A preparation method of 4-fluoro-3-nitrotrifluorotoluene

Abstract

The present invention provides a method for preparing 4-fluoro-3-nitrobenzotrifluoride. The preparation method of the present invention comprises the following steps: in an organic solvent, 4-chloro-3-nitrobenzotrifluoride and KF are subjected to fluorination reaction to obtain 4-fluoro-3-nitrobenzotrifluoride; the raw material of the fluorination reaction is composed of the organic solvent, the 4-chloro-3-nitrobenzotrifluoride and the KF. The preparation method does not use a catalyst, and can also achieve high yield, good purity and short reaction time; at the same time, it is easy to operate, low in cost, less waste pollution, and more conducive to industrial application.

Description

Technical Field

[0001] The invention belongs to the field of organic chemistry and relates to a method for preparing 4-fluoro-3-nitrotrifluorotoluene. Background Art

[0002] The molecular formula of 2-nitro-4-trifluoromethylbenzonitrile is C8H3F3N2O2, the relative molecular mass is 216.1, the melting point is 44-47℃, the boiling point is 156-158℃18mm Hg(lit.), the density is 1.56g / mL, and it is a yellow crystalline solid at room temperature. 2-nitro-4-trifluoromethylbenzonitrile is widely used in medicine, pesticides, chemicals and other fields. It is an important intermediate for the synthesis of insecticides 4-benzoylisoxazole, isoxathiapiprolin, and herbicide 5-cyclopropylisoxazole. The synthesis of the above-mentioned compounds and their intermediates is disclosed in patent CN 1359372A, and is also mentioned in European patent applications.

[0003] Patent publication number CN 1359372 A discloses a method for synthesizing 2-nitro-4-trifluoromethylbenzonitrile: 4-chloro-3-nitrotrifluorotoluene and cuprous cyanide, a phase transfer catalyst or an alkali metal cyanide, cuprous bromide, a phase transfer catalyst or in the presence of a metal lithium salt are reacted in an organic solvent to prepare 2-nitro-4-trifluoromethylbenzonitrile. The preparation method has high cost, complicated operation, various raw materials, and great difficulty in post-processing recovery and application.

[0004] The molecular formula of 4-fluoro-3-nitrobenzotrifluoride is C7H3F4NO2, the relative molecular mass is 209.1, the relative density is 1.494, the boiling point is 92℃ (15mmHg), the refractive index is 1.4620, and it is a light yellow-green liquid at room temperature. 4-fluoro-3-nitrobenzotrifluoride is an important intermediate, which is used in the fields of medicine, pesticide, chemical organic synthesis, etc., and is used to synthesize the pesticide 4-benzoylisoxazole, isoxathiapiprolin, and the herbicide 5-cyclopropylisoxazole.

[0005] Patent US4424396 and magazines have reported the use of the same raw material 4-chloro-3-nitrobenzotrifluoride to synthesize the target product 4-fluoro-3-nitrobenzotrifluoride. For example, Journal of Organic Chemistry, 1991, vol.56, #22, p.6406-6411 discloses that KF prepared by a "spray drying" process (the surface area of ​​the material droplets increases after atomization) is added to sulfolane, and the target product 4-fluoro-3-nitrobenzotrifluoride is synthesized under the catalysis of tetramethylammonium chloride. The yield of 80% can be achieved only in the presence of raw materials of special processes and phase transfer catalysts. There is also Advanced Synthesis and Catalysis, 2008, vol.350, #17, p.2677-2682, KF and bis(diphenylphosphine)imide chloride are added to DMSO to synthesize the target product with a yield of 72%. In the literature that has been consulted, a catalyst must be added to synthesize the target product. The above synthesis routes are all costly and have complex raw materials. Summary of the invention

[0006] In order to overcome the problems of high production cost, serious three-waste pollution, and difficult post-treatment in the prior art, the present invention develops a preparation method for 4-fluoro-3-nitrotrifluorotoluene with high yield, good purity and short reaction time, and the process is simple, the operation is convenient, the cost is low, the waste pollution is less, and it is more conducive to industrial application.

