A method for reducing a nitro-substituted aromatic compound

Abstract

The present invention provides a method for reducing nitro-substituted aromatic compounds. The nitro-substituted aromatic compounds are dispersed in a solution, and then a catalyst and a reducing agent are added. Through light irradiation in a flow reactor at different temperatures, the composition of the mobile phase, the reaction time, and the pH are regulated to reduce the nitro-substituted aromatic compounds to the corresponding azo aromatic compounds and azoxy aromatic compounds. Compared with a batch reactor, this method has high conversion efficiency, can be continuous, can regulate the product selectivity, has mild conditions, and is environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for reducing nitro-substituted aromatic compounds. Background Art

[0002] Azo aromatic compounds and azoxy aromatic compounds are important organic synthesis intermediates and raw materials, and are widely used in the synthesis of pesticides, pharmaceuticals, dyes, surfactants, photosensitive materials, etc.

[0003] Regarding their preparation, azo aromatic compounds and azoxy aromatic compounds can be obtained by reducing their corresponding nitro-substituted aromatic compounds. The main industrial methods for reducing nitro-substituted aromatic compounds include metal reduction method, sulfide reduction method, catalytic hydrogenation reduction method, hydrazine hydrate reduction method, and electrochemical reduction method, etc. The metal reduction method uses metal as a reducing agent, and the nitro-substituted aromatic compound undergoes a reduction reaction to obtain an aromatic amine, while the metal itself is oxidized. This method has the advantages of high product selectivity and good quality, but the main disadvantage is that it will produce a large amount of saline wastewater and waste residue. At present, in China, the iron powder reduction method is still mainly used. The reduction of nitro-substituted aromatic compounds with iron powder needs to be carried out in an acidic medium, and after the reaction, alkali needs to be added to neutralize the acid, so a large amount of saline wastewater and iron mud containing organic matter will be produced. The catalytic hydrogenation reduction method is to reduce nitro with hydrogen in the presence of a catalyst, and it is widely used in the industrial production of aniline, and it is impossible to selectively obtain the corresponding azo aromatic compounds and azoxy aromatic compounds. It requires precious metal catalysts, and most of them need to be carried out under pressure and the catalyst needs to be strictly avoided from contacting air during use to prevent passivation and deactivation. The sulfide reduction method has mild reaction conditions, but the yield is low, and a large amount of sulfur-containing wastewater will be discharged after the reaction, seriously polluting the environment. The hydrazine hydrate reduction method is environmentally friendly and simple to operate, but the disadvantages are high cost and low selectivity for azo aromatic compounds and azoxy aromatic compounds. These methods cannot regulate the selective formation of products in real time and effectively, the catalytic process cannot be continuous and recyclable, and either they are not green enough or the cost is high. Therefore, it is a very meaningful work to develop a method for reducing nitro-substituted aromatic compounds that is green, environmentally friendly, and can continuously regulate the product selectivity.

[0004] Aiming at the problems existing in the prior art, the present invention provides a method for reducing nitro-substituted aromatic compounds, which can continuously regulate the product selectivity, and the system can be recycled, green and environmentally friendly. Summary of the Invention

[0005] The present invention provides a method for reducing nitro-substituted aromatic compounds. The technical solution of the present invention comprises dispersing the nitro-substituted aromatic compound in a solution, then adding a catalyst and a reducing agent, and subjecting the solution to light exposure in a flow reactor at different temperatures while regulating the composition, flow rate, and pH of the mobile phase to reduce the nitro-substituted aromatic compound to the corresponding azo aromatic compound or azoxy aromatic compound.

[0006] The flow reactor consists of a transparent reaction tube, a pump, a light source, and a material collection tank. The material collection tank is filled with a mobile phase catalyst, a reducing agent, and a substrate. The pump provides power to make the mobile phase flow, driving the catalyst, reducing agent, and substrate to flow. The light source provides illumination above the reaction tube. The reaction process involves adding the catalyst, substrate, solvent, and reducing agent to the material collection tank, adjusting the pH of the solution, adding a stirrer, and stirring on a magnetic stirring heating plate. The outlet of the material collection tank is connected to the pump, which is then connected to the reaction tube. The other side of the reaction tube is connected to the inlet of the material collection tank. A light source is used to illuminate the reaction tube from above. The reactants flow into the reaction tube and react under illumination. The reaction circulates through the pump until the set reaction time is reached.

