A method for preparing p-trifluoromethoxyaniline by continuous hydrogenation

Abstract

The present invention relates to the field of p-trifluoromethoxyaniline production, and in particular to a method for preparing p-trifluoromethoxyaniline by continuous hydrogenation. The method for preparing p-trifluoromethoxyaniline by continuous hydrogenation of the present invention comprises the following steps: p-trifluoromethoxynitrobenzene and a solvent are mixed and then continuously catalytically hydrogenated in a fixed bed reactor to obtain p-trifluoromethoxyaniline; wherein the solvent is p-trifluoromethoxyaniline and hydrogen is a hydrogen source. The method of the present invention uses p-trifluoromethoxyaniline as a solvent, and no other solvent is introduced, thereby reducing waste discharge caused by the solvent and being environmentally friendly; no solvent separation step is required, the operation steps are simplified, the operation is convenient, and the cost is reduced; the reaction product of the method of the present invention has high selectivity, no N-alkylated byproducts produced by using alcohol solvents, and good product quality.

Description

Technical Field

[0001] The invention relates to the field of p-trifluoromethoxyaniline production, and in particular to a method for preparing p-trifluoromethoxyaniline by continuous hydrogenation. Background Art

[0002] p-Trifluoromethoxyaniline is an important intermediate, which is widely used in the synthesis of various fine chemical products in the fields of pesticides and medicines, such as indoxacarb, chlorpyrifos, and thiophanate-methyl.

[0003] At present, the industrial production of p-trifluoromethoxyaniline mainly adopts p-trifluoromethoxynitrobenzene as raw material, in a solvent such as methanol, and under the action of a catalyst, a method for intermittent kettle hydrogenation reduction reaction is carried out to obtain the product. The catalyst can be selected from Pd / C, Raney nickel, etc. However, the operating conditions are more harsh, the risk is high, the process is complicated, and the reaction time is long. Each hydrogenation process requires operations such as feeding, gas replacement, reaction solution standing, and filtering catalyst, and the production efficiency is low.

[0004] In recent years, some improvements have been made to the batch hydrogenation process. Chinese patent CN111072502 discloses a method for preparing aniline by continuous hydrogenation in a fixed bed. The method uses silicon dioxide as a carrier to prepare a loaded metal nickel-iron-zinc catalyst, and uses methanol, ethanol or isopropanol as a solvent. The continuous catalytic hydrogenation reaction is carried out at 100-120°C and a pressure of 1-3MPa. The yield of the hydrogenation reaction product is high. Chinese patent CN109796346A discloses a method for preparing aromatic amines by continuous hydrogenation of nitro compounds. The method uses nanoporous palladium as a catalyst and methanol as a solvent. The hydrogenation reaction is carried out at 20-100°C and a pressure of 0.1-1MPa. The reaction selectivity is high, but the cost of preparing the catalyst is high and large-scale production is difficult. Chinese patent CN113856565 discloses a device and method for producing trifluoromethoxyaniline by continuous hydrogenation in a micro-packed bed device. The method uses methanol as a solvent and Pd / C as a catalyst. The hydrogenation reaction is carried out at 60°C and 2MPa. The reaction conversion rate is greater than 99.9% and the selectivity is greater than 97%. Summary of the invention

[0005] Although the existing technical means adopt a continuous process, they all use alcohols such as methanol as solvents, which requires an additional step of separating the solvent. At the same time, N-methylated by-products may be produced, which makes separation difficult, affects the quality of the product, and limits the application of the product in some fields.

[0006] The technical problem to be solved by the present invention is to provide a method for preparing trifluoromethoxyaniline by continuous hydrogenation, which overcomes the problems of complicated operation, high safety risk and impurities generated during the reaction process in the prior art.

[0007] In view of the shortcomings of the prior art, one of the purposes of the present invention is to provide a method for preparing trifluoromethoxyaniline by continuous hydrogenation.

[0008] The technical solution of the present invention:

[0009] The invention provides a method for preparing p-trifluoromethoxyaniline by continuous hydrogenation, comprising the following steps: mixing p-trifluoromethoxynitrobenzene and a solvent and then continuously catalytically hydrogenating the mixture in a fixed bed reactor to obtain p-trifluoromethoxyaniline; wherein the solvent is p-trifluoromethoxyaniline and hydrogen is a hydrogen source.

[0010] Preferably, the mass concentration of trifluoromethoxynitrobenzene is 3 to 20%, preferably 5 to 10%, based on the total weight of trifluoromethoxynitrobenzene and the solvent.

[0011] Preferably, the temperature of the catalytic hydrogenation reaction is 40-150°C.

[0012] Preferably, the pressure of the catalytic hydrogenation reaction is 0.1 to 3 MPa; preferably 1 to 3 MPa.

