A method of electrochemically preparing a bromide

Abstract

The application discloses a method for electrochemically preparing bromides, and the method uses alkali metal bromide as a bromine source, uses carbon paper with deposited oxygen-deficient cobaltosic oxide as a working electrode, and adopts a three-electrode system to electrocatalytically prepare bromides from aromatic compounds; the method for preparing the carbon paper with deposited oxygen-deficient cobaltosic oxide comprises the following steps: immersing the carbon paper into a cobalt salt aqueous solution to perform electrodeposition, and then performing two-step calcination treatment to obtain the carbon paper; the first step of the calcination treatment is performed in air, the calcination temperature is 200-400 DEG C, and the calcination time is 1-3 hours; the second step of the calcination treatment is performed in argon gas containing 2-10 vol% hydrogen, the calcination temperature is 200-400 DEG C, and the calcination time is 5-30 min. The method disclosed by the application realizes bromination of specific sites of aromatic compounds at normal temperature and pressure, and the electrocatalyst has excellent catalytic activity for various substrates, and is suitable for a wide range of applications.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and more particularly to a method for the electrochemical preparation of brominated compounds. Background Technology

[0002] Brominated products are important intermediates in the synthesis of many chemical drugs. The commonly used industrial bromination methods require the use of bromine water or other bromine sources and oxidants. The reaction conditions are harsh, the energy consumption is high, the synthesis steps are complicated, and the yield of the target brominated product is not high.

[0003] Electrochemical synthesis processes are carried out at ambient temperature and pressure, with adjustable redox capabilities, facilitating large-scale production and representing a promising new green synthesis technology. However, current research on electrocatalytic synthesis of brominated compounds is limited. Limited studies use bromoethane as a bromine source, but bromoethane is still synthesized from bromine water, which still suffers from high energy consumption and heavy pollution, failing to address the issue of bromine water production at its source. More importantly, traditional use of bromine water as a bromine source results in two or more products: para-substitution (80-90%) and meta-substitution, making precise bromine substitution at specific sites impossible. Furthermore, reported electrode materials exhibit low catalytic activity and cannot significantly reduce the overpotential of the electrocatalytic reaction. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention discloses an electrochemical method for preparing brominated compounds. Using oxygen-rich, defective cobalt tetroxide prepared through a specific process as an electrocatalyst and alkali metal bromides as a bromine source, the method achieves bromination of specific sites in aromatic compounds at room temperature and pressure. Furthermore, this electrocatalyst can reduce the overpotential of the bromination reaction and exhibits excellent catalytic activity for a variety of substrates, making it widely applicable.

[0005] The specific technical solution is as follows:

[0006] An electrochemical method for preparing brominated compounds uses alkali metal bromides as the bromine source, carbon paper deposited with oxygen-rich cobalt tetroxide as the working electrode, and a three-electrode system to electrocatalyze the preparation of brominated compounds from aromatic compounds.

[0007] The method for preparing carbon paper with oxygen-rich defective cobalt tetroxide deposited includes:

[0008] Carbon paper is immersed in a cobalt salt aqueous solution for electrodeposition, followed by a two-step calcination process to prepare the product.

[0009] The electrodeposition occurs in a three-electrode system, with carbon paper as the working electrode.

[0010] The two-step calcination process is as follows: the first step is calcination in an air atmosphere at a temperature of 200–400°C for 1–3 hours; the second step is calcination in an argon atmosphere containing 2–10 vol% hydrogen at a temperature of 200–400°C for 5–30 minutes.

[0011] This invention discloses a carbon paper deposited with oxygen-defective cobalt tetroxide, prepared using the aforementioned specific process, as a working electrode. The oxygen-defective cobalt tetroxide deposited on the carbon paper can serve as an electrocatalyst, efficiently catalyzing the bromination reaction of aromatic compounds to prepare brominated products. More importantly, using this electrocatalyst, bromination of aromatic compounds at specific sites (preferably para-position, and ortho-position if para-position is hindered) can be achieved at room temperature and pressure, with a selectivity of up to 99% or higher for generating substituted brominated products.