[0007] The reaction conditions for a method for reducing a nitro-substituted aromatic compound can be carried out according to the following conditions: the concentration of the substrate is 0.1-1.0 mol / L, the amount of the catalyst is 0.5-20 wt% of the substrate mass, the reducing agent is one or more of an alcohol such as methanol, ethanol, or isopropanol, the amount of the reducing agent is 20-30 times the molar amount of the nitro-substituted aromatic compound, the mobile phase is one or more of water and acetonitrile, the mobile phase volume is 10-50 mL, 1 mol / L NaOH is used to adjust the mobile phase pH, the mobile phase pH range can be 5-10, the reaction temperature is 20-50°C, the pump provides a mobile phase flow rate of 0.01-10 mL / min, and the reaction time is 2-24 h. The illumination wavelength is 200-600 nm; the illumination intensity range is 50-200 mW / cm 2 .

[0008] Beneficial effects of the present invention

[0009] The present invention relates to a method for preparing corresponding azobenzene, azoxybenzene and aniline by reducing nitro-substituted aromatic compounds.

[0010] The faster the flow rate, the faster the reaction rate. Reaction efficiency in a flow reactor is higher than in a tank reactor. As the flow rate increases, residence time decreases, reducing aniline selectivity and increasing azobenzene selectivity in the resulting product. This allows for the regulation of product selectivity under mild, environmentally friendly conditions.

[0011] Regulation of the reduction of nitro-substituted aromatic compounds by light shows that light is a necessary condition for inducing the reaction. The shorter the wavelength of light, the more it promotes the hydrogenation of azoxybenzene to azobenzene, but does not further hydrogenate it to aniline. Therefore, the selectivity of azobenzene and azoxybenzene can be regulated by changing the wavelength of light.

[0012] The reaction can occur within the pH range of 6 - 10, and the main product is azobenzene. The higher the pH value, the lower the selectivity of azobenzene and aniline, and the higher the selectivity of azoxybenzene.

[0013] The catalytic reactions can occur with different catalysts such as eosin (Eosin Y), acridine, 5-aminolevulinic acid (ALA), hematoporphyrin monomethyl ether (HMME), as well as Ru, Rh, Pb, Pt, Au, Ag, Cu, Fe, Ni, Co catalysts supported on TiO2, CeO2, Al2O3, ZrO2, CdS, and the main product obtained is azobenzene, with slightly different selectivities.

[0014] Temperature increases the reaction rate but causes over-hydrogenation, increasing the selectivity of the product aniline and being unfavorable for selectively obtaining azobenzene and azoxybenzene.

[0015] The mobile phase can be acetonitrile, water, or directly the reducing agent ethanol, and the reaction can occur to selectively obtain azobenzene.

[0016] The reaction can occur with mono-substituted and multi-substituted electron-donating and electron-withdrawing substituents, and azobenzene is selectively obtained.

[0017] The reaction can occur with nitro-substituted heterocyclic aromatic compounds such as imidazole heterocyclic and pyridine heterocyclic compounds, and azo products are selectively obtained.

[0018] In summary, compared with the autoclave reactor, it has the advantages of adjustable product selectivity, mild conditions, and environmental friendliness, so it has certain industrial application value. Specific Embodiments

[0019] To further illustrate the present invention in detail, several specific comparative implementation cases are given below.

[0020] 1. Comparative Example

[0021] In the comparative examples, the autoclave reactor used was made of quartz glass. The reactor body was a cylindrical tube with an inner diameter of 4 cm, an outer diameter of 6 cm, and a height of 4 cm, open at the upper end. The cover was a quartz glass sheet with a diameter of 6 cm and a thickness of 1 cm. There was a rubber ring slot between the reactor body and the cover, which was clamped tightly with a U-shaped bayonet clip with screw holes and fixed with screws. During the reaction process, the catalyst, substrate, solvent, and reducing agent were added to the reactor body, the pH of the solution was adjusted, a magnetic stirrer was added, sealed with a rubber ring, the reactor cover was covered, the U-shaped bayonet clip was fixed with screws, placed on a magnetic stirring heating plate for stirring, and light was irradiated from above the reactor using a light source.