[0007] The invention provides a method for preparing 4-fluoro-3-nitrobenzotrifluoride, which comprises the following steps: in an organic solvent, subjecting 4-chloro-3-nitrobenzotrifluoride and KF to a fluorination reaction to obtain 4-fluoro-3-nitrobenzotrifluoride;

[0008]

[0009] The raw materials for the fluorination reaction consist of the organic solvent, the 4-chloro-3-nitrobenzotrifluoride and the KF.

[0010] In the fluorination reaction, the organic solvent may be a conventional organic solvent for fluorination reactions in the art, preferably an aprotic polar solvent, more preferably DMF, DMA, acetonitrile, sulfolane or DMSO; for example, sulfolane or DMF.

[0011] In the fluorination reaction, the molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent can be the conventional amount used in the fluorination reaction in the art, preferably 1.0-2.5 mol / L; more preferably 1.4-2.4 mol / L, such as 1.9 mol / L.

[0012] In the fluorination reaction, the molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride can be the conventional amount used in the fluorination reaction in the art, preferably (1.0-2.0):1; more preferably (1.0-1.5):1, for example 1.3:1.

[0013] In the fluorination reaction, the reaction temperature of the fluorination reaction can be a conventional temperature of fluorination reaction in the art, preferably 25°C-250°C, more preferably 130-180°C, such as 150-180°C.

[0014] In the fluorination reaction, the progress of the fluorination reaction is monitored by a conventional detection method in the art (such as GC monitoring), and the endpoint is preferably when the concentration of the 4-chloro-3-nitrobenzotrifluoride in the reaction solution is less than 1%.

[0015] In the fluorination reaction, the 4-chloro-3-nitrobenzotrifluoride is added into a mixed solution of KF and the organic solvent; the adding time is 1-10 hours, preferably 3-7 hours, more preferably 5-7 hours.

[0016] In the fluorination reaction, the post-treatment can refer to the conventional post-treatment operation method in the art; preferably, the post-treatment includes the following steps:

[0017] (1) filtering the reaction solution after the fluorination reaction is completed, recovering the filtrate and the filter cake, wherein the filtrate is the crude product and the filter cake is KF and / or KCl;

[0018] (2) The filtrate is distilled to obtain the 4-fluoro-3-nitrotrifluorotoluene and the organic solvent.

[0019] Preferably, the distillation is vacuum distillation, such as vacuum rectification.

[0020] In the fluorination reaction, when the boiling point of the organic solvent is higher than 209.6° C., after the 4-fluoro-3-nitrobenzotrifluoride is obtained by distillation in the post-treatment step (2), the organic solvent can be kept in the container for further use.

[0021] In the fluorination reaction, the organic solvent is DMF or sulfolane; the molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent is 1.9 mol / L; the molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride is 1.3:1; the reaction temperature of the fluorination reaction is 150-180° C.; and the addition time is 5-7 hours.

[0022] The present invention also provides a method for preparing 2-nitro-4-trifluoromethylbenzonitrile, which comprises the following steps:

[0023] (1) the fluorination reaction occurs under the conditions and parameters of any one of the present invention;

[0024] (2) cyaniding 4-fluoro-3-nitrobenzotrifluoride with metal cyanide to obtain 2-nitro-4-trifluoromethylbenzonitrile;

[0025]

[0026] In the cyanation reaction, the cyanation reaction may occur in the presence of an organic solvent or in the absence of a solvent.

[0027] In the cyanation reaction, the organic solvent is a non-protonic polar solvent.

[0028] In the cyanidation reaction, the temperature of the cyanidation reaction is 150-180°C.

[0029] In the cyanation reaction, the boiling point of the organic solvent is higher than or equal to the temperature of the cyanation reaction.

[0030] In the cyanation reaction, the raw materials of the cyanation reaction consist of the organic solvent, the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide; or consist of the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide.

