseous mixture containing trifluoroacetyl fluoride is generated during electrolysis and discharged from the reactor.

[0057] (2) Absorption and alkaline hydrolysis transformation

[0058] The gaseous mixture extracted in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride, and then passed into 20mL of 20wt% potassium hydroxide aqueous solution for complete absorption, yielding a trifluoroacetyl fluoride absorbent. Potassium hydroxide is first added to the obtained trifluoroacetyl fluoride absorbent to adjust the pH to 11~12 to ensure complete alkaline hydrolysis of the trifluoroacetyl fluoride; then 2g of calcium oxide is added, and the mixture is stirred at room temperature for 30 minutes to allow residual fluoride ions in the system to precipitate as calcium fluoride. The mixture is then filtered, and the filtrate is collected to obtain the first filtrate.

[0059] (3) Refining and purification

[0060] The first filtrate obtained in step (2) was mixed with anhydrous ethanol at a volume ratio of 1:2. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 80-90°C to obtain crude potassium trifluoroacetate. Anhydrous ethanol preheated to 50-60°C was added to the obtained crude potassium trifluoroacetate, and the solid-liquid ratio (g:mL) was controlled at 1:6. A single hot extraction was performed by stirring continuously at 50-60°C for 30 minutes. After the hot extraction, the mixture was filtered while hot, and the filtrate was collected to obtain the second filtrate. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 70-80°C. The obtained solid was dried under vacuum at 50-60°C for 12 hours to obtain purified potassium trifluoroacetate (1.03g).

[0061] (4) Acidification distillation

[0062] The purified potassium trifluoroacetate obtained in step (3) was placed in a flask and acidified by slowly adding concentrated sulfuric acid (95wt%~98wt%) dropwise while cooling in an ice-water bath at 0~4℃ and stirring. The pH value of the system was monitored simultaneously, and the addition was stopped when the pH value stabilized at 2.0±0.2. The reaction equation is: 2CF3COOK+H2SO4→2CF3COOH+K2SO4. The acidified mixture was then distilled at atmospheric pressure, and the fraction distilled at 71~75℃ was accurately collected to obtain high-purity trifluoroacetic acid (0.77g, with a total yield of 10.6% based on anhydrous acetic anhydride). The purity of the product was determined by... 19 The purity of trifluoroacetic acid was determined by the F NMR peak area normalization method. 20 mg of the sample was dissolved in 0.5 mL of deuterated dimethyl sulfoxide (DMSO-d6), and the concentration was measured using a Bruker AVANCE NEO 600 NMR spectrometer. 19 F NMR spectrum, relaxation delay time 10 s, 64 scans. Only the characteristic fluorine peak of trifluoroacetic acid (δ-76.5 ppm) was observed in the spectrum, and no other fluorine signals were detected. Three parallel determinations were performed, and the average value was taken. The results showed that the purity of the obtained trifluoroacetic acid was 99.5% (relative standard deviation <0.5%).

[0063] Example 3:

[0064] A method for preparing trifluoroacetic acid from acetic acid via electrolytic fluorination includes the following steps:

[0065] (1) Electrolytic fluorination reaction

[0066] In a 50mL closed electrolytic reactor resistant to fluorine corrosion (PEEK material), 1mL of anhydrous acetic acid and 3g of anhydrous potassium fluoride were mixed thoroughly, and then 20mL of liquid anhydrous hydrogen fluoride was introduced. High-purity nickel sheets measuring 1cm × 2cm were used as the cathode and anode, respectively, with an electrode spacing of 1.5cm. Under continuous stirring (600rpm), the reaction system temperature was kept constant at 5℃, and a constant voltage electrolysis mode was adopted, with the electrolysis voltage set to 6V (at which point the initial current density was 1mA / cm). 2 The electrolysis reaction is initiated, and the cumulative charge is monitored in real time. Electrolysis is terminated when the cumulative charge reaches 1.92 kC (approximately 0.19 times the theoretical charge). A gaseous mixture containing trifluoroacetyl fluoride is generated during electrolysis and discharged from the reactor.

[0067] (2) Absorption and alkaline hydrolysis transformation

[0068] The gaseous mixture extracted in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride, and then passed into 20mL of 20wt% potassium hydroxide aqueous solution for complete absorption, yielding a trifluoroacetyl fluoride absorbent. Potassium hydroxide is first added to the obtained trifluoroacetyl fluoride absorbent to adjust the pH to 11~12 to ensure complete alkaline hydrolysis of the trifluoroacetyl fluoride; then 2g of calcium oxide is added, and the mixture is stirred at room temperature for 30 minutes to allow residual fluoride ions in the system to precipitate as calcium fluoride. The mixture is then filtered, and the filtrate is collected to obtain the first filtrate.