[0022] Comparative Example 1:

[0023] Using an autoclave reactor, the substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Eosin Y, and the amount of catalyst used was 10 wt% of the substrate mass. The solvent was water with a volume of 30 mL. The reducing agent was ethanol, and the amount of reducing agent used was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8.5 using 1 mol / L NaOH. The stirring speed was 400 rpm, the reaction temperature was 25 °C, the reaction time was 15 h, and 365 nm light was used for irradiation with a light intensity of 100 mW / cm 2 . The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 23%, the selectivity of azobenzene was 28%, the selectivity of aniline was 62%, and the selectivity of azoxybenzene was 10%.

[0024] Comparative Example 2:

[0025] Using an autoclave reactor, the substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was HMME, and the amount of catalyst used was 10 wt% of the substrate mass. The solvent was water with a volume of 30 mL. The reducing agent was isopropanol, and the amount of reducing agent used was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8.5 using 1 mol / L NaOH. The stirring speed was 400 rpm, the reaction temperature was 25 °C, the reaction time was 15 h, and 365 nm light was used for irradiation with a light intensity of 100 mW / cm 2 . The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 19%, the selectivity of azobenzene was 28%, the selectivity of aniline was 66%, and the selectivity of azoxybenzene was 6%.

[0026] Comparative Example 3:

[0027] Using a batch reactor, the substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Pt / TiO2, and the dosage of the catalyst is 10 wt% of the substrate mass. The solvent is acetonitrile with a volume of 30 mL. The reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L NaOH is used to adjust the pH of the solution to 8.5. The stirring speed is 400 rpm, the reaction temperature is 25 °C, the reaction time is 15 h, 365 nm light is used for illumination, and the light intensity is 100 mW / cm 2 . The obtained sample is qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene is 9%, the selectivity of azobenzene is 38%, the selectivity of aniline is 36%, and the selectivity of azoxybenzene is 26%.

[0028] Comparative Example 4:

[0029] Using a batch reactor, the substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Pt / CeO2, and the dosage of the catalyst is 10 wt% of the substrate mass. The solvent, which is also the reducing agent, is ethanol with a volume of 30 mL. The dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L NaOH is used to adjust the pH of the solution to 8.5. The stirring speed is 400 rpm, the reaction temperature is 25 °C, the reaction time is 15 h, 365 nm light is used for illumination, and the light intensity is 100 mW / cm 2 . The obtained sample is qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene is 15%, the selectivity of azobenzene is 30%, the selectivity of aniline is 46%, and the selectivity of azoxybenzene is 24%.

[0030] In the above 4 comparative examples, the four catalysts can all catalyze the reaction in the reaction kettle. The homogeneous catalyst has better catalytic activity than the supported heterogeneous catalyst, but generally has lower efficiency, lower selectivity for azo aromatic compounds and azoxy aromatic compounds, and aniline is the main product.

[0031] To further illustrate the present invention in detail, some specific implementation cases are given below, but the present invention is not limited to these examples.

[0032] In the examples, the flow reactor used consists of a transparent reaction tube, a pump, a light source, and a material collection tank. The material collection tank contains the mobile phase, catalyst, reducing agent, and substrate. The pump provides power to make the mobile phase flow, driving the catalyst, reducing agent, and substrate to flow. The light source provides illumination above the reaction tube.

[0033] The length of the transparent reaction tube is 5 m, the inner diameter (diameter) is 2.5 mm, and the material is transparent glass; the pump provides a mobile phase flow rate of 0.01 - 10 mL / min, and a peristaltic pump is used; the wavelength of the light source is 365 nm or 455 nm, 525 nm, the light intensity is adjustable, and a COB light source is used; the volume of the material collection tank is 100 mL, which is a glass tank with material inlets and outlets at both the upper and lower ends.

[0034] The reaction process is as follows: Add the catalyst, substrate, solvent, and reducing agent into the material collection tank, adjust the pH of the solution, add a magnetic stir bar, place it on a magnetic stirring heating plate and stir. The outlet at the lower end of the material collection tank is connected to the pump, the pump is connected to one end of the reaction tube, and the other side of the reaction tube is connected to the inlet at the upper end of the material collection tank. Use a light source to shine light from above the horizontally placed reaction tube. The reaction solution flows into the reaction tube and reacts under illumination, and circulates through the pump until the set reaction time is reached.

