A process for the preparation of trichlorotrifluoroethane and trifluoroacetic acid

Abstract

The application relates to the field of organic synthesis, in particular to a preparation method of trichlorotrifluoroethane and trifluoroacetic acid, which comprises the following steps: adding trichloroethylene, a catalyst and anhydrous hydrogen fluoride into a pressure kettle, stirring, slowly heating and performing a fluorination reaction, stopping the fluorination reaction, not releasing the hydrogen chloride gas generated in the reaction process, and cooling to-33 DEG C to 0 DEG C; introducing chlorine gas into the reaction kettle, closing the valve of the pressure kettle, slowly heating and reacting, controlling the temperature in the kettle at 30-40 DEG C after the reaction is completed, slowly releasing the gas in the kettle into alkali water absorption, finally discharging the remaining liquid from the bottom valve of the kettle, and adding the liquid into the alkali water for quenching; adding water, standing and separating, and taking the lower oily substance as a trichlorotrifluoroethane crude product; and performing rectification to obtain a finished product. The application can avoid separation and purification of a low-boiling-point fluorination intermediate 1,1,1-trifluoro-2-chloroethane, avoid loss of the intermediate in a post-treatment operation process, and simplify the operation.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, specifically a method for preparing trichlorotrifluoroethane and trifluoroacetic acid. Background Technology

[0002] Trifluoroacetic acid (TCA) is an important fluorinated intermediate in aliphatic compounds. Due to its unique trifluoromethyl structure, it can participate in various organic synthesis reactions, including the synthesis of various herbicides containing trifluoromethyl groups and heterocycles, as well as novel herbicides with pyridinyl and quinolinyl groups. As a very strong protic acid, it is widely used as a catalyst in the alkylation, acylation, and olefin polymerization of aromatic compounds. As a solvent, TCA is an excellent solvent for fluorination, nitration, and halogenation reactions. In particular, its derivative, trifluoroacetyl, provides excellent protection for hydroxyl and amino groups, playing a crucial role in the synthesis of amino acids and peptides, particularly in removing the tert-butyloxycarbonyl protecting group from amino acids. The route using compound I (trichloroethylene) as a starting material to prepare TCA is widely used; the specific synthetic route is shown in the diagram below. Figure 1 As shown.

[0003] Companies such as KaliChemie in Germany, Sinochem Lantian, and Changshu Sanaifu all use compound II (1,1,1-trifluoro-2-chloroethane) from the above route as raw material, chlorinate it to obtain compound III (1,1,1-trifluoro-2,2,2-trichloroethane), and then oxidize, alkali melt, and acidify it to obtain trifluoroacetic acid.

[0004] In the aforementioned technology, 1,1,1-trifluoro-2-chloroethane is obtained by a one-step anhydrous hydrofluorination reaction using trichloroethylene as a raw material. These two steps of high-temperature and high-pressure fluorination and chlorination are the difficulties in production operation. Moreover, after the fluorination reaction is completed in the original process, the gas needs to be discharged and post-processed to obtain the key intermediate 1,1,1-trifluoro-2-chloroethane in the process. It is difficult to collect during the pilot test, resulting in a low process yield. The pilot test operation is complicated, the yield is low, and the environmental pollution is significant. It is necessary to optimize the synthesis method. Summary of the Invention

[0005] To avoid the post-processing of the low-boiling-point intermediate compound II (1,1,1-trifluoro-2-chloroethane), the present invention aims to provide a method for preparing trichlorotrifluoroethane and trifluoroacetic acid.

