A process for the preparation of indoles
By using catalyst A, which consists of pretreated activated carbon and copper oxide, the problems of low ethylene glycol conversion and indole selectivity were solved, achieving efficient and environmentally friendly indole synthesis.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EAST CHINA ENGINEERING SCIENCE AND TECHNOLOGY CO LTD
- Filing Date
- 2026-04-24
- Publication Date
- 2026-07-07
AI Technical Summary
Existing catalysts are unstable, resulting in low ethylene glycol conversion, as well as low indole selectivity and yield. Traditional indole synthesis methods suffer from problems such as expensive raw materials, harsh reaction conditions, and environmental pollution.
Catalyst A is composed of pretreated activated carbon and copper oxide supported on its surface. It is prepared by in-situ reduction to enhance the stability and performance of the catalyst, thereby achieving high conversion of ethylene glycol and high selectivity of indole.
It improves the conversion rate of ethylene glycol and the selectivity of indole, simplifies the reaction steps, reduces environmental pollution, and conforms to the principles of green chemistry.
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Abstract
Description
Technical Field
[0001] This invention relates to the technical field of indole synthesis via the alkanolamine method, and more particularly to a method for preparing indole. Background Technology
[0002] Indole and its derivatives are an extremely important class of nitrogen-containing heterocyclic compounds, whose structures are widely found in natural substances and bioactive molecules. In the pharmaceutical field, indole is the core skeleton of many drugs, such as the anti-inflammatory drug indomethacin and the antihypertensive drug indapamide. Furthermore, indole is a key structural unit in many antitumor drugs. In agricultural chemistry, indole compounds are the active ingredients in many highly effective herbicides, insecticides, and plant growth regulators (such as the classic plant endogenous hormone indole-3-acetic acid). In the fragrance, dye, and polymer materials industries, indole also plays an irreplaceable role.
[0003] Traditional indole synthesis methods, such as the Fischer indole synthesis, while widely used, typically have some limitations. These traditional methods not only use expensive or toxic phenylhydrazine-based raw materials and require harsh reaction conditions, but also generate a large amount of waste and have low atom economy. Therefore, developing a new synthetic route with inexpensive and readily available raw materials, simple reaction steps, environmental friendliness, and compliance with green chemistry principles has significant industrial and academic value.
[0004] In recent years, the preparation of indole from ethylene glycol and aniline has attracted widespread attention from researchers. This route uses ethylene glycol and aniline, both bulk chemical raw materials, as starting materials to directly construct the indole ring through a catalytic cyclization reaction. It has the following potential advantages: high atom economy: the main byproducts are hydrogen and water, avoiding the formation of salt byproducts in traditional methods; environmental friendliness: no corrosive reagents such as strong acids are used, reducing the pressure on waste treatment; green raw materials: ethylene glycol, as a bulk chemical, has a stable source, conforming to the principles of green chemistry; and a simple route: the reaction can be achieved in one step, making the process more efficient. However, due to the instability and poor catalytic performance of existing catalysts, the conversion rate of ethylene glycol in this synthetic route is low, and the selectivity and yield of the indole product are also low.
[0005] Therefore, there is an urgent need to develop a new type of high-performance catalyst for the synthesis of indole via the alcoholamine method, so as to promote the widespread application of indole. Summary of the Invention
[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing indole. The preparation method can achieve high conversion rate of ethylene glycol and high selectivity for indole.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0008] This invention provides a method for preparing indole, comprising the following steps:
[0009] The indole was prepared by reacting aniline and ethylene glycol in the presence of a catalyst.
[0010] The catalyst was prepared by in-situ reduction of catalyst A.
[0011] The catalyst A consists of pretreated activated carbon and copper oxide supported on its surface;
[0012] The pretreated activated carbon is obtained by ultrasonically cleaning and drying activated carbon in acetone.
[0013] The ultrasonic cleaning time is preferably 1-10 h; more preferably 8-10 h.
[0014] Preferably, the active component in the catalyst of this invention is copper;
[0015] Preferably, the copper content in the catalyst is 5wt%-40wt%; more preferably, it is 5wt%, 10wt%, 15wt%, 20wt% or 40wt%.