[0035] 1. Regulation of the reduction of nitro-substituted aromatic compounds by the flow state of the mobile phase

[0036] Example 1:

[0037] Using a flow reactor, the substrate is nitrobenzene with a concentration of 0.1 mol / L, the catalyst used is eosin (Eosin Y), the dosage of the catalyst is 10 wt% of the substrate mass, the mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 0.1 mL / min, the residence time is 245 min, the reducing agent is ethanol, the dosage of the reducing agent is 30 times the molar amount of nitrobenzene, use 1 mol / L NaOH to adjust the solution pH to 8.5, the reaction temperature is 25 °C, the total reaction time is 245 min, use 455 nm light illumination, and the light intensity is 100 mW / cm 2 . The obtained sample is qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene is 28%, the selectivity of azobenzene is 52%, the selectivity of aniline is 28%, and the selectivity of azoxybenzene is 20%.

[0038] Example 2:

[0039] Using a flow reactor, the substrate is nitrobenzene with a concentration of 0.1 mol / L, the catalyst used is eosin (Eosin Y), the dosage of the catalyst is 10 wt% of the substrate mass, the mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 0.1223 mL / min, the residence time is 200 min, the reducing agent is ethanol, the dosage of the reducing agent is 30 times the molar amount of nitrobenzene, use 1 mol / L NaOH to adjust the solution pH to 8.5, the reaction temperature is 25 °C, the total reaction time is 200 min, use 455 nm light illumination, and the light intensity is 100 mW / cm 2The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 42%, the selectivity for azobenzene was 58%, the selectivity for aniline was 22%, and the selectivity for azoxybenzene was 20%.

[0040] Example 3:

[0041] A flow reactor was used. The substrate was nitrobenzene with a concentration of 0.1 mol / L. Eosin Y was used as the catalyst, and the amount of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 0.5 mL / min, the residence time was 49 min, ethanol was used as the reducing agent, and the amount of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8.5. The reaction temperature was 25 °C, the total reaction time was 15 h, and 455 nm light was used for illumination with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 62%, the selectivity for azobenzene was 70%, the selectivity for aniline was 20%, and the selectivity for azoxybenzene was 10%.

[0042] Example 4:

[0043] A flow reactor was used. The substrate was nitrobenzene with a concentration of 0.1 mol / L. Eosin Y was used as the catalyst, and the amount of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, ethanol was used as the reducing agent, and the amount of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8.5. The reaction temperature was 25 °C, the reaction time was 15 h, and 455 nm light was used for illumination with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 99%, the selectivity for azobenzene was 78%, the selectivity for aniline was 15%, and the selectivity for azoxybenzene was 7%.

[0044] Example 5:

[0045] A flow reactor was used. The substrate was nitrobenzene with a concentration of 0.1 mol / L. Eosin Y was used as the catalyst, and the amount of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 5 mL / min, the residence time was 5 min, ethanol was used as the reducing agent, and the amount of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8.5. The reaction temperature was 25 °C, the reaction time was 12 h, and 455 nm light was used for illumination with a light intensity of 100 mW / cm 2The obtained sample was qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 99%, the selectivity of azobenzene was 77%, the selectivity of aniline was 14%, and the selectivity of azoxybenzene was 9%.

[0046] Example 6:

[0047] A flow reactor was used. The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Eosin Y, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 10 mL / min, the residence time was 3 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8.5, the reaction temperature was 25 °C, the total reaction time was 12 h, and 455 nm light was used with a light intensity of 100 mW / cm 2 The obtained sample was qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene was 99%, the selectivity of azobenzene was 79%, the selectivity of aniline was 10%, and the selectivity of azoxybenzene was 11%.

[0048] When regulating the reduction of nitro-substituted aromatic compounds by controlling the flow state of the mobile phase, the faster the flow rate, the faster the reaction rate. Compared with Comparative Example 1 in the comparative examples, it can be seen from the conversion rate of nitrobenzene that the reaction efficiency in the flow reactor is higher than that in the batch reactor. It can be seen from the product selectivity that as the flow rate increases and the residence time decreases, the selectivity of aniline in the generated products decreases, and the selectivity of azobenzene increases, thus realizing continuous and adjustable product selectivity, with mild regulation conditions and environmental friendliness.

[0049] 2. Regulation of the reduction of nitro-substituted aromatic compounds by light

[0050] Example 1:

[0051] A flow reactor was used. The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Eosin Y, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8.5, the reaction temperature was 25 °C, the total reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2 The obtained sample was qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time and was complete after 12 h of reaction. The selectivity of azobenzene was 68%, the selectivity of aniline was 22%, and the selectivity of azoxybenzene was 10%.

