Method for synthesizing polyfluorophenol by using lanthanum cerium copper catalyst

Abstract

The application discloses a method for synthesizing polyfluorophenol by using a lanthanum-cerium-copper catalyst, and the method is characterized in that the lanthanum-cerium-copper catalyst is prepared by using a coprecipitation method. A mixture of water and dimethyl sulfoxide is used as a solvent, polyfluorobromobenzene is hydrolyzed under alkaline conditions, and then polyfluorophenol is obtained by using concentrated hydrochloric acid. The method has the advantages of low cost, simple process, convenient separation and reuse of the catalyst, high product yield, less waste discharge, great potential for large-scale industrialization, and high social and economic effects, and can be used for producing liquid crystal grade polyfluorophenol.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of LCD liquid crystal intermediates, in particular to a synthesis method of multi-fluorophenol liquid crystal intermediates. BACKGROUND

[0002] Liquid crystal display (LCD) is the dominant product of the present display, with the advantages of light weight, thin volume, small power, etc. It is not only applied to mobile phones, computers, televisions, advertising screens and other electronic products closely related to our lives, but also widely used in military, aerospace and other high-tech fields, with a huge market size.

[0003] Liquid crystal material is one of the core materials for manufacturing liquid crystal display, which plays a key role in the quality of liquid crystal display. According to its application mode in liquid crystal display, liquid crystal material mainly includes the following three types: (1) twisted nematic liquid crystal display (TN-LCD), mainly applied to low-end liquid crystal display such as calculators, watches, instruments and meters; (2) super twisted nematic liquid crystal display (STN-LCD), mainly applied to text and image display with low requirements for monitors and desktop computers; (3) thin film transistor liquid crystal display (TFT-LCD), also known as "true color" display, with the advantages of low energy consumption, high resistivity, fast response speed, high dielectric constant, etc., which can meet the requirements of large display capacity, high gray level, strong color display capability and adaptation to digital reality, and is the mainstream of high-end liquid crystal display, widely used in most flat panel display fields such as mobile phones, televisions, computers and electronic players.

[0004] One of the key steps in manufacturing liquid crystal material is to prepare liquid crystal intermediates. Fluorine-containing liquid crystal intermediates applied to thin film transistor liquid crystal display (TFT-LCD) are the current development hotspot. Fluorophenol compounds are an important class of fluorine-containing liquid crystal intermediates, such as 3,4,5-trifluorophenol, pentafluorophenol, 3,5-difluorophenol, 3,5-difluoro-4-trifluoromethylphenol and 3,5-difluoro-4-trifluoromethoxyphenol.

[0005]

[0006] Existing synthesis process of multi-fluorophenol of formula 1

[0007] The existing synthesis process of polyfluorophenol liquid crystal intermediate (Formula 1) is relatively complex, mainly including: (1) diazotization hydrolysis method, in which polyfluorobromobenzene is used as raw material to prepare polyfluorophenol through three steps of amination, diazotization and hydrolysis. This process has the disadvantages of multiple reaction steps, large amount of waste water, difficult separation of by-products, low product purity, and difficult to meet the requirements of product appearance and color; (2) Grignard reagent method, in which polyfluorobromobenzene is used as raw material to prepare Grignard reagent, and then the Grignard reagent is reacted with borate ester to generate fluorobenzene boronic acid, and then polyfluorophenol is prepared through oxidation. This process has the disadvantages of harsh reaction conditions, great safety hazard, serious environmental pollution and high cost of raw materials. Most of the production processes of polyfluorophenol compounds are mastered by foreign companies, resulting in high price of the products, slow research progress, and finally affecting the development of TFT-LCD liquid crystal materials in China. Therefore, it has great economic and theoretical value to carry out the green synthesis process research of polyfluorophenol liquid crystal intermediate. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a synthesis method of polyfluorophenol, which has the advantages of simple process, high yield of target product, easy separation and less three waste emissions.

[0009] The object of the present application is achieved by the following technical scheme: the lanthanum-cerium-copper catalyst is prepared by a coprecipitation method. A mixture of water and dimethyl sulfoxide is used as a solvent, and polyfluorophenol is obtained by hydrolysis of polyfluorobromobenzene under alkaline conditions and then treatment with concentrated hydrochloric acid.