[0016] Preferably, in this invention, the activated carbon in the catalyst has a size of 300-1200 μm;
[0017] Preferably, the average pore size of the mesopores in the activated carbon of the catalyst is 5-20 nm; more preferably, it is 12-19 nm.
[0018] After in-situ reduction, the interaction between copper in the catalyst and the pretreated activated carbon is enhanced, effectively reducing copper aggregation on the support surface, resulting in excellent catalytic performance and good stability. Furthermore, the catalyst possesses excellent diffusion channels, significantly improving the ethylene glycol conversion and indole selectivity in the preparation of indole via the alkanolamine method.
[0019] Preferably, the reducing agent for in-situ reduction is selected from hydrogen or palladium on carbon.
[0020] More preferably, when the reducing agent is hydrogen, the hydrogen introduction rate is 70-90 mL / min; more preferably, it is 80 mL / min.
[0021] Preferably, the reaction temperature is 280℃-300℃; more preferably, it is 285℃-295℃.
[0022] Preferably, the ratio of the catalyst to aniline is 4 mL: (8-10) mol; more preferably, it is 4 mL: 9 mol.
[0023] Preferably, the molar ratio of aniline to ethylene glycol is (8-10):1; more preferably, it is 9:1.
[0024] The present invention does not impose any special limitations on the equipment used in the above-mentioned method for preparing indole.
[0025] In some specific embodiments of the present invention, a reactor liner is preferred.
[0026] The catalyst loading amount in the reactor liner is preferably 4 mL by volume, and the catalyst morphology remains particulate solid.
[0027] Preferably, the catalyst A is obtained by impregnation of pretreated activated carbon, copper salt precursor and water, followed by calcination.
[0028] Preferably, the calcination temperature is 200°C-500°C.
[0029] The calcination temperature is preferably 200°C-300°C; more preferably 200°C.
[0030] The calcination time is preferably 1-4 h. Preferably, the mass ratio of copper to pretreated activated carbon in the copper salt precursor is (0.05-1):1; more preferably (0.05-0.4):1; and even more preferably 0.05:1, 0.1:1, 0.15:1, 0.2:1, or 0.4:1.
[0031] Preferably, the copper salt precursor of the present invention is selected from one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, and sodium ethylenediaminetetraacetate.
[0032] Preferably, the process before calcination includes drying.
[0033] Preferably, the drying temperature is 100℃-200℃; more preferably, it is 100℃-150℃.
[0034] Preferably, the drying time is 1-6 hours.
[0035] Compared with existing technologies, the indole preparation method provided by this invention includes the following steps: aniline and ethylene glycol are mixed and reacted under the action of a catalyst to prepare the indole; the catalyst is prepared by in-situ reduction of catalyst A; catalyst A consists of pretreated activated carbon and copper oxide supported on its surface; the pretreated activated carbon is obtained by ultrasonically cleaning and drying activated carbon in acetone. This preparation method is simple and efficient, and the synthesis of indole using this method can achieve high conversion rate of ethylene glycol and high selectivity for indole. Attached Figure Description
[0036] Figure 1 Nitrogen adsorption-desorption curves of Cu-supported activated carbon catalysts prepared in Example 1 (left figure) and Example 2 (right figure), respectively;
[0037] Figure 2 The ethylene glycol conversion curves are shown for the Cu-supported activated carbon catalysts prepared in Examples 1-6, respectively, when applied to the production of indole from aniline and ethylene glycol.
[0038] Figure 3 The indole selectivity curves are shown for the Cu-supported activated carbon catalysts prepared in Examples 1-6, respectively, when applied to the production of indole from aniline and ethylene glycol.
[0039] Figure 4 The indole yield curves are shown for the Cu-supported activated carbon catalysts prepared in Examples 1-6, respectively, when applied to the production of indole from aniline and ethylene glycol. Detailed Implementation
[0040] To further illustrate the present invention, the method for preparing indole provided by the present invention will be described in detail below with reference to embodiments.
