A method for preparing benzamide by photocatalytic benzonitrile using an acoustic-photoreactor

Abstract

The present invention discloses a method for preparing benzamide by photocatalytically removing benzonitrile from a sono-photoreactor. The method comprises reacting an alkaline aqueous solution containing benzonitrile and a catalyst with O2 in the sono-photoreactor, collecting the effluent, and obtaining a reaction solution containing benzamide. The catalyst is a g-C3N4 nanosheet that has been subjected to a composite exfoliation process using two or more exfoliation methods. The reaction volume is small and the reaction time is extremely short. The sono-photoreactor is a microreactor that combines an ultrasonic device with a microfluidic chip. This method can achieve the purpose of expanding the contact area between the liquid and the catalyst, enhancing the mixing effect of the liquid and the catalyst, and reducing the flow pressure of the mixed liquid in the inner tube. The combination of the microreactor and the ultrasonic device can reduce the problems of uneven solid-liquid mixing and solid catalyst deposition during the reaction process in the microreactor.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for preparing benzamide by photocatalytically catalyzing benzonitrile using an acousto-photoreactor. Background Art

[0002] The energy crisis is a global issue facing humanity. As countries continue to promote economic development, greenhouse gas emissions are surging. Establishing and improving a green, low-carbon, circular development system and improving the energy structure have become increasingly important. Energy and the environment are two key aspects of sustainable development for human society. Solar energy, as an inexhaustible non-fossil energy source, has played a significant role in addressing the fossil fuel depletion and environmental pollution challenges facing the 21st century. In particular, photocatalytic conversion using abundant and sustainable biomass and inexhaustible solar energy as the sole energy input effectively promotes carbon recycling, not only reducing CO2 emissions but also helping to alleviate the energy crisis.

[0003] Photocatalytic technology offers advantages such as environmental friendliness, mild reaction conditions, low cost, cleanliness, and high efficiency. It is widely used in water splitting, carbon dioxide conversion, degradation of organic pollutants, bacterial disinfection, and the selective synthesis of organic compounds. Carbon-based materials, such as graphene, carbon nanotubes, and activated carbon, are a widely used substrate. Considering the cost of carbon-based materials, biomass-derived carbon materials have attracted increasing attention due to their low cost, ease of synthesis, and high physicochemical stability. Carbon is abundant in the Earth's surface, low cost, non-toxic, and biocompatible. Photocatalytic oxidation performance depends on two key factors: the catalyst's physicochemical properties (specific surface area, pore structure, and distribution of active sites) and its photoelectrochemical properties (visible light absorption capacity, photogenerated charge separation and transport properties). Researchers aim to modify semiconductor materials to produce photocatalysts with advantages such as high specific surface area, high stability, suppression of electron-hole recombination, and the ability to utilize visible light. Common modification methods include heterostructure construction, atomic doping, morphology manipulation, and precious metal deposition. g-C3N4 is a recently developed 2D sheet material with widespread applications in materials, energy, catalysis, and other fields. g-C3N4 is a planar 2D layered structure similar to graphene, with superior flexibility compared to 3D porous materials. Its basic repeating unit structure is a 3-s-triazine ring.

[0004] Benzamide is a colorless, flaky crystal with a melting point of 132-133°C and a boiling point of 290°C. It is soluble in ethanol and hot water, neutral, and exhibits amide properties. Hydrolysis produces benzoic acid and ammonia. Benzamide is an important chemical intermediate widely used in dyes and synthetic pharmaceuticals. In existing methods, benzamide is often prepared by reacting benzoyl chloride with aqueous ammonia. The reaction proceeds as follows: ammonium carbonate and aqueous ammonia are first added to a reaction vessel and stirred. Benzoyl chloride is then added dropwise at a temperature below 40°C. Stir for 30 minutes until the odor of benzoyl chloride disappears. The crude product is filtered, washed, and recrystallized from distilled water to obtain the finished product. In this method, the intermediate benzoyl chloride is produced by reacting benzoic acid with thionyl chloride. Because this reaction requires an excess of more than 100% thionyl chloride to achieve complete reaction, the utilization rate of the thionyl chloride is low, and any excess thionyl chloride can cause environmental pollution and operational safety hazards. Furthermore, this process involves multiple steps, the acyl chloride is highly toxic, and determining the reaction endpoint is difficult. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies of the prior art and provide a method for preparing benzamide from benzonitrile by photocatalysis using an acousto-photoreactor.

