Preparation method of o-difluorobenzene

Abstract

The invention relates to a preparation method of o-difluorobenzene, which comprises the following steps: (1) dissolving o-fluorobenzene fluoboric acid diazonium salt in a solvent to obtain a mixed solution; (2) carrying out a reaction on the mixed solution obtained in the step (1) under microwave heating, and collecting a reaction distillate; and (3) carrying out post-treatment on the distillate obtained in the step (2) to obtain the o-difluorobenzene. According to the present invention, by introducing the microwave-enhanced cracking process of the o-fluorobenzene fluoboric acid diazonium salt, the thermal decomposition caused by non-uniform heating is effectively reduced, the generation of the by-product is reduced, and the yield of the o-difluorobenzene is increased.

Description

Technical Field

[0001] The invention relates to the technical field of pharmaceutical chemistry, and in particular to a method for preparing o-difluorobenzene. Background Art

[0002] Aromatic fluorides play an important role in the fields of medicine, pesticides, energy and liquid crystals. The reason is that fluorine has a strong electronegativity and has a significant inhibitory or promoting effect on biological activity. There are three common synthesis methods, namely, diazotization fluorination of aromatic amines, halogen exchange fluorination and special fluorinating agent fluorination.

[0003] As an important intermediate, o-difluorobenzene can be used as a precursor of difluoronitrobenzene, which is a widely used target molecule and is often used in drug synthesis, such as the synthesis of linezolid, difluorophenyl salicylic acid and fluoroquinolone antibacterial agents. At present, its production method mainly uses the Halex reaction of o-dichlorobenzene to synthesize, and uses difluoroaniline or o-phenylenediamine to synthesize using the Balz-Schiemann reaction. Among them, the Balz-Schiemann reaction is a reaction in which an aromatic diazonium salt reacts with fluoroboric acid to generate a diazonium fluoroborate with low solubility, and the diazonium fluoroborate is cracked under heating or light to release nitrogen and produce an aromatic fluoride.

[0004] The Balz-Schiemann reaction does not require the introduction of other halogens and has high selectivity, but it has many problems such as: (1) the interaction between the mixed layer and the unmixed layer in the container; (2) the waste gas treatment process will produce acidic wastewater containing sodium fluoroborate and sodium borate; (3) uneven heating or hydrolysis of o-fluorophenyl diazonium fluoroborate will lead to uncontrollable thermal decomposition reactions and more by-products; (4) the reaction time is long and the yield is low.

[0005] Therefore, how to achieve efficient cracking of o-fluorobenzene diazonium fluoroborate to synthesize o-difluorobenzene has become a problem that needs to be solved urgently. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention introduces microwave to enhance the cracking process of o-fluorophenyl diazonium fluoroborate.

[0007] The present invention provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0008] (1) dissolving o-fluorophenyl diazonium fluoroborate in 1,2,4-trichlorobenzene to obtain a mixed solution;

[0009] (2) reacting the mixed solution in step (1) under microwave heating, and collecting the reaction distillate;

[0010] (3) post-treating the distillate of step (2) to obtain the o-difluorobenzene.

[0011] The present invention introduces microwaves to act on polar molecules in a substance, so that the arrangement position of polar molecules changes rapidly, and friction generates heat. At the same time, the molecular chains in the substance are broken, which can accelerate the cracking process and promote the cracking reaction. Compared with the traditional heating method, the speed is faster, and the organic matter can be heated evenly without delayed reaction. Using 1,2,4-trichlorobenzene as a thermal cracking solvent can increase the product yield without using a catalyst. Its moderate polarity and boiling point can increase the heating efficiency of microwaves while preventing the occurrence of explosive boiling, so that the reaction mixture heats up rapidly while the internal temperature is uniform, avoiding the occurrence of side reactions to produce a large amount of tar byproducts, and improving the yield of o-difluorobenzene.

[0012] Preferably, the molar ratio of o-fluorophenyl diazonium fluoroborate to 1,2,4-trichlorobenzene is 1:1 to 1:5, for example, 1:1, 1:2, 1:3, 1:4 or 1:5, and more preferably 1:2.3 to 1:3.5.

[0013] Preferably, the water content of the o-fluorophenyl diazonium fluoroborate is less than 2wt%, for example, it may be 0.1wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 1.5wt% or 1.9wt%, etc., preferably the water content is less than 1wt%.

[0014] Preferably, the inorganic salt content of the o-fluorophenylfluoroboric acid is less than 10wt%, for example, it can be 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 9.5wt%, etc., preferably, the inorganic salt content is less than 8wt%.