[0031] In the cyanation reaction, the organic solvent is DMSO, DMF, DMA or sulfolane; preferably DMSO or DMF.

[0032] In the cyanidation reaction, the metal cyanide may be a conventional metal cyanide used in cyanidation reactions in the art, preferably KCN, NaCN, CuCN, potassium ferrocyanide and potassium ferrocyanide, more preferably KCN, NaCN, such as KCN.

[0033] In the cyanation reaction, when the organic solvent is DMF, the temperature of the cyanation reaction is preferably 150°C.

[0034] In the cyanation reaction, when the cyanation reaction occurs in the presence of an organic solvent, the molar volume ratio of the 4-fluoro-3-nitrobenzotrifluoride to the organic solvent can be a conventional amount used in cyanation reactions in the art, preferably 1.0-2.6 mol / L; for example, 1.5-2.1 mol / L.

[0035] In the cyanation reaction, the molar ratio of cyano group in the metal cyanide to 4-fluoro-3-nitrobenzotrifluoride can be the conventional amount used in cyanation reactions in the art, preferably (0.95-1.0):1.0; more preferably (0.95-0.97):1.0, for example 0.95:1.0 or 0.96:1.0.

[0036] In the cyanation reaction, the progress of the cyanation reaction is monitored by a conventional detection method in the art (such as GC), and the endpoint is preferably when the concentration of the 4-fluoro-3-nitrobenzotrifluoride in the reaction solution is less than 0.1%.

[0037] In the cyanidation reaction, the post-treatment can refer to the conventional post-treatment operation method in the art; preferably, the post-treatment includes the following steps:

[0038] (1) filtering the reaction solution after the cyanation reaction is completed, recovering the filtrate and the filter cake, wherein the filtrate is a crude product and the filter cake is a metal fluoride salt;

[0039] (2) The filtrate is distilled to recover the organic solvent to obtain 2-nitro-4-trifluoromethylbenzonitrile.

[0040] In the post-treatment, the distillation is vacuum distillation, such as vacuum rectification.

[0041] In a preferred embodiment, the raw materials of the cyanation reaction are composed of the organic solvent, the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide; the organic solvent is DMSO or DMF; the metal cyanide is KCN; the molar volume ratio of the 4-fluoro-3-nitrobenzotrifluoride to the organic solvent is 1.5-2.1 mol / L; the molar ratio of the cyanide in the metal cyanide to the 4-fluoro-3-nitrobenzotrifluoride is 0.95:1.0 or 0.96:1.0.

[0042] In a preferred embodiment, the raw materials for the cyanation reaction are composed of the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide; the metal cyanide is KCN; and the molar ratio of the cyanide in the metal cyanide to the 4-fluoro-3-nitrobenzotrifluoride is 0.95:1.0 or 0.96:1.0.

[0043] Without violating the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0044] The "boiling point" referred to in the present invention refers to the temperature at which a pure substance boils under 1 standard atmosphere pressure.

[0045] The reagents and raw materials used in the present invention are all commercially available. KF manufacturer: Aladdin, AR, powder, 99%.

[0046] The positive and progressive effects of the present invention are as follows: the product obtained by the preparation method disclosed in the present invention (1) has a high yield and good purity; (2) does not use a catalyst and can also achieve a short reaction time; (3) has a simple process, convenient operation, low cost, less waste pollution, and is more conducive to industrial application. DETAILED DESCRIPTION

[0047] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0048] Example 1

[0049] The reaction equation is:

[0050]

[0051] Experimental feeding table:

[0052]

[0053] 150.8 g of potassium fluoride and 1350.0 g of solvent sulfolane were added to a 2L reaction flask, the temperature was raised to 150°C, 450.0 g of raw material 4-chloro-3-nitrobenzotrifluoride was added dropwise for 5 hours, the reaction was kept at 150°C, and the reaction progress was monitored by GC. When the raw material 4-chloro-3-nitrobenzotrifluoride was ≤1.0%, the reaction was continued for 10 hours, the temperature was lowered to room temperature, the generated potassium chloride and potassium fluoride were filtered out, the filtrate was distilled, and the product was distilled to obtain anhydrous light yellow liquid 4-fluoro-3-nitrobenzotrifluoride. The product purity was 99.0% as determined by GC, and the bottom of the kettle was recovered and reused with a yield of 90.0%.

