A preparation method of 3,4,5-trifluorobromobenzene

Abstract

The present invention provides a method for preparing 3,4,5-trifluorobromobenzene, which uses 2,3,4-trifluoro-6-bromoaniline as a starting material, first converts it into sulfate, and then sequentially undergoes diazotization reaction and deamination reaction to prepare the 3,4,5-trifluorobromobenzene, wherein the deamination reaction uses a C containing α-H 2～6 The preparation method provided by the present invention avoids the production of large amounts of phosphorus-containing wastewater, effectively reduces the occurrence of side reactions during the deamination reaction, significantly improves the yield and purity of the target product, and reduces the pressure of the subsequent purification process. The preparation method provided by the present invention is clean and environmentally friendly, has low production costs, high production efficiency, and good process safety, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of preparation of fine chemical intermediates, and in particular to a method for preparing 3,4,5-trifluorobromobenzene. Background Art

[0002] 3,4,5-Trifluorobromobenzene (also known as 1-bromo-3,4,5-trifluorobenzene, CAS No. 138526-69-9) is an important fine chemical intermediate, particularly in the pharmaceutical and pesticide fields, where its downstream products are widely used. Furthermore, 3,4,5-Trifluorobromobenzene is a crucial liquid crystal intermediate, and high-purity 3,4,5-Trifluorobromobenzene is crucial for producing high-quality liquid crystal products.

[0003] At present, the synthesis processes of 3,4,5-trifluorobromobenzene mainly include the following:

[0004] (1) The method disclosed in Chinese patent CN 201310580913.0 uses 2,3,4-trifluoroaniline as the starting material, disperses the raw material in water, adds bromine dropwise for bromination, and obtains 2,3,4-trifluoro-6-bromoaniline through post-treatment. Then, sodium nitrite is dissolved in sulfuric acid and added dropwise to obtain the diazonium salt prepared from 2,3,4-trifluoro-6-bromoaniline. The diazonium salt is then added dropwise to a hypophosphorous acid and copper catalyst system for diazo deamination. Finally, 3,4,5-trifluorobromobenzene is obtained through post-treatment such as steam distillation and rectification.

[0005] This method uses phosphorus-containing reagents during diazo deamination, which will produce a large amount of phosphorus-containing wastewater. The treatment of the three wastes is very difficult, which is inconsistent with the safe and environmentally friendly production concept that the country has always advocated. In addition, the yield of the target product is not high.

[0006] (2) The method disclosed in Chinese patent CN 201510082492.8 uses 2,3,4-trifluoroaniline as a starting material, reacts with sulfuric acid in the presence of water and acetic acid to obtain 2,3,4-trifluoroaniline sulfate, then adds bromine to the sulfate, and then drops hydrogen peroxide to react to obtain 2,3,4-trifluoro-6-bromoaniline sulfate, then adds sodium hypophosphite and copper salt to the 2,3,4-trifluoro-6-bromoaniline sulfate mixture, and then drops sodium nitrite aqueous solution at -5-0°C, and the reaction solution is subjected to layered distillation to obtain 3,4,5-trifluorobromobenzene.

[0007] This method also uses phosphorus-containing reagents. After repeated verification in small-scale tests, a large amount of hydrolysis and defluorination impurities are produced during the reaction, and the yield does not reach the reported yield. Since the boiling point of the impurities is very close to that of the target product, a very high distillation tower is required to separate the impurities, which consumes a lot of energy and is complicated to operate.

[0008] (3) The method disclosed in Chinese patent CN 201810888990.5 uses 1,2,3-trifluorobenzene as the starting material, disperses the raw material in a solvent, adds an aqueous sodium bromide solution containing a buffer (sodium dihydrogen phosphate), then adds a sodium hypochlorite solution dropwise for bromination, desolventizes the organic phase to obtain a crude 3,4,5-trifluorobromobenzene, and finally melt crystallizes the crude product to obtain 3,4,5-trifluorobromobenzene.

[0009] This method also uses phosphorus-containing reagents, which will produce phosphorus-containing wastewater that is difficult to treat. Moreover, the isomer impurities produced are difficult to separate and require low-temperature melting and recrystallization at -20°C, making it difficult to industrialize.

