A method for preparing 2,3,4-trifluoronitrobenzene

Abstract

This invention belongs to the field of organic synthesis, specifically relating to a method for preparing 2,3,4-trifluoronitrobenzene. Specifically, it involves continuous nitration of 1,2,3-trichlorobenzene as a starting material and continuous production of 2,3,4-trifluoronitrobenzene via fluorination microchannels. This method has the advantages of simple process, low cost, high yield, high intrinsic safety, high production efficiency, and environmental friendliness. It does not require the addition of a phase transfer catalyst, does not use polar organic solvents in the reaction, and can be continuously produced, making it suitable for industrial scale-up.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis, and specifically relates to a method for preparing 2,3,4-trifluoronitrobenzene. Background Technology

[0002] 2,3,4-Trifluoronitrobenzene (CAS No.: 771-69-7) is a pale yellow oily liquid. Its main use in the pharmaceutical industry is in the synthesis of first-generation fluoroquinolone drugs such as ofloxacin (oxazine, trade name Tarivid), levofloxacin, and lomefloxacin (Lamfloxacim). Simultaneously, 2,3,4-trifluoronitrobenzene has also found significant applications in the pesticide field. N-acyl-N-(2,3,4-trifluoroaniline)propionate compounds derived from it have achieved control efficacy of over 70% against wheat sheath blight and gray mold in cucurbits in indoor fungicidal bioactivity screening tests. Some compounds have efficacy comparable to carbendazim. 2,3,4-Trifluoronitrobenzene was reduced, brominated, and diazotized to prepare 3,4,5-trifluorobromobenzene. 3,4,5-Trifluorobromobenzene is an important pesticide intermediate, mainly used in the synthesis of the succinate dehydrogenase inhibitor (SDHI) fungicide fluopyram. Simultaneously, 3,4,5-trifluorobromobenzene is also an important liquid crystal intermediate used in the production of fourth-generation TFT color liquid crystal materials. 2,3,4-Trifluoronitrobenzene, as an important chemical intermediate, has wide applications in the pharmaceutical, pesticide, and liquid crystal industries.

[0003]

[0004] Currently, 2,3,4-trifluoronitrobenzene is synthesized from 2,6-dichloroaniline via diazo fluorination, nitration, and chloro-fluorine exchange reactions, with an overall yield of approximately 62% (based on 2,6-dichloroaniline). Two key reactions in this synthesis are the decomposition of the diazonium salt of fluoroboric acid, which is highly vigorous, exothermic, and readily forms tar-like substances. In the fluorination reaction, dimethyl sulfoxide and sulfolane are frequently used as solvents in the literature, resulting in large quantities and difficult recovery. The reaction route is as follows:

[0005]

[0006] Chinese patent CN01127025 reports a process using o-chloronitrobenzene as a starting material, first preparing 2,3-dichloronitrobenzene through chlorination; then obtaining 2,3,4-trifluoronitrobenzene through a four-step reaction involving fluorination, high-temperature chlorination, nitration, and secondary fluorination, with an overall yield of approximately 30% (based on 2,3-dichloronitrobenzene). While this process uses o-chloronitrobenzene, which is cheaper than 2,6-dichloroaniline, as a raw material and avoids the diazotization reaction and explosion risks during production, the secondary chlorination and denitrification reaction after fluorination of 2,3-dichloronitrobenzene requires harsh conditions and high reaction temperatures. The use of hazardous chlorine gas at these high temperatures poses a high safety risk, and the equipment investment is high. Furthermore, the fluorination reaction, which involves cumbersome wastewater treatment, results in significant environmental costs, making it unsuitable for industrial production. The reaction route is as follows:

[0007]

