Method for preparing fluorobenzene derivative from substituted aniline tetrafluoroborate

Abstract

The invention discloses a method for preparing a fluorobenzene derivative from diazonium salt of substituted aniline, which comprises the following steps: carrying out ion exchange reaction on diazonium fluoroborate of substituted aniline at low temperature in the presence of a solvent and anhydrous hydrogen fluoride, and then heating and decomposing to obtain the fluorobenzene derivative. The method avoids the generation of water and boron trifluoride in the existing fluorobenzene derivative preparation process, and is beneficial to industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing fluorobenzene derivatives from substituted aniline tetrafluoroborate. Background Art

[0002] At present, the main methods for preparing fluorobenzene derivatives from substituted aniline are the Schiemann method and the direct fluorination method with hydrogen fluoride. The Schiemann method is to directly heat and decompose the tetrafluoroborate of substituted aniline in the presence of a solvent to obtain a fluorobenzene derivative:

[0003] However, this method produces a large amount of gas during the pyrolysis process, which poses an explosion risk. Diazonium fluoroborate usually needs to be added in batches during the reaction, which is cumbersome to operate. The boron trifluoride gas produced also makes post-processing difficult.

[0004] The direct fluorination method with hydrogen fluoride (patent CN111269082A) is to add sodium nitrite to substituted aniline at low temperature in the presence of hydrogen fluoride for diazotization, and then heat and decompose to obtain fluorobenzene derivatives:

[0005] However, this method produces water in the diazotization step. When hydrogen fluoride meets water, it is extremely corrosive to the reaction equipment. At the same time, side reactions such as diazonium salt hydrolysis will occur, affecting the yield and product quality. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing fluorobenzene derivatives from substituted aniline tetrafluoroborate in view of the shortcomings of the existing fluorination process. The method uses substituted aniline as a raw material to first prepare diazonium fluoroborate, and then prepares the fluorobenzene derivatives through low-temperature reaction and heating decomposition in the presence of an organic solvent and hydrogen fluoride.

[0007] The specific plan is as follows: A method for preparing a fluorobenzene derivative by replacing a tetrafluoroborate, characterized in that a fluoroborate diazonium salt of a substituted aniline as shown in formula (1) is first reacted at low temperature in the presence of a solvent and anhydrous hydrogen fluoride, and then heated and decomposed to obtain a fluorobenzene derivative as shown in formula (2), and the reaction process is as follows:

[0008] In the formula, R is a substituted alkyl, nitro, alkoxy or carboxyl group; and the solvent is chlorobenzene, dichloroethane or o-dichlorobenzene.

[0009] Furthermore, the substituent R is 2-CF3, 4-CF3, 3-NO2, 4-NO2, 3-OCH3, 4-OCH3, 2-COOH, 3-COOH or 4-COOH.

[0010] Furthermore, the molar ratio of the diazonium fluoroborate salt of substituted aniline to anhydrous hydrogen fluoride is 1:50-90, etc., and the preferred molar ratio is 1:70.

[0011] Furthermore, the low temperature reaction temperature is 25 - 35 °C, the reaction time is 1 - 4 h, preferably 25 °C, the reaction time is 1.5 h.

[0012] Furthermore, the thermal decomposition temperature is 55 - 150 °C.

[0013] After the reaction is completed, the anhydrous hydrogen fluoride is distilled and recovered, pure water is added into the reaction kettle and stirred to separate the layers, the water layer is recovered as a fluoroboric acid aqueous solution, and the organic layer is separated by distillation to separate the fluorobenzene derivatives and recover the chlorobenzene.

[0014] Beneficial effects of the present invention: The fluoroborate diazonium salt of substituted aniline reacts with anhydrous hydrogen fluoride under low temperature conditions to achieve conversion of tetrafluoroborate diazonium salt and fluorodiazonium salt, and then heats and decomposes to obtain fluorobenzene derivatives, with HBF4 and N2 as by-products. Compared with the prior art in which BF3 is produced, the risk of explosion during the reaction is reduced, and the problem of difficulty in post-treatment caused by the production of boron trifluoride gas in the reaction and the problem of water produced in the reaction with substituted aniline as a raw material and corrosion of equipment by hydrogen fluoride when it comes into contact with water is also solved. DETAILED DESCRIPTION

[0015] In order to better understand the present invention, the present invention is further described below through examples. The examples are only used to explain the present invention and will not substantially limit the present invention.