[0054] Hydrogen spectrum analysis: 1 H NMR (600MHz, CDC13) δ8.59-8.44(m,2H),7.65(dd,J=9.0,2.2Hz,1H),7.03(d,J=9.0Hz,1H),4.03-3.99(m,2H),3.60-3.56(m,2H).

[0055] GC analysis method

[0056] Sample preparation method: sampling, filtration and filtrate proofing.

[0057]

[0058]

[0059] Experimental feeding table:

[0060]

[0061] 366.0g 4-fluoro-3-nitrobenzotrifluoride, 108.1g potassium cyanide, 1098.0g solvent DMF were added to a 2L reaction flask, the temperature was raised to 150°C, the reaction progress was monitored by GC, and the temperature was kept for 8 to 12 hours until the raw material 4-fluoro-3-nitrobenzotrifluoride was completely reacted and no longer proceeded, the temperature was lowered to room temperature, filtered, and dried to obtain a total of 91.8g KF solid, which was recycled. DMF and 4-fluoro-3-nitrobenzotrifluoride were recovered from the filtrate, and 2-nitro-4-trifluoromethylbenzonitrile was obtained by post-treatment. The product purity was 99.4% and the yield was 90.0% as detected by GC.

[0062] Hydrogen spectrum analysis: 1H NMR (400 MHz, CDCl3): δ 8.60 (s, 1H), 8.14-8.04 (m, 2H).

[0063] Experimental feeding table:

[0064]

[0065] 91.8 g of dry filter cake (ground into powder, KF solid recovered in the previous step) and 825.6 g of solvent sulfolane were added to a 2 L reaction flask, the temperature was raised to 150° C., 275.2 g of raw material 4-chloro-3-nitrobenzotrifluoride was added dropwise for 5 hours, and the reaction was kept at 150° C. The reaction progress was monitored by GC, i.e., the reaction was carried out for 8 to 12 hours. When the raw material 4-chloro-3-nitrobenzotrifluoride was ≤1.0%, the temperature was lowered to room temperature, filtered, and the filtrate was distilled to obtain the product, and anhydrous light yellow liquid 4-fluoro-3-nitrobenzotrifluoride was obtained. The product purity was 99.0% as determined by GC, and the bottom of the kettle was recovered and reused with a yield of 90.0%.

[0066] Hydrogen spectrum analysis: 1H NMR (600 MHz, CDC13) δ 8.59-8.44 (m, 2H), 7.65 (dd, J = 9.0, 2.2 Hz, 1H), 7.03 (d, J = 9.0 Hz, 1H), 4.03-3.99 (m, 2H), 3.60-3.56 (m, 2H).

[0067] Example 2

[0068] The reaction equation is:

[0069]

[0070] Experimental feeding table:

[0071]

[0072] 139.2g potassium fluoride and 1350.0g solvent sulfolane were added to a 2L reaction flask, the temperature was raised to 150°C, 450.0g raw material 4-chloro-3-nitrobenzotrifluoride was added dropwise for 4 hours, the reaction was kept at 150°C, and the reaction progress was monitored by GC. When the raw material 4-chloro-3-nitrobenzotrifluoride was ≤1.0%, the reaction was continued for 10 hours, the temperature was lowered to room temperature, the generated potassium chloride and potassium fluoride were removed by filtration, the filtrate was rectified, and the product was distilled to obtain anhydrous light yellow liquid 4-fluoro-3-nitrobenzotrifluoride. The product purity was 99.1% as determined by GC, and the bottom of the kettle was recovered and reused with a yield of 88.0%. Its hydrogen spectrum was the same as that in Example 1.