[0008] In their new method for synthesizing 2,3,4-trifluoronitrobenzene, Gu Jiansong and Zhang Haibin reported a nitration and fluorination reaction of 1,2,3-trichlorobenzene as a raw material, with a purity of 99%, but a yield of only 60%. Chinese patent CN201710446278.5 also reports the preparation of 2,3,4-trichloronitrobenzene from 1,2,3-trichlorobenzene by nitration substitution. KF is then added, and the mixture is dehydrated under TBAB catalysis. The reaction is then carried out at 180°C. After the reaction, the mixture is filtered, and the filtrate is distilled under reduced pressure and then fed into an anhydrous reactor. KF is added again, and the mixture is dehydrated under reduced pressure under TBAF catalysis. The reaction is then carried out under ultrasonic power conditions of 120°C and 30 kHz. Finally, 2,3,4-trifluoronitrobenzene is obtained by distillation. Clearly, to improve the yield, two fluorination processes are required, and potassium fluoride also needs to be dehydrated twice and ultrasonic catalysis is necessary. This not only increases the operational difficulty and requires significant equipment investment, but also makes industrialization difficult. The reaction route is as follows:

[0009]

[0010] Chinese patent CN201910974492.7 reports a process for obtaining 2,3,4-trifluoronitrobenzene from 2,3,4-trichloronitrobenzene via a fluorination reaction involving antimony pentafluoride and hydrogen fluoride. In this process, antimony pentafluoride and hydrogen fluoride react to generate the superacid fluoroantimony acid HSbF6. Because fluoroantimony acid is relatively dangerous and prone to accidents, and the container for holding fluoroantimony acid must be made of Teflon (i.e., polytetrafluoroethylene), this places high demands on the microchannel reaction equipment using fluoroantimony acid. Furthermore, microchannel fluorination reaction equipment made of Teflon is difficult to process and manufacture, making industrialization unsuitable.

[0011]

[0012] WO01 / 81274 reports the use of phosphazene salts to fluorinate {tetra[tris(dimethylamino)phosphine-amino]phosphine}[(Me2N3),P=N]4P + F - The fluorination of chlorobenzene is carried out by a fluorinating agent. Although this fluorinating agent has a high reaction yield and good fluorination effect, it has poor atom economy, generates a large amount of wastewater, and its high price leads to high production costs, making it unsuitable for industrialization.

[0013] 2,6-Dichlorofluorobenzene is produced from 2,6-dichloroaniline and o-chloronitrobenzene through dangerous reactions such as diazotization and chlorination. This nitration then produces 3-fluoro-2,4-dichloronitrobenzene, the precursor for 2,3,4-trifluoronitrobenzene. Diazotization, chlorination, and nitration are all key hazardous processes of national concern. 2,3,4-trifluoronitrobenzene is produced from 3-fluoro-2,4-dichloronitrobenzene via a potassium fluoride fluorination process. The fluorination process requires the use of spray-dried anhydrous potassium fluoride to improve reactivity. Furthermore, due to the low solubility of potassium fluoride in conventional organic solvents, phase transfer catalysts are often added to increase the yield. Conventional batch fluorination processes also suffer from high reaction temperatures and long reaction times, large reactor sizes, low production efficiency, and unstable product quality. These pain points and difficulties are increasingly failing to meet market demands.

[0014] While using 1,2,3-trichlorobenzene as a raw material avoids dangerous processes such as diazotization and chlorination, the nitration reaction of 1,2,3-trichlorobenzene to produce the intermediate product 2,3,4-trichloronitrobenzene, employs concentrated nitric acid or mixed acids as nitrating agents. This nitration reaction is characterized by high exothermic reaction, heterogeneous mass and heat transfer, and other features. Traditional processes mostly employ batch or semi-batch reactors. Reactor processes are batch production, technologically outdated, with large material volumes per reactor, poor mass and heat transfer efficiency, and relatively slow material dispersion, easily leading to raw material accumulation. Temperature rise and fall are conducted through a jacket, but the distance between the jacket wall and the material center is relatively large, resulting in slow heat conduction, long heating and cooling times, and the inability to remove reaction heat in a timely manner. This can lead to localized overheating during the reaction. Furthermore, the thermometer detection point is some distance from both the jacket wall and the material center, resulting in a certain lag in temperature measurement. For dangerous processes such as nitration with fast reaction rates and high exothermic reactions, the actual temperature value cannot be displayed accurately and promptly, easily leading to thermal runaway and explosion accidents. The batch reactor process involves a large volume of material and a large potential energy scale. Once thermal runaway occurs, the heat released by the nitration reaction will cause the temperature of a large amount of material to rise, triggering side reactions such as polynitration and oxidation, leading to high-temperature decomposition of the material and potentially causing an explosion with unimaginable consequences. This does not meet the development requirements of "green chemistry and intrinsic safety".