[0015] The invention reduces the influence of hydrolysis and impurities on the reaction and improves the yield of o-difluorobenzene by controlling the water content of o-fluorobenzene diazonium fluoroborate to be lower than 2wt% and the inorganic salt content to be lower than 10wt%.

[0016] Preferably, the temperature of the heating reaction in step (2) is 150°C to 250°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C or 250°C, etc., preferably 180°C to 220°C.

[0017] Preferably, the reaction time of the heating reaction is 60 to 180 min, for example, it can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min or 180 min.

[0018] Preferably, the heating power of the microwave heating in step (2) is 0.1-1 kw / kg, for example, it can be 0.1 kw / kg, 0.2 kw / kg, 0.4 kw / kg, 0.6 kw / kg, 0.8 kw / kg or 1 kw / kg.

[0019] The present invention further optimizes the reaction time and heating power of microwave heating, improves reaction efficiency, reduces the occurrence of side reactions, and further improves the yield of o-difluorobenzene.

[0020] Preferably, the heating rate of the microwave heating is 1 to 5°C / min, for example, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min or 5°C / min.

[0021] Preferably, tail gas treatment is performed during the reaction of step (2).

[0022] Preferably, the tail gas treatment includes at least two stages of tail gas absorption.

[0023] Preferably, the solvent for tail gas absorption is potassium hydroxide solution and / or potassium carbonate solution.

[0024] Preferably, potassium hydroxide and / or potassium carbonate are continuously added to the tail gas absorption solvent during the reaction in step (2).

[0025] The present invention arranges two-stage tail gas absorption, utilizes alkali solution to absorb the generated acidic gas, and continuously adds alkali during the reaction, which can fully absorb the reaction waste gas and avoid generating a large amount of acidic waste water.

[0026] Preferably, the post-treatment in step (3) comprises washing the distillate in step (2) with a sodium hydroxide solution, standing the solution to separate the layers after washing, and collecting the lower white emulsion.

[0027] Preferably, the concentration of the sodium hydroxide solution is 2-5%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0028] Preferably, the molar ratio of sodium hydroxide to o-fluorophenyl diazonium fluoroborate is 1:3 to 1:10, for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0029] Preferably, the post-treatment in step (3) further comprises adding anhydrous magnesium sulfate to the white emulsion, stirring to remove water from the white emulsion, and then filtering to remove the anhydrous magnesium sulfate to obtain a crude product.

[0030] Preferably, the anhydrous magnesium sulfate is added in an amount of 1 to 5 wt% of the mass of the white emulsion, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, etc., preferably 1 to 3 wt%.

[0031] Preferably, the stirring time is 1 to 5 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h.

[0032] Preferably, the post-treatment in step (3) further comprises adding the crude product into dried zeolite and heating it, and collecting product fractions.

[0033] Preferably, the product fraction is a fraction at 80°C to 90°C.

[0034] As a preferred technical solution, the method for preparing o-difluorobenzene provided by the present invention comprises the following steps:

[0035] (1) dissolving o-fluorophenyl diazonium fluoroborate in 1,2,4-trichlorobenzene at a molar ratio of 1:1 to 1:5 to obtain a mixed solution, wherein the water content of the o-fluorophenyl diazonium fluoroborate is less than 2wt%, and the inorganic salt content of the o-fluorophenyl diazonium fluoroborate is less than 10wt%;

[0036] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate, the heating reaction temperature is 150° C. to 250° C., the reaction time is 60 to 180 min, the heating power of the microwave heating is 0.1 to 1 kW / kg, and the heating rate is 1 to 5° C. / min; and two-stage tail gas treatment is provided, the tail gas absorption solvent is potassium hydroxide solution and / or potassium carbonate solution, and potassium hydroxide and / or potassium carbonate are continuously added to the tail gas absorption solvent during the reaction;

[0037] (3) The distillate of step (2) is washed with a sodium hydroxide solution having a mass concentration of 2 to 5%, wherein the molar ratio of the sodium hydroxide to o-fluorobenzene diazonium fluoroborate is 1:3 to 1:10, and after washing, the solution is allowed to stand for stratification, and the lower layer of white emulsion is collected; anhydrous magnesium sulfate is added to the white emulsion, wherein the amount of anhydrous magnesium sulfate added is 1 to 5 wt% of the mass of the white emulsion, and after stirring for 1 to 5 hours to remove water from the emulsion, the anhydrous magnesium sulfate is filtered to remove the crude product; the crude product is added to a dried zeolite and heated, and the fraction of the product at 80°C to 90°C is collected to obtain the o-difluorobenzene. Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] (1) The present invention utilizes microwaves to enhance the process of generating o-difluorobenzene from o-fluorobenzene diazonium fluoroborate, thereby achieving rapid cracking, reducing the generation of by-products due to uneven heating, and reducing energy consumption.

