A preparation method of 2,4,5-trifluorophenylacetic acid

Abstract

The invention discloses a method for preparing 2,4,5-trifluorophenylacetic acid, and relates to the technical field of organic chemical industry. Aluminum chloride is added to 1,2,4-trifluorobenzene, methyl bromide is introduced under stirring to react, a solvent and sodium hydrogen are continuously added to the obtained 2,4,5-trifluorotoluene, carbon dioxide is continuously introduced, and reacted at 25-35 DEG C to obtain 2,4,5-trifluorophenylacetic acid sodium, filtered, quenched, and then adjusted to pH below 2 with 30%wt hydrochloric acid, and 2,4,5-trifluorophenylacetic acid solid is obtained by filtration. The whole reaction process is simple to operate, the reaction conditions are mild, the environmental pollution is small, it is suitable for industrial production, and the yield and purity of the product are high.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemical industry, and in particular to a method for preparing 2,4,5-trifluorophenylacetic acid. Background Art

[0002] 2,4,5-Trifluorophenylacetic acid is an important intermediate for the synthesis of sitagliptin. The methods reported in the literature are mainly as follows:

[0003] a. After 2,4,5-trifluorobromobenzene is made into a Grignard reagent, it is coupled with allyl bromide, and then the double bond is oxidized to obtain 2,4,5-trifluorophenylacetic acid; US Patent No. 6870067 discloses a method for synthesizing trifluoropropylacetic acid, in which 2,4,5-trifluorobromobenzene is made into a Grignard reagent, reacted with allyl bromide, and then oxidized with periodic acid under the catalysis of ruthenium trichloride to obtain 2,4,5-trifluorophenylacetic acid. However, the Grignard reaction in this method often uses low-boiling volatile solvents such as ether, which are prone to explosion, poor production safety, unstable Grignard reagents, low product yields, and the catalyst ruthenium trichloride and oxidant periodic acid used are expensive, which is not suitable for industrial production.

[0004] b. 1,2,4-trifluorobenzene is chloromethylated to obtain 2,4,5-trifluorobenzyl chloride, which is then reacted with carbon dioxide to obtain 2,4,5-trifluorophenylacetic acid. Chinese patent CN101092345 discloses a method for preparing 2,4,5-trifluorophenylacetic acid, which uses 1,2,4-trifluorobenzene as a raw material, firstly undergoes a chloromethylation reaction to obtain 2,4,5-trifluorobenzyl chloride, which is then reacted with carbon monoxide under the action of a catalyst to obtain 2,4,5-trifluorophenylacetic acid. This method still has the disadvantage of producing more three wastes from the chloromethylation.

[0005] c. 1,2,4-trifluorobenzene was used as the raw material to prepare 2,4,5-trifluorobenzene through chloromethylation reaction of polyformaldehyde / zinc chloride / hydrochloric acid, and then directly carbonylated with CO / methanol / NaOH using sodium cobalt tetracarbonyl as the catalyst to obtain 2,4,5-trifluorobenzoic acid. The literature "Synthesis of 2,4,5-trifluorophenylacetic acid, 2011, 18 (3): 4-6" reported that 1,2,4-trifluorobenzene was used as the raw material to prepare 2,4,5-trifluorophenylacetic acid through chloromethylation, carbonylation and hydrolysis. When synthesizing 2,4,5-trifluorobenzyl chloride, m(C6H3F3):m(polyformaldehyde)=1.0:0.875~0.865, and the reaction time was 10 h; when synthesizing 2,4,5-trifluorophenylacetic acid, m(C7H4F3Cl):m(cat)=1:0.275~0.25, and the reaction temperature was 40℃. Under these conditions, the total yield of the product is above 60%, and the mass fraction of 2,4,5-trifluorophenylacetic acid is above 99%. The chloromethylation reaction of this method is highly corrosive, seriously polluting, and has a low yield. The catalyst for the carbonylation reaction, sodium cobalt tetracarbonyl, is expensive and difficult to obtain. The catalyst and CO are highly toxic, and pressurized equipment is required, which has certain industrialization difficulties.