[0015] The fluorination process of 2,3,4-trichloronitrobenzene using potassium fluoride as the fluorine source still suffers from the drawbacks of batch fluorination, such as: difficulty in recovering high-boiling-point polar solvents (DMSO, DMF, sulfolane), high reaction temperature and long reaction time, the need for phase transfer catalysts, and low reaction yield. Although ultrasonic catalysis can improve the yield, industrialization remains fraught with difficulties. Using antimony pentafluoride / hydrogen fluoride as the fluorine source poses high industrial safety risks and does not align with the current trend of green development in the fine chemical industry. Furthermore, the method of preparing fluorides from 2,3,4-trifluoronitrobenzene via fluorine-chlorine exchange using aryl chlorides as raw materials commonly uses hydrogen fluoride and fluoride salts as fluorine sources. Fluorination processes using hydrogen fluoride as the fluorine source suffer from severe equipment corrosion and significant safety risks. However, the use of fluoride salts, represented by potassium fluoride, usually requires the addition of a large amount of highly polar solvents and phase transfer catalysts to aid dissolution. The production of aryl fluorides using traditional hydrogen fluoride and potassium fluoride as fluorine sources is becoming increasingly unsuitable for advanced production concepts that prioritize environmental protection, safety, greenness, and economy.

[0016] Therefore, there is still a real and urgent need to develop new processes for the synthesis of 2,3,4-trifluoronitrobenzene. Summary of the Invention

[0017] This invention addresses the shortcomings of existing technologies by providing a method for preparing 2,3,4-trifluoronitrobenzene. Specifically, it involves continuous nitration of 1,2,3-trichlorobenzene as a starting material and continuous production of 2,3,4-trifluoronitrobenzene via fluorination microchannels. This method has the advantages of simple process, low cost, high yield, high intrinsic safety, high production efficiency, and environmental friendliness. It does not require the addition of a phase transfer catalyst, does not use polar organic solvents in the reaction, and can be continuously produced, making it suitable for industrial scale-up.

[0018] Compared with existing technologies, this invention uses 1,2,3-trichlorobenzene, nitric acid, and sulfuric acid as raw materials, and reacts them in a microchannel reactor. This process boasts high mass and heat transfer efficiency, low liquid holdup, good safety performance, minimal acidic wastewater generation, environmentally friendly operation, short cycle time, and the ability to operate continuously without scale-up effects. It safely produces 2,3,4-trichloronitrobenzene, the raw material for 2,3,4-trifluoronitrobenzene. The reaction of 2,3,4-trichloronitrobenzene with tetraethylammonium trifluoride as a fluorine source in a microchannel reactor yields 2,3,4-trifluoronitrobenzene in high yield. No phase transfer catalyst is required, the reaction does not use polar organic solvents, the operation is simple, the reaction yield is high, continuous production is possible, and there is minimal waste and low cost.

[0019] The specific technical solution adopted in this invention is as follows:

[0020] A method for preparing 2,3,4-trifluoronitrobenzene includes the following steps:

[0021] Step 1: Using 1,2,3-trichlorobenzene, sulfuric acid, and nitric acid as raw materials, a continuous reaction is carried out in a microchannel reactor to obtain 2,3,4-trichloronitrobenzene. The reaction equation is shown below:

[0022]

[0023] Further steps include:

[0024] Sulfuric acid and nitric acid were mixed to form a mixed acid solution, and 1,2,3-trichlorobenzene and chlorinated hydrocarbon solvents were mixed to form a mixed solution. The mixed solution prepared by 1,2,3-trichlorobenzene and chlorinated hydrocarbon solvents and the mixed acid solution were respectively fed into a microchannel reactor for continuous nitration reaction. After quenching, washing with water, solvent removal and crystallization, 2,3,4-trichloronitrobenzene product was obtained.