[0010] The reaction chemical formula of the present application is:

[0011]

[0012] X = H or CH3, M = Na or K

[0013] In the above technical scheme, the lanthanum-cerium-copper catalyst is prepared by a coprecipitation method, specifically, nitrate salts of lanthanum, cerium and copper are reacted in water under alkaline conditions to obtain a solid precipitate, and the solid is calcined in an air atmosphere to obtain the lanthanum-cerium-copper catalyst;

[0014] The calcination temperature is 700-900 DEG C, preferably 800-850 DEG C;

[0015] The molar ratio of lanthanum element to cerium element in the lanthanum-cerium-copper catalyst is 1:2-2:1, preferably 1:1-1.2;

[0016] The molar ratio of lanthanum element to copper element in the lanthanum-cerium-copper catalyst is 1:0.2-1:0.05, preferably 1:0.1-0.15.

[0017] The multi-fluorobromobenzene is one or two or more of pentafluorobromobenzene, 3,4,5-trifluorobromobenzene, 3,5-difluorobromobenzene, 3,5-difluoro-4-trifluoromethylbromobenzene and 3,5-difluoro-4-trifluoromethoxybromobenzene.

[0018] The mass ratio of the lanthanum cerium copper catalyst and the multi-fluorobromobenzene is 1:5-1:16, preferably 1:8-10.

[0019] The mass ratio of the water and dimethyl sulfoxide mixture and the multi-fluorobromobenzene is 2:1-7:1, preferably 3:1-6:1; the volume ratio of water and dimethyl sulfoxide is 1:2-2:1, preferably 1:1-2.

[0020] The multi-fluorobromobenzene is hydrolyzed under alkaline conditions, and then treated with concentrated hydrochloric acid to obtain the multi-fluorophenol, the base is one or two of sodium hydroxide or potassium hydroxide, the molar ratio of the multi-fluorobromobenzene and the base is 1:2-2:1, preferably 1:1-1.5; the pH is adjusted to 2-3 by using concentrated hydrochloric acid.

[0021] The reaction temperature is 80-120℃, preferably 90-110℃; the reaction time is 6-15h, preferably 8-12h.

[0022] The method has the advantages of simple process, high yield, less three-waste emissions, large-scale industrialization potential, liquid crystal grade purity of multi-fluorophenol, and high social and economic effect.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The lanthanum cerium copper catalyst is used, the catalyst is easy to separate, and the service life is long;

[0025] (2) Water is used as a nucleophile and a source of phenolic hydroxyl, which is non-corrosive and has low requirements on equipment;

[0026] (3) The raw materials are cheap and easy to obtain;

[0027] (4) The reaction conditions are mild.

[0028] The method has the advantages of simple process, convenient catalyst separation and reuse, high product yield, less three-waste emissions, large-scale industrialization potential, liquid crystal grade purity of multi-fluorophenol, and high social and economic effect. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below with reference to embodiments, but the scope of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1: Preparation method of lanthanum-cerium-copper catalyst

[0031] In a 50 mL round-bottom flask, a PTFE magnetic stirrer, 2.153 g of cerium nitrate hexahydrate, 2.148 g of lanthanum nitrate hexahydrate, and 20 mL of deionized water were added sequentially. The mixture was stirred until dissolved, and then 0.2307 g of copper nitrate hydrate was added. 0.5 mol / L sodium carbonate was slowly added to adjust the pH to 8. The reaction solution was transferred to a 100 mL hydrothermal reactor and hydrothermally reacted at 200 °C for 24 h. After the reaction, the solid was separated by centrifugation (10000 r / min, 10 min), calcined in air at 800 °C (heating rate 5 °C / min) for 1 h, and then slowly cooled to 30 °C (cooling rate 5 °C / min). The black solid was ground into powder in an agate mortar to obtain a lanthanum-cerium-copper catalyst (labeled Cat-800-1-1-0.1, with a lanthanum-cerium-copper molar ratio of 1:1:0.1), with a mass of 1.5133 g.