[0006] d. Chinese patent CN116730824B discloses a method for synthesizing 2,4,5-trifluorophenylacetic acid, comprising mixing 1,2,4-trifluorobenzene and a catalyst AlCl3, adding ethylene oxide liquid dropwise at 5°C, and heating to carry out Friedel-Crafts alkylation to obtain 2,4,5-trifluorophenylethanol; reacting 2,4,5-trifluorophenylethanol with hydrogen peroxide under the catalysis of sodium molybdate to obtain an oxidation product 2,4,5-trifluorophenylacetic acid; filtering the 2,4,5-trifluorophenylacetic acid, adding it to a sodium hydroxide solution, keeping the temperature and stirring, cooling and standing, separating the liquids, adjusting the acid, converting sodium trifluorophenylacetate into its free acid, and then crystallizing, filtering, and drying to obtain a 2,4,5-trifluorophenylacetic acid solid. However, ethylene oxide is flammable, explosive, toxic and has poor safety. At the same time, the temperature of the Friedel-Crafts reaction is 100-120°C, the reaction conditions are more stringent, and the impurity selectivity of the multi-substituted Friedel-Crafts alkylation is higher, resulting in more impurities in the product. In addition, sodium aluminate is used as a catalyst, which has poor safety.

[0007] In summary, the current preparation method of 2,4,5-trifluorophenylacetic acid has the following problems: 1. The prepared intermediate Grignard reagent is unstable, and the yield of the final product is basically around 60%, the reaction yield is low, and the raw materials used, such as the catalyst ruthenium trichloride and the oxidant periodic acid, are expensive. 2. The chloromethylation process is highly corrosive and there are many wastes, etc., based on the purpose of improving the reaction yield, reducing production costs, and being environmentally friendly. Summary of the invention

[0008] The technical problem to be solved by the present invention is: in view of the deficiencies in the prior art, a method for preparing 2,4,5-trifluorophenylacetic acid is provided, the reaction process is simple to operate, the yield and purity of the product are high, and the product is environmentally friendly.

[0009] In order to solve the above technical problems, the technical solution of the present invention is:

[0010] A method for preparing 2,4,5-trifluorophenylacetic acid comprises the following steps:

[0011] A: Add aluminum chloride to 1,2,4-trifluorobenzene, introduce methyl bromide under stirring, heat to 35°C and react for 5 hours, wash the reaction liquid with sodium carbonate aqueous solution, wash with water until neutral, and distill under reduced pressure to obtain 2,4,5-trifluorotoluene;

[0012] The specific reaction equation is:

[0013]

[0014] B: Add solvent and sodium hydrogen to 2,4,5-trifluorotoluene, continue to introduce carbon dioxide, react at 25-35°C to obtain sodium 2,4,5-trifluorophenylacetate, filter, quench, adjust the pH to below 2 with 30%wt hydrochloric acid, and filter to obtain 2,4,5-trifluorophenylacetic acid solid.

[0015] The specific reaction equation is:

[0016]

[0017]

[0018] Preferably, in step A, the molar ratio of 1,2,4-trifluorobenzene, aluminum chloride and methyl bromide is 1.67:0.034:0.34.

[0019] Preferably, the stirring speed during the reaction in step A is 280-350 rpm.

[0020] Preferably, the concentration of the sodium carbonate aqueous solution in step A is 5%wt, and the mass ratio of 1,2,4-trifluorobenzene to the sodium carbonate aqueous solution is 1:0.757w / w.

[0021] Preferably, during the reduced pressure distillation in step A, at a vacuum degree of 15 mmHg, a fraction at 57-59° C. is collected, which is 1,2,4-trifluorobenzene.

[0022] Preferably, during the reduced pressure distillation in step A, the fraction at 70-72° C. is collected at a vacuum degree of 10 mmHg, which is 2,4,5-trifluorotoluene.

[0023] Preferably, in step B, the molar ratio of 2,4,5-trifluorotoluene to sodium hydrogen is 1:1.1-1.3.

[0024] Preferably, the solvent in step B is one of anhydrous tetrahydrofuran, diethyl ether and isopropyl ether.

[0025] Preferably, in step B, the volume ratio of 2,4,5-trifluorotoluene mass to solvent is 1:3.42 g / mL, and the pressure of carbon dioxide is maintained at 2 MPa during the reaction.