[0025] The nitration reaction temperature in the microchannel reactor is 50-75℃; further, the nitration reaction temperature is 55-85℃.

[0026] The residence time of the nitration reaction in the microchannel reactor is 30-150 s; further, the residence time of the nitration reaction is 90-120 s.

[0027] The pressure of the nitration reaction in the microchannel reactor is adjusted to 0.3-2.0 MPa by a back pressure valve.

[0028] The nitration reaction pressure is 0.4-0.6 MPa.

[0029] The chlorinated solvent is one of 1,2-dichloroethane, 1,1-dichloroethane, 1,3-dichloropropane, 1,2-dichloropropane, and n-chlorobutane; the mass ratio of its amount to that of the raw material 1,2,3-trichlorobenzene is (1:1) to (1:3).

[0030] The sulfuric acid and nitric acid used to prepare the mixed acid solution have a mass concentration of 60-98%.

[0031] The molar ratio of 1,2,3-trichlorobenzene, nitric acid and sulfuric acid is 1:1-1.25:1-1.65, and more preferably 1:1.06:1.35.

[0032] The internal channel shape of the microchannel reactor is one of heart-shaped, umbrella-shaped, Chinese character-shaped, or rhomboid, and is more preferably heart-shaped or umbrella-shaped.

[0033] Step 2: Using tetraethylammonium trihydrofluoride as a fluorine source, a continuous reaction is carried out in a microchannel reactor to obtain 2,3,4-trifluoronitrobenzene. The reaction equation is as follows:

[0034]

[0035] Further steps include:

[0036] 2,3,4-Trichloronitrobenzene is heated to 60-80 degrees Celsius in a heated storage tank to melt it into a flowing liquid; at the same time, tetraethylammonium fluoride trihydrofluoride is stored in a storage tank at 120 degrees Celsius, at which point tetraethylammonium fluoride trihydrofluoride is also a flowing liquid.

[0037] 2,3,4-trichloronitrobenzene and tetraethylammonium trifluorofluoride were fed separately into a microchannel reactor in liquid form for continuous fluorination reaction. After quenching, washing, solvent removal and distillation, the 2,3,4-trifluoronitrobenzene product was obtained.

[0038] In this step, the temperature of the fluorination reaction in the microchannel reactor is 140-200℃, and more preferably 160℃.

[0039] The residence time of the fluorination reaction in the microchannel reactor is 30-150 min, more preferably 48 min.

[0040] The pressure of the fluorination reaction in the microchannel reactor is adjusted to 0.6-3.0 MPa by a back pressure valve.

[0041] The fluorination reaction is carried out at a pressure of 0.8-1 MPa, and the fluorination reaction does not use solvents or phase transfer catalysts.

[0042] The molar ratio of 2,3,4-trichloronitrobenzene to tetraethylammonium trihydrofluoride is 1:3-8, and is further limited to a molar ratio of 1:4.

[0043] The fluorination microchannel reactor can be made of silicon carbide or Hastelloy, with silicon carbide being preferred. The nitration microchannel reactor is made of Hastelloy.

[0044] The above-described preparation method achieves a two-step overall yield of approximately 87% for 2,3,4-trifluoronitrobenzene from 1,2,3-trichlorobenzene. This surpasses existing processes using 2,6-dichloroaniline or o-chloronitrobenzene as raw materials. It also overcomes the problem reported in existing literature where the intermediate product of 2,4-difluoro-3-chloro-nitrobenzene cannot be further converted to 2,3,4-trifluoronitrobenzene in a microchannel fluorination process using potassium fluoride or anhydrous hydrogen fluoride as the fluorine source after nitration of 1,2,3-trichlorobenzene. The above-described preparation process offers advantages such as low cost, high yield, high intrinsic safety, low waste, simple operation, and low equipment investment. Detailed Implementation