[0039] (2) The present invention uses 1,2,4-trichlorobenzene as a cracking solvent, which can increase the product yield without using a catalyst. Its moderate polarity and boiling point can improve the heating efficiency of microwaves and increase the cracking reaction yield.

[0040] (3) The present invention is provided with a two-stage alkaline liquid tail gas absorption device, which utilizes the neutralization reaction to absorb the generated acidic gas, thereby avoiding the generation of a large amount of acidic wastewater. DETAILED DESCRIPTION

[0041] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0042] Example 1

[0043] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0044] (1) o-Fluorobenzene diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:3.5, wherein the o-Fluorobenzene diazonium fluoroborate has a water content of 0.15 wt % and an inorganic salt content of 5.57 wt %.

[0045] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 0.3 kw / kg, the temperature is increased to 180° C. at 2° C. / min, the reaction time is 180 min, and the reaction distillate is collected. A two-stage tail gas absorption device is also provided, the solvent of the tail gas absorption device is potassium hydroxide solution, and potassium hydroxide is continuously added to the tail gas absorption device during the reaction.

[0046] (3) washing the distillate of step (2) with a 2% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 1 wt% anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and then filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0047] Example 2

[0048] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0049] (1) o-fluorophenyl diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:1, wherein the o-fluorophenyl diazonium fluoroborate has a water content of 1.5 wt % and an inorganic salt content of 2.33 wt %.

[0050] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 0.5 kw / kg, the temperature is increased to 220° C. at 3° C. / min, the reaction time is 120 min, and the reaction distillate is collected. A two-stage tail gas absorption device is also provided, the solvent of the tail gas absorption device is potassium hydroxide solution, and potassium hydroxide is continuously added to the tail gas absorption device during the reaction.

[0051] (3) washing the distillate of step (2) with a 3% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 2 wt % anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0052] Example 3

[0053] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0054] (1) o-fluorophenyl diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:2, wherein the o-fluorophenyl diazonium fluoroborate has a water content of 0.5 wt % and an inorganic salt content of 6.75 wt %.

[0055] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 0.2 kw / kg, the temperature is increased to 150° C. at 1° C. / min, the reaction time is 180 min, and the reaction distillate is collected. A two-stage tail gas absorption device is provided at the same time, the solvent of the tail gas absorption device is potassium carbonate solution, and potassium carbonate is continuously added to the tail gas absorption device during the reaction.

[0056] (3) washing the distillate of step (2) with a 1% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 3 wt % anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0057] Example 4

[0058] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0059] (1) o-fluorophenyl diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:3, wherein the o-fluorophenyl diazonium fluoroborate has a water content of 1.2 wt % and an inorganic salt content of 8.84 wt %.

[0060] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 1 kW / kg, the temperature is raised to 250°C at 5°C / min, the reaction time is 60 min, and the reaction distillate is collected. A two-stage tail gas absorption device is also provided, the solvent of the tail gas absorption device is potassium carbonate solution, and potassium carbonate is continuously added to the tail gas absorption device during the reaction.

[0061] (3) washing the distillate of step (2) with a 5% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 5 wt % anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0062] Example 5

[0063] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0064] (1) o-fluorophenyl diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:4, wherein the o-fluorophenyl diazonium fluoroborate has a water content of 0.4 wt% and an inorganic salt content of 7.25 wt%.

[0065] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 0.7 kw / kg, the temperature is increased to 200° C. at 3° C. / min, the reaction time is 90 min, and the reaction distillate is collected. A two-stage tail gas absorption device is also provided, the solvent of the tail gas absorption device is a hydrogen oxidizing agent solution, and potassium hydroxide is continuously added to the tail gas absorption device during the reaction.

[0066] (3) washing the distillate of step (2) with a 2% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 4 wt % anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0067] Example 6

[0068] This embodiment provides a method for preparing o-difluorobenzene, which comprises the following steps:

[0069] (1) o-fluorophenyl diazonium fluoroborate is dissolved in 1,2,4-trichlorobenzene at a molar ratio of 1:5, wherein the o-fluorophenyl diazonium fluoroborate has a water content of 1.8 wt % and an inorganic salt content of 4.57 wt %.

[0070] (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate; the microwave heating power is 0.8 kw / kg, the temperature is increased to 180° C. at 3.5° C. / min, the reaction time is 120 min, and the reaction distillate is collected. A two-stage tail gas absorption device is also provided, the solvent of the tail gas absorption device is a hydrogen oxidizing agent solution, and potassium hydroxide is continuously added to the tail gas absorption device during the reaction.