[0006] In order to solve the above technical problems, the present invention discloses a method for preparing benzamide by photocatalytically treating benzonitrile with an acousto-photoreactor. An alkaline aqueous solution containing benzonitrile and a catalyst is reacted with O2 in an acousto-photoreactor, and the effluent is collected to obtain a reaction solution containing benzamide.

[0007] The catalyst is a g-C3N4 nanosheet that has been subjected to composite exfoliation by two or more exfoliation methods; the exfoliation method includes thermal oxidation etching, chemical method, ultrasonic method, or microwave method.

[0008] The pH of the alkaline aqueous solution is adjusted by an alkaline reagent, and the alkaline reagent includes any one or a combination of NaOH, KOH, Na2CO3 and K2CO3; the pH value of the alkaline aqueous solution is 10-12.

[0009] Wherein, the concentration of benzonitrile in the alkaline aqueous solution is 0.1-0.3 mmol / mL, preferably 0.2 mmol / mL.

[0010] Wherein, the concentration of the catalyst in the alkaline aqueous solution is 1-3 mg / mL, preferably 2 mg / mL.

[0011] The alkaline aqueous solution containing benzonitrile and the catalyst is pumped into the sono-optical reactor at a rate of 0.1-1 mL / min; and the O2 is pumped into the sono-optical reactor at a rate of 1-10 mL / min.

[0012] The acousto-optic reactor comprises one or more ultrasonic vibrators, a microfluidic chip and a light source; the ultrasonic vibrator is assembled on one side of the microfluidic chip, and the microfluidic chip is placed under the irradiation of the light source.

[0013] The light source is placed on the other side of the microfluidic chip, and the light source is 25-35 cm away from the microfluidic chip so that the center of the light spot is irradiated on the microfluidic chip.

[0014] The inner diameter of the microfluidic chip is 1-3 mm, and the reaction volume is 1-10 mL.

[0015] Wherein, the ultrasonic frequency of the ultrasonic vibrator is 50-150W, preferably 100W.

[0016] Wherein, the light source is a xenon lamp, preferably an XHA350w xenon lamp, and the reaction wavelength is above 400nm.

[0017] Wherein, the reaction temperature is 20-30°C; and the reaction time is 5-90 minutes.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0019] (1) The photocatalytic carbon nitride nanosheets in the reaction system of the present invention are obtained by combining two exfoliation methods. Compared with bulk carbon nitride, they have a higher specific surface area, can inhibit electron-hole recombination, and have better photoelectrochemical performance.

[0020] (2) The reaction system of the present invention adopts a photocatalytic system, which uses benzonitrile and a photocatalyst to react in an alkaline aqueous solution containing sodium hydroxide, which is not likely to cause environmental pollution and operational safety hazards, and this process has fewer operating steps.

[0021] (3) The device combining photocatalysis and acousto-optic reactor used in the present invention has a small reaction volume and extremely short reaction time. The acousto-optic reactor is a microreactor that combines an ultrasonic device and a microfluidic chip. It can achieve the purpose of expanding the contact area between the liquid and the catalyst, enhancing the mixing effect of the liquid and the catalyst, reducing the flow pressure of the mixed liquid in the inner tube, and weakening the problem of easy deposition of solid catalysts during the reaction process in the microreactor.

[0022] (4) The conversion rate of formamide in the method provided by the present invention is as high as 100%, and the selectivity of the target product is as high as 99%. The photocatalytic process in the system of the method is simple and environmentally friendly, and the reaction conditions of the method are mild. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0024] Figure 1 Schematic diagram of the structure of the micro-reaction device used in the present invention.

[0025] Figure 2 This is a diagram of the reaction process observed by TLC thin layer chromatography in Example 7.

[0026] Figure 3 This is the NMR spectrum of the reaction raw material benzonitrile.

[0027] Figure 4 This is the gas chromatogram of the reaction raw material benzonitrile.

[0028] Figure 5 This is the NMR spectrum of the product benzamide.