[0045] The following detailed description, in conjunction with specific embodiments, further illustrates the above-mentioned content of the present invention. However, it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0046] Example 1

[0047] The production method of 2,3,4-trichloronitrobenzene uses 1,2,3-trichlorobenzene, sulfuric acid, and nitric acid mixed acid as raw materials, and reacts them continuously in a microchannel reactor to obtain 2,3,4-trichloronitrobenzene. The reaction equation is shown below:

[0048]

[0049] The specific steps are as follows:

[0050] A commercially available microchannel reactor I was used. The reactor channel size was 1mm*1.5mm, the liquid holding capacity of a single channel was 1.6mL, and the total liquid holding capacity was approximately 17.2mL. The channel had a heart-shaped flow guiding structure. The nitration reaction was carried out.

[0051] Take 270g of raw material 1,2,3-trichlorobenzene (1.488mol, 1.0eq.), dissolve it in 316g of dichloroethane, and prepare a 1,2,3-trichlorobenzene solution;

[0052] Take 210g (2.10mol, 1.41eq.) of sulfuric acid with a mass concentration of 98% and 103.52g (1.577mol, 1.059eq.) of fuming nitric acid with a mass concentration of 96% and prepare a mixed acid.

[0053] Start the metering pump, set the feed flow rate of 1,2,3-trichlorobenzene solution to 7.3 mL / min, the feed flow rate of mixed acid to 3.6 mL / min, set the heat transfer oil temperature of the microchannel reactor to 65℃, and the residence time of the material in the microchannel reactor to 90 s; adjust the pressure in the microchannel reactor to 0.8 MPa through the back pressure valve, and start continuous feeding nitration.

[0054] Post-processing: The material emanating from the microchannel reactor was quenched in a treatment tank filled with ice water. After stirring to room temperature, the mixture was separated, and the lower organic phase was collected. Samples were taken and tested, showing a raw material conversion rate of 98.8%, nitration product of 97.8%, and dinitrate impurities of 0.5%. After purification, 330.6 g of 2,3,4-trichloronitrobenzene (purity 98%) was obtained, with a yield of approximately 98.11%.

[0055] Example 2

[0056] The production method of 2,3,4-trichloronitrobenzene uses a commercially available microchannel reactor II. Each reactor panel has a liquid holding capacity of 8.0 mL, with a total of 8 panels and a total liquid holding capacity of approximately 64 mL. The channels have an "umbrella" shaped structure, and the nitration reaction is carried out.

[0057] Take 642.6g of raw material 1,2,3-trichlorobenzene (3.54mol, 1eq.), dissolve it in 709g of 1,3-dichloropropane, and prepare a 1,2,3-trichlorobenzene solution;

[0058] Take 562g (5.62mol, 1.587eq.) of 98% sulfuric acid and 278.9g (4.25mol, 1.20eq.) of 96% fuming nitric acid and prepare a mixed acid.

[0059] Start the metering pump, set the feed flow rate of 1,2,3-trichlorobenzene solution to 27.87 mL / min, the feed flow rate of mixed acid to 15.13 mL / min, set the heat transfer oil temperature of the microchannel reactor to 65℃, and the residence time of the material in the microchannel reactor to 65 s; adjust the pressure in the microchannel reactor to 0.6 MPa through the back pressure valve, and start continuous feeding nitration.

[0060] Post-processing: The material emanating from the microchannel reactor was quenched in a treatment tank filled with ice water. After stirring to room temperature, the mixture was separated, and the lower organic phase was collected. Samples were taken and tested, revealing a raw material conversion rate of 99.6%, nitration product of 97.1%, and dinitrate impurities of 0.2%. After purification, 774.3 g of 2,3,4-trichloronitrobenzene (purity 98%) was obtained, with a yield of 96.5%.