[0012] Experiments revealed that, compared to only performing the first or second calcination step, the oxygen-rich defective cobalt tetroxide deposited using the aforementioned specific process exhibited higher catalytic activity. This was further demonstrated at a current density of 10 mA / cm². -2 The overpotential data at that time also support the above conclusion.

[0013] In the method for preparing carbon paper with oxygen-rich defective cobalt tetroxide:

[0014] The concentration of the cobalt salt aqueous solution is 0.05–0.5 M, and the cobalt salt is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate.

[0015] The three-electrode system uses a platinum sheet as the counter electrode and Ag / AgCl as the reference electrode. The cyclic voltammetry scan range is 0 to -1.2V, the scan rate is 50 to 200mV / s, and the number of scan cycles is 20 to 200. Preferably, the number of scan cycles is 50 to 100, and more preferably 100.

[0016] Preferably, the second step of calcination treatment is carried out at a calcination temperature of 250–350°C.

[0017] Further preferred, the second step of calcination treatment involves a calcination temperature of 300–350°C and a calcination time of 5–15 minutes.

[0018] More preferably, in the second step of calcination, the calcination temperature is 300℃ and the calcination time is 15min.

[0019] Experiments have shown that as the second-step calcination process is continuously optimized, the catalytic activity for bromination of aromatic compounds is also continuously improved.

[0020] The electrochemical method for preparing bromine derivatives specifically includes:

[0021] An aqueous solution of alkali metal bromide and an organic solvent are added to a separable electrolytic cell, and an aromatic compound is added to the anode cell. Carbon paper with oxygen-rich cobalt tetroxide deposited on it is used as the working electrode, platinum foil as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction is carried out after energizing.

[0022] The alkali metal bromide is selected from one or more of sodium bromide, potassium bromide, and lithium bromide; sodium bromide is preferred.

[0023] The concentration of the alkali metal bromide aqueous solution is 0.05–1 M; preferably 0.1–1.0 M, more preferably 0.5 M.

[0024] The organic solvent is selected from one or more of acetonitrile, acetone, and N,N-dimethylformamide; preferably acetonitrile.

[0025] The volume ratio of the alkali metal bromide aqueous solution to the organic solvent is 1:0.5 to 2.0; preferably 1:1. Experiments have shown that when the two are mixed in equal volumes, the yield of the para-substituted bromide is the highest (if a functional group is present at the para position, the yield of the ortho-substituted bromide is the highest).

[0026] The aromatic compound is selected from one or more of anisole, m-methyl anisole, 8-methoxypsoralen, gemfibrozil methyl ester, naproxen methyl ester, adapalene methyl ester, and δ-tocopherol methyl ester.

[0027] In the anode cell, the concentration of the aromatic compound is 10-100 mM; preferably 10-50 mM, more preferably 33 mM.

[0028] The energizing process, with an Ag / AgCl electrode as a reference, involves a voltage of 1.0–2.0V and a duration of 0.5–4h; preferably, the voltage is 1.1–1.3V and the duration is 0.5–2h; more preferably, the voltage is 1.1V and the duration is 2h.

[0029] Experiments have shown that the continuously optimized process described above can not only further improve the yield of brominated products, but also further improve the Faraday efficiency.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention discloses an electrochemical method for preparing brominated compounds. The method uses alkali metal bromides as the bromine source and carbon paper deposited with oxygen-defective cobalt tetroxide (CO) prepared using a specific process as the working electrode. The CO deposited on the carbon paper serves as an electrocatalyst, efficiently catalyzing the bromination reaction of aromatic compounds to prepare brominated compounds. This preparation process is inexpensive; for example, sodium bromide can be directly extracted from seawater, making it inexpensive, environmentally friendly, and easy to store. The catalyst exhibits extremely high catalytic activity, reducing the overpotential of the bromination reaction and enabling the bromination of aromatic compounds at room temperature and pressure. The reaction conditions are mild, and energy consumption is low. More importantly, this catalyst can achieve bromination at specific sites (para or ortho) of aromatic compounds, with a selectivity of 99% or higher for para or ortho substitution products. The method also uses a separable electrolytic cell as the reactor, resulting in high Faraday efficiency and high energy utilization. Attached Figure Description

[0032] Figure 1 SEM image of carbon paper with oxygen-rich defects and cobalt tetroxide deposited, prepared in Example 1;