[0073] Experimental feeding table:

[0074]

[0075]

[0076] 360.0g 4-fluoro-3-nitrobenzotrifluoride, 107.4g potassium cyanide, 1080.0g solvent acetonitrile were added to a 2L reaction flask, the temperature was raised to 80°C, the reaction progress was monitored by GC, and the temperature was kept for 10-12h until the raw material 4-fluoro-3-nitrobenzotrifluoride was completely reacted and no longer proceeded, the temperature was lowered to room temperature, filtered, and dried to obtain a total of 92.3g KF solid, which was recycled. Acetonitrile and 4-fluoro-3-nitrobenzotrifluoride were recovered from the filtrate, and 2-nitro-4-trifluoromethylbenzonitrile was obtained by post-treatment. The product purity was 99.3% and the yield was 50.0% after GC detection. Its hydrogen spectrum was the same as that of Example 1.

[0077] Example 3

[0078] The reaction equation is:

[0079]

[0080] Experimental feeding table:

[0081]

[0082] 150.8g potassium fluoride, 1350.0g solvent sulfolane, 450.0g raw material 4-chloro-3-nitrobenzotrifluoride were added to a 2L reaction flask, and the temperature was raised to 180°C for reaction. The reaction was monitored by GC. When the raw material 4-chloro-3-nitrobenzotrifluoride was ≤1.0%, the reaction was continued for 10 hours, and the temperature was lowered to room temperature. The generated potassium chloride and potassium fluoride were filtered out, and the filtrate was rectified to obtain the product, and anhydrous light yellow liquid 4-fluoro-3-nitrobenzotrifluoride was obtained. The purity of the product was 99.2% as determined by GC. The bottom of the kettle was recovered and reused with a yield of 85.0%. Its hydrogen spectrum was the same as that in Example 1.

[0083] Experimental feeding table:

[0084]

[0085]

[0086] 355.0g 4-fluoro-3-nitrobenzotrifluoride and 104.8g potassium cyanide were added to a 2L reaction flask, and the temperature was raised to 150°C. The reaction progress was monitored by GC, and the temperature was kept for 8-12h until the reaction of the raw material 4-fluoro-3-nitrobenzotrifluoride was completed and no longer continued. The temperature was lowered to room temperature, filtered, and dried to obtain a total of 90.8g KF solid, which was recycled. The filtrate was used to recover 4-fluoro-3-nitrobenzotrifluoride, and post-processed to obtain 2-nitro-4-trifluoromethylbenzonitrile. The product purity was 99.1% and the yield was 70.0% after GC detection. Its hydrogen spectrum was the same as that of Example 1.

[0087] Example 4

[0088] The reaction equation is:

[0089]

[0090] Experimental feeding table:

[0091]

[0092] 150.8g potassium fluoride and 1350.0g solvent sulfolane were added to a 2L reaction flask, the temperature was raised to 130°C, 450.0g raw material 4-chloro-3-nitrobenzotrifluoride was added dropwise for 5 hours, the reaction was kept at 130°C, and the reaction progress was monitored by GC. When the raw material 4-chloro-3-nitrobenzotrifluoride was ≤1%, that is, the reaction was carried out for 8-12 hours, the temperature was lowered to room temperature, the generated potassium chloride and potassium fluoride were filtered out, and the filtrate was rectified to obtain the product, and anhydrous light yellow liquid 4-fluoro-3-nitrobenzotrifluoride was obtained. The product purity was 99.4% after GC detection, and the bottom of the kettle was recovered and reused, with a yield of 75.0%. Its hydrogen spectrum was the same as that in Example 1.

[0093] Experimental feeding table:

[0094]

[0095]

[0096] 313g 4-fluoro-3-nitrobenzotrifluoride, 93.4g potassium cyanide, 782.5g solvent DMSO were added to a 2L reaction flask, the temperature was raised to 180°C, the reaction progress was monitored by GC, and the temperature was kept for 10 to 12 hours until the raw material 4-fluoro-3-nitrobenzotrifluoride was completely reacted and no longer proceeded, the temperature was lowered to room temperature, filtered, and dried to obtain a total of 81.6g KF solid crude product, which was recycled. DMSO was recovered from the filtrate, and 2-nitro-4-trifluoromethylbenzonitrile was obtained by post-treatment. The product purity was 99.2% and the yield was 85.0% after GC detection. Its hydrogen spectrum was the same as that of Example 1.