[0061] 2,3,4-trichloronitrobenzene prepared in Example 1 or 2 was reacted to obtain 2,3,4-trifluoronitrobenzene, and tetraethylammonium trihydrofluoride was used as a raw material. The reaction was carried out continuously in a microchannel reactor to obtain 2,3,4-trifluoronitrobenzene. The reaction equation is shown below:

[0062]

[0063] Example 3:

[0064] The commercially available Corning G1 silicon carbide microchannel reactor is used, with a liquid holding volume of about 10 ml in a single module and no metal contact in the reaction path.

[0065] Reaction solution A is 787.22 g of 2,3,4-trichloronitrobenzene liquid (3.47 mol, 1 eq.) prepared in Example 1 and stored in a storage tank at a constant temperature of 80 degrees Celsius. Reaction solution B is 2910.11 g of tetraethylammonium fluoride trihydrofluorate liquid (13.9 mol, 4.0 eq.) stored in a silicon carbide storage tank at a constant temperature of 120 degrees Celsius.

[0066] Reaction solution A was pumped into a preheating coil at 150°C using a metering pump at a flow rate of 1 mL / min, with a residence time of 1 min. Reaction solution B was pumped into the preheating coil at 150°C using a metering pump at a flow rate of 6.15 mL / min, with a residence time of 1 min.

[0067] Preheated reaction solutions A and B flow into a continuous flow microchannel reactor. The reactor temperature is 150℃, and the pressure inside is adjusted to 0.9MPa via a back pressure valve. The residence time is 48min. The material from the microchannel reactor outlet is fed into a processing tank made of HASS alloy containing ice water. Dichloromethane is added for extraction, and the aqueous layer is separated to obtain the organic phase. Sampling and monitoring show that 2,3,4-trifluoronitrobenzene is 95.6% and 2,4-difluoro-3-chloronitrobenzene is 1.6%. After solvent removal and distillation, 557.55g of 2,3,4-trifluoronitrobenzene (purity: 97.2%) is obtained, with a yield of approximately 90.7%.

[0068] Example 4:

[0069] The reactor uses a silicon carbide microchannel continuous flow reactor customized from Kairui. Each module holds approximately 15 ml of liquid, and there are 15 modules in total. The reaction path has no metal contact.

[0070] Reaction solution A is 1349.52 g of 2,3,4-trichloronitrobenzene liquid (5.96 mol, 1 eq.) prepared in Example 1 and stored in a storage tank at a constant temperature of 80 degrees Celsius. Reaction solution B is 4988.7 g of tetraethylammonium fluoride trihydrofluorate liquid (23.84 mol, 4.0 eq.) stored in a silicon carbide storage tank at a constant temperature of 120 degrees Celsius.

[0071] Reaction solution A was pumped into a preheating coil at 160°C using a metering pump at a flow rate of 1 mL / min, with a residence time of 1 min. Reaction solution B was pumped into the same preheating coil at 160°C using a metering pump at a flow rate of 6.15 mL / min, with a residence time of 1 min. The preheated reaction solutions A and B flowed into a continuous flow microchannel reactor at 160°C. The pressure inside the microchannel reactor was adjusted to 0.9 MPa via a back pressure valve, and the residence time was 55 min. The material exiting the microchannel reactor was fed into a processing tank made of HASS alloy containing ice water. Dichloromethane was added for extraction, and the aqueous layer was separated to obtain the organic phase. Sampling and monitoring revealed 96.2% 2,3,4-trifluoronitrobenzene and 1.98% 2,4-difluoro-3-chloronitrobenzene. After solvent removal and distillation, 913.32 g of 2,3,4-trifluoronitrobenzene (purity: 97.0%) was obtained, with a yield of approximately 86.5%.