[0006] The specific technical solution of the present invention is as follows: A method for preparing trifluorotrichloroethane includes the following steps: Step (1) Fluorination Trichloroethylene, catalyst, and anhydrous hydrogen fluoride are added to a pressure vessel, stirred, and the temperature is slowly increased to carry out the fluorination reaction. After the fluorination reaction is completed, there is no need to release the hydrogen chloride gas generated during the reaction. The temperature is then lowered to -33°C to 0°C. Step (2) Chlorination Chlorine gas is introduced into the reactor, the valve of the pressure vessel is closed, the temperature is slowly increased and the reaction is carried out. After the reaction is completed, the temperature inside the reactor is controlled at 30~40℃, and the gas inside the reactor is slowly released to be absorbed by the alkaline water. Finally, the remaining liquid is released from the bottom valve of the reactor and added dropwise to the alkaline water for quenching. Add water, let stand and separate into layers. The lower oily layer is crude trifluorotrichloroethane. Distill to obtain the final product.

[0007] This invention provides a one-pot method for preparing 1,1,1-trifluoro-2,2,2-trichloroethane, which avoids the separation and purification of the fluorination intermediate 1,1,1-trifluoro-2-trichloroethane, avoids the loss of the low-boiling-point intermediate 1,1,1-trifluoro-2-trichloroethane during post-processing, simplifies the operation, and achieves a chemical purity of over 99.2%.

[0008] As a preferred option, in step (1), the catalyst is a Lewis acid, and the amount added is 0.005 to 0.015 times the mass of trichloroethylene.

[0009] As a preferred option, in step (1), the amount of anhydrous hydrogen fluoride added is 0.4 to 0.5 times the mass of trichloroethylene, the fluorination reaction temperature is 40℃ to 60℃, and the reaction time is 4 to 8 hours.

[0010] As a preferred option, in step (2), the amount of chlorine added is 0.85 to 0.95 times the mass of trichloroethylene, the reaction temperature is 40°C to 50°C, and the reaction time is 12 to 24 hours.

[0011] As a preferred option, in step (2), after the reaction is completed, the temperature inside the reactor is controlled at 30~40℃.

[0012] As a preferred option, in step (2), the alkaline water is 30% alkaline water, and the amount used is 5~8 L.

[0013] The present invention also relates to a method for preparing trifluoroacetic acid, including the above-described preparation method. Attached Figure Description

[0014] Figure 1 This is a roadmap for the preparation of trifluoroacetic acid using trichloroethylene as a raw material in existing technologies; Figure 2 The liquid phase detection spectrum of the product in Example 1 of this invention; Figure 3 The CNMR spectrum of the product in Example 1 of this invention; Figure 4This is the mass spectrometry spectrum of the product in Example 1 of the present invention; Figure 5 The liquid phase detection spectrum of 1,1,1-trifluoro-2,2,2-trichloroethane as shown in Formula III in Example 2 of the present invention is shown. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0016] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0017] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0018] In the existing technology, 1,1,1-trifluoro-2-chloroethane has a boiling point of 6~7℃ and is easily vaporized at room temperature and pressure. It is difficult to collect during the small-scale test, resulting in a low process yield. The small-scale test operation is complicated, the yield is low, and the environmental pollution is significant.

[0019] Furthermore, this invention provides a method for preparing trifluorotrichloroethane, comprising the following steps: Step (1) Fluorination Trichloroethylene, catalyst, and anhydrous hydrogen fluoride are added to a pressure vessel, stirred, and the temperature is slowly increased to carry out the fluorination reaction. After the fluorination reaction is completed, there is no need to release the hydrogen chloride gas generated during the reaction. The temperature is then lowered to -33°C to 0°C. Step (2) Chlorination Chlorine gas is introduced into the reactor, the valve of the pressure vessel is closed, the temperature is slowly increased and the reaction is carried out. After the reaction is completed, the temperature inside the reactor is controlled at 30~40℃, and the gas inside the reactor is slowly released to be absorbed by the alkaline water. Finally, the remaining liquid is released from the bottom valve of the reactor and added dropwise to the alkaline water for quenching. Add water, let stand and separate into layers. The lower oily layer is crude trifluorotrichloroethane. Distill to obtain the final product.