[0029] Figure 6 This is the gas chromatogram of the reaction solution in Example 5. DETAILED DESCRIPTION

[0030] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0031] The preparation methods of the catalysts UCN-thermal oxidation-ultrasound and UCN-thermal oxidation-chemical in the following examples are:

[0032] (1) UCN-thermal oxidation-ultrasound: An appropriate amount of urea was weighed into a muffle furnace and yellow g-C3N4 powder (UCN) was prepared by high-temperature calcination (calcination temperature of 550°C, heating rate of 5°C / min, calcination for 4 h in air atmosphere). It was then thermally oxidized in a muffle furnace (temperature of 500°C, heating rate of 5°C / min, and continued for 2 h in air atmosphere) to obtain a light yellow powder (UCN-thermal oxidation). Finally, isopropanol was added to form a solution with a concentration of 3 mg / mL. The solution was ultrasonicated in a 100 W ultrasonic instrument for more than 10 h, then washed three times with water, three times with alcohol, and dried to obtain a milky white powder (UCN-thermal oxidation-ultrasound).

[0033] (2) UCN-thermal oxidation-chemistry: An appropriate amount of urea was weighed into a muffle furnace and yellow g-C3N4 powder (UCN) was prepared by high-temperature calcination (calcination temperature of 550°C, heating rate of 5°C / min, calcination for 4 h in air atmosphere). It was then thermally oxidized in a muffle furnace (temperature of 500°C, heating rate of 5°C / min, and continued for 2 h in air atmosphere) to obtain a light yellow powder (UCN-thermal oxidation). 98% concentrated sulfuric acid was added to prepare a solution with a concentration of 25 mg / mL. The solution was stirred in the dark for more than 14 h, and then 100 mL of water was added and ultrasonicated in a 100 W ultrasonic instrument for 1 h. Finally, the solution was washed with water three times, washed with alcohol three times, and dried to obtain a white powder (UCN-thermal oxidation-chemistry).

[0034] The schematic diagram of the reaction apparatus described in the following embodiments is as follows Figure 1 As shown, it includes two ultrasonic vibrators, a microfluidic chip and a light source; the two ultrasonic vibrators are assembled on one side of the microfluidic chip, and the light source is placed on the other side of the microfluidic chip. The light source is about 30 cm away from the microfluidic chip so that the center of the light spot is irradiated on the microfluidic chip; the inner diameter of the microfluidic chip is 2 mm, and the reaction volume is 2 mL; the ultrasonic frequency of the ultrasonic vibrator is 100 W; and the light source is an XHA350W xenon lamp.

[0035] The nuclear magnetic and gas chromatography of the reaction raw material benzonitrile described in the following embodiment are as follows Figure 3 and Figure 4 shown.

[0036] Example 1:

[0037] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of a catalyst (UCN-thermal oxidation-ultrasound). 1 mol / L KOH solution was added to adjust the pH to 10. The reaction mixture was then pumped simultaneously into an acousto-optic reactor with oxygen at a flow rate ratio of 1:10. The reaction was maintained at 25°C for 10 minutes. After the reaction, the effluent was collected and the reaction progress was assessed by TLC. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 58.4%, and the benzamide yield was 55.2%.

[0038] Example 2:

[0039] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of a catalyst (UCN-thermal oxidation-ultrasound). A 1 mol / L KOH solution was added to adjust the pH to 10. The solution and oxygen were then pumped simultaneously into an acousto-optic reactor at a flow rate ratio of 1:10. The reaction was conducted for 20 minutes at a temperature of 25°C. After the reaction, the effluent was collected and the reaction progress was assessed by TLC. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 74.3%, and the benzamide yield was 70.8%.

[0040] Example 3:

[0041] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of a catalyst (UCN-thermal oxidation-ultrasound). A 1 mol / L KOH solution was added to adjust the pH to 10. The solution and oxygen were then pumped simultaneously into an acousto-optic reactor at a flow rate ratio of 1:10. The reaction was maintained at 25°C for 30 minutes. After the reaction, the effluent was collected and the reaction progress was assessed by TLC. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 82.1%, and the benzamide yield was 80.5%.

[0042] Example 4:

[0043] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of a catalyst (UCN-thermal oxidation-ultrasound). A 1 mol / L KOH solution was added to adjust the pH to 10. The reaction mixture was then pumped simultaneously into an acousto-optic reactor with oxygen at a flow rate ratio of 1:10. The reaction was conducted for 40 minutes at a temperature of 25°C. After the reaction, the effluent was collected and the reaction progress was assessed by TLC. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 89.4%, and the benzamide yield was 85.8%.