[0071] (3) washing the distillate of step (2) with a 2% sodium hydroxide solution, allowing the solution to stand for stratification, and collecting the lower white emulsion; adding 2 wt % anhydrous magnesium sulfate to the white emulsion in multiple portions, stirring to remove water from the emulsion, and filtering to remove the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to dried zeolite and heating the product, and collecting the product fraction at 80° C. to 90° C.

[0072] Example 7

[0073] This embodiment provides a method for preparing o-difluorobenzene. Except that the water content of o-fluorobenzene diazonium fluoroborate in step (1) is 3.15 wt %, other conditions are the same as those in Example 1.

[0074] Example 8

[0075] This embodiment provides a method for preparing o-difluorobenzene. Except that the o-fluorobenzene diazonium fluoroborate salt contains 10.16 wt % of inorganic salt in step (1), other conditions are the same as those in Example 1.

[0076] Example 9

[0077] This embodiment provides a method for preparing o-difluorobenzene. Except that the reaction time in step (2) is 50 min, other conditions are the same as those in Example 1.

[0078] Example 10

[0079] This embodiment provides a method for preparing o-difluorobenzene. Except that the microwave heating power in step (2) is 0.05 kw / kg, other conditions are the same as those in Example 1.

[0080] Embodiment 11

[0081] This embodiment provides a method for preparing o-difluorobenzene. Except that the microwave heating power in step (2) is 1.5 kw / kg, other conditions are the same as those in Example 1.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing o-difluorobenzene. Except that the heating method adopts the traditional electric heating method, other conditions are the same as those in Example 1.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing o-difluorobenzene. Except for using o-dichlorobenzene as the thermal cracking solvent, other conditions are the same as those in Example 1.

[0086] Test Results

[0087] Table 1

[0088]

[0089]

[0090] The test results show that:

[0091] (1) It can be seen from Examples 1 to 6 that the present invention can achieve efficient cleavage of o-fluorobenzene diazonium fluoroborate by microwave heating to enhance the process of cleavage of o-fluorobenzene diazonium fluoroborate to produce o-difluorobenzene, and achieve the technical effects of high yield and high energy utilization.

[0092] (2) It can be seen from Examples 1 and 7 to 8 that the water content of o-fluorophenyl diazonium fluoroborate in Example 7 is 3.15wt%, compared with 0.15wt% in Example 1, and the pure yield is reduced from 82.3% in Example 1 to 68.7% in Example 7. The o-fluorophenyl diazonium fluoroborate in Example 8 contains 10.16wt% of inorganic salt, compared with 5.57wt% of inorganic salt in Example 1, and the pure yield is reduced from 82.3% in Example 1 to 71.6% in Example 8. The present invention can effectively avoid the influence of impurities and further improve the yield by further controlling the water content and inorganic salt content of o-fluorophenyl diazonium fluoroborate.

[0093] (3) It can be seen from Examples 1 and 9 to 11 that when the reaction time of Example 9 is reduced to 50 min, compared with the reaction time of 180 min in Example 1, the net yield is reduced from 82.3% in Example 1 to 71.5% in Example 9, the microwave heating power is reduced from 0.3 kw / kg in Example 1 to 0.05 kw / kg in Example 10, the net yield is reduced to 77.6%, and the microwave heating power is increased to 1.5 kw / kg, the net yield is reduced to 81.2%. The present invention further improves the yield by further optimizing the reaction time and heating power of the microwave reaction.

[0094] (3) It can be seen from Example 1 and Comparative Example 1 that the pure yield of Comparative Example 1, which adopts ordinary electric heating, drops sharply from 82.3% of Example 1 to 68.3% compared with the microwave heating of Example 1. The present invention can prevent the side reaction caused by uneven heating by microwave heating, while when microwave heating is not adopted, it is impossible to achieve efficient cleavage of o-fluorophenyl diazonium fluoroborate.

[0095] (4) It can be seen from Example 1 and Comparative Example 2 that in Comparative Example 2, o-dichlorobenzene is used as the solvent, and the pure yield is reduced from 82.3% in Example 1 to 35.4% compared with Example 1, which uses 1,2,4-trichlorobenzene as the solvent. The present invention uses 1,2,4-trichlorobenzene as the solvent to increase the product yield without using a catalyst, and its moderate polarity and boiling point can improve the heating efficiency of microwaves and improve the yield of the cracking reaction.

[0096] In summary, the present invention prepares o-difluorobenzene by cracking o-fluorobenzene diazonium fluoroborate through microwave heating, avoids the side reactions caused by traditional uneven heating, promotes the efficient cracking of o-fluorobenzene diazonium fluoroborate, optimizes the reaction solvent and reaction temperature under microwave heating, and improves the yield of o-difluorobenzene.