[0020] The reaction routes involved in this invention are as follows: Figure 1 As shown, the details are as follows: In step (1), trichloroethylene and catalyst can be added to the stainless steel pressure vessel in the required amount. After the pressure vessel is cooled to the required temperature, an anhydrous hydrogen fluoride cylinder is connected. The anhydrous hydrogen fluoride cylinder is placed in a 50°C water bath, and the anhydrous hydrogen fluoride is forced into the pressure vessel by the pressure of the cylinder itself. Stirring is started, and the temperature is slowly increased to the reaction temperature to obtain the reaction system of compound II. The reaction system of compound II is then cooled.

[0021] In step (2), a chlorine cylinder can be connected, and the chlorine gas can be forced into the pressure vessel using the pressure of the cylinder itself. The valve is closed, the stirring is turned on, and the temperature is slowly raised to the reaction temperature. After the reaction is complete, the temperature inside the vessel is lowered, and the valve on the vessel is slowly opened to release the gas inside the vessel into the alkaline water for absorption. After the gas inside the vessel is released, the bottom valve is opened to release the liquid inside the vessel, which is then added dropwise to the alkaline water for quenching. The liquid is separated to obtain the crude product of compound III, which is then distilled to obtain the finished product 1,1,1-trifluoro-2,2,2-trichloroethane.

[0022] The method of this invention is a one-pot method for preparing 1,1,1-trifluoro-2,2,2-trichloroethane. It avoids the separation and purification of the fluorination intermediate 1,1,1-trifluoro-2-trichloroethane, avoids the loss of the low-boiling-point intermediate 1,1,1-trifluoro-2-trichloroethane during post-processing, and simplifies the operation. The resulting chemical purity can reach over 99.2%.

[0023] In one embodiment, in step (1), the catalyst is a Lewis acid, and the amount added is 0.005 to 0.015 times the mass of trichloroethylene.

[0024] Using this amount of Lewis acid as a catalyst can enhance the nucleophilicity of hydrogen fluoride, activate the C-Cl bond, promote the nucleophilic substitution reaction, and improve the selectivity and yield of the reaction.

[0025] In one embodiment, in step (1), the amount of anhydrous hydrogen fluoride added is 0.4 to 0.5 times the mass of trichloroethylene, the fluorination reaction temperature is 40°C to 60°C, and the reaction time is 4 to 8 hours.

[0026] Regarding the amount of hydrogen fluoride used: Theoretically, this reaction requires 3.0 eq. HF. If the HF equivalent is too low, fluorination will be incomplete, resulting in excessive residual chlorine in the intermediates, which will affect the subsequent chlorine reaction and the purity of the final product. If the HF equivalent is too high, it may produce over-fluorinated products (such as perfluorinated compounds) or increase side reactions, while also increasing the amount of HF used and the burden of subsequent processing.

[0027] Regarding fluorination temperature: at lower temperatures (<40℃), the reaction rate is slow and fluorination is incomplete; at higher temperatures (>60℃), side reactions increase. 40~60℃ can ensure a high reaction rate while maintaining high selectivity.

[0028] Lewis acid catalysts are prone to decomposition or deactivation at high temperatures. This temperature range can maintain their active form and control the stability of the catalyst.

[0029] HF is highly corrosive, and a moderate temperature can reduce the corrosion rate of the reactor while avoiding excessive pressure due to high temperature, thus reducing safety risks.

[0030] Regarding the reaction time, fluorination is a multi-step cascade reaction (Cl is gradually replaced by F), and sufficient time is required for the intermediate to be converted to the target degree of fluorination, so as to provide a suitable precursor for subsequent reactions.

[0031] Excessive time may lead to product decomposition, isomerization, or reverse reaction with accumulated HCl. 4-8 hours represents the optimized result, maximizing conversion to a plateau while minimizing byproducts. Maintaining a reasonable time while ensuring yield is beneficial for production cycle economics.

[0032] In one embodiment, in step (2), the amount of chlorine added is 0.85 to 0.95 times the mass of trichloroethylene, the reaction temperature is 40°C to 50°C, and the reaction time is 12 to 24 hours.