[0052] Example 2:

[0053] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L of NaOH is used to adjust the pH of the solution to 8.5, the reaction temperature is 25 °C, the reaction time is 15 h, 525 nm light is used for illumination, and the light intensity is 100 mW / cm 2 . The obtained samples are qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increases with time, and the reaction is complete after 14 h. The selectivity of azobenzene is 21%, the selectivity of aniline is 13%, and the selectivity of azoxybenzene is 66%.

[0054] Example 3:

[0055] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L of NaOH is used to adjust the pH of the solution to 8.5, the reaction temperature is 25 °C, the reaction time is 15 h, and there is no light illumination. The obtained samples are qualitatively and quantitatively analyzed using GC-MS and GC. Nitrobenzene is basically not converted.

[0056] Comparing Example 4 in the regulation of the reduction of nitro-substituted aromatic compounds by the flow state of the mobile phase and Examples 1, 2, and 3 in the regulation of the reduction of nitro-substituted aromatic compounds by light illumination. From the comparison between Example 3 and other examples with light illumination in the regulation of the reduction of nitro-substituted aromatic compounds by light illumination, it is concluded that light is a necessary condition for inducing the reaction to occur; when the illumination wavelengths are 365 nm and 455 nm, azobenzene is the main product, when the wavelength is 525 nm, azoxybenzene is the main product, and aniline is a small amount of product. It is speculated that the shorter the illumination wavelength, the more it promotes the hydrogenation conversion of azoxybenzene to azobenzene, but it does not further hydrogenate to aniline. Therefore, the selectivity of azobenzene and azoxybenzene can be regulated by changing the illumination wavelength, thereby achieving continuous and adjustable selectivity of the product. The regulation conditions are mild and environmentally friendly.

[0057] 3. Influence of pH on the reduction of nitro-substituted aromatic compounds

[0058] Example 1:

[0059] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is acridine, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L of NaOH is used to adjust the pH of the solution to 6. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained sample is analyzed qualitatively and quantitatively using GC-MS and GC. The conversion rate of nitrobenzene increases with time. The reaction is complete after 15 h of reaction time. The selectivity of azoxybenzene is 1%, the selectivity of aniline is 13%, and the selectivity of azobenzene is 88%.

[0060] Example 2:

[0061] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is acridine, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L of NaOH is used to adjust the pH of the solution to 7. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained sample is analyzed qualitatively and quantitatively using GC-MS and GC. The conversion rate of nitrobenzene increases with time. The reaction is complete after 15 h of reaction time. The selectivity of azoxybenzene is 5%, the selectivity of aniline is 10%, and the selectivity of azobenzene is 85%.

[0062] Example 3:

[0063] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is acridine, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. 1 mol / L of NaOH is used to adjust the pH of the solution to 8. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained sample is analyzed qualitatively and quantitatively using GC-MS and GC. The conversion rate of nitrobenzene increases with time. The reaction is complete after 15 h of reaction time. The selectivity of azoxybenzene is 9%, the selectivity of aniline is 10%, and the selectivity of azobenzene is 81%.

[0064] Example 4:

[0065] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is acridine, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The pH of the solution is adjusted to 10 with 1 mol / L NaOH. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained samples are analyzed qualitatively and quantitatively by GC-MS and GC. The conversion rate of nitrobenzene increases with time, and the reaction is complete after 15 h. The selectivity of azoxybenzene is 20%, the selectivity of aniline is 5%, and the selectivity of azobenzene is 75%.

[0066] The reaction can occur within the pH range of 6 - 10, and the main product is azobenzene. The higher the pH value, the lower the selectivities of azobenzene and aniline, and the higher the selectivity of azoxybenzene.

[0067] 4. Influence of the catalyst on the reduction of nitro-substituted aromatic compounds

[0068] Example 1:

[0069] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is acridine, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The pH of the solution is adjusted to 8 with 1 mol / L NaOH. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained samples are analyzed qualitatively and quantitatively by GC-MS and GC. The conversion rate of nitrobenzene increases with time, and the reaction is complete after 15 h. The selectivity of azoxybenzene is 16%, the selectivity of aniline is 4%, and the selectivity of azobenzene is 80%.