[0013] Preferably, the mass space velocity of the catalytic hydrogenation reaction relative to trifluoromethoxynitrobenzene is 0.05 to 4 h -1 .

[0014] Preferably, the catalyst is loaded in the middle constant temperature zone of the fixed bed reactor.

[0015] Preferably, the catalyst is selected from one or more of Pd / C, Pd / Al2O3, Pt / C and Ni / SiO2; preferably Ni / SiO2.

[0016] Preferably, the temperature of the catalytic hydrogenation reaction is 80 to 120°C, preferably 80 to 100°C.

[0017] Preferably, the molar ratio of hydrogen to p-trifluoromethoxynitrobenzene is 3 to 6:1, preferably 3 to 4:1.

[0018] Preferably, the fixed bed reactor is a micro-packed bed reactor.

[0019] Beneficial effects of the present invention:

[0020] The method of the invention adopts trifluoromethoxyaniline as a solvent, and no other solvent is introduced, thereby reducing waste discharge caused by the solvent and being environmentally friendly; no solvent separation step is required, the operation steps are simplified, the operation is convenient, and the cost is reduced; the reaction product of the method of the invention has high selectivity, no N-alkylation byproducts generated by using alcohol solvents, and good product quality. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and technical effect of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention is described clearly and completely. The embodiments described below are part of the embodiments of the present invention, not all of them. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] The mass space velocity of the catalytic hydrogenation reaction relative to p-fluoromethoxynitrobenzene in the present invention refers to the ratio of the mass flow rate of p-fluoromethoxynitrobenzene to the catalyst loading amount.

[0023] In order to overcome the problems of complicated operation, high safety risk, and impurities generated during the reaction process in the prior art, the present invention provides a method for producing p-trifluoromethoxyaniline in an efficient, safe, environmentally friendly and low-cost manner. The present invention adopts a fixed bed reactor, p-trifluoromethoxynitrobenzene as a raw material, and p-trifluoromethoxyaniline, a hydrogenated product, as a solvent, to continuously hydrogenate and reduce p-trifluoromethoxynitrobenzene under the action of a catalyst to prepare p-trifluoromethoxyaniline. The reaction equation is as follows:

[0024]

[0025] The whole process is simple, overcoming the disadvantages of the prior art, such as high risk, the need to separate the solvent from the reaction product, and complicated operation. The operation cost is reduced, and no solvent waste gas is generated, which is environmentally friendly. At the same time, there is no N-alkylated product in the reaction product, and the product quality is good.

[0026] In a specific embodiment of the present invention, the present invention provides a method for preparing p-trifluoromethoxyaniline by continuous hydrogenation, comprising the following steps: mixing p-trifluoromethoxynitrobenzene and a solvent and then continuously catalytically hydrogenating them in a fixed bed reactor to obtain p-trifluoromethoxyaniline; wherein the solvent is p-trifluoromethoxyaniline and hydrogen is a hydrogen source.

[0027] In a preferred embodiment of the present invention, the catalyst is added to the constant temperature zone of the fixed bed reactor, the temperature is increased and the flow rate and pressure of hydrogen are adjusted, a 3-20% mass concentration of p-trifluoromethoxynitrobenzene solution (with p-trifluoromethoxyaniline as solvent) is pumped into the fixed bed reactor, the temperature of the reactor is controlled, and the reaction product p-trifluoromethoxyaniline is collected in a receiving tank. During the process, samples are taken and analyzed at regular intervals.

[0028] Wherein, the temperature of the catalytic hydrogenation reaction is 40 to 150°C;

[0029] The catalyst is selected from one or more of Pd / C, Pd / Al2O3, Pt / C and Ni / SiO2; preferably Ni / SiO2 catalyst. Preferably, the temperature of the catalytic hydrogenation reaction is 80-120°C, preferably 80-100°C.

[0030] The pressure of the catalytic hydrogenation reaction is 0.1-3 MPa, preferably 1-3 MPa.

[0031] The mass space velocity of the catalytic hydrogenation reaction relative to p-fluoromethoxynitrobenzene is 0.05 to 4 h -1

[0032] The molar ratio of hydrogen to p-trifluoromethoxynitrobenzene is 3-6:1, preferably 3-4:1.

[0033] The fixed bed reactor is a micro-packed bed reactor.