[0010] (4) The method disclosed in the non-patent literature (European Journal of Organic Chemistry, (3), 447-451; 2003) uses 1,2,3-trifluorobenzene as the starting material, first undergoes a lithium metalation reaction to obtain an aryl lithium compound, and then undergoes a bromination reaction to obtain the corresponding brominated polyfluorobenzene.

[0011] This method requires strict control of anhydrous and oxygen-free reaction conditions, and the reaction has poor regioselectivity, side reactions, a large number of impurities in the product, and high raw material prices.

[0012] (5) The method disclosed in PCT patent WO 2017060905A1 is to mix 3,4,5-trifluorobenzoic acid and bromoisocyanurate, and then add a mixture of bromine and trichlorobromomethane dropwise to the mixture at 120°C under the irradiation of a 3W LED lamp. After reacting for 24 hours, sodium sulfite is added to neutralize the mixture, and then anhydrous sodium sulfate is added to dry the mixture, filter it, and concentrate it to obtain the final product.

[0013] This method has harsh conditions and the cost of the raw materials used is relatively high, making it unsuitable for large-scale production.

[0014] Based on the above situation, it can be seen that the current preparation method of 3,4,5-trifluorobromobenzene still has many problems, especially environmental pollution and unsatisfactory yield. Therefore, it is urgent to find a new preparation method of 3,4,5-trifluorobromobenzene. Summary of the Invention

[0015] To overcome the deficiencies in the prior art, the present invention aims to provide a method for preparing 3,4,5-trifluorobromobenzene, which does not produce difficult-to-treat phosphorus-containing wastewater and significantly improves the yield and purity of the target product.

[0016] The preparation method of 3,4,5-trifluorobromobenzene provided by the present invention uses 2,3,4-trifluoro-6-bromoaniline as a starting material, firstly converts it into sulfate, and then sequentially undergoes diazotization reaction and deamination reaction to prepare the 3,4,5-trifluorobromobenzene, wherein the deamination reaction uses a C containing α-H 2～6 Alcohols are used as reducing agents, copper or copper salts are used as catalysts, and a mixed solvent consisting of an organic solvent immiscible with water and water is used as a reaction medium.

[0017] In the preparation method provided by the present invention, the reaction medium forms an immiscible acid-water layer and an organic layer, the diazonium salt product generated by the diazotization reaction reacts with an inorganic catalyst in the acid-water layer to generate a free radical intermediate, and then the free radical intermediate is transferred to the organic layer via an organic solvent immiscible with water, and is reduced to trifluorobromobenzene by an alcohol reducing agent in the organic layer. This avoids the free radical intermediate from side reactions with water, hydrogen ions or other substances in the acid-water layer, thereby avoiding the generation of impurities such as hydrolysis products and defluorination products (the reaction mechanism is shown below). At the same time, impurities caused by unstable decomposition of the diazonium salt in the reaction system are reduced and potential safety risks are reduced. Therefore, the preparation method of the present invention can significantly improve the purity and yield of the target product.

[0018]

[0019] Furthermore, compared to existing hypophosphorous acid reduction processes, the preparation method provided by the present invention avoids the generation of large amounts of phosphorus-containing wastewater, simplifies waste treatment, is environmentally friendly, and aligns with the nationally advocated safety and environmentally friendly production philosophy. Due to the reduced impurity content, the preparation method of the present invention also significantly reduces the pressure of the subsequent purification process, eliminating the need for complex equipment such as high-resolution distillation towers and high energy consumption, thereby significantly reducing overall production costs.

[0020] In some embodiments of the preparation method according to the present invention, the deamination reaction may include the following process: mixing the reducing agent, the catalyst and the reaction medium to form a mixed solution (for example, mixing in any order to form a mixed solution), and then adding the diazonium salt product after the diazotization reaction to the mixed solution, thereby ensuring that the free radical intermediate is immediately transferred to the organic layer once generated, thereby reducing the occurrence of side reactions. In some preferred embodiments, the temperature when the diazonium salt product is added can be 20 to 30 ° C. In some more preferred embodiments, the diazonium salt product can be added to the mixed solution in a dropwise manner, and the time of the dropwise addition can be 1 to 5 hours.