[0016] Example 1 Preparation of raw material 2-trifluoromethyl diazonium fluoroborate

[0017] Take 98% sulfuric acid (0.20 mol, 19.6 g) in a three-necked reaction bottle and dilute it with pure water (4.36 mol, 78.4 g). Add o-trifluoromethylaniline (0.10 mol, 16.1 g) to dilute sulfuric acid to form a salt, first heat it to 60°C to completely dissolve the aniline sulfate salt, then cool it to -5-0°C, take sodium nitrite (0.11 mol, 7.6 g) and dissolve it in pure water (1.26 mol, 22.8 g) and slowly add it to the reaction solution, control the temperature at -5-0°C and stir to react for 1 h. Add 50% fluoroboric acid (0.11 mol, 19.3 g) to the diazo solution, control the temperature at -5-0°C and stir to react for 1 h. After the reaction was completed, the diazonium fluoroborate was separated by filtration, washed with 50 mL of water, then with 50 mL of ethanol, and finally with 50 mL of ether. After washing, it was dried under reduced pressure to obtain 21.7 g of anhydrous diazonium fluoroborate with a yield of 83.5%.

[0018] Example 2 Preparation of 2-trifluoromethylfluorobenzene

[0019] Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of o-dichlorobenzene (0.45 mol, 66.2 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 5℃ for 1 h, and then heat to 85℃ for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25℃ and hydrogen fluoride was distilled and recovered. Pure water was added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110℃ was collected to obtain 11.2 g of o-fluorotrifluorotoluene product with a purity of 99.8% and a yield of 68.1%.

[0020] 1 H NMR (400 MHz, DMSO-d6) δ 7.62 (s, 1H), 7.52 (m, 3H). 19 F NMR (377 MHz, Chloroform-d) δ -62.97(s, 3F), -110.96(s, 1F).

[0021] Example 3 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl diazonium fluoroborate (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 35°C for 1 h, and then heat to 85°C for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, and the organic layer was distilled at atmospheric pressure. The fraction at 110°C was collected to obtain 11.6 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and the yield was 70.5%.

[0022] Example 4 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (5.00 mol, 100.0 g), react at 25℃ for 1 h, and then heat to 85℃ for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25℃ and hydrogen fluoride was distilled and recovered. Pure water was added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110℃ was collected to obtain 10.2 g of o-fluorotrifluorotoluene product with a purity of 99.8% and a yield of 62.1%.

[0023] Example 5 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 25℃ for 1 h, and then heat to 85℃ for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25℃ and hydrogen fluoride was distilled and recovered. Pure water was added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110℃ was collected to obtain 14.1 g of o-fluorotrifluorotoluene product with a purity of 99.8% and a yield of 86.2%.

[0024] Example 6 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (9.00 mol, 180.0 g), react at 25°C for 1 h, and then heat to 85°C for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 MPa. After the reaction was completed, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110°C was collected to obtain 11.8 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and the yield was 72.1%.

[0025] Example 7 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 25℃ for 4 h, and then heat to 85℃ for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25℃ and hydrogen fluoride was distilled and recovered. Pure water was added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110℃ was collected to obtain 8.6 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and the yield was 65.1%.

[0026] Example 8 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), and heat it to 85°C for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110°C was collected to obtain 7.6 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and the yield was 46.4%.

[0027] Example 9 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 25℃ for 1 h, then heat to 50℃ for the first stage of decomposition, keep warm for 1 h, heat to 70℃ for the second stage of decomposition, keep warm for 1 h, heat to 85℃ for the third stage of decomposition, keep warm for 1 h, control the pressure in the reactor to 1.0 Mpa during the reaction, cool to 25℃ after the reaction, and distill to recover hydrogen fluoride. Then add pure water to the autoclave, stir and separate, recover the fluoroboric acid solution in the water layer, distill the organic layer at atmospheric pressure, collect the fraction at 110℃ to obtain 14.0 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and a yield of 85.1%.