[0041] This invention does not impose any special restrictions on the source of any of the following raw materials; any commercially available products are acceptable.
[0042] The instruments used in the following embodiments include:
[0043] BET (American Micro Instruments ASAP 2020 PLUS Fast Specific Surface Area and Pore Size Analyzer).
[0044] Gas chromatography (Agilent Technologies, GC7890B gas chromatograph).
[0045] Example 1
[0046] Step 1: Preparation of CuO / C activated carbon catalyst supported on CuO (Cu element content is 10wt%).
[0047] CuO-supported activated carbon was prepared by impregnation. 4 g of activated carbon support (300 μm in size) was weighed, placed in 100 mL of acetone, and sonicated for 10 h. After washing with water, it was dried in an oven at 60°C. The pretreated activated carbon was added to 100 mL of deionized water containing 0.4 g of copper ions (derived from the copper salt precursor copper nitrate), transferred to an oven, and dried at 110°C for 4 h. The sample was then removed, cooled to room temperature, and calcined in a tube furnace at 200°C for 1 h to obtain the final sample, denoted as 10wt%Cu-C, where 10wt% represents the Cu content.
[0048] The BET specific surface area and pore size distribution of the CuO-supported activated carbon samples prepared above are shown in the figure. Figure 1 As shown in the curve in the left figure (Sample 1), the results indicate that it has a typical mesoporous structure with an average pore size of 19 nm.
[0049] Step 2: Performance evaluation of CuO-supported activated carbon catalyst in the synthesis of indole via the alkanolamine method.
[0050] 4 mL of the catalyst was loaded into the reactor liner, and the reaction system was then purged with hydrogen for 20 min. The temperature was maintained at 120 °C for 2 h, then increased to 290 °C, and ethylene glycol and aniline were fed into the reactor at a rate of 0.01 mL / min. The molar ratio of ethylene glycol to aniline was 1:9. Hydrogen was continuously introduced to reduce the catalyst (hydrogen flow rate of 80 mL / min), and the flow rate of the pump (using a peristaltic pump to pump the mixture of ethylene glycol and aniline into the reactor liner) was 0.01 mL / min. Samples were taken from the cold trap for analysis every 1 h. During the test, the vaporization chamber temperature was maintained at 200 °C, the reactor outlet pipeline temperature was 65 °C, and a two-stage condenser was connected in series at the reactor outlet: condenser #1 at 65 °C and condenser #2 at 20 °C. After the reaction, the reactor apparatus was cleaned with ethanol and then purged with nitrogen to remove residual ethanol.
[0051] Example 2
[0052] Step 1: Preparation of CuO / C activated carbon catalyst supported on CuO (Cu element content is 15wt%).
[0053] CuO-supported activated carbon was prepared by impregnation. 4 g of activated carbon support (300 μm in size) was weighed and placed in 100 mL of acetone, sonicated for 10 h, washed with water, and dried in an oven at 60 °C. The pretreated activated carbon was added to 100 mL of deionized water containing 0.6 g of copper ions (derived from the copper salt precursor copper nitrate), transferred to an oven, and dried at 110 °C for 4 h. The sample was then removed, cooled to room temperature, and calcined in a tube furnace at 200 °C for 1 h to obtain the final sample, denoted as 15wt%Cu-C, where 15wt% represents the Cu content.
[0054] The BET specific surface area and pore size distribution of the CuO-supported activated carbon samples prepared above are listed in... Figure 1 This indicates that it has a typical mesoporous structure with an average pore size of 12 nm.
[0055] Step 2: Performance evaluation of CuO-supported activated carbon catalyst in the synthesis of indole via the alkanolamine method.