[0032] The preparation methods for Cat-700-1-1-0.1 and Cat-900-1-1-0.1 are the same as those for Cat-800-1-1-0.1, with the only difference being the pyrolysis (i.e., calcination) temperature. The pyrolysis temperatures for Cat-700-1-1-0.1 and Cat-900-1-1-0.1 are 700℃ and 900℃, respectively, and their masses are 1.562g and 1.5243g, respectively.

[0033] The preparation methods of Cat-800-1-2-0.2, Cat-800-1-2-0.05, Cat-800-2-1-0.2, and Cat-800-2-1-0.05 are the same as those of Cat-800-1-1-0.1, with the only difference being the molar ratio of lanthanum, cerium, and copper. In the preparation process, the amount of lanthanum hexahydrate used is 2.148 g, and the amounts of cerium hexahydrate and copper hydrate are determined according to the molar ratio of lanthanum, cerium, and copper in the prepared catalyst. The molar ratio of lanthanum, cerium, and copper in Cat-800-1-2-0.2 is 1:2:0.2, and the mass is 1.4079g. The molar ratio of lanthanum, cerium, and copper in Cat-800-1-2-0.05 is 1:2:0.05, and the mass is 1.533g. The molar ratio of lanthanum, cerium, and copper in Cat-800-2-1-0.2 is 2:1:0.2, and the mass is 1.4262g. The molar ratio of lanthanum, cerium, and copper in Cat-800-2-1-0.05 is 2:1:0.05, and the mass is 1.5407g.

[0034] Example 2

[0035] In a 100 mL reaction flask, add a magnetic stir bar (the same applies below), 20 mmol of pentafluorobromobenzene (4.92 g), 0.984 g of Cat-800-1-1-0.1, 14.76 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:2), and 20 mmol of sodium hydroxide (0.8 g). Stir the mixture at 90 °C for 8 h. After the reaction is complete, centrifuge to separate the catalyst (10000 r / min, 10 min). Add concentrated hydrochloric acid (36-38% by mass) to the supernatant to adjust the pH to 2-3 (2.9 in this case), extract with ethyl acetate (10 mL × 2 times), and recover the ethyl acetate by vacuum distillation. Pentafluorophenol was obtained by column chromatography with a yield of 90% (3.32 g, purity: 98%); it was a colorless liquid; 1H NMR (400 MHz, DMSO-d6) δ 9.58 (s); 13C NMR (101 MHz, DMSO-d6) δ 144.6, 143.4, 135.9, 130.1.

[0036] Example 3

[0037] In a 100 mL reaction flask, a magnetic stir bar, 20 mmol of 3,4,5-trifluorobromobenzene (4.198 g), 0.4198 g of Cat-700-1-1-0.1, 25.188 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:1), and 40 mmol of sodium hydroxide (1.6 g) were added sequentially. The mixture was stirred at 80 °C for 15 h. After the reaction was completed, the catalyst was separated by centrifugation (10000 r / min, 10 min). The supernatant was adjusted to pH 2-3 (2.7 in this case) by adding concentrated hydrochloric acid (36-38% by mass), and extracted with ethyl acetate (10 mL × 2 times). The ethyl acetate was recovered by vacuum distillation. 3,4,5-Trifluorophenol was obtained by column chromatography with a yield of 97% (2.87 g, purity: 98%); colorless liquid; 1H NMR (400 MHz, DMSO-d6) δ 9.45 (s), 6.73 (d); 13CNMR (101 MHz, DMSO-d6) δ 157.3, 152.5, 132.7, 101.2.

[0038] Example 4

[0039] In a 100 mL reaction flask, a magnetic stir bar, 20 mmol of 3,5-difluorobromobenzene (3.839 g), 0.2559 g of Cat-900-1-1-0.1, 26.873 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 2:1), and 10 mmol of sodium hydroxide (0.4 g) were added sequentially. The mixture was stirred at 110 °C for 12 h. After the reaction was completed, the catalyst was separated by centrifugation (10000 r / min, 10 min). The supernatant was adjusted to pH 2-3 (2.5 in this case) by adding concentrated hydrochloric acid (36-38% by mass), and extracted with ethyl acetate (10 mL × 2 times). The ethyl acetate was recovered by vacuum distillation. 3,5-Difluorophenol was obtained by column chromatography with a yield of 93% (2.418 g, purity: 98%); colorless liquid; 1H NMR (400 MHz, DMSO-d6) δ 9.45 (s), 6.75 (d), 6.24 (s); 13C NMR (101 MHz, DMSO-d6) δ 165.9, 161.7, 98, 97.3.