[0034] The method for preparing p-trifluoromethoxyaniline by continuous hydrogenation of the present invention is described in detail below by means of specific examples. In the examples, all the raw reagent materials are commercially available, and the experimental methods without specifying the specific conditions are conventional methods and conventional conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0035] Pt / C catalyst was purchased from Oushisheng (Beijing) Technology Co., Ltd., with a Pt content of 1%;

[0036] Pd / C catalyst was purchased from Oushisheng (Beijing) Technology Co., Ltd., with a Pd content of 5%;

[0037] Ni / SiO2 catalyst was purchased from Oushisheng (Beijing) Technology Co., Ltd.; Ni content 20%, silicon dioxide content 80%;

[0038] Pd / Al2O3 catalyst was purchased from Oushisheng (Beijing) Technology Co., Ltd., with a Pd content of 3%;

[0039] p-Trifluoromethoxyaniline is produced by Jinkai (Liaoning) Life Science Co., Ltd., and its content is greater than 99%;

[0040] p-Trifluoromethoxynitrobenzene is produced by Jinkai (Liaoning) Life Science Co., Ltd., and its content is greater than 99%;

[0041] The micro-packed bed reactor was purchased from Oushisheng (Beijing) Technology Co., Ltd., model H-Flow-S10.

[0042] Example 1

[0043] 5g of Pt / C catalyst was tightly packed in a micro-packed bed reactor. With p-trifluoromethoxyaniline as solvent, p-trifluoromethoxynitrobenzene was prepared into a p-trifluoromethoxyaniline solution with a mass concentration of 10wt% (density of 1.3329g / mL). The back pressure valve pressure was set to 2MPa. The preheating temperature and reaction temperature were both 80°C, the standard volume flow rate of hydrogen was 50ml / min, and after the system was stable, a 10% mass concentration of p-trifluoromethoxynitrobenzene / p-trifluoromethoxyaniline solution was continuously added to the micro-packed bed reactor by a pump, and the liquid flow rate was adjusted to 1.0ml / min. The reaction product was analyzed by gas chromatography, the detector was FID, the chromatographic column model was DB-5, 30mx0.32mm, and the conversion rate of the raw material was measured to be 99.92%, the selectivity was 99.5%, and the purity of p-trifluoromethoxyaniline was 99.4%.

[0044] Example 2

[0045] 5g Ni / SiO2 catalyst is tightly packed in a fixed bed reactor. p-Trifluoromethoxynitrobenzene is prepared into a p-trifluoromethoxyaniline solution with a mass concentration of 10wt%. The back pressure valve pressure is set to 3MPa. The preheating temperature and the reaction temperature are both 90°C, the standard volume flow rate of hydrogen is 100ml / min, and after the system is stable, a p-trifluoromethoxynitrobenzene / p-trifluoromethoxyaniline solution with a mass concentration of 10% is continuously added to the fixed bed reactor by a pump, and the liquid flow rate is adjusted to 2.0ml / min. The reaction product is analyzed using the gas chromatography conditions of Example 1, and the conversion rate of the raw material is measured to be 99.98%, the selectivity is 99.7%, and the purity of p-trifluoromethoxyaniline is 99.6%.

[0046] Example 3

[0047] 5g of Pd / C catalyst was tightly packed in a micro-packed bed reactor. Using p-trifluoromethoxyaniline as solvent, p-trifluoromethoxynitrobenzene was prepared into a p-trifluoromethoxyaniline solution with a mass concentration of 5wt% (density of 1.3265g / mL). The back pressure valve pressure was set to 2.5MPa. The preheating temperature and reaction temperature were both 95°C, the standard volume flow rate of hydrogen was 65ml / min, and after the system was stable, a 5% mass concentration of p-trifluoromethoxynitrobenzene / p-trifluoromethoxyaniline solution was continuously added to the micro-packed bed reactor by a pump, and the liquid flow rate was adjusted to 2.3ml / min. The reaction product was analyzed using the gas chromatography conditions of Example 1, and the conversion rate of the raw material was measured to be 99.9%, and the selectivity was 99.6%. The purity of p-trifluoromethoxyaniline was 99.4%.

[0048] Example 4

[0049] 5g of Pd / Al2O3 catalyst was tightly packed in a micro-packed bed reactor. Using p-trifluoromethoxyaniline as solvent, p-trifluoromethoxynitrobenzene was prepared into a p-trifluoromethoxyaniline solution with a mass concentration of 3wt% (density of 1.324g / mL). The back pressure valve pressure was set to 0.1MPa. The preheating temperature and reaction temperature were both 120°C, the standard volume flow rate of hydrogen was 2.5ml / min, and after the system was stable, a 3% mass concentration of p-trifluoromethoxynitrobenzene / p-trifluoromethoxyaniline solution was continuously added to the micro-packed bed reactor by a pump, and the liquid flow rate was adjusted to 0.125ml / min. The reaction product was analyzed using the gas chromatography conditions of Example 1, and the conversion rate of the raw material was measured to be 99.8%, and the selectivity was 99.7%. The purity of p-trifluoromethoxyaniline was 99.5%.