[0069] (3) Refining and purification

[0070] The first filtrate obtained in step (2) was mixed with anhydrous ethanol at a volume ratio of 1:2. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 80-90°C to obtain crude potassium trifluoroacetate. Anhydrous ethanol preheated to 50-60°C was added to the obtained crude potassium trifluoroacetate, and the solid-liquid ratio (g:mL) was controlled at 1:6. A single hot extraction was performed by stirring continuously at 50-60°C for 30 minutes. After the hot extraction, the mixture was filtered while hot, and the filtrate was collected to obtain the second filtrate. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 70-80°C. The obtained solid was dried under vacuum at 50-60°C for 12 hours to obtain purified potassium trifluoroacetate (0.33g).

[0071] (4) Acidification distillation

[0072] The purified potassium trifluoroacetate obtained in step (3) was placed in a flask and acidified by slowly adding concentrated sulfuric acid (95wt%~98wt%) dropwise while cooling in an ice-water bath at 0~4℃ and stirring. The pH value of the system was monitored simultaneously, and the addition was stopped when the pH value stabilized at 2.0±0.2. The reaction equation is: 2CF3COOK+H2SO4→2CF3COOH+K2SO4. The acidified mixture was then distilled at atmospheric pressure, and the fraction distilled at 71~75℃ was accurately collected to obtain high-purity trifluoroacetic acid (0.19g, with a total yield of 9.54% based on anhydrous acetic acid). The purity of the product was determined by... 19 The purity of trifluoroacetic acid was determined by the F NMR peak area normalization method. 20 mg of the sample was dissolved in 0.5 mL of deuterated dimethyl sulfoxide (DMSO-d6), and the concentration was measured using a Bruker AVANCE NEO 600 NMR spectrometer. 19 F NMR spectrum, relaxation delay time 10 s, 64 scans. Only the characteristic fluorine peak of trifluoroacetic acid (δ-76.5 ppm) was observed in the spectrum, and no other fluorine signals were detected. Three parallel determinations were performed, and the average value was taken. The results showed that the purity of the obtained trifluoroacetic acid was 99.5% (relative standard deviation <0.5%).

[0073] Example 4:

[0074] A method for preparing trifluoroacetic acid from acetyl chloride via electrolytic fluorination includes the following steps:

[0075] (1) Electrolytic fluorination reaction

[0076] In a 50 mL closed PEEK-resistant electrolytic reactor, 1 mL of anhydrous acetyl chloride, 3 g of anhydrous potassium fluoride, and anhydrous nickel dichloride (in a 1:1 molar ratio to anhydrous acetyl chloride) were mixed thoroughly. Then, 20 mL of liquid anhydrous hydrogen fluoride was introduced. High-purity nickel sheets (1 cm × 2 cm) were used as the cathode and anode, respectively, with an electrode spacing of 1.5 cm. Under continuous stirring (600 rpm), the reaction system temperature was kept constant at 5 °C. A constant voltage electrolysis mode was adopted, with the electrolysis voltage set to 6 V (at which point the initial current density was 5 mA / cm²). 2 The electrolysis reaction is initiated, and the cumulative charge is monitored in real time. Electrolysis is terminated when the cumulative charge reaches 9.37 kC (approximately 1.15 times the theoretical charge). A gaseous mixture containing trifluoroacetyl fluoride is generated during electrolysis and discharged from the reactor.

[0077] (2) Absorption and alkaline hydrolysis transformation

[0078] The gaseous mixture extracted in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride, and then passed into 20mL of 20wt% potassium hydroxide aqueous solution for complete absorption, yielding a trifluoroacetyl fluoride absorbent. Potassium hydroxide is first added to the obtained trifluoroacetyl fluoride absorbent to adjust the pH to 11~12 to ensure complete alkaline hydrolysis of the trifluoroacetyl fluoride; then 2g of calcium oxide is added, and the mixture is stirred at room temperature for 30 minutes to allow residual fluoride ions in the system to precipitate as calcium fluoride. The mixture is then filtered, and the filtrate is collected to obtain the first filtrate.

[0079] (3) Refining and purification

[0080] The first filtrate obtained in step (2) was mixed with anhydrous ethanol at a volume ratio of 1:2. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 80-90°C to obtain crude potassium trifluoroacetate. Anhydrous ethanol preheated to 50-60°C was added to the obtained crude potassium trifluoroacetate, and the solid-liquid ratio (g:mL) was controlled at 1:6. A single hot extraction was performed by stirring continuously at 50-60°C for 30 minutes. After the hot extraction, the mixture was filtered while hot, and the filtrate was collected to obtain the second filtrate. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 70-80°C. The obtained solid was dried under vacuum at 50-60°C for 12 hours to obtain purified potassium trifluoroacetate (0.522g).