[0028] Example 10 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 25°C for 1 h, and then heat to 55°C for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 MPa. After the reaction, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110°C was collected to obtain 5.3 g of o-fluorotrifluorotoluene product with a purity of 99.8%, and the yield was 32.2%.

[0029] Example 11 Preparation of 2-trifluoromethylfluorobenzene Take o-trifluoromethyl fluoroborate diazonium salt (0.10 mol, 25.9 g) in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), react at 25℃ for 1 h, and then heat to 115℃ for decomposition reaction until no gas continues to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction, the temperature was lowered to 25℃ and hydrogen fluoride was distilled and recovered. Pure water was added to the autoclave and stirred to separate the layers. The fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 110℃ was collected to obtain 13.3 g of o-fluorotrifluorotoluene product with a purity of 99.8% and a yield of 81.1%.

[0030] Example 12 Preparation of 3-nitrofluorobenzene

[0031] 3-nitrofluoroboric acid diazonium salt (0.10 mol, 23.7 g) was placed in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), and reacted at 25°C for 1 h, and then heated to 120°C for decomposition reaction until no gas continued to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 MPa. After the reaction was completed, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 200°C was collected to obtain 9.8 g of a light yellow liquid product with a purity of 99.2%, and a yield of 69.2%.

[0032] 1 H NMR (400 MHz, CDCl3) δ 8.05 (d, 1H), 7.91(m, 1H), 7.57(m, 1H),7.44(m, 1H). 19 F NMR (377 MHz, Chloroform-d) δ -109.15(s, 1F).

[0033] Example 13 Preparation of 4-nitrofluorobenzene

[0034] 4-nitrofluoroboric acid diazonium salt (0.10 mol, 23.7 g) was placed in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), and reacted at 25°C for 1 h, and then heated to 100°C for decomposition reaction until no gas continued to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 MPa. After the reaction was completed, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 200°C was collected to obtain 9.9 g of a light yellow liquid product with a purity of 99.3%, and a yield of 70.3%.

[0035] 1 H NMR (400 MHz, DMSO-d6) δ 8.27 (m, 2H), 7.45 (m, 2H). 19 F NMR (377 MHz, DMSO) δ -102.79(s, 1F).

[0036] Example 14 Preparation of 3-fluoroanisole

[0037] 3-Methoxyfluoroboric acid diazonium salt (0.10 mol, 22.2 g) was placed in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), and reacted at 25°C for 1 h, and then heated to 55°C for decomposition reaction until no gas continued to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction was completed, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, and the organic layer was distilled at atmospheric pressure. The fraction at 158°C was collected to obtain 9.4 g of a light yellow liquid product with a purity of 99.4%, and a yield of 74.3%.

[0038] 1 H NMR (400 MHz, DMSO-d6) δ 7.31 (m, 1H), 6.77 (m, 3H), 3.77 (s, 3H). 19 F NMR (377 MHz, Chloroform-d) δ -107.06 (s, 1F).

[0039] Example 15 Preparation of m-fluorobenzoic acid

[0040] 3-Carboxyfluoroboric acid diazonium salt (0.10 mol, 23.6 g) was placed in a high-pressure reactor, in the presence of chlorobenzene (0.45 mol, 50.6 g) and anhydrous hydrogen fluoride (7.00 mol, 140.0 g), and reacted at 25°C for 1 h, and then heated to 100°C for decomposition reaction until no gas continued to be produced. During the reaction, the pressure in the reactor was controlled to be 1.0 Mpa. After the reaction was completed, the temperature was lowered to 25°C and hydrogen fluoride was distilled and recovered. Pure water was then added to the autoclave, stirred and layered, the fluoroboric acid solution in the water layer was recovered, the organic layer was distilled, the 140°C fraction was collected, and chlorobenzene was recovered. The temperature was lowered to -5°C to precipitate 9.4 g of a light yellow crystalline product with a purity of 98.2%, and the yield was 89.1%.