[0070] Example 2:

[0071] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is 5-aminolevulinic acid (ALA), and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The pH of the solution is adjusted to 8 with 1 mol / L NaOH. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for azoxybenzene was 20%, the selectivity for aniline was 8%, and the selectivity for azobenzene was 72%.

[0072] Example 3:

[0073] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was hematoporphyrin monomethyl ether (HMME), and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8 using 1 mol / L NaOH. The reaction temperature was 25 °C, the reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for azoxybenzene was 20%, the selectivity for aniline was 37%, and the selectivity for azobenzene was 53%.

[0074] Example 4:

[0075] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Pt / TiO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8 using 1 mol / L NaOH. The reaction temperature was 25 °C, the reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 10 h. The selectivity for azoxybenzene was 17%, the selectivity for aniline was 7%, and the selectivity for azobenzene was 76%.

[0076] Example 5:

[0077] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Pb / TiO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8 using 1 mol / L NaOH. The reaction temperature was 25 °C, the reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 12 h. The selectivity for azoxybenzene was 15%, the selectivity for aniline was 17%, and the selectivity for azobenzene was 68%.

[0078] Example 6:

[0079] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Rh / TiO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 12 h. The selectivity for azoxybenzene was 24%, the selectivity for aniline was 17%, and the selectivity for azobenzene was 59%.

[0080] Example 7:

[0081] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Au / TiO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for azoxybenzene was 20%, the selectivity for aniline was 23%, and the selectivity for azobenzene was 57%.

[0082] Example 8:

[0083] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Cu / TiO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 15 h, the conversion rate was 53%, the selectivity for azoxybenzene was 19%, the selectivity for aniline was 24%, and the selectivity for azobenzene was 57%.

[0084] Example 9:

[0085] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Pt / CeO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 12 h, the reaction was complete. The selectivity for azobenzene was 10%, the selectivity for aniline was 17%, and the selectivity for azoxybenzene was 83%.

[0086] Example 10:

[0087] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Pt / Al2O3, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 15 h, the reaction was complete. The selectivity for azoxybenzene was 30%, the selectivity for aniline was 36%, and the selectivity for azobenzene was 44%.

[0088] Example 11:

[0089] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was Pt / ZrO2, and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. 1 mol / L NaOH was used to adjust the pH of the solution to 8. The reaction temperature was 25 °C, the reaction time was 15 h, 365 nm light was used for illumination, and the light intensity was 100 mW / cm 2The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 15 h, the conversion was 67%, the selectivity for azoxybenzene was 20%, the selectivity for aniline was 37%, and the selectivity for azobenzene was 53%.

[0090] In the examples comparing the effects of different catalysts on the reduction of nitro-substituted aromatic compounds, reactions can occur with eosin (Eosin Y), acridine, 5-aminolevulinic acid (ALA), hematoporphyrin monomethyl ether (HMME), and catalysts loaded with Ru, Rh, Pb, Pt, Au, Ag, Cu, Fe, Ni, Co on TiO2, CeO2, Al2O3, ZrO2, CdS. The main product obtained is azobenzene, with slightly different selectivities.

[0091] 5. Influence of temperature on the reduction of nitro-substituted aromatic compounds

[0092] Example 1:

[0093] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was eosin (Eosin Y), and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8.5 using 1 mol / L NaOH. The reaction temperature was 40 °C, the reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 12 h, the reaction was complete. The selectivity for azoxybenzene was 21%, the selectivity for aniline was 30%, and the selectivity for azobenzene was 49%.

[0094] Example 2:

[0095] The substrate was nitrobenzene with a concentration of 0.1 mol / L. The catalyst used was eosin (Eosin Y), and the dosage of the catalyst was 10 wt% of the substrate mass. The mobile phase was water with a volume of 30 mL, the flow rate of the mobile phase was 1 mL / min, the residence time was 25 min, the reducing agent was ethanol, and the dosage of the reducing agent was 30 times the molar amount of nitrobenzene. The pH of the solution was adjusted to 8.5 using 1 mol / L NaOH. The reaction temperature was 50 °C, the reaction time was 15 h, and 365 nm light was used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time. At a reaction time of 10 h, the reaction was complete. The selectivity for azoxybenzene was 14%, the selectivity for aniline was 43%, and the selectivity for azobenzene was 43%.