[0081] (4) Acidification distillation

[0082] The purified potassium trifluoroacetate obtained in step (3) was placed in a flask and acidified by slowly adding concentrated sulfuric acid (95wt%~98wt%) dropwise while cooling in an ice-water bath at 0~4℃ and stirring. The pH value of the system was monitored simultaneously, and the addition was stopped when the pH value stabilized at 2.0±0.2. The reaction equation is: 2CF3COOK+H2SO4→2CF3COOH+K2SO4. The acidified mixture was then distilled under normal pressure, and the fraction distilled at 71~75℃ was accurately collected to obtain high-purity trifluoroacetic acid (0.39g, with a total yield of 24.3% based on anhydrous acetyl chloride). The purity of the product was determined by... 19 The purity of trifluoroacetic acid was determined by the F NMR peak area normalization method. 20 mg of the sample was dissolved in 0.5 mL of deuterated dimethyl sulfoxide (DMSO-d6), and the concentration was measured using a Bruker AVANCE NEO 600 NMR spectrometer. 19 F NMR spectrum, relaxation delay time 10 s, 64 scans. Only the characteristic fluorine peak of trifluoroacetic acid (δ-76.5 ppm) was observed in the spectrum, and no other fluorine signals were detected. Three parallel determinations were performed, and the average value was taken. The results showed that the purity of the obtained trifluoroacetic acid was 99.5% (relative standard deviation <0.5%).

[0083] Example 5:

[0084] A method for preparing trifluoroacetic acid from acetyl chloride via electrolytic fluorination includes the following steps:

[0085] (1) Electrolytic fluorination reaction

[0086] In a 50 mL closed PEEK-resistant electrolytic reactor, 1 mL of anhydrous acetyl chloride, 3 g of anhydrous potassium fluoride, and anhydrous cobalt dichloride (in a 1:1 molar ratio to anhydrous acetyl chloride) were mixed thoroughly. Then, 20 mL of liquid anhydrous hydrogen fluoride was introduced. High-purity nickel sheets (1 cm × 2 cm) were used as the cathode and anode, respectively, with an electrode spacing of 1.5 cm. Under continuous stirring (600 rpm), the reaction system temperature was kept constant at 5 °C. A constant voltage electrolysis mode was adopted, with the electrolysis voltage set to 6 V (at which point the initial current density was 15 mA / cm²). 2 The electrolysis reaction is initiated, and the cumulative charge is monitored in real time. Electrolysis is terminated when the cumulative charge reaches 12.55 kC (approximately 1.54 times the theoretical charge). A gaseous mixture containing trifluoroacetyl fluoride is generated during electrolysis and discharged from the reactor.

[0087] (2) Absorption and alkaline hydrolysis transformation

[0088] The gaseous mixture extracted in step (1) is condensed and separated at -10~-5℃ to remove the entrained hydrogen fluoride, and then passed into 20mL of 20wt% potassium hydroxide aqueous solution for complete absorption, yielding a trifluoroacetyl fluoride absorbent. Potassium hydroxide is first added to the obtained trifluoroacetyl fluoride absorbent to adjust the pH to 11~12 to ensure complete alkaline hydrolysis of the trifluoroacetyl fluoride; then 2g of calcium oxide is added, and the mixture is stirred at room temperature for 30 minutes to allow residual fluoride ions in the system to precipitate as calcium fluoride. The mixture is then filtered, and the filtrate is collected to obtain the first filtrate.

[0089] (3) Refining and purification

[0090] The first filtrate obtained in step (2) was mixed with anhydrous ethanol at a volume ratio of 1:2. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 80-90°C to obtain crude potassium trifluoroacetate. Anhydrous ethanol preheated to 50-60°C was added to the obtained crude potassium trifluoroacetate, and the solid-liquid ratio (g:mL) was controlled at 1:6. A single hot extraction was performed by stirring continuously at 50-60°C for 30 minutes. After the hot extraction, the mixture was filtered while hot, and the filtrate was collected to obtain the second filtrate. The solvent was removed by rotary evaporation under reduced pressure in a water bath at 70-80°C. The obtained solid was dried under vacuum at 50-60°C for 12 hours to obtain purified potassium trifluoroacetate (0.76g).