[0026] Preferably, the quenching process in step B is to add the filter cake obtained by filtration into ice water to quench the unreacted sodium hydrogen.

[0027] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] 1. The present invention uses 1,2,4-trifluorobenzene as a raw material, does not use raw materials with low safety factors such as ethylene oxide and sodium aluminate, and obtains the final product through three-step reactions of Friedel-Crafts alkylation, nucleophilic addition and hydrolysis. The reaction steps are short and the purity is high. The yield of Friedel-Crafts alkylation reaction is 94.05% (calculated as methyl bromide), and the yield range of nucleophilic addition and acidification reaction is 85.96%-96.71% (calculated as 2,4,5-trifluorotoluene), thereby improving the reaction yield.

[0029] 2. The present invention uses sodium hydrogen and carbon dioxide to react 2,4,5-trifluorotoluene with nucleophilic addition to generate sodium 2,4,5-trifluorophenylacetate, and uses hydrochloric acid to adjust the pH to below 2 to obtain the target product. The entire reaction process is simple to operate, the reaction conditions are mild, the environmental pollution is small, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a gas chromatogram of 2,4,5-trifluorotoluene in Example 1 of the present invention;

[0031] Figure 2 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 1 of the present invention;

[0032] Figure 3 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 2 of the present invention;

[0033] Figure 4 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 3 of the present invention;

[0034] Figure 5 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 4 of the present invention;

[0035] Figure 6 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 5 of the present invention;

[0036] Figure 7 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 6 of the present invention;

[0037] Figure 8 is a gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 7 of the present invention;

[0038] Fig. 9 It is the gas chromatogram of 2,4,5-trifluorophenylacetic acid in Example 8 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the embodiments. Example 1

[0040] (1) Friedel-Crafts alkylation reaction:

[0041] 660.4 g 1,2,4-trifluorobenzene and 13.34 g aluminum chloride were added to a 2L stainless steel reactor, the system was cooled to 0°C, 94.94 g methyl bromide gas was introduced under stirring, the temperature was slowly raised to 35°C, and the reaction was carried out for 5 hours. 500 g of 5% wt sodium carbonate aqueous solution was added to the reaction liquid and slurried at room temperature for 30 minutes. The layers were separated, and an equal mass of water was added to the organic phase to wash it until neutral. The mixture was then distilled under reduced pressure and heated at a vacuum degree of 15 mmHg. The 57-59°C fraction was collected, which was 1,2,4-trifluorobenzene with a gas phase purity of 99.9% and could be recycled. The remaining liquid was heated at a vacuum degree of 10 mmHg, and the 70-72°C fraction was collected, which was 2,4,5-trifluorotoluene with a mass of 137.49, a gas phase purity of 99.95%, and a yield of 94.05% (as methyl bromide).

[0042] (2) Nucleophilic addition and acidification reaction:

[0043] Add 50 mL of anhydrous tetrahydrofuran to a 250 mL reaction bottle, add 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene under stirring, cool to 0-5 ° C, add 2.64 g (0.11 mol) of sodium hydrogen, stir for 2 h, then transfer all the reaction liquid to a 500 mL reactor, rinse the remaining material in the reaction bottle with 50 mL of tetrahydrofuran and bring it into the reactor, evacuate, replace with nitrogen three times, heat to 25 ° C, introduce carbon dioxide to a pressure of 2 MPa, keep the reaction warm until the pressure no longer decreases, and then continue to introduce carbon dioxide to a pressure of 2 MPa, introduce two The reaction was stopped, the temperature was lowered to 20°C, filtered, the filtrate was heated to 70°C, tetrahydrofuran was recovered by atmospheric distillation, the remaining liquid was heated and rectified under a vacuum degree of 10 mmHg, the 70-72°C fraction was collected to recover 2,4,5-trifluorotoluene, the filter cake was slowly added to 50 g of ice water for quenching, and then the pH value was adjusted to less than 2 with 30%wt hydrochloric acid, the temperature was kept below 20°C for filtration and drying to obtain 16.71 g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.95% (GC) and a yield of 87.85% (based on 2,4,5-trifluorotoluene). Example 2

[0044] Changing the amount of sodium hydrogen in the nucleophilic addition reaction in step (2) of Example 1