[0096] As can be seen from the examples in the influence of temperature on the reduction of nitro-substituted aromatic compounds, temperature increases the reaction rate but leads to over-hydrogenation, increasing the selectivity of the product aniline and being unfavorable for selectively obtaining azobenzene and azoxybenzene.

[0097] 6. Influence of Mobile Phase and Reducing Agent on the Reduction of Nitro-Substituted Aromatic Compounds

[0098] Example 1:

[0099] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is acetonitrile with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained sample was qualitatively and quantitatively analyzed using GC-MS and GC. The conversion of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity of azoxybenzene was 14%, the selectivity of aniline was 16%, and the selectivity of azobenzene was 70%.

[0100] Example 2:

[0101] The substrate is nitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase, which is also the reducing agent, is ethanol with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 . The obtained sample was qualitatively and quantitatively analyzed using GC-MS and GC. The conversion of nitrobenzene increased with time, and the reaction was complete after 12 h. The selectivity of azoxybenzene was 16%, the selectivity of aniline was 21%, and the selectivity of azobenzene was 63%.

[0102] As can be seen from the examples of the influence of mobile phase and reducing agent on the reduction of nitro-substituted aromatic compounds, when the mobile phase is acetonitrile, water, or directly the reducing agent ethanol, the reaction can occur, and azobenzene can be selectively obtained.

[0103] 7. Influence of Substituents on the Reduction of Nitro-Substituted Aromatic Compounds

[0104] Example 1:

[0105] The substrate is p-nitrotoluene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for the oxidation of 4,4'-azotoluene was 12%, the selectivity for p-toluidine was 17%, and the selectivity for 4,4'-azotoluene was 71%.

[0106] Example 2:

[0107] The substrate is p-chloronitrobenzene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for the oxidation of p-chloroazobenzene was 17%, the selectivity for p-chloroaniline was 28%, and the selectivity for p-chloroazobenzene was 55%.

[0108] Example 3:

[0109] The substrate is 4-chloro-2-nitrotoluene with a concentration of 0.1 mol / L. The catalyst used is Eosin Y, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, the reducing agent is ethanol, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, and 365 nm light is used with a light intensity of 100 mW / cm 2 The obtained samples were qualitatively and quantitatively analyzed using GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity for 4,4'-chloro-2,2'-oxazotoluene was 20%, the selectivity for 4-chloro-2-aminotoluene was 20%, and the selectivity for 4,4'-chloro-2,2'-azotoluene was 60%.

[0110] It can be seen from the examples of the influence of substituents on the reduction of nitro-substituted aromatic compounds that the reaction can occur in the presence of mono-substituted and multi-substituted electron-donating and electron-withdrawing substituents, and azobenzene can be selectively obtained.

[0111] 8. Influence of the Reduction of Nitro-Substituted Heterocyclic Aromatic Compounds

[0112] Example 1:

[0113] The substrate is 2-nitroimidazole with a concentration of 0.1 mol / L. Eosin Y is used as the catalyst, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, ethanol is used as the reducing agent, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, 365 nm light is used, and the light intensity is 100 mW / cm 2 . The obtained sample was analyzed qualitatively and quantitatively by GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity of oxidized 2,2'-azobisimidazole was 13%, the selectivity of 2-aminoimidazole was 15%, and the selectivity of 2,2'-azobisimidazole was 72%.

[0114] Example 2:

[0115] The substrate is 3-nitropyridine with a concentration of 0.1 mol / L. Eosin Y is used as the catalyst, and the dosage of the catalyst is 10 wt% of the substrate mass. The mobile phase is water with a volume of 30 mL, the flow rate of the mobile phase is 1 mL / min, the residence time is 25 min, ethanol is used as the reducing agent, and the dosage of the reducing agent is 30 times the molar amount of nitrobenzene. The reaction temperature is 25 °C, the reaction time is 15 h, 365 nm light is used, and the light intensity is 100 mW / cm 2 . The obtained sample was analyzed qualitatively and quantitatively by GC-MS and GC. The conversion rate of nitrobenzene increased with time, and the reaction was complete after 15 h. The selectivity of oxidized 3,3'-azobipyridine was 9%, the selectivity of 3-aminopyridine was 12%, and the selectivity of 3,3'-azobipyridine was 79%.