[0041] 1 H NMR (400 MHz, DMSO-d6) δ 13.28 (s, 1H), 7.80 (d, J = 7.6 Hz, 1H), 7.66 (d, J = 9.6 Hz, 1H), 7.57 (m, 1H), 7.50 (m, 1H). 19 F NMR (377 MHz, DMSO) δ -112.60(s, 1F).

[0042] Table 1 Summary of Examples

[0043] Combined with Table 1, it can be seen that when the substituent is 2-CF3, a higher yield of 86.2% is obtained when the HF feed amount is 70eq, and when the HF dosage is too much or too little, the reaction will be affected. When the HF dosage is 50eq, the yield is the lowest, which is 62.1%; the temperature and low-temperature reaction time have a greater impact on the reaction. When the temperature is 25-35°C, the yield is greater than 70%, and when the temperature is reduced to 5°C, the yield is only 68.1%; when the low-temperature reaction time is 1h, the reaction yield is 86.2%, and when the low-temperature reaction time is extended or shortened, the reaction is adversely affected, and if the reaction is not subjected to low-temperature reaction, the yield is only 46.4%, and the yield is reduced to 65.1% when the reaction time is extended.

[0044] Comparative Example 1 Preparation of 2-trifluoromethyl fluorobenzene by Schiemann method Take o-dichlorobenzene (0.45 mol, 66.2 g) in a high-pressure reactor, add 2-trifluoromethyl diazonium fluoroborate (0.1 mol, 25.9 g), then heat to 150°C for pyrolysis reaction, pyrolysis until no gas is generated, and control the pressure in the reactor to be 1.0 MPa during the reaction. After the reaction, cool to 25°C and pass boron trifluoride gas and nitrogen into the aqueous solution of hydrogen fluoride for absorption. Distill the chlorobenzene layer to separate 2-trifluoromethyl fluorobenzene and recover chlorobenzene. The fluoroboric acid in the water layer is used to prepare diazonium fluoroborate. Finally, 12.5 g of a light yellow liquid product with a purity of 98.5% is obtained, and the yield is 76.2%.

[0045] Comparative Example 2 Preparation of 3-nitrofluorobenzene by Schiemann method Take o-dichlorobenzene (0.45 mol, 66.2 g) in a high-pressure reactor, add 3-nitrofluoroborate diazonium salt (0.1 mol, 23.7 g), and then heat it to 150℃ for pyrolysis reaction. Pyrolysis is performed until no gas is generated. During the reaction, the pressure in the reactor is controlled to be 1.0 MPa. After the reaction is completed, the temperature is lowered to 25℃. Boron trifluoride gas and nitrogen are passed into the aqueous solution of hydrogen fluoride for absorption. The chlorobenzene layer is distilled to separate 3-nitrofluorobenzene and recover chlorobenzene. The aqueous layer fluoroboric acid is used to prepare fluoroborate diazonium salt. Finally, 6.1 g of a light yellow liquid product with a purity of 98.2% is obtained, and the yield is 43.0%.

[0046] Comparative Example 3 Preparation of 4-nitrofluorobenzene by Schiemann method Take o-dichlorobenzene (0.45 mol, 66.2 g) in a high-pressure reactor, add 4-nitrofluoroborate diazonium salt (0.10 mol, 23.7 g), and then heat it to 150℃ for pyrolysis reaction. Pyrolysis is performed until no gas is generated. During the reaction, the pressure in the reactor is controlled to be 1.0 MPa. After the reaction is completed, the temperature is lowered to 25℃. Boron trifluoride gas and nitrogen are passed into the aqueous solution of hydrogen fluoride for absorption. The chlorobenzene layer is distilled to separate 4-nitrofluorobenzene and recover chlorobenzene. The aqueous layer fluoroboric acid is used to prepare fluoroborate diazonium salt. Finally, 5.6 g of a light yellow liquid product with a purity of 98.2% is obtained, and the yield is 39.8%.