[0033] Regarding the amount of chlorine used, an excess of chlorine in this reaction (above the theoretical amount of 1 eq.) ensures that the intermediate is completely converted into the target product that is fully chlorinated / fluorinated, preventing the reaction from stalling or generating hydrogen-containing byproducts due to insufficient chlorine.

[0034] Meanwhile, an appropriate excess of chlorine helps drive the reaction toward the target product and inhibits the formation of other isomers or overchlorinated products. However, an excess of chlorine (≤2.5 eq.) can avoid side reactions such as overchlorination or carbon-carbon bond breaking.

[0035] Regarding the reaction temperature, below 40℃, insufficient chlorine activation results in a slow reaction rate, potentially leading to incomplete conversion; above 50℃, side reactions may occur (such as chlorine attacking the CF bond, product decomposition, polymerization, etc.). A mild heating range of 40~50℃ can maintain high selectivity while ensuring a reasonable reaction rate.

[0036] This temperature range ensures effective dissolution of chlorine while preventing a rapid increase in pressure inside the reactor (chlorine is a gas) due to excessively high temperatures, thus guaranteeing operational safety.

[0037] Regarding the reaction time, this reaction involves multiple chlorination steps and has slow reaction kinetics. A sufficient time of 12–24 h allows the intermediate to be fully converted into the target product, achieving a high conversion rate. However, excessively long times may trigger side reactions. This reaction time range can ensure the reaction conversion rate while suppressing the accumulation of byproducts.

[0038] In one implementation method, in step (2), after the reaction is complete, the temperature inside the reactor is controlled at 30~40℃. This temperature range ensures that the gas is discharged slowly and steadily. A temperature of 30~40℃ is conducive to the effective dissolution and reaction of the gas in the alkaline solution. Too low a temperature may reduce the absorption rate, while too high a temperature may cause the alkaline solution to evaporate.

[0039] In one implementation method, in step (2), the alkali solution is a 30% alkali solution, and the amount used is 5-8 L. The 30% liquid alkali is a commercially available product, which is a 30% sodium hydroxide aqueous solution. This amount ensures complete neutralization of the reaction tail gas and the feed liquid, while adding the feed liquid dropwise to a sufficient amount of alkali solution is an exothermic neutralization process. The amount of alkali solution provides a sufficiently large heat capacity and contact area, which can effectively buffer and disperse heat and prevent local overheating.

[0040] This invention also provides a method for preparing trifluoroacetic acid, including the preparation method described above.

[0041] Trifluoroacetic acid was subsequently prepared using conventional methods.

[0042] This invention eliminates the need for refining 1,1,1-trifluoro-2-chloroethane. 1,1,1-trifluoro-2-chloroethane itself is a refrigerant with a very low boiling point and is highly volatile. This invention effectively avoids material loss during the process using a one-pot method, and also saves energy consumption in purifying 1,1,1-trifluoro-2-chloroethane. Furthermore, the reaction in this invention is a pressurized reaction, not an atmospheric pressure reaction, so there is no need to continuously introduce chlorine gas, which reduces the amount of chlorine gas used and the post-processing costs.

[0043] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing trichlorotrifluoroethane and trifluoroacetic acid provided by the present invention.

[0044] Example 1 The preparation method of trifluorotrichloroethane in this embodiment includes the following steps: Step (1) Add 1000 g of trichloroethylene and 10 g of antimony pentachloride to a 10 L pressure vessel, connect an anhydrous hydrogen fluoride cylinder, press in 450 g of anhydrous hydrogen fluoride, close the valve, turn on the stirrer, slowly raise the temperature to 42℃, keep the reaction at this temperature for 4 h, and then lower the pressure vessel to -10℃.