[0040] Example 5

[0041] In a 100 mL reaction flask, a magnetic stir bar, 20 mmol of 3,5-difluoro-4-trifluoromethylbromobenzene (5.199 g), 0.5199 g of Cat-800-1-2-0.2, 15.597 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:1), and 10 mmol of sodium hydroxide (0.4 g) were added sequentially. The mixture was stirred at 120 °C for 6 h. After the reaction was completed, the catalyst was separated by centrifugation (10000 r / min, 10 min). The supernatant was adjusted to pH 2-3 (2.9 in this case) by adding concentrated hydrochloric acid (36-38% by mass), and extracted with ethyl acetate (10 mL × 2 times). The ethyl acetate was recovered by vacuum distillation. 3,5-Difluoro-4-trifluoromethylphenol was obtained by column chromatography with a yield of 98% (3.881, purity: 98%); it was a colorless liquid; 1H NMR (400MHz, DMSO-d6) δ 9.45(s), 6.68(d); 13C NMR (101MHz, DMSO-d6) δ 165.0, 160.6, 110.5, 99.9, 97.6.

[0042] Example 6

[0043] In a 100 mL reaction flask, a magnetic stir bar, 20 mmol of 3,5-difluoro-4-trifluoromethoxybromobenzene (5.518 g), 0.5518 g of Cat-800-1-2-0.05, 11.036 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:1), and 10 mmol of sodium hydroxide (0.4 g) were added sequentially. The mixture was stirred at 80 °C for 15 h. After the reaction was completed, the catalyst was separated by centrifugation (10000 r / min, 10 min). The supernatant was adjusted to pH 2-3 (2.9 in this case) by adding concentrated hydrochloric acid (36-38% by mass), and extracted with ethyl acetate (10 mL × 2 times). The ethyl acetate was recovered by vacuum distillation. 3,5-Difluoro-4-trifluoromethoxyphenol was obtained by column chromatography with a yield of 96% (4.109, purity: 98%); it was a colorless liquid; 1H NMR (400MHz, DMSO-d6) δ 9.07(s), 6.75(d); 13C NMR (101MHz, DMSO-d6) δ 155.1, 154.0, 129.7, 128.4, 100.8.

[0044] Example 7

[0045] In a 100 mL reaction flask, add a magnetic stir bar (the same applies below), 20 mmol of pentafluorobromobenzene (4.92 g), 0.492 g of Cat-800-2-1-0.2, 14.76 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:2), and 20 mmol of potassium hydroxide (1.12 g). Stir the mixture at 90 °C for 8 h. After the reaction is complete, centrifuge the catalyst (10000 r / min, 10 min). Add concentrated hydrochloric acid (36-38% by mass) to the supernatant to adjust the pH to 2-3 (2.9 in this case), extract with ethyl acetate (10 mL × 2 times), and recover the ethyl acetate by vacuum distillation. Pentafluorophenol was obtained by column chromatography with a yield of 85% (3.136 g, purity: 98%); it was a colorless liquid; 1H NMR (400 MHz, DMSO-d6) δ 9.58 (s); 13C NMR (101 MHz, DMSO-d6) δ 144.6, 143.4, 135.9, 130.1.

[0046] Example 8

[0047] In a 100 mL reaction flask, add a magnetic stir bar (the same applies below), 20 mmol of pentafluorobromobenzene (4.92 g), 0.492 g of Cat-800-2-1-0.05, 14.76 g of a mixed solvent of water and dimethyl sulfoxide (water to dimethyl sulfoxide volume ratio 1:2), and 20 mmol of potassium hydroxide (1.12 g). Stir the mixture at 90 °C for 8 h. After the reaction is complete, centrifuge the catalyst (10000 r / min, 10 min). Add concentrated hydrochloric acid (36-38% by mass) to the supernatant to adjust the pH to 2-3 (2.9 in this case), extract with ethyl acetate (10 mL × 2 times), and recover the ethyl acetate by vacuum distillation. Pentafluorophenol was obtained by column chromatography with a yield of 86% (3.172 g, purity: 98%); it was a colorless liquid; 1H NMR (400 MHz, DMSO-d6) δ 9.58 (s); 13C NMR (101 MHz, DMSO-d6) δ 144.6, 143.4, 135.9, 130.1.