[0056] 4 mL of the catalyst was loaded into the reactor liner, and the reaction system was then purged with hydrogen for 20 min. The temperature was maintained at 120 °C for 2 h, then increased to 290 °C, and ethylene glycol and aniline were added to the reactor at a rate of 0.01 mL / min. The molar ratio of ethylene glycol to aniline was 1:9. Hydrogen was continuously introduced to reduce the catalyst (hydrogen introduction rate of 80 mL / min). Samples were taken from the cold trap for analysis every 1 h. During the test, the vaporization chamber temperature was maintained at 200 °C, the reactor outlet pipeline temperature was 65 °C, and a two-stage condenser was connected in series at the reactor outlet: condenser #1 at 65 °C and condenser #2 at 20 °C. After the reaction, the reactor apparatus was cleaned with ethanol and then purged with nitrogen to remove residual ethanol.
[0057] Example 3
[0058] Same as Example 1, except that the mass of copper ions is 0.2 g, the final catalyst is denoted as 5wt%Cu-C, where 5wt% represents the Cu content, and the catalyst has a uniform mesoporous structure.
[0059] Example 4
[0060] Same as Example 1, except that the mass of copper ions is 0.8 g, the final catalyst is denoted as 20wt%Cu-C, where 20wt% represents the Cu content, and the catalyst has a uniform mesoporous structure.
[0061] Example 5
[0062] Same as Example 1, except that the mass of copper ions is 1.2 g, and the final catalyst is denoted as 30wt%Cu-C, where 30wt% represents the Cu content, and the catalyst has a uniform mesoporous structure.
[0063] Example 6
[0064] Similar to Example 1, except that the mass of copper ions is 1.6 g, the Cu content in the final catalyst is 40 wt%, and the catalyst has a uniform mesoporous structure.
[0065] Figure 2-4 The figures show the conversion rate of ethylene glycol, indole selectivity, and indole yield of the CuO-supported activated carbon catalyst in the production of indole from aniline ethylene glycol. The results indicate that using the 10 wt% Cu-C catalyst prepared in Example 1 to catalyze the production of indole from aniline ethylene glycol, the conversion rate of ethylene glycol (e.g., ...) is... Figure 2 As shown, the indole selectivity reached 100% after 1 hour of reaction (as indicated). Figure 3 (as shown) and yield (as shown) Figure 4 (As shown) it also remained at around 50% after 2 hours.
[0066] Using the 15wt% Cu-C catalyst prepared in Example 2 to catalyze the conversion of aniline ethylene glycol to indole, the conversion rate of ethylene glycol remained at around 100%, and the indole selectivity and yield also reached 70%, demonstrating excellent performance.
[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
[0068] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.
Claims
1. A method for preparing indole, characterized in that, Includes the following steps: The indole was prepared by reacting aniline and ethylene glycol in the presence of a catalyst. The catalyst was prepared by in-situ reduction of catalyst A. The catalyst A consists of pretreated activated carbon and copper oxide supported on its surface; The pretreated activated carbon is obtained by ultrasonically cleaning and drying activated carbon in acetone.
2. The preparation method according to claim 1, characterized in that, The active component in the catalyst is copper; The catalyst contains 5wt%-40wt% copper.
3. The preparation method according to claim 1 or 2, characterized in that, The activated carbon in the catalyst has a size of 300-1200 μm; The average pore size of the mesopores in the activated carbon of the catalyst is 5-20 nm.
4. The preparation method according to claim 1, characterized in that, The reducing agent for in-situ reduction is selected from hydrogen or palladium on carbon.
5. The preparation method according to claim 4, characterized in that, When the reducing agent is hydrogen, the hydrogen introduction rate is 70-90 mL / min.
6. The preparation method according to claim 1, characterized in that, The reaction temperature is 280℃-300℃.
7. The preparation method according to claim 1, characterized in that, The ratio of the catalyst to aniline is 4 mL: (8-10) mol; The molar ratio of aniline to ethylene glycol is (8-10):
1.
8. The preparation method according to claim 1, characterized in that, Catalyst A is obtained by impregnation of pretreated activated carbon, copper salt precursor and water, followed by calcination. The calcination temperature is 200°C-500°C.
9. The preparation method according to claim 8, characterized in that, The mass ratio of copper to pretreated activated carbon in the copper salt precursor is (0.05-1):
1.
10. The preparation method according to claim 9, characterized in that, The copper salt precursor is selected from one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, and sodium ethylenediaminetetraacetate.