[0045] Step (2): Connect a chlorine cylinder to the gas inlet of the pressure vessel, pressurize 900 g of chlorine gas into the vessel, slowly raise the temperature to 42℃ and react for 15 h, lower the temperature to 33℃, slowly release the gas in the vessel into 6 L of 30% alkaline water for absorption. After the gas is released, open the bottom valve of the vessel to release the remaining liquid, add it dropwise to the above 6 L of 30% alkaline water for quenching, add 4 L of water, let it stand to separate into layers, the lower oily substance is the crude product of compound III, perform packed column distillation to obtain 1098 g of compound III product, with a yield of 77% and a purity of 99.2%.

[0046] Example 2 The preparation method of trifluorotrichloroethane in this embodiment includes the following steps: Step (1) Add 1000 g of trichloroethylene and 10 g of antimony pentachloride to a 10 L pressure vessel, connect an anhydrous hydrogen fluoride cylinder, press in 460 g of anhydrous hydrogen fluoride, close the valve, turn on the stirrer, slowly raise the temperature to 45°C, keep the reaction at this temperature for 5 h, and then lower the pressure vessel to 0°C.

[0047] Step (2): Connect a chlorine cylinder to the inlet of the pressure vessel and pressurize 930 g of chlorine into the vessel. Slowly raise the temperature to 45°C and react for 13 h. Then lower the temperature to 37°C and slowly release the gas from the vessel into 6 L of 30% alkaline water for absorption. After the gas is released, open the bottom valve of the vessel to release the remaining liquid. Add the liquid dropwise to the above 6 L of 30% alkaline water for quenching. Add 4 L of water and let it stand to separate into layers. The lower oily layer is the crude product of compound III. Perform packed column distillation to obtain 1087 g of compound III product, with a yield of 76% and a purity of 99.3%.

[0048] Example 3 The preparation method of trifluorotrichloroethane in this embodiment includes the following steps: Step (1) Add 1000 g of trichloroethylene and 10 g of antimony pentachloride to a 10 L pressure vessel, connect an anhydrous hydrogen fluoride cylinder, press in 457 g of anhydrous hydrogen fluoride, close the valve, turn on the stirrer, slowly raise the temperature to 43℃, keep the reaction at this temperature for 6 h, and then lower the pressure vessel to -12℃.

[0049] Step (2): Connect a chlorine cylinder to the inlet of the pressure vessel and pressurize 910 g of chlorine into the vessel. Slowly raise the temperature to 41°C and react for 17 h. Then lower the temperature to 35°C and slowly release the gas from the vessel into 6 L of 30% alkaline water for absorption. After the gas is released, open the bottom valve of the vessel to release the remaining liquid. Add the liquid dropwise to the above 6 L of 30% alkaline water for quenching. Add 4 L of water and let it stand to separate into layers. The lower oily layer is the crude product of compound III. Perform packed column distillation to obtain 1092 g of compound III product, with a yield of 76% and a purity of 99.2%.

[0050] Comparative Example 1 Unlike Example 1, the catalyst used was aluminum trichloride.

[0051] Comparative Example 2 Unlike Example 1, the amount of chlorine added was 500 g.

[0052] Comparative Example 3 Unlike Example 1, the reaction temperature in step (1) is 60 °C.

[0053] Comparative Example 4 Unlike Example 1, the reaction time in step (1) is 12 h.

[0054] Comparative Example 5 Unlike Example 1, the reaction temperature in step (2) is 20 °C.

[0055] Comparative Example 6 Unlike Example 1, the reaction time in step (2) is 30 h.

[0056] The 1,1,1-trifluoro-2,2,2-trichloroethane prepared in this embodiment and the comparative example were analyzed by liquid chromatography, CNMR, and mass spectrometry, as follows: Liquid chromatography: Agilent 1260DAD high performance liquid chromatograph CNMR: Bruker BioSpin GmbH 400MHz Nuclear Magnetic Resonance Spectrometer Mass spectrometry detection: Agilent 8890-7000D mass spectrometer The detection conditions for liquid chromatography are shown in Table 1: Table 1. Detection conditions for liquid chromatography The mass spectrometry detection conditions are shown in Table 2: Table 2 GC-MS detection conditions The liquid phase detection spectrum of the product in Example 1 is as follows: Figure 2 As shown, the product purity can reach 99.21%, indicating high product quality.