[0045] 50 mL of anhydrous tetrahydrofuran was added to 200 mL of reaction fluorine, 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 was added under stirring, the temperature was cooled to 0-5 ° C, 2.88 g (0.12 mol) of sodium hydrogen was added, and the mixture was stirred for 2 h. The reaction liquid was then transferred to a 500 mL reactor. The residual material in the reaction bottle was rinsed with 50 mL of tetrahydrofuran and brought into the reactor. The reaction was evacuated, replaced with nitrogen three times, and the temperature was raised to 40 ° C. Carbon dioxide was introduced to a pressure of 2 MPa. The reaction was kept warm until the pressure no longer decreased and carbon dioxide was continued to be introduced to a pressure of 2 MPa. Two The reaction was stopped, the temperature was lowered to 20°C, filtered, the filtrate was heated to 70°C, tetrahydrofuran was recovered by atmospheric distillation, the remaining liquid was heated and rectified under a vacuum degree of 10 mmHg, 70-72°C fraction was collected to recover 2,4,5-trifluorotoluene, the filter cake was slowly added to 50 g of ice water for quenching, and then 30% wt hydrochloric acid was used to adjust the pH value to less than 2, the temperature was kept below 20°C for filtration and drying to obtain 16.88 g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.89% (GC) and a yield of 88.69% (based on 2,4,5-trifluorotoluene). Example 3

[0046] Changing the amount of sodium hydrogen in the nucleophilic addition reaction in step (2) of Example 1

[0047] Add 50 mL of anhydrous tetrahydrofuran to a 250 mL reaction bottle, add 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 under stirring, cool to 0-5 ° C, add 3.12 g (0.13 mol) of sodium hydrogen, stir for 2 h, then transfer all the reaction liquid to a 500 mL reactor, rinse the remaining material in the reaction bottle with 50 mL of tetrahydrofuran and bring it into the reactor, evacuate, replace with nitrogen three times, heat to 25 ° C, introduce carbon dioxide to a pressure of 2 MPa, keep warm and react until the pressure no longer decreases, and then continue to introduce carbon dioxide to a pressure of 2 MPa, and introduce The reaction was stopped, the temperature was lowered to 20°C, and the filtrate was heated to 70°C and distilled at atmospheric pressure to recover tetrahydrofuran. The remaining liquid was heated and rectified under a vacuum degree of 10 mmHg, and the 70-72°C fraction was collected to recover 2,4,5-trifluorotoluene. The filter cake was slowly added to 50 g of ice water for quenching, and then 31.6 g of 30% wt hydrochloric acid was used to adjust the pH value to less than 2. The temperature was kept below 20°C for filtration and drying to obtain 89.28 g of 2,4,5-trifluorophenylacetic acid as a white solid with a content of 99.91% (GC) and a yield of 89.28% (based on 2,4,5-trifluorotoluene). Example 4

[0048] Changing the solvent type in the nucleophilic addition reaction in step (2) of Example 1

[0049] Add 50 mL of ether to a 250 mL reaction bottle, add 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 under stirring, reduce the temperature to 0-5 ° C, add 2.88 g (0.12 mol) of sodium hydrogen, stir for 2 h, then transfer all the reaction liquid to a 500 mL reactor, rinse the residual material in the reaction bottle with 50 mL of ether and bring it into the reactor, evacuate, replace with nitrogen three times, heat to 25 ° C, introduce carbon dioxide to a pressure of 2 MPa, keep the reaction until the pressure no longer decreases, and then continue to introduce carbon dioxide to a pressure of 2 MPa, introduce twice , the passage time is 2h, the reaction is stopped, the temperature is lowered to 20℃, filtered, the filtrate is heated to 70℃, and the ether is recovered by atmospheric distillation. The remaining liquid is heated and rectified under a vacuum degree of 10mmHg, and the 70-72℃ fraction is collected to recover 2,4,5-trifluorotoluene. The filter cake is slowly added to 50g of ice water for quenching, and then 30%wt hydrochloric acid 31.6g is used to adjust the pH value to less than 2. Keep the temperature below 20℃, filter and dry to obtain 16.36g of white solid 2,4,5-trifluorophenylacetic acid, with a content of 99.90% (GC) and a yield of 85.96% (based on 2,4,5-trifluorotoluene). Example 5