[0021] The reducing agent of the present invention can be a broadly defined "alcohol", which can contain α-H and hydroxyl groups in its molecular structure. In addition to common alcohols, it can also include substances such as formic acid and glucose. In some embodiments of the preparation method according to the present invention, the reducing agent can be a C containing α-H 2～6 In some preferred embodiments, the reducing agent may be a C 2～4 Saturated aliphatic monohydric alcohols include, but are not limited to, one or more of ethanol, propanol, isopropanol, and n-butanol. In some more preferred embodiments, the reducing agent may be ethanol, isopropanol, or a mixture thereof in any proportion. In some most preferred embodiments, the reducing agent may be isopropanol.

[0022] In some embodiments of the preparation method according to the present invention, the molar ratio of the reducing agent to the 2,3,4-trifluoro-6-bromoaniline may be 1.0 to 3.0: 1. In some preferred embodiments, the molar ratio of the reducing agent to the 2,3,4-trifluoro-6-bromoaniline may be 1.1 to 2.0: 1, including but not limited to about 1.1: 1, about 1.2: 1, about 1.3: 1, about 1.4: 1, about 1.5: 1, about 1.6: 1, about 1.7: 1, about 1.8: 1, about 1.9: 1, about 2.0: 1, or any combination of molar ratio intervals.

[0023] In some embodiments of the preparation method according to the present invention, the water-immiscible organic solvent may be a conventionally used water-immiscible aromatic hydrocarbon, alkane, halogenated aromatic hydrocarbon, halogenated alkane, ether or ester solvent. In some preferred embodiments, the water-immiscible organic solvent may be C 4～10 Alkane solvents, C 6～10 Halogenated aromatic solvents or C 1～4 The halogenated alkane solvent is a halogenated alkane solvent, wherein the halogenated atom can be one or more of F, Cl, and Br. In some more preferred embodiments, the water-immiscible organic solvent includes, but is not limited to, one or more of heptane, n-hexane, petroleum ether, chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, m-dichlorobenzene, trichlorobenzene, toluene, xylene, dichloromethane, dichloroethane, tetrachloroethylene, methyl tert-butyl ether, and ethyl acetate. In some further preferred embodiments, the water-immiscible organic solvent can be heptane or dichloromethane, which, after forming a reaction medium with water, produces a higher reaction yield and fewer impurities.

[0024] In some embodiments of the preparation method according to the present invention, the mass ratio of the water-immiscible organic solvent to water may be 0.5 to 2.0: 1. In some preferred embodiments, the mass ratio of the water-immiscible organic solvent to water may be 0.8 to 1.2: 1, including but not limited to a mass ratio of about 0.8: 1, about 0.9: 1, about 1.0: 1, about 1.1: 1, about 1.2: 1, or any combination of mass ratio intervals.

[0025] In some embodiments of the preparation method according to the present invention, the catalyst can be a copper catalyst commonly used in the art. In some preferred embodiments, the catalyst includes but is not limited to one or more of copper powder, cuprous chloride, cuprous oxide, copper sulfate, and cupric oxide. In some more preferred embodiments, the catalyst can use copper powder.

[0026] In some embodiments of the preparation method according to the present invention, the molar ratio of the catalyst to the 2,3,4-trifluoro-6-bromoaniline may be 0.05 to 0.25: 1. In some preferred embodiments, the molar ratio of the catalyst to the 2,3,4-trifluoro-6-bromoaniline may be 0.08 to 0.15: 1, including but not limited to about 0.08: 1, about 0.09: 1, about 0.10: 1, about 0.11: 1, about 0.12: 1, about 0.13: 1, about 0.14: 1, about 0.15: 1, or any combination of molar ratio ranges.

[0027] In some embodiments of the preparation method according to the present invention, the 2,3,4-trifluoro-6-bromoaniline is reacted with concentrated sulfuric acid to produce the corresponding sulfate, wherein the mass concentration of the concentrated sulfuric acid can be between 95% and 98%, and the molar ratio of 2,3,4-trifluoro-6-bromoaniline to concentrated sulfuric acid can be 1:2.0-4.0. If the amount of concentrated sulfuric acid is too low, the resulting sulfate easily agglomerates. Therefore, in some preferred embodiments, the molar ratio of 2,3,4-trifluoro-6-bromoaniline to concentrated sulfuric acid can be preferably 1:3.0-3.5. In other preferred embodiments, the reaction temperature of 2,3,4-trifluoro-6-bromoaniline and concentrated sulfuric acid can be controlled at 70-75°C. If the temperature is too low, 2,3,4-trifluoro-6-bromoaniline easily adheres to the wall.