[0057] Figure 3 The CNMR spectra of the product in Example 1 of this invention (124.46, 121.66, 118.85, 116.04, 91.01, 90.59, 90.17, 89.75) are consistent with the CNMR data reported in the literature, proving the correctness of the product structure. Figure 4The mass spectra of the product in Example 1 of this invention show that the precise mass of the product is 185.96, which is consistent with the molecular weight of 1,1,1-trifluoro-2,2,2-trichloroethane.

[0058] Example 2: Liquid phase detection spectrum of the product is as follows Figure 5 As shown, the product purity can reach 99.29%, indicating high product quality.

[0059] The remaining specific results are shown in Table 3: Table 3 Comparison of product yield and purity results between the examples and comparative examples. As can be seen from Comparative Example 1, the use of other catalysts led to a decrease in yield and also affected the purity to some extent.

[0060] As can be seen from Comparative Example 2, insufficient chlorine leads to reaction stagnation or the formation of hydrogen-containing byproducts, which ultimately has a significant impact on yield and purity.

[0061] As can be seen from Comparative Example 3, excessively high temperatures increase side reactions, leading to a certain degree of decrease in yield and a significant impact on purity.

[0062] As can be seen from Comparative Example 4, if this step takes too long, it may lead to product decomposition, isomerization, or reverse reaction with accumulated HCl, which in turn will result in a significant decrease in yield and also have a certain impact on purity.

[0063] Comparative Example 5 shows that when the temperature is below 40℃, the chlorine gas is not sufficiently activated, the reaction rate is too slow, the conversion is incomplete, which seriously affects the yield and also affects the purity to some extent.

[0064] Comparative Example 6 shows that an excessively long reaction time in this step may trigger side reactions, affecting the yield and purity.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing trifluorotrichloroethane, characterized in that, Includes the following steps: Step (1) Fluorination Trichloroethylene, catalyst, and anhydrous hydrogen fluoride are added to a pressure vessel, stirred, and the temperature is slowly increased to carry out the fluorination reaction. After the fluorination reaction is completed, there is no need to release the hydrogen chloride gas generated during the reaction. The temperature is then lowered to -33°C to 0°C. Step (2) Chlorination Chlorine gas is introduced into the reactor, the valve of the pressure vessel is closed, the temperature is slowly increased and the reaction is carried out. After the reaction is completed, the temperature inside the reactor is controlled at 30~40℃, and the gas inside the reactor is slowly released to be absorbed by the alkaline water. Finally, the remaining liquid is released from the bottom valve of the reactor and added dropwise to the alkaline water for quenching. Add water, let stand and separate into layers. The lower oily layer is crude trifluorotrichloroethane. Distill to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step (1), the catalyst is Lewis acid, and the amount added is 0.005 to 0.015 times the mass of trichloroethylene.

3. The preparation method according to claim 1, characterized in that, In step (1), the amount of anhydrous hydrogen fluoride added is 0.4 to 0.5 times the mass of trichloroethylene, the fluorination reaction temperature is 40℃ to 60℃, and the reaction time is 4 to 8 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the amount of chlorine added is 0.85 to 0.95 times the mass of trichloroethylene, the reaction temperature is 40°C to 50°C, and the reaction time is 12 to 24 hours.

5. The preparation method according to claim 1, characterized in that, In step (2), after the reaction is complete, the temperature inside the reactor is controlled at 30~40℃.

6. The preparation method according to claim 1, characterized in that, In step (2), the alkaline solution is 30% alkaline solution, and the amount used is 5~8 L.

7. A method for preparing trifluoroacetic acid, characterized in that: The preparation method includes any one of claims 1 to 6.

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