[0097] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing o-difluorobenzene, characterized in that: The preparation method comprises the following steps: (1) dissolving o-fluorophenyl diazonium fluoroborate in 1,2,4-trichlorobenzene to obtain a mixed solution; (2) reacting the mixed solution in step (1) under microwave heating, and collecting the reaction distillate; (3) post-treating the distillate of step (2) to obtain the o-difluorobenzene.

2. The preparation method according to claim 1, characterized in that: The molar ratio of o-fluorobenzene diazonium fluoroborate to 1,2,4-trichlorobenzene in step (1) is 1:1 to 1:5, preferably 1:2.3 to 1:3.5; Preferably, the water content of the o-fluorophenyl diazonium fluoroborate is less than 2wt%, preferably less than 1wt%; Preferably, the inorganic salt content of the o-fluorophenylfluoroboric acid is less than 10 wt %, preferably less than 8 wt %.

3. The preparation method according to claim 1 or 2, characterized in that: The reaction temperature of the microwave heating in step (2) is 150°C to 250°C, preferably 180°C to 220°C; Preferably, the reaction time of the microwave heating is 60 to 180 minutes.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The power of the microwave heating in step (2) is 0.1-1 kw / kg; Preferably, the heating rate of the microwave heating is 1-5°C / min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The preparation method further comprises step (2) treating tail gas during the reaction; Preferably, the tail gas treatment comprises at least two stages of tail gas absorption; Preferably, the solvent for tail gas absorption is potassium hydroxide solution and / or potassium carbonate solution; Preferably, during the reaction in step (2), potassium hydroxide and / or potassium carbonate are continuously added to the solvent for absorbing the tail gas.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The post-treatment in step (3) comprises washing the distillate in step (2) with a sodium hydroxide solution, allowing the distillate to stand for stratification after washing, and collecting the lower white emulsion; Preferably, the mass concentration of the sodium hydroxide solution is 2-5%; Preferably, the molar ratio of the sodium hydroxide to the diazonium fluoroborate of o-fluorophenyl is 1:3 to 1:

10.

7. The preparation method according to claim 6, characterized in that: The post-treatment in step (3) further comprises adding anhydrous magnesium sulfate to the white emulsion, stirring to remove water from the white emulsion, and then filtering to remove the anhydrous magnesium sulfate to obtain a crude product; Preferably, the amount of anhydrous magnesium sulfate added is 1 to 5 wt % of the mass of the white emulsion, preferably 1 to 3 wt %; Preferably, the stirring time is 1 to 5 hours.

8. The preparation method according to claim 7, characterized in that: The post-treatment in step (3) further comprises adding the crude product into dried zeolite and heating it, and collecting product fractions.

9. The preparation method according to claim 8, characterized in that: The product fraction is a fraction at 80°C to 90°C.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The preparation method comprises the following steps: (1) dissolving o-fluorophenyl diazonium fluoroborate in 1,2,4-trichlorobenzene at a molar ratio of 1:1 to 1:5 to obtain a mixed solution, wherein the water content of the o-fluorophenyl diazonium fluoroborate is less than 2wt%, and the inorganic salt content of the o-fluorophenyl diazonium fluoroborate is less than 10wt%; (2) reacting the mixed solution in step (1) under microwave heating, collecting the reaction distillate, the heating reaction temperature is 150° C. to 250° C., the reaction time is 60 to 180 min, the heating power of the microwave heating is 0.1 to 1 kW / kg, and the heating rate is 1 to 5° C. / min; and two-stage tail gas treatment is provided, the tail gas absorption solvent is potassium hydroxide solution and / or potassium carbonate solution, and potassium hydroxide and / or potassium carbonate are continuously added to the tail gas absorption solvent during the reaction; (3) washing the distillate of step (2) with a sodium hydroxide solution having a mass concentration of 2 to 5%, wherein the molar ratio of the sodium hydroxide to o-fluorophenyl diazonium fluoroborate is 1:3 to 1:10, allowing the solution to stand for stratification after washing, and collecting the lower layer of white emulsion; adding anhydrous magnesium sulfate to the white emulsion, wherein the amount of anhydrous magnesium sulfate added is 1 to 5 wt % of the mass of the white emulsion, stirring for 1 to 5 h to remove water from the white emulsion, and filtering out the anhydrous magnesium sulfate to obtain a crude product; adding the crude product to a dried zeolite and heating it, and collecting a fraction of the product at 80° C. to 90° C. to obtain the o-difluorobenzene.

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