[0033] Figure 2 The paramagnetic spectrum of the oxygen-rich defective cobalt tetroxide prepared in Example 1 is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to embodiments and accompanying drawings. However, it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] Example 1

[0036] Carbon paper was cut to 10*20mm size, washed twice with deionized water and ethanol respectively, and then vacuum dried. The carbon paper was used as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. Cyclic voltammetry was performed 100 times in a three-electrode system from 0 to -1.2V at a scan rate of 100mV / s. After naturally drying, the carbon paper was calcined at 300℃ for 2 hours in air. After cooling to room temperature, it was rinsed with deionized water to obtain a cobalt tetroxide electrode, labeled Co3O4@CP. The Co3O4@CP was then calcined at 300℃ for 15 minutes in a hydrogen-argon mixture atmosphere containing 5 vol% hydrogen to obtain a carbon paper electrode with deposited oxygen-rich cobalt tetroxide, labeled Co-O. V @CP.

[0037] Figure 1 This is a SEM image of the carbon paper with oxygen-rich defects of cobalt tetroxide prepared in this embodiment. Observing this image, it can be seen that cobalt tetroxide exhibits a typical thin-layer nanosheet structure, which is uniformly grown on the surface of carbon paper fibers, and the nanosheets are connected to each other.

[0038] Figure 2 This is the paramagnetic spectrum of the oxygen-rich defective cobalt tetroxide prepared in this embodiment. Observing this spectrum, it can be found that at g = 2.003, the oxygen-rich defective cobalt tetroxide (Co-O)... V @CP exhibits higher strength compared to air-calcined cobalt tetroxide (Co3O4@CP), indicating that the cobalt tetroxide contains more unpaired electrons after calcination with a hydrogen-argon mixture, and also indicating that Co-O V @CP electrode materials contain more oxygen vacancies.

[0039] Catalytic activity test

[0040] A mixture of 7.5 mL acetonitrile and 7.5 mL 0.5 M NaBr aqueous solution was added to the cathode and anode cells of the separable electrolytic cell, respectively. An additional 0.5 mmol of anisole was added to the anode cell. The carbon paper electrode, platinum sheet, and Ag / AgCl electrode prepared in this example, deposited with oxygen-rich defective cobalt tetroxide, were used as the working electrode, counter electrode, and reference electrode, respectively. The working electrode and reference electrode were placed in the anode cell, and the counter electrode was placed in the cathode cell. The reaction was carried out at a constant voltage of 1.1 V for 2 hours.

[0041] Example 2

[0042] The carbon paper electrode with oxygen-rich defective cobalt tetroxide prepared in Example 1 was used. The catalytic activity test was basically the same as that in Example 1, except that the composition of the mixed solution added to the cathode and anode cells was replaced with 5 mL of acetonitrile and 10 mL of 0.5 M NaBr aqueous solution.

[0043] Example 3

[0044] The carbon paper electrode with oxygen-rich defect cobalt tetroxide deposited in Example 1 was prepared and the catalytic activity test was basically the same as that in Example 1. The only difference was that the composition of the mixed solution added to the cathode and anode cells was replaced with 10 mL of acetonitrile and 5 mL of 0.5 M NaBr aqueous solution.

[0045] The electrocatalytic activity results of Examples 1 to 3 above are listed in Table 1 below.

[0046] Table 1

[0047]

[0048] Examples 4-5

[0049] The carbon paper electrode with oxygen-rich defect cobalt tetroxide prepared in Example 1 was subjected to catalytic activity tests that were basically the same as those in Example 1, except that 7.5 mL of 0.5 M sodium bromide aqueous solution was replaced with 7.5 mL of 0.5 M potassium bromide aqueous solution and 7.5 mL of 0.5 M lithium bromide aqueous solution, respectively.

[0050] The electrocatalytic activity results of Examples 1, 4-5 above are listed in Table 2 below.

[0051] Table 2

[0052]

[0053] Examples 6-11

[0054] The carbon paper electrode with oxygen-rich, defective cobalt tetroxide deposited in Example 1 was used. The catalytic activity test was essentially the same as in Example 1, except that the substrates were replaced with equimolar amounts of m-methyl anisole, 8-methoxypsoralen, gemfibrozil methyl ester, naproxen methyl ester, adapalene methyl ester, and δ-tocopherol methyl ester, respectively. Their structural formulas are listed in Table 3 below. The electrocatalytic activity results for Examples 1 and 6–11 are also shown in Table 3 below.