[0097] Example 5

[0098] The reaction equation is:

[0099] Experimental feeding table:

[0100]

[0101] 366.0g 4-fluoro-3-nitrobenzotrifluoride and 81.5g NaCN were added to a 2L reaction flask. 1098.0g DMF solvent was heated to 150°C, and the reaction progress was monitored by GC. The temperature was kept for 10 hours until the raw material 4-fluoro-3-nitrobenzotrifluoride was completely reacted and no longer reacted. The temperature was cooled to room temperature, filtered, and dried to obtain a total of 91.8g KF solid, which was recycled. DMF and 4-fluoro-3-nitrobenzotrifluoride were recovered from the filtrate, and post-processed to obtain 2-nitro-4-trifluoromethylbenzonitrile, 332.8g. The product purity was 99% and the yield was 88.0% after GC detection. Its hydrogen spectrum was the same as that of Example 1.

[0102] Comparative Example 1

[0103] Feeding amount:

[0104]

[0105] Experimental operation:

[0106] 10.9 g of sodium fluoride and 135.0 g of solvent sulfolane were added to a 250 mL reaction flask, the temperature was raised to 150° C., 45.0 g of raw material 4-chloro-3-nitrotrifluorotoluene was added dropwise for 5 hours, and the reaction was kept at 150° C. The reaction progress was monitored by GC. The percentage of raw materials was 99.6%, and there was basically no product peak.

[0107] Conclusion: NaF does not react.

Claims

1. A method for preparing 2-nitro-4-trifluoromethylbenzonitrile, characterized in that: The preparation method comprises the following steps: (1) In an organic solvent, 4-chloro-3-nitrobenzotrifluoride and KF undergo fluorination reaction to obtain 4-fluoro-3-nitrobenzotrifluoride; ， The raw materials of the fluorination reaction are composed of the organic solvent, the 4-chloro-3-nitrobenzotrifluoride and the KF; (2) cyaniding 4-fluoro-3-nitrotoluene trifluoride with metal cyanide to obtain 2-nitro-4-trifluoromethylbenzonitrile; ； The temperature of the cyanidation reaction is 150-180°C; The cyanation reaction occurs in the presence of an organic solvent or in the absence of a solvent; In the cyanation reaction, the organic solvent is DMSO or DMF; In the cyanidation reaction, the metal cyanide is KCN or NaCN.

2. The preparation method according to claim 1, characterized in that The fluorination reaction satisfies one or more of the following conditions: ① The molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent is 1.0-2.5 mol / L; ② The molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride is (1.0-2.0): 1; ③ The reaction temperature of the fluorination reaction is 25°C-250°C; ④ The 4-chloro-3-nitrobenzotrifluoride is added into a mixed solution of KF and the organic solvent; ⑤ The post-treatment of the fluorination reaction comprises the following steps: (1) filtering the reaction solution after the fluorination reaction is completed, and recovering the filtrate and filter cake, wherein the filtrate is a crude product and the filter cake is KF and / or KCl; (2) The filtrate is distilled to obtain the 4-fluoro-3-nitrotrifluorotoluene and the organic solvent.

3. The preparation method according to claim 2, characterized in that: The fluorination reaction satisfies one or more of the following conditions: ① The organic solvent is DMF, DMA, acetonitrile, sulfolane or DMSO; ② The molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent is 1.4-2.4 mol / L; ③ The molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride is (1.0-1.5): 1; ④ The reaction temperature of the fluorination reaction is 130-180°C; ⑤ The adding time is 1-10h; ⑥The distillation is a reduced pressure distillation.