[0028] In some embodiments of the preparation method according to the present invention, the diazotization reagent in the diazotization reaction can be selected from nitrosylsulfuric acid or sodium nitrite, and the molar ratio of the diazotization reagent to the 2,3,4-trifluoro-6-bromoaniline can be 1.01 to 1.30: 1. In some preferred embodiments, the molar ratio of the diazotization reagent to the 2,3,4-trifluoro-6-bromoaniline can be 1.01 to 1.05: 1, including but not limited to a molar ratio of about 1.01: 1, about 1.02: 1, about 1.03: 1, about 1.04: 1, about 1.05: 1, or any combination of molar ratio intervals.

[0029] In some embodiments of the preparation method according to the present invention, the reaction temperature of the diazotization reaction can be 20-25° C. Too high a temperature will easily decompose the diazonium salt, while too low a temperature will easily increase the reaction impurities.

[0030] In some embodiments of the preparation method according to the present invention, the reaction temperature of the deamination reaction can be 20-30°C. When the temperature is too high, the reaction speed is accelerated, but the yield is easily affected. When the temperature is too low, the reaction speed is slow and more impurities are easily generated. In some preferred embodiments, the reaction temperature of the deamination reaction can be 25-30°C.

[0031] In some embodiments of the preparation method according to the present invention, the preparation method may further include: after the deamination reaction is completed, separating the organic layer, extracting the aqueous layer with an organic solvent, combining the organic phases, washing with water, concentrating, and then performing reduced pressure distillation to obtain the 3,4,5-trifluorobromobenzene. Due to the reduced impurity content, the preparation method of the present invention only requires a simple purification process to purify the target product, without the need for complex equipment and high energy consumption. The organic solvent used to extract the aqueous layer can also be a conventionally used water-immiscible aromatic hydrocarbon, alkane, halogenated alkane, ether, or ester solvent, and can be the same as or different from the organic solvent used in the reaction medium.

[0032] The preparation method provided by the present invention adopts an alcohol reducing agent, a copper catalyst, and a mixed reaction medium of an organic solvent and water in the deamination reaction step, avoiding the use of conventional phosphorus-containing reagents such as hypophosphorous acid, thereby avoiding the generation of a large amount of phosphorus-containing wastewater, which is in line with the concept of green chemistry. The preparation method provided by the present invention can also effectively reduce the occurrence of side reactions during the deamination reaction, significantly reduce the impurity content, greatly improve the yield and purity of the target product, and also reduce the pressure of the subsequent purification process. Therefore, the preparation method provided by the present invention is clean and environmentally friendly, has low production cost, high production efficiency, and good process safety, and is therefore suitable for large-scale industrial production. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below with reference to specific embodiments.

[0034] Unless otherwise specified, the raw materials or reagents used in the examples and comparative examples of the present invention are all commercially available products.

[0035] Unless otherwise specified, the percentages used in the examples and comparative examples of the present invention are all percentages by mass.

[0036] Example 1

[0037] Copper powder / isopropyl alcohol / heptane-water system

[0038] Diazo salt formation: Add 322 g (3.25 mol) of 98% H2SO4 to a 1 L four-necked flask. Add 230.6 g (1 mol) of 2,3,4-trifluoro-6-bromoaniline dropwise at room temperature. After the addition is complete, raise the temperature to 70-75°C and hold for 1 hour. Cool to 20-25°C and add 320.6 g (1.02 mol) of 40% nitrosylsulfuric acid dropwise at 20-30°C over approximately 1 hour. After the addition is complete, hold at 20-25°C for 2 hours. Cool to 15-20°C to obtain 873.0 g of the diazonium compound.

[0039] Deamination: In a 2 L four-necked flask, add 225 g of water, 212.5 g of heptane, 91.0 g (1.5 mol) of isopropanol, and 7.7 g (0.12 mol) of copper powder. Control the temperature to 20-30°C. Add the diazonium compound dropwise, maintaining the internal temperature at 25-30°C, over approximately 2 hours. Incubate for 1 hour. After the reaction, separate the layers, extract the aqueous layer with 100 g of heptane, combine the organic layers, wash once with 100 g of water, remove the solvent, and distill under reduced pressure to yield 206.2 g of 3,4,5-trifluoroaniline with a purity of 99.7% (GC) and a yield of 97.5%.