[0044] Example 5:

[0045] Weigh 1 mmol of benzonitrile raw material and add it to 5 mL of aqueous solution containing 10 mg of catalyst (UCN-thermal oxidation-ultrasound). Add 1 mol / L KOH solution to adjust the pH to 10. Then, it is pumped into the sono-optical reactor simultaneously with oxygen at a flow rate ratio of 1:10. The residence time is 60 minutes and the reaction temperature is 25°C. After the reaction is completed, the effluent is collected and the reaction progress is determined by TLC thin-layer chromatography. The yield of the generated benzamide is detected by gas chromatography. Figure 6 As shown, the conversion rate of benzonitrile was 94.1%, and the yield of benzamide was 84.0%.

[0046] Example 6:

[0047] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of catalyst (UCN-Thermal Oxidation-Chemical). 1 mol / L KOH solution was added to adjust the pH to 10. The mixture was then pumped simultaneously into an acousto-optic reactor with oxygen at a flow rate ratio of 1:10. The reaction was conducted for 40 minutes at a temperature of 25°C. After the reaction, the effluent was collected and the progress of the reaction was assessed by TLC. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 94.9%, and the benzamide yield was 93.7%.

[0048] Example 7:

[0049] Weigh 1 mmol of benzonitrile raw material and add it to 5 mL of aqueous solution containing 10 mg of catalyst (UCN-thermal oxidation-chemistry). Add 1 mol / L KOH solution to adjust the pH to 10, and then pump it into the sono-optical reactor simultaneously with oxygen at a flow rate ratio of 1:50. The residence time is 40 minutes and the reaction temperature is 25°C. After the reaction is completed, the effluent is collected and the degree of reaction is determined by TLC thin-layer chromatography. The yield of the generated benzamide is detected by gas chromatography. The reaction process is observed by TLC thin-layer chromatography, as shown in the following figure. Figure 2 As shown (left: benzonitrile, middle: reaction solution, right: benzamide), the changes in the reaction raw material point and the product point were observed. The raw material became lighter and lighter, and the product point became thicker and thicker. It was observed that the raw material was basically reacted. The conversion rate and yield were detected by gas phase. The conversion rate of benzonitrile was 100.0%, the yield of benzamide was 99.9%, and the NMR of the product was as follows Figure 5 shown.

[0050] Comparative Example 1

[0051] 1 mmol of benzonitrile raw material was weighed and added to 5 mL of aqueous solution containing 10 mg of catalyst (NC-800, for specific preparation methods, see Wang, K., Jiang, P., Yang, M., Ma, P., Qin, J., Huang, X., … Li, R. (2019). Metal-free nitrogen-doped carbon nanosheets: a catalyst for the direct synthesis of imines undermild conditions. Green Chemistry, 21(9), 2448–2461. doi: 10.1039 / c9gc00908f). 1 mol / L KOH solution was added to adjust the pH to 10. Then, it was pumped into the sono-optical reactor (light source: XHA-350w xenon lamp) at a flow rate ratio of 1:50 with oxygen at the same time. The residence time was 40 min and the reaction temperature was 25 ° C. After the reaction was completed, the effluent was collected and the degree of reaction was judged by TLC thin-layer chromatography. The yield of benzamide generated by the reaction was detected by gas chromatography. The conversion rate of benzonitrile was measured to be 92.9%, and the yield of benzamide was 90.1%.

[0052] Comparative Example 2

[0053] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of catalyst (UCN-Thermal Oxidation-Chemical). 1 mol / L KOH solution was added to adjust the pH to 10. The mixture was then pumped simultaneously into an acousto-photoreactor (with the light source turned off) with a flow rate ratio of 1:50. The residence time was 40 minutes and the reaction temperature was 60°C. After the reaction, the effluent was collected and the reaction progress was determined by TLC thin-layer chromatography. The yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 77.8%, and the benzamide yield was 74.2%.