[0048] Comparative Example 1

[0049] The process and conditions are the same as in Example 1, except that no catalyst is used.

[0050] Compared with the reaction results without using a catalyst, the lanthanum-cerium-copper catalyst used in this invention has obvious advantages; without a catalyst, the reaction does not occur.

[0051] Comparative Example 2

[0052] The process and conditions were the same as in Example 1, except that: when the reaction temperature of the comparative examples was 60°C, the yield of pentafluorophenol was 17%; when the reaction temperature of the comparative examples was 170°C, the yield of pentafluorophenol was 31%.

[0053] Results show that, compared with results from other reaction temperatures, the reaction temperature of this invention (80-120℃) has significant advantages. When the reaction temperature is below 80℃, the conversion rate is low, and the product yield is less than 20%; when the reaction temperature is above 120℃, the reaction selectivity is poor, and there are more byproducts.

[0054] Comparative Example 3

[0055] The process and conditions are the same as in Example 1, except that:

[0056] Using 14.76 g of 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide, or xylene as the reaction solvent to replace the mixed solvent of water and dimethyl sulfoxide, the pentafluorophenol separation yields were 10%, 9%, 4%, and 6%, respectively.

[0057] Results show that the mixed solvent of water and dimethyl sulfoxide used in this invention has significant advantages compared to other reaction solvents. When 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide, and xylene are used as reaction solvents, the yield of polyfluorophenol is less than 11%.

Claims

1. A method for preparing a lanthanum cerium copper catalyst, characterized by, In a 50 mL round bottom flask, a four-fluorine magnetic stirring rotor, 2.153 g of cerium nitrate hexahydrate, 2.148 g of lanthanum nitrate hexahydrate and 20 mL of deionized water were sequentially added, stirred and dissolved, 0.2307 g of copper nitrate hydrate was added, 0.5 mol / L sodium carbonate was slowly added to adjust pH = 8, the reaction liquid was transferred to a 100 mL hydrothermal kettle, and hydrothermal reaction was carried out at 200 ℃ for 24 h, after the reaction was completed, the solid was centrifuged at 10000 r / min for 10 min, calcination was carried out at 800 ℃ with a heating rate of 5 ℃ / min in an air atmosphere for 1 h, the black solid was slowly cooled to 30 ℃ with a cooling rate of 5 ℃ / min, and the black solid was ground into powder in a corundum mortar to obtain a lanthanum-cerium-copper catalyst, the molar ratio of lanthanum-cerium-copper was 1:1:0.1, and the catalyst was marked as Cat-800-1-1-0.

1. The preparation methods of Cat-700-1-1-0.1 and Cat-900-1-1-0.1 and the preparation process and conditions of Cat-800-1-1-0.1 are consistent, and the difference is only that the pyrolysis, i.e. calcination temperature, is different. The pyrolysis temperatures of Cat-700-1-1-0.1 and Cat-900-1-1-0.1 are 700 ℃ and 900 ℃, respectively. The preparation process and conditions of Cat-800-1-2-0.2 and Cat-800-1-2-0.05 are consistent with those of Cat-800-1-1-0.1, and the difference is only that the molar ratio of lanthanum-cerium-copper is different. The molar ratio of lanthanum-cerium-copper in Cat-800-1-2-0.2 is 1:2:0.2, and the molar ratio of lanthanum-cerium-copper in Cat-800-1-2-0.05 is 1:2:0.

05.