[0040] Example 2

[0041] Cuprous chloride / isopropyl alcohol / chlorobenzene-water system

[0042] Diazo salt: prepared according to Example 1.

[0043] Deamination: In a 2 L four-necked flask, add 225 g of water, 212.5 g of chlorobenzene, 91.0 g (1.5 mol) of isopropyl alcohol, and 11.9 g (0.12 mol) of cuprous chloride. Control the temperature to 20-30°C. Add 873.0 g of the diazonium compound dropwise. Maintain the internal temperature at 25-30°C over approximately 2 hours. Incubate for 1 hour. After the reaction, separate the layers, extract the aqueous layer with 100 g of heptane, combine the organic layers, wash once with 100 g of water, remove the solvent, and distill under reduced pressure to yield 203.9 g of 3,4,5-trifluoroaniline with a purity of 99.6% (GC) and a yield of 96.2%.

[0044] Example 3

[0045] Cuprous oxide / isopropyl alcohol / heptane-water system

[0046] Diazo salt: prepared according to Example 1.

[0047] Deamination: In a 2 L four-necked flask, add 225 g of water, 212.5 g of heptane, 91.0 g (1.5 mol) of isopropanol, and 17.2 g (0.12 mol) of cuprous oxide. Control the temperature to 20-30°C. Add 873.0 g of the diazonium compound dropwise. Maintain the internal temperature at 25-30°C over approximately 2 hours. Incubate for 1 hour. After the reaction, separate the layers, extract the aqueous layer with 100 g of heptane, combine the organic layers, wash once with 100 g of water, remove the solvent, and distill under reduced pressure to yield 202.9 g of 3,4,5-trifluoroaniline with a purity of 99.6% (GC) and a yield of 95.8%.

[0048] Example 4

[0049] Copper powder / isopropyl alcohol / dichloromethane-water system

[0050] Diazo salt: prepared according to Example 1.

[0051] Deamination: In a 2 L four-necked flask, add 225 g of water, 212.5 g of dichloromethane, 91.0 g (1.5 mol) of isopropyl alcohol, and 7.7 g (0.12 mol) of copper powder. Control the temperature to 20-30°C. Add 873.0 g of the diazonium compound dropwise. Maintain the internal temperature at 20-30°C over approximately 2 hours. Incubate for 1 hour. After the reaction is complete, separate the layers, extract the aqueous layer with 100 g of heptane, combine the organic layers, wash once with 100 g of water, remove the solvent, and distill under reduced pressure to obtain 201.2 g of 3,4,5-trifluoroaniline with a purity of 99.6% (GC) and a yield of 95.0%.

[0052] Comparative Example 1

[0053] Copper powder / isopropyl alcohol / water system

[0054] Diazo salt: prepared according to Example 1.

[0055] Deamination: In a 2 L four-necked flask, add 225 g of water, 91.0 g (1.5 mol) of isopropyl alcohol, and 7.7 g (0.12 mol) of copper powder. Control the temperature to 20-30°C. Add 873.0 g of the diazonium compound dropwise. Maintain the internal temperature at 25-30°C over approximately 2 hours. Incubate for 1 hour. After the reaction, extract with 100 g of heptane, wash the extract once with 100 g of water, remove the solvent, and distill under reduced pressure to yield 93.3 g of 3,4,5-trifluoroaniline with a purity of 95.7% (GC) and a yield of 42.4%.

[0056] Comparative Example 2

[0057] Copper powder / isopropyl alcohol / heptane system

[0058] Diazo salt: prepared according to Example 1.

[0059] Deamination: In a 2 L four-necked flask, add 212.5 g of heptane, 91.0 g (1.5 mol) of isopropanol, and 7.7 g (0.12 mol) of copper powder. Control the temperature to 20-30°C. Add 873.0 g of the diazonium compound dropwise, maintaining the internal temperature at 25-30°C, over approximately 2 hours. Incubate for 1 hour. After the reaction, add 225 g of water, stir, and separate the layers. Extract the aqueous layer with 100 g of heptane. Combine the organic layers, wash once with 100 g of water, remove the solvent, and distill under reduced pressure to yield 77.9 g of 3,4,5-trifluoroaniline with a purity of 95.5% (GC) and a yield of 35.4%.

[0060] Comparative Example 3

[0061] Example 1 of Chinese patent CN 201510082492.8 was repeated to obtain 180.2 g of the product 3,4,5-trifluorobromobenzene with a purity of 97.3% and a yield of 82.9%.