[0091] (4) Acidification distillation

[0092] The purified potassium trifluoroacetate obtained in step (3) was placed in a flask and acidified by slowly adding concentrated sulfuric acid (95wt%~98wt%) dropwise while cooling in an ice-water bath at 0~4℃ and stirring. The pH value of the system was monitored simultaneously, and the addition was stopped when the pH value stabilized at 2.0±0.2. The reaction equation is: 2CF3COOK+H2SO4→2CF3COOH+K2SO4. The acidified mixture was then distilled at atmospheric pressure, and the fraction distilled at 71~75℃ was accurately collected to obtain high-purity trifluoroacetic acid (0.57g, with a total yield of 35.5% based on anhydrous acetyl chloride). The purity of the product was determined by... 19 The purity of trifluoroacetic acid was determined by the F NMR peak area normalization method. 20 mg of the sample was dissolved in 0.5 mL of deuterated dimethyl sulfoxide (DMSO-d6), and the concentration was measured using a Bruker AVANCE NEO 600 NMR spectrometer. 19 F NMR spectrum, relaxation delay time 10 s, 64 scans. Only the characteristic fluorine peak of trifluoroacetic acid (δ-76.5 ppm) was observed in the spectrum, and no other fluorine signals were detected. Three parallel determinations were performed, and the average value was taken. The results showed that the purity of the obtained trifluoroacetic acid was 99.5% (relative standard deviation <0.5%).

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this patent fall within the scope of protection and disclosure of this patent.

Claims

1. A method for preparing trifluoroacetic acid from acetyl chloride via electrolytic fluorination, characterized in that: Includes the following steps: (1) Electrolytic fluorination: In a closed electrolytic reactor, anhydrous acetyl chloride, anhydrous potassium fluoride and anhydrous chloride are mixed evenly, and liquid anhydrous hydrogen fluoride is introduced. Constant voltage electrolysis is performed with nickel sheet as cathode and anode. The gaseous mixture containing trifluoroacetyl fluoride generated during the electrolysis process is discharged from the reactor. (2) Absorption and alkaline conversion: After the gaseous mixture derived in step (1) is condensed and separated to remove the entrained hydrogen fluoride, it is passed into an alkaline solution for complete absorption to obtain trifluoroacetyl fluoride absorption solution; alkali metal hydroxides are first added to the obtained trifluoroacetyl fluoride absorption solution to adjust the pH value to strong alkalinity so that the trifluoroacetyl fluoride is completely alkalinely decomposed, and then alkaline earth metal oxides or hydroxides are added to make the residual fluoride ions in the system generate fluoride precipitates. After filtration, the filtrate is collected to obtain the first filtrate. (3) Refining and purification: The first filtrate obtained in step (2) is mixed with an alcohol solvent, and the solvent is removed by rotary evaporation under reduced pressure to obtain crude potassium trifluoroacetate; the crude potassium trifluoroacetate is subjected to thermal extraction with an alcohol solvent; after the thermal extraction is completed, it is filtered while hot and the filtrate is collected to obtain the second filtrate; the solvent is removed by rotary evaporation under reduced pressure and the filtrate is dried under vacuum to obtain refined potassium trifluoroacetate; (4) Acidification distillation: The refined potassium trifluoroacetate obtained in step (3) is acidified with an inorganic strong acid under ice-water bath and stirring conditions; the acidified mixture is distilled under normal pressure, and the fraction with a boiling range of 70~75℃ is collected to obtain high-purity trifluoroacetic acid.

2. The method according to claim 1, characterized in that: In step (1), the molar ratio of anhydrous acetyl chloride, anhydrous potassium fluoride, anhydrous chloride and liquid anhydrous hydrogen fluoride is 1:1.2~4.0:0.8~1.2:70~75; the anhydrous chloride is anhydrous nickel dichloride or anhydrous cobalt dichloride.

3. The method according to claim 1, characterized in that: In step (1), the electrolysis temperature is 0~10℃; the electrolysis voltage is 5~7V.

4. The method according to claim 1, characterized in that: In step (2), the temperature of the condensation separation is -10~-5℃.

5. The method according to claim 1, characterized in that: In step (2), the alkaline solution is a 20wt% aqueous solution of potassium hydroxide; the alkali metal is potassium or sodium; and the alkaline earth metal is calcium or magnesium.

6. The method according to claim 1, characterized in that: In step (3), the alcohol solvent is anhydrous ethanol or anhydrous methanol; the temperature of the hot extraction is 50~60℃, the solid-liquid ratio is controlled at 1g:4mL~1g:6mL during the hot extraction, and the hot extraction is performed 1~3 times, each time for 30 minutes.

7. The method according to claim 1, characterized in that: In step (4), the amount of inorganic strong acid added is based on adjusting the pH value of the system to 2.0±0.

2.

8. The method according to claim 1, characterized in that: In step (4), the inorganic strong acid is concentrated sulfuric acid of 95wt%~98wt%.

9. The use of the method according to any one of claims 1 to 8 in the preparation of trifluoroacetic acid.

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