[0050] Changing the solvent type in the nucleophilic addition reaction in step (2) of Example 1

[0051] Add 50 mL of isopropyl ether to 200 mL of reaction fluorine, add 14.61 g (0.1 mol, 146.110) of 2,4,5-trifluorotoluene obtained in Example 1 under stirring, reduce the temperature to 0-5 ° C, add 2.88 g (0.12 mol) of sodium hydrogen, stir for 2 h, then transfer all the reaction liquid to a 500 mL reactor, rinse the residual material in the reaction bottle with 50 mL of isopropyl ether and bring it into the reactor, evacuate, replace with nitrogen three times, heat to 25 ° C, introduce carbon dioxide to a pressure of 2 MPa, keep the reaction warm until the pressure no longer decreases and continue to introduce carbon dioxide To the pressure of 2MPa, pass twice, the passing time is 2h, stop the reaction, cool to 20℃, filter, heat the filtrate to 80℃, distill and recover isopropyl ether, the remaining liquid is heated and rectified under a vacuum degree of 10mmHg, collect the 70-72℃ fraction to recover 2,4,5-trifluorotoluene, and slowly add the filter cake to 50g ice water for quenching, and then adjust the pH value to less than 2 with 31.6g of 30%wt hydrochloric acid, keep the temperature below 20℃, filter and dry to obtain 16.51g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.90% (GC) and a yield of 86.78%. Example 6

[0052] Changing the reaction temperature of the nucleophilic addition in step (2) of Example 1

[0053] 50 mL of anhydrous tetrahydrofuran was added to 200 mL of reaction fluorine, 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 was added under stirring, the temperature was reduced to 0-5 ° C, 2.88 g (0.12 mol) of sodium hydrogen was added, and the mixture was stirred for 2 h. The reaction liquid was then transferred to a 500 mL reactor. The residual material in the reaction bottle was rinsed with 50 mL of tetrahydrofuran and brought into the reactor. Vacuuming was performed, nitrogen was replaced three times, the temperature was raised to 30 ° C, carbon dioxide was introduced to a pressure of 2 MPa, and the reaction was kept warm until the pressure no longer decreased and carbon dioxide was continued to be introduced to a pressure of 100 MPa. 2MPa, passed twice, the passing time was 2h, the reaction was stopped, the temperature was lowered to 20℃, filtered, the filtrate was heated to 70℃, tetrahydrofuran was recovered by atmospheric distillation, the remaining liquid was heated and rectified under a vacuum degree of 10mmHg, and the 70-72℃ fraction was collected to recover 2,4,5-trifluorotoluene, the filter cake was slowly added to 50g of ice water for quenching, and then 30%wt hydrochloric acid 31.6g was used to adjust the pH value to less than 2, the temperature was kept below 20℃, filtered and dried to obtain 18.40g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.90% (GC) and a yield of 96.71%. Example 7

[0054] Changing the reaction temperature of the nucleophilic addition in step (2) of Example 1

[0055] Add 50 mL of anhydrous tetrahydrofuran to 200 mL of reaction fluorine, add 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 under stirring, reduce the temperature to 0-5°C, add 2.88 g (0.12 mol) of sodium hydrogen, stir for 2 h, then transfer all the reaction liquid to a 500 mL reactor, rinse the residual material in the reaction bottle with 50 mL of tetrahydrofuran and bring it into the reactor, evacuate, replace with nitrogen three times, heat to 35°C, introduce carbon dioxide to a pressure of 2 MPa, keep the reaction until the pressure no longer decreases, and continue to introduce carbon dioxide to a pressure of 2 MPa. a, pass twice, the passing time is 2h, stop the reaction, cool to 20℃, filter, raise the temperature of the filtrate to 70℃, distill at atmospheric pressure to recover tetrahydrofuran, and the remaining liquid is heated and rectified under a vacuum degree of 10mmHg, collect the 70-72℃ fraction to recover 2,4,5-trifluorotoluene, slowly add the filter cake into 50g ice water to quench the unreacted sodium hydrogen, and then adjust the pH value to less than 2 with 30%wt hydrochloric acid 31.6g, keep the temperature below 20℃, filter and dry to obtain 17.53g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.93% (GC) and a yield of 92.18%. Example 8