2. A method for the catalytic synthesis of polyfluorophenol using lanthanum cerium copper, characterized by, In a 100 mL reaction bottle, a magnetic rotor, 20 mmol of pentafluorobromobenzene, 0.984 g of Cat-800-1-1-0.1 according to claim 1, 14.76 g of a mixed solvent of water and dimethyl sulfoxide in a volume ratio of 1:2, 20 mmol of sodium hydroxide were sequentially added, and stirring reaction was carried out at 90 ℃ for 8 h. After the reaction was completed, the catalyst was centrifuged at 10000 r / min for 10 min, 36-38% concentrated hydrochloric acid was added to the supernatant to adjust pH = 2.9, 10 mL x 2 times of ethyl acetate was used for extraction, ethyl acetate was recovered by reduced pressure distillation, and pentafluorophenol was obtained by column chromatography, with a yield of 90%.

3. A method for the synthesis of polyfluorophenol catalyzed by lanthanum cerium copper, characterized in that, In a 100 mL reaction bottle, magnetic sub, 20 mmol 3, 4, 5-trifluorobromobenzene, 0.4198 g Cat-700-1-1-0.1 described in claim 1, 25.188 g mixed solvent of water and dimethyl sulfoxide in a volume ratio of 1:1, 40 mmol sodium hydroxide were added in turn, stirred at 80℃ for 15 h, after the reaction was completed, the catalyst was centrifuged at 10000 r / min for 10 min, 36-38% concentrated hydrochloric acid was added to the supernatant to adjust pH=2.7, extracted with ethyl acetate 10 mL x 2 times, recovered ethyl acetate by reduced pressure distillation, and 3, 4, 5-trifluorophenol was obtained by column chromatography, with a yield of 97%.

4. A method for the synthesis of polyfluorophenol catalyzed by lanthanum cerium copper, characterized in that, In a 100 mL reaction bottle, magnetic sub, 20 mmol 3, 5-difluorobromobenzene, 0.2559 g Cat-900-1-1-0.1 described in claim 1, 26.873 g mixed solvent of water and dimethyl sulfoxide in a volume ratio of 1:1, 10 mmol sodium hydroxide were added in turn, stirred at 110℃ for 12 h, after the reaction was completed, the catalyst was centrifuged at 10000 r / min for 10 min, 36-38% concentrated hydrochloric acid was added to the supernatant to adjust pH=2.5, extracted with ethyl acetate 10 mL x 2 times, recovered ethyl acetate by reduced pressure distillation, and 3, 5-difluorophenol was obtained by column chromatography, with a yield of 93%.

5. A method for the synthesis of polyfluorophenol catalyzed by lanthanum cerium copper, characterized in that, In a 100 mL reaction bottle, magnetic sub, 20 mmol 3, 5-difluoro-4-trifluoromethylbromobenzene, 0.5199 g Cat-800-1-2-0.2 described in claim 1, 15.597 g mixed solvent of water and dimethyl sulfoxide in a volume ratio of 1:1, 10 mmol sodium hydroxide were added in turn, stirred at 120℃ for 6 h, after the reaction was completed, the catalyst was centrifuged at 10000 r / min for 10 min, 36-38% concentrated hydrochloric acid was added to the supernatant to adjust pH=2.9, extracted with ethyl acetate 10 mL x 2 times, recovered ethyl acetate by reduced pressure distillation, and 3, 5-difluoro-4-trifluoromethylphenol was obtained by column chromatography, with a yield of 98%.

6. A method for the catalytic synthesis of polyfluorophenol using lanthanum cerium copper, characterized by, In a 100 mL reaction bottle, magnetic sub, 20 mmol 3, 5-difluoro-4-trifluoromethylbromobenzene, 0.5518 g Cat-800-1-2-0.05 described in claim 1, 11.036 g mixed solvent of water and dimethyl sulfoxide in a volume ratio of 1:1, 10 mmol sodium hydroxide were added in turn, stirred at 80℃ for 15 h, after the reaction was completed, the catalyst was centrifuged at 10000 r / min for 10 min, 36-38% concentrated hydrochloric acid was added to the supernatant to adjust pH=2.9, extracted with ethyl acetate 10 mL x 2 times, recovered ethyl acetate by reduced pressure distillation, and 3, 5-difluoro-4-trifluoromethoxyphenol was obtained by column chromatography, with a yield of 96%.

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