[0072] Comparative Example 1:

[0073] Add 600g of 98% concentrated sulfuric acid (6.0mol), 500g of 1,2,3-trichlorobenzene (2.755mol, 1.0eq.), and 750g of dichloroethane to a reaction flask. Heat the mixture with stirring, maintaining the temperature at 75-80℃. Slowly add 227.09g of 96% fuming nitric acid (3.46mol, 1.25eq.). After the addition is complete, maintain the temperature at 80-85℃ for 3 hours. Samples were taken for analysis; the conversion rate of the raw materials was 97%, the nitration product was 92%, and the dinitrate impurity was 3.8%. The reaction was then complete. The mixture was allowed to stand at the set temperature for separation. After purification, 556.2g of 2,3,4-trichloronitrobenzene (purity: 95%) was obtained, with a yield of 89.1%.

[0074] Comparative Example 2:

[0075] 49.96 g of 2,3,4-trichloronitrobenzene (0.22 mol, 1.0 eq.) and 230.8 g of tetraethylammonium fluoride trihydrofluoride (1.10 mol, 5.0 eq.) were added to a 500 mL Hastelloy reactor. The mixture was slowly heated under stirring, maintaining the temperature at 180 °C for 20 hours. After cooling, a sample was taken to determine the raw material conversion rate: 93.1%. Further analysis revealed 72.0% of 2,3,4-trifluoronitrobenzene and 19.4% of 2,4-difluoro-3-chloronitrobenzene. Extraction with dichloromethane was performed, and the aqueous layer was separated to obtain the organic phase. After solvent removal and distillation, 23.76 g of 2,3,4-trifluoronitrobenzene (purity: 95.0%) was obtained, with a yield of 61%.

[0076] Comparative Examples 1 and 2 employed a batch reactor, which, compared to the technical solution of this application, resulted in lower yields and longer reaction times compared to the examples.

[0077] Comparative Example 3:

[0078] The commercially available Corning G1 silicon carbide microchannel reactor is used, with a liquid holding volume of about 10 ml in a single module and no metal contact in the reaction path.

[0079] Reaction solution A consists of 472.33 g of 2,3,4-trichloronitrobenzene liquid (2.08 mol, 1 eq.) stored in a constant temperature 80°C storage tank. Reaction solution B consists of 604.2 g of potassium fluoride (10.4 mol, 5.0 eq.) and the phase transfer catalyst tetraphenylphosphine bromide (26.16 g, 0.062 mol, 0.03 eq.) dissolved in 2.43 kg of sulfolane and stirred until homogeneous.

[0080] Reaction solution A was pumped into a preheating coil at 150°C using a metering pump at a flow rate of 1 mL / min, with a residence time of 1 min. Reaction solution B was pumped into the same preheating coil at 150°C using a metering pump at a flow rate of 10.28 mL / min, with a residence time of 1 min. The preheated reaction solutions A and B flowed into a continuous flow microchannel reactor at 150°C. The pressure inside the microchannel reactor was adjusted to 0.9 MPa via a back pressure valve, and the residence time was 130 min. The material exiting the microchannel reactor was fed into a processing tank containing ice water. Dichloromethane was added for extraction, and the aqueous layer was separated to obtain the organic phase. Sampling and monitoring revealed 40.6% 2,3,4-trifluoronitrobenzene, 20.8% 2,4-difluoro-3-chloronitrobenzene, and 35.2% 2,3,4-trichloronitrobenzene remaining in the raw material.

[0081] Comparative Example 4:

[0082] The commercially available Corning G1 silicon carbide microchannel reactor is used, with a liquid holding volume of about 10 ml in a single module and no metal contact in the reaction path.

[0083] Reaction solution A consists of 188.93g of 2,3,4-trichloronitrobenzene liquid (0.91mol, 1eq.) stored in a constant-temperature storage tank at 80 degrees Celsius, and reaction solution B consists of 84g of anhydrous hydrogen fluoride liquid (4.55mol, 5.0eq.) stored in a constant-temperature silicon carbide storage tank at 0 degrees Celsius.