[0116] It can be seen from the examples of the influence of the reduction of nitro-substituted heterocyclic aromatic compounds that the reaction can occur for nitro-substituted heterocyclic aromatic compounds such as imidazole heterocyclic and pyridine heterocyclic compounds, and azo products can be selectively obtained.

Claims

1. A method for reducing nitro-substituted aromatic compounds, characterized in that: A reaction solution containing a nitro-substituted aromatic compound, a catalyst, and a reducing agent is introduced into a reaction tube of a flow reactor. During the flow of the reaction solution, a photocatalytic reaction occurs in the reaction tube to reduce the nitro-substituted aromatic compound to two or more of the corresponding azo aromatic compound and azoxy aromatic compound. The nitro-substituted aromatic compound is nitrobenzene; the catalyst is acridine; the reducing agent is ethanol. The flow reactor includes a transparent reaction tube with two open ends, a liquid pump, a light source, and a material collection tank. The two open ends of the transparent reaction tube are respectively connected to the material collection tank. A liquid pump is provided on the pipeline connecting the open end of the reaction tube to the material collection tank. A light source is provided on one side of the reaction tube. The material collection tank contains the reaction solution. The pump provides power to make the reaction solution flow in the reaction tube. The light source on one side of the reaction tube provides light for the reaction solution flowing inside the reaction tube. The length of the transparent reaction tube is 0.5 - 10 m, the inner diameter is 1 - 10 mm, and the material is one or more of glass, quartz, and transparent plastic; the liquid pump is selected from one or more of a peristaltic pump, a metering pump, and a syringe pump; the light wavelength is 365 nm, and the light source is one or two of a xenon lamp and an LED lamp; the volume of the material collection tank is 30 - 500 mL, and it is a glass tank or a stainless steel tank with reaction solution inlets and outlets provided at the upper and lower ends. The reaction process is as follows: Add the reaction solution into the material collection tank, add a magnetic stir bar, place it on a magnetic stirring hot plate and stir. Connect the lower outlet of the material collection tank to the inlet of the pump, connect the outlet of the pump to one open end of the reaction tube, and connect the other open end of the reaction tube to the upper inlet of the material collection tank. Use the light source to shine light on the reaction tube from one side. The reaction solution flows to the illuminated area of the reaction tube to react and circulates through the pump until the set reaction time is reached. The pH value range of the reaction solution is 5 - 10; the reaction time is 2 - 24 h, and the reaction temperature is 20 - 50 °C.

2. The method according to claim 1, wherein: The dosage of the catalyst is 0.5 - 20 wt% of the mass of the substrate nitro-substituted aromatic compound; the dosage of the reducing agent is 1 - 100 times the mass of the substrate nitro-substituted aromatic compound. The reaction is carried out in the mobile phase. The concentration of the substrate nitro-substituted aromatic compound is 0.001 - 10.0 mol / L. The mobile phase is one or more of water, acetonitrile, benzene, toluene, xylene, acetone, or ethanol as a reducing agent is directly used as the mobile phase. The volume of the mobile phase is 5 - 500 mL. One or more of NaOH, KOH, LiOH, Na2CO3, and NaHCO3 are used to adjust the pH value of the reaction solution. The liquid pump provides a flow rate of the reaction solution of 0.01 - 10 mL / min; the light intensity range is 30 - 300 mW / cm 2 .

3. The method according to claim 1, wherein: The residence time of the reaction solution flowing through the photoreaction tube is 1 min to 24 h, and the residence time of the reaction solution flowing through the photoreaction tube is less than or equal to the reaction time.

4. The method according to claim 1, wherein: The residence time of the reaction solution flowing through the photoreaction tube is 3 min to 12 h.

5. The method according to claim 1, wherein: The reaction conditions are as follows: the concentration of the substrate nitro-substituted aromatic compound is 0.1 - 1.0 mol / L, the dosage of the catalyst is 0.5 - 20 wt% of the mass of the substrate nitro-substituted aromatic compound, the dosage of the reducing agent is 20 - 30 times the molar amount of the nitro-substituted aromatic compound, the mobile phase is one or both of water and acetonitrile, the volume of the mobile phase is 10 - 50 mL, the pH value range of the reaction solution is adjusted using 1 mol / L NaOH, the flow rate of the mobile phase provided by the pump is 0.01 - 10 mL / min; the light intensity range is 50 - 200 mW / cm 2 .