[0054] Comparative Example 3

[0055] 1 mmol of benzonitrile starting material was added to 5 mL of aqueous solution containing 10 mg of catalyst (UCN-Thermal Oxidation-Chemical). 1 mol / L KOH solution was added to adjust the pH to 10. The solution and oxygen were then pumped simultaneously into an acousto-photoreactor (using a 12 W blue light source) at a flow rate ratio of 1:50. The residence time was 40 minutes and the reaction temperature was 25°C. After the reaction, the effluent was collected and the reaction progress was determined by TLC thin-layer chromatography, and the yield of benzamide was determined by gas chromatography. The measured benzonitrile conversion was 55.7%, and the benzamide yield was 53.1%.

[0056] Experimental results show that due to the high transmission rate of the sono-optical reactor of the present invention, the by-products of the reactants in the present invention are small and the reaction time is very short; the device combining photocatalysis and sono-optical reactor used in the present invention has a small reaction volume and extremely short reaction time, and the sono-optical reactor is a microreactor combining an ultrasonic device and a microfluidic chip, which can expand the contact area between the liquid and the catalyst, enhance the mixing effect of the liquid and the catalyst, and weaken the problem of easy deposition of solid catalysts during the reaction process in the microreactor.

[0057] The present invention provides a method for preparing benzamide from benzonitrile using a photocatalytic acousto-photoreactor. Numerous methods and approaches exist for implementing this technical solution. The above merely represents a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for preparing benzamide by photocatalytic benzonitrile using an acousto-photoreactor, characterized in that: An alkaline aqueous solution containing benzonitrile and a catalyst is reacted with O2 in an acousto-optic reactor, and the effluent is collected to obtain a reaction solution containing benzamide; the catalyst is a g-C3N4 nanosheet that has been subjected to a composite exfoliation method of thermal oxidation etching and chemical exfoliation, specifically: urea is weighed in a muffle furnace, and calcined at 550°C, a heating rate of 5°C / min, and an air atmosphere for 4 hours to prepare a yellow g-C3N4 powder; it is further subjected to thermal oxidation modification in a muffle furnace, at a temperature of 500°C, a heating rate of 5°C / min, and an air atmosphere for 2 hours to obtain a light yellow powder; 98% concentrated sulfuric acid is added to prepare a solution with a concentration of 25 mg / mL, stirred in the dark for more than 14 hours, and then 100mL of water is added and ultrasonicated in a 100W ultrasonic instrument for 1 hour, and finally washed three times with water and three times with alcohol, and dried to obtain a white powder.

2. The method according to claim 1, characterized in that The pH of the alkaline aqueous solution is adjusted by an alkaline reagent, and the alkaline reagent includes any one or a combination of NaOH, KOH, Na2CO3 and K2CO3.

3. The method according to claim 1, characterized in that The pH value of the alkaline aqueous solution is 10-12.

4. The method according to claim 1, characterized in that The concentration of benzonitrile in the alkaline aqueous solution is 0.1-0.3 mmol / mL; the concentration of the catalyst in the alkaline aqueous solution is 1-3 mg / mL.

5. The method according to claim 1, characterized in that: The concentration of benzonitrile in the alkaline aqueous solution is 0.2 mmol / mL; the concentration of the catalyst in the alkaline aqueous solution is 2 mg / mL.

6. The method according to claim 1, characterized in that The alkaline aqueous solution containing benzonitrile and the catalyst is pumped into the sono-optical reactor at a rate of 0.1-1 mL / min; and the O2 is pumped into the sono-optical reactor at a rate of 1-10 mL / min.

7. The method according to claim 1, characterized in that: The acousto-optic reactor comprises one or more ultrasonic vibrators, a microfluidic chip and a light source.

8. The method according to claim 7, characterized in that: The ultrasonic vibrator is assembled on one side of the microfluidic chip, and the microfluidic chip is placed under the irradiation of a light source; the light source is 25-35 cm away from the microfluidic chip so that the center of the light spot is irradiated on the microfluidic chip; the inner diameter of the microfluidic chip is 1-3 mm, and the reaction volume is 1-10 mL.

9. The method according to claim 7, characterized in that: The ultrasonic frequency of the ultrasonic vibrator is 50-150W.

10. The method according to claim 7, characterized in that: The ultrasonic frequency of the ultrasonic vibrator is 100W.

11. The method according to claim 7, characterized in that: The light source is a xenon lamp.

12. The method according to claim 7, characterized in that: The light source is an XHA350w xenon lamp, and the reaction wavelength is above 400nm.

13. The method according to claim 1, characterized in that: The reaction temperature is 20-30° C.; the reaction time is 5-90 min.

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