4. The preparation method according to claim 3, characterized in that: The fluorination reaction satisfies one or more of the following conditions: ① The organic solvent is DMF or sulfolane; ② The molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent is 1.9 mol / L; ③ The molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride is 1.3:1; ④ The reaction temperature of the fluorination reaction is 150-180°C; ⑤ The adding time is 3-7h.

5. The preparation method according to claim 4, characterized in that: In the fluorination reaction, the adding time is 5-7h.

6. The preparation method according to claim 1, characterized in that: The post-treatment of the fluorination reaction comprises the following steps: (1) filtering the reaction solution after the fluorination reaction is completed, and recovering the filtrate and filter cake, wherein the filtrate is a crude product and the filter cake is KF and / or KCl; (2) The filtrate is subjected to vacuum distillation to obtain the 4-fluoro-3-nitrotrifluorotoluene and the organic solvent.

7. The preparation method according to claim 4, characterized in that: In the fluorination reaction, the organic solvent is DMF or sulfolane; the molar volume ratio of the 4-chloro-3-nitrobenzotrifluoride to the organic solvent is 1.9 mol / L; the molar ratio of the KF to the 4-chloro-3-nitrobenzotrifluoride is 1.3:1; the reaction temperature of the fluorination reaction is 150-180° C.; and the addition time is 5-7 hours.

8. The preparation method according to claim 1, characterized in that: The cyanation reaction occurs in the presence of an organic solvent or in the absence of a solvent; the organic solvent is DMSO or DMF; The temperature of the cyanidation reaction is 150-180°C; The boiling point of the organic solvent is higher than or equal to the temperature of the cyanation reaction.

9. The preparation method according to claim 8, characterized in that: The cyanidation reaction satisfies one or more of the following conditions: ① The raw materials of the cyanation reaction are composed of the organic solvent, the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide; or are composed of the 4-fluoro-3-nitrobenzotrifluoride and the metal cyanide; ② The molar ratio of cyano group to 4-fluoro-3-nitrobenzotrifluoride in the metal cyanide is (0.95-1.0):1.0; ③ When the cyanation reaction occurs in the presence of an organic solvent, the molar volume ratio of the 4-fluoro-3-nitrobenzotrifluoride to the organic solvent is 1.0-2.6 mol / L; ④ The post-treatment of the cyanidation reaction comprises the following steps: (1) filtering the reaction solution after the cyanation reaction is completed, and recovering the filtrate and filter cake, wherein the filtrate is a crude product and the filter cake is a metal fluoride salt; (2) The filtrate is distilled to recover the organic solvent to obtain 2-nitro-4-trifluoromethylbenzonitrile.

10. The preparation method according to claim 9, characterized in that: The cyanidation reaction satisfies one or more of the following conditions: ① The molar ratio of cyano group to 4-fluoro-3-nitrotrifluorotoluene in the metal cyanide is (0.95-0.97):1.0; ② When the cyanation reaction occurs in the presence of an organic solvent, the molar volume ratio of the 4-fluoro-3-nitrobenzotrifluoride to the organic solvent is 1.5-2.1 mol / L; ③ In the post-treatment, the distillation is a reduced pressure distillation.

11. The preparation method according to claim 10, characterized in that: The cyanidation reaction satisfies one or more of the following conditions: ① When the organic solvent is DMF, the temperature of the cyanation reaction is 150° C.; ② The metal cyanide is KCN; ③ The molar ratio of cyano group to 4-fluoro-3-nitrotrifluorotoluene in the metal cyanide is 0.95:1.0 or 0.96:1.

0.

12. The preparation method according to claim 8, characterized in that: The post-treatment of the cyanidation reaction comprises the following steps: (1) filtering the reaction solution after the cyanation reaction is completed, and recovering the filtrate and filter cake, wherein the filtrate is a crude product and the filter cake is a metal fluoride salt; (2) The filtrate is subjected to vacuum distillation to recover the organic solvent to obtain 2-nitro-4-trifluoromethylbenzonitrile.

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