[0056] Changing the reaction temperature of the nucleophilic addition in step (2) of Example 1

[0057] 50 mL of anhydrous tetrahydrofuran was added to 200 mL of reaction fluorine, 14.61 g (0.1 mol) of 2,4,5-trifluorotoluene obtained in Example 1 was added under stirring, the temperature was reduced to 0-5°C, 2.88 g (0.12 mol) of sodium hydrogen was added, and the mixture was stirred for 2 h. The reaction liquid was then transferred to a 500 mL reactor, and the residual material in the reaction bottle was rinsed with 50 mL of tetrahydrofuran and brought into the reactor. The reaction was evacuated, replaced with nitrogen three times, and heated to 40°C. Carbon dioxide was introduced to a pressure of 2 MPa. The reaction was kept warm until the pressure no longer decreased, and carbon dioxide was continued to be introduced to a pressure of 2 MPa, passed twice, the passing time was 2h, the reaction was stopped, the temperature was lowered to 20℃, filtered, the filtrate was heated to 70℃, tetrahydrofuran was recovered by atmospheric distillation, the remaining liquid was heated and rectified under a vacuum degree of 10mmHg, the 70-72℃ fraction was collected to recover 2,4,5-trifluorotoluene, the filter cake was slowly added to 50g ice water for quenching, and then 30%wt hydrochloric acid was used to adjust the pH value to less than 2, the temperature was kept below 20℃, filtered and dried to obtain 17.22g of 2,4,5-trifluorophenylacetic acid as a white solid, with a content of 99.90% (GC) and a yield of 90.52%.

[0058] It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

Claims

1. A method for preparing 2,4,5-trifluorophenylacetic acid, characterized in that The following steps are involved: A: Aluminum trichloride was added to 1,2,4-trifluorobenzene, methyl bromide was introduced under stirring, the temperature was raised to 35°C and the reaction was carried out for 5 hours, the reaction liquid was washed with sodium carbonate aqueous solution, washed with water until neutral, and distilled under reduced pressure to obtain 2,4,5-trifluorotoluene, wherein the molar ratio of 1,2,4-trifluorobenzene, aluminum trichloride and methyl bromide was 1.67:0.034:0.34; B: Add solvent and sodium hydrogen to 2,4,5-trifluorotoluene, continue to introduce carbon dioxide, react at 25-35°C to obtain sodium 2,4,5-trifluorophenylacetate, filter, add the filter cake obtained by filtration into ice water to quench unreacted sodium hydrogen, adjust the pH to below 2 with hydrochloric acid, and filter to obtain 2,4,5-trifluorophenylacetic acid solid, wherein the mass ratio of 2,4,5-trifluorotoluene to the volume ratio of the solvent is 1:3.42 g / mL, and the pressure of carbon dioxide is maintained at 2 MPa during the reaction, wherein the molar ratio of 2,4,5-trifluorotoluene to sodium hydrogen is 1:1.1-1.

3.

2. A method for preparing 2,4,5-trifluorophenylacetic acid as claimed in claim 1, characterized in that: The stirring speed during the reaction in step A is 280-350 rpm.

3. A method for preparing 2,4,5-trifluorophenylacetic acid as claimed in claim 1, characterized in that: The concentration of the sodium carbonate aqueous solution in step A is 5%wt, and the mass ratio of 1,2,4-trifluorobenzene to the sodium carbonate aqueous solution is 1:0.757w / w.

4. A method for preparing 2,4,5-trifluorophenylacetic acid as claimed in claim 1, characterized in that: During the reduced pressure distillation in step A, at a vacuum degree of 15 mmHg, a fraction at 57-59° C. was collected, which was 1,2,4-trifluorobenzene.

5. The method for preparing 2,4,5-trifluorophenylacetic acid according to claim 1, characterized in that: During the reduced pressure distillation in step A, under a vacuum degree of 10 mmHg, a fraction at 70-72° C. is collected, which is 2,4,5-trifluorotoluene.

6. A method for preparing 2,4,5-trifluorophenylacetic acid as claimed in claim 1, characterized in that: The solvent in step B is one of anhydrous tetrahydrofuran, ether and isopropyl ether.

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