[0062] The above examples and comparative examples demonstrate that existing methods for preparing 3,4,5-trifluorobromobenzene (e.g., Comparative Example 3) are complex, yield unsatisfactory, and produce large amounts of difficult-to-treat phosphorus-containing wastewater. The preparation method provided by the present invention significantly improves the production efficiency of 3,4,5-trifluorobromobenzene through the effective combination of a reducing agent, a catalyst, and a reaction medium, without generating phosphorus-containing wastewater.

[0063] Unless otherwise defined, the terms used in the present invention have the same meanings as those commonly understood by those skilled in the art.

[0064] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, but is only limited by the claims.

Claims

1. A method for preparing 3,4,5-trifluorobromobenzene, which uses 2,3,4-trifluoro-6-bromoaniline as a starting material, first converts it into a sulfate, and then sequentially undergoes a diazotization reaction and a deamination reaction to prepare the 3,4,5-trifluorobromobenzene, characterized in that: The deamination reaction uses a C containing α-H 2～4 A saturated aliphatic monohydric alcohol is used as a reducing agent, copper or a copper salt is used as a catalyst, and a mixed solvent consisting of an organic solvent immiscible with water and water is used as a reaction medium, wherein the copper salt is selected from one or more of cuprous chloride, cuprous oxide, copper sulfate, and copper oxide, and the organic solvent immiscible with water is selected from one or more of heptane, n-hexane, petroleum ether, chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, m-dichlorobenzene, trichlorobenzene, toluene, xylene, dichloromethane, and dichloroethane.

2. The preparation method according to claim 1, characterized in that The reducing agent is ethanol and / or isopropanol.

3. The preparation method according to claim 1, characterized in that The molar ratio of the reducing agent to the 2,3,4-trifluoro-6-bromoaniline is 1.0 to 3.0:

1.

4. The preparation method according to claim 3, characterized in that The molar ratio of the reducing agent to the 2,3,4-trifluoro-6-bromoaniline is 1.1 to 2.0:

1.

5. The preparation method according to claim 1, characterized in that The mass ratio of the organic solvent immiscible with water to water is 0.5 to 2.0:

1.

6. The preparation method according to claim 5, characterized in that The mass ratio of the organic solvent immiscible with water to water is 0.8 to 1.2:

1.

7. The preparation method according to claim 1, characterized in that The molar ratio of the catalyst to the 2,3,4-trifluoro-6-bromoaniline is 0.05-0.25:

1.

8. The preparation method according to claim 7, characterized in that The molar ratio of the catalyst to the 2,3,4-trifluoro-6-bromoaniline is 0.08-0.15:

1.

9. The preparation method according to claim 1, characterized in that The 2,3,4-trifluoro-6-bromoaniline reacts with concentrated sulfuric acid with a mass concentration of 95-98% to prepare sulfate, and the molar ratio of the 2,3,4-trifluoro-6-bromoaniline to the concentrated sulfuric acid is 1:2.0-4.

0.

10. The preparation method according to claim 9, characterized in that The molar ratio of the 2,3,4-trifluoro-6-bromoaniline to the concentrated sulfuric acid is 1:3.0-3.

5.

11. The preparation method according to claim 1, characterized in that In the diazotization reaction, the diazotization reagent is selected from nitrosylsulfuric acid or sodium nitrite, and the molar ratio of the diazotization reagent to the 2,3,4-trifluoro-6-bromoaniline is 1.01 to 1.30:

1.

12. The preparation method according to claim 11, characterized in that The molar ratio of the nitrosylsulfuric acid or sodium nitrite to the 2,3,4-trifluoro-6-bromoaniline is 1.01 to 1.05:

1.

13. The preparation method according to claim 1, characterized in that The reaction temperature of the diazotization reaction is 20-25° C.; and / or The reaction temperature of the deamination reaction is 20-30°C.

14. The preparation method according to claim 13, characterized in that The reaction temperature of the deamination reaction is 25-30°C.

15. The preparation method according to any one of claims 1 to 14, characterized in that: The preparation method further comprises: after the deamination reaction is completed, separating the organic layer, extracting the aqueous layer with an organic solvent, combining the organic phases, washing with water, concentrating, and then performing reduced pressure distillation to obtain the 3,4,5-trifluorobromobenzene.

Images