[0084] Reaction solution A was pumped into a preheating coil at 150°C using a metering pump at a flow rate of 1 mL / min, with a residence time of 1 min. The preheated reaction solutions A and B were then pumped into a continuous flow microchannel reactor at a flow rate of 10.28 mL / min using a metering pump. The microchannel reactor temperature was 150°C, and the pressure inside the reactor was adjusted to 1 MPa via a back pressure valve. The residence time was 140 min. The material emanating from the microchannel reactor was transferred to a processing tank made of HASS alloy containing ice water. Dichloromethane was added for extraction, and the aqueous layer was separated to obtain the organic phase. Sampling and monitoring revealed 50% 2,3,4-trifluoronitrobenzene, 18.6% 2,4-difluoro-3-chloronitrobenzene, and 28.2% 2,3,4-trichloronitrobenzene remaining in the raw material.

[0085] Although Comparative Examples 3 and 4 used microchannel fluorination reactors, the fluorine sources were potassium fluoride and anhydrous hydrogen fluoride, respectively. A comparison with the examples shows that the microchannel fluorination reaction using potassium fluoride and anhydrous hydrogen fluoride as fluorine sources was ineffective, exhibiting defects such as incomplete reaction of the raw materials, failure to convert the 2,4-difluoro-3-chloro-nitrobenzene intermediate product into the final product, and low content of the target product. Therefore, the technical solution of this application is significantly superior to the prior art.

[0086] For those skilled in the art, the specific embodiments are merely illustrative descriptions of the present invention. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A process for the preparation of 2,3,4-trifluoronitrobenzene, characterized in that: The method comprises the following steps: Step one: prepare a mixed acid solution by mixing sulfuric acid and nitric acid, and prepare a mixed solution by mixing 1,2,3-trichlorobenzene and a chlorinated hydrocarbon solvent; continuously feed the mixed solution of 1,2,3-trichlorobenzene and the chlorinated hydrocarbon solvent and the mixed acid solution into a micro-channel reactor for continuous nitration reaction, and then quench, wash with water, remove the solvent, and crystallize to obtain 2,3,4-trichloronitrobenzene; The molar ratio of the 1,2,3-trichlorobenzene, the nitric acid and the sulfuric acid is 1:1.06:1.35; the temperature of the nitration reaction in the micro-channel reactor is 50-75℃, and the pressure of the nitration reaction is 0.4-0.6 MPa; the residence time of the nitration reaction in the micro-channel reactor is 90-120 s; the chlorinated hydrocarbon solvent is one of 1,2-dichloroethane, 1,1-dichloroethane, 1,3-dichloropropane, 1,2-dichloropropane and n-chlorobutane; the mass ratio of the chlorinated hydrocarbon solvent to the raw material 1,2,3-trichlorobenzene is (1:1)-(1:3); Step two: continuously react 2,3,4-trichloronitrobenzene with tetraethylammonium fluoride trihydrofluoride as a fluorine source in a micro-channel reactor to obtain 2,3,4-trifluoronitrobenzene, specifically as follows: continuously feed 2,3,4-trichloronitrobenzene and tetraethylammonium fluoride trihydrofluoride in liquid form into a micro-channel reactor for continuous fluorination reaction, and then quench, wash with water, remove the solvent, and rectify to obtain 2,3,4-trifluoronitrobenzene; The molar ratio of 2,3,4-trichloronitrobenzene to tetraethylammonium fluoride trihydrofluoride is 1:4; the temperature of the fluorination reaction in the micro-channel reactor is 160℃, the pressure of the fluorination reaction is 0.8-1 MPa, and the residence time of the fluorination reaction in the micro-channel reactor is 48 min.

2. The process for the preparation of 2,3,4-trifluoronitrobenzene according to claim 1, characterized in that: The mass concentration of the sulfuric acid used for preparing the mixed acid solution is 60-98%, and the mass concentration of the nitric acid used is 60-98%.

3. The process for the preparation of 2,3,4-trifluoronitrobenzene according to claim 1, characterized in that: The internal channel of the micro-channel reactor is in one of a heart shape, an umbrella shape, a middle Chinese character shape and a diamond shape.

4. The process for the preparation of 2,3,4-trifluoronitrobenzene according to claim 1, characterized in that: The material of the micro-channel reactor for the fluorination reaction is silicon carbide or hastelloy.

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