[0047] Comparative Example 4 Preparation of 3-fluoroanisole by Schiemann method Take o-dichlorobenzene (0.45 mol, 66.2 g) in a high-pressure reactor, add 3-methoxyfluoroborate diazonium salt (0.10 mol, 22.2 g), then heat to 150℃ for pyrolysis reaction, pyrolysis until no gas is generated, and control the pressure in the reactor to be 1.0 MPa during the reaction. After the reaction, cool to 25℃ and pass boron trifluoride gas and nitrogen into the aqueous solution of hydrogen fluoride for absorption. Distill the chlorobenzene layer to separate 3-methoxyfluorobenzene by distillation and recover chlorobenzene. The aqueous layer fluoroboric acid is used to prepare fluoroborate diazonium salt. Finally, 5.3 g of a light yellow liquid product with a purity of 99.1% is obtained, and the yield is 41.9%.

[0048] Comparative Example 5 Preparation of m-fluorobenzoic acid by Schiemann method Take o-dichlorobenzene (0.45 mol, 66.2 g) in a high-pressure reactor, add 3-carboxyfluoroborate diazonium salt (0.10 mol, 23.7 g), and then heat to 150°C for pyrolysis reaction. Pyrolysis is performed until no gas is generated. During the reaction, the pressure in the reactor is controlled to be 1.0 MPa. After the reaction is completed, the temperature is lowered to 25°C. Boron trifluoride gas and nitrogen are passed into the aqueous solution of hydrogen fluoride for absorption. The chlorobenzene layer is distilled to separate the m-fluorobenzoic acid and recover the chlorobenzene. The aqueous layer fluoroboric acid is used to prepare fluoroborate diazonium salt. Finally, 2.2 g of a light yellow crystalline product with a purity of 99.1% is obtained, and the yield is 15.8%.

[0049] In the above embodiment of the present invention, a fluorobenzene derivative with a purity greater than 98.0% is obtained. Compared with the direct thermal decomposition method of diazonium fluoroborate, this method solves the problem of difficulty in post-treatment caused by the production of boron trifluoride during the reaction. Compared with the direct fluorination method of hydrogen fluoride, the problem of corrosion of equipment by hydrogen fluoride caused by the presence of water in the reaction and the occurrence of side reactions affecting the yield and product quality is solved.

Claims

1. A method for preparing fluorobenzene derivatives by replacing tetrafluoroborate, characterized in that: The fluoroborate diazonium salt of substituted aniline as shown in formula (1) is first reacted at low temperature in the presence of a solvent and anhydrous hydrogen fluoride, and then heated to decompose to obtain a fluorobenzene derivative as shown in formula (2). The reaction process is as follows: ， In the formula, R is a substituted alkyl group, a nitro group, an alkoxy group or a carboxyl group.

2. The method for preparing fluorobenzene derivatives by substituting tetrafluoroborate as claimed in claim 1, characterized in that: The benzene substituent R is 2-CF3, 4-CF3, 2-NO2, 3-NO2, 4-NO2, 2-OCH3, 3-OCH3, 4-OCH3, 2-COOH, 3-COOH or 4-COOH.

3. The method for preparing fluorobenzene derivatives by substituting tetrafluoroborate as claimed in claim 1, characterized in that: The solvent is chlorobenzene, ethylene dichloride or o-dichlorobenzene.

4. The method for preparing fluorobenzene derivatives by substituting tetrafluoroborate as claimed in claim 1, characterized in that: The molar ratio of the diazonium fluoroborate salt of substituted aniline to anhydrous hydrogen fluoride is 1:50-90.

5. The method for preparing fluorobenzene derivatives by substituting tetrafluoroborate as claimed in claim 1, characterized in that: The low temperature reaction temperature is 25 - 35 ℃ and the reaction time is 1 - 4 h.

6. The method for preparing fluorobenzene derivatives by substituting tetrafluoroborate as claimed in claim 1, characterized in that: The heating decomposition temperature is 55-150℃.

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