[0050] Example 5

[0051] 5g of Pd / C catalyst was tightly packed in a micro-packed bed reactor. Using p-trifluoromethoxyaniline as solvent, p-trifluoromethoxynitrobenzene was prepared into a p-trifluoromethoxyaniline solution with a mass concentration of 20wt% (density of 1.3461g / mL). The back pressure valve pressure was set to 2MPa. The preheating temperature and the reaction temperature were both 40°C, the standard volume flow rate of hydrogen was 50ml / min, and after the system was stable, a 20% mass concentration of p-trifluoromethoxynitrobenzene / p-trifluoromethoxyaniline solution was continuously added to the micro-packed bed reactor by a pump, and the liquid flow rate was adjusted to 0.29ml / min. The reaction product was analyzed using the gas chromatography conditions of Example 1, and the conversion rate of the raw material was measured to be 93.4%, the selectivity was 98.5%, and the purity of p-trifluoromethoxyaniline was 91.6%.

[0052] Comparative Example 1

[0053] 5g of Pd / C catalyst was tightly packed in a micro-packed bed reactor. Using methanol as solvent, p-trifluoromethoxynitrobenzene was prepared into a methanol solution with a mass concentration of 20wt% (density of 0.8699g / mL). The back pressure valve pressure was set to 2MPa. The preheating temperature and reaction temperature were both 40°C, the standard volume flow rate of hydrogen was 50ml / min, and after the system was stable, a 20% mass concentration of p-trifluoromethoxynitrobenzene / methanol solution was continuously added to the micro-packed bed reactor with a pump, and the liquid flow rate was adjusted to 0.44ml / min. The reaction product was analyzed using the gas chromatography conditions of Example 1, and the conversion rate of the raw material was 87.4% and the selectivity was 97.3%. The purity of p-trifluoromethoxyaniline was 85.0%, and the content of N-methylated product was 0.3%.

[0054] From the results of Examples 1-5, it can be seen that the method of the present invention is used to prepare p-trifluoromethoxyaniline, the conversion rate of the raw materials is above 93%, the selectivity is above 98%, and the purity of the prepared p-trifluoromethoxyaniline is 91%; compared with Example 5, Comparative Example 1 uses methanol as a solvent to prepare p-trifluoromethoxyaniline, the conversion rate of the raw materials is 87.4%, the selectivity is 97.3%, the purity of p-trifluoromethoxyaniline is 85.0%, and the content of N-methylated products in the prepared p-trifluoromethoxyaniline is 0.3%.

[0055] In summary, the method of the present invention uses trifluoromethoxyaniline as a solvent, and no other solvents are introduced, thereby reducing waste emissions caused by the solvent and being environmentally friendly; no solvent separation step is required, the operation steps are simplified, the operation is convenient, and the cost is reduced; the reaction product of the method of the present invention has high selectivity, no N-alkylated by-products generated by using alcohol solvents, and good product quality.

[0056] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing p-trifluoromethoxyaniline by continuous hydrogenation, characterized in that: The method comprises the following steps: mixing p-trifluoromethoxynitrobenzene and a solvent and then continuously catalytically hydrogenating the mixture in a fixed bed reactor to obtain p-trifluoromethoxyaniline; wherein the solvent is p-trifluoromethoxyaniline and hydrogen is a hydrogen source; wherein the mass concentration of p-trifluoromethoxynitrobenzene is 3-10% based on the total weight of p-trifluoromethoxynitrobenzene and the solvent; The temperature of the catalytic hydrogenation reaction is 80-120°C; The catalyst is Ni / SiO2.

2. The method according to claim 1, characterized in that The pressure of the catalytic hydrogenation reaction is 0.1-3 MPa.

3. The method according to claim 2, characterized in that The pressure of the catalytic hydrogenation reaction is 1-3 MPa.

4. The method according to claim 1, characterized in that: The mass space velocity of the catalytic hydrogenation reaction relative to trifluoromethoxynitrobenzene is 0.05-4h -1 .

5. The method according to claim 2, characterized in that: The mass space velocity of the catalytic hydrogenation reaction relative to trifluoromethoxynitrobenzene is 0.05-4h -1 .

6. The method according to claim 1, characterized in that The catalyst is loaded in the middle constant temperature zone of the fixed bed reactor.

7. The method according to claim 2, characterized in that The catalyst is loaded in the middle constant temperature zone of the fixed bed reactor.

8. The method according to claim 4, characterized in that The catalyst is loaded in the middle constant temperature zone of the fixed bed reactor.

9. The method according to any one of claims 1 to 8, characterized in that: The molar ratio of hydrogen to p-trifluoromethoxynitrobenzene is 3-6.

10. The method according to claim 9, characterized in that The molar ratio of hydrogen to trifluoromethoxynitrobenzene is 3-4.

11. The method according to any one of claims 1 to 8, characterized in that: The fixed bed reactor is a micro-packed bed reactor.

12. The method according to claim 9, characterized in that The fixed bed reactor is a micro-packed bed reactor.

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