[0055] Table 3

[0056]

[0057] Observations of Examples 1, 6-11 show that when using the catalytic system disclosed in this invention, para-substitution is preferred when generating brominated products. When the para position is occupied by other substituents, ortho-substitution is preferred. However, regardless of the type of substitution, the selectivity of the prepared brominated products is as high as 98% or more.

[0058] Examples 12-13

[0059] The preparation process of carbon paper electrodes with oxygen-rich defects and cobalt tetroxide is basically the same as that in Example 1, except that the time for the second calcination treatment is replaced by 5 min and 30 min respectively instead of 15 min.

[0060] The carbon paper electrodes with oxygen-rich cobalt tetroxide deposited in Examples 12 and 13 were used as working electrodes, and the catalytic activity tests were exactly the same as in Example 1.

[0061] The electrocatalytic activity results of Examples 1 and 12-13 are shown in Table 4 below.

[0062] Table 4

[0063] serial number Secondary calcination reaction time (min) Yield (%) Example 1 15 94 Example 12 5 86 Example 13 30 82

[0064] Example 14

[0065] The carbon paper electrode with oxygen-rich defects and cobalt tetroxide deposited in Example 1 was prepared. The catalytic activity test was basically the same as that in Example 1, except that the applied voltage was 1.3V and the reaction time was 0.5 hours.

[0066] Examples 15-16

[0067] The preparation process of carbon paper electrodes with oxygen-rich defects and cobalt tetroxide is basically the same as that in Example 1, except that the temperature in the second calcination process is replaced by 250°C and 350°C respectively instead of 300°C.

[0068] The carbon paper electrodes with oxygen-rich cobalt tetroxide deposited in Examples 15 and 16 were used as working electrodes, and the catalytic activity tests were exactly the same as in Example 1.

[0069] The electrocatalytic activity results of Examples 1 and 15-16 are shown in Table 5 below.

[0070] Table 5

[0071] serial number Secondary calcination reaction temperature (°C) Yield (%) Example 1 300 94 Example 15 250 77 Example 16 350 84

[0072] Comparative Example 1

[0073] The catalytic activity test was basically the same as in Example 1. The only difference was that the working electrode was carbon paper that had not undergone electrodeposition and calcination processes.

[0074] Comparative Example 2

[0075] The cobalt tetroxide electrode labeled Co3O4@CP prepared in Example 1 was used directly as the working electrode, and the other raw materials and conditions were basically the same as those disclosed in the catalytic activity test in Example 1.

[0076] The electrocatalytic activity results of the above comparative examples and Example 1 are listed in Table 3 below.

[0077] Table 6

[0078]

[0079] Comparative Example 3

[0080] The catalytic activity test was basically the same as in Example 1. The only difference was that the electrolytic cell used was an undivided electrolytic cell.

[0081] The Faraday efficiency data for Comparative Example 3 and Example 1 are listed in Table 7 below. Observing the data in Table 7, it can be seen that using a divisible electrolytic cell can significantly improve the Faraday efficiency, thereby increasing the utilization rate of electrical energy.

[0082] Table 7

[0083] serial number Is it a separate electrolytic cell? Faraday efficiency (%) Example 1 yes 91 Comparative Example 3 no 57

[0084] Comparative Example 4

[0085] The catalytic activity test was basically the same as in Example 1. The only difference was that the applied voltage was 0.9V and the reaction time was 4 hours.

[0086] The electrocatalytic activity results of Comparative Example 4 and Examples 1 and 14 are listed in Table 8 below.

[0087] Table 8

[0088] catalyst Voltage (V) Reaction time (h) Yield (%) Faraday efficiency (%) Example 1 1.1 2 94 91 Example 14 1.3 0.5 89 83 Comparative Example 4 0.9 4 39 69

Claims

1. A method for the electrochemical preparation of brominated products, characterized in that, Using alkali metal bromides as the bromine source and carbon paper deposited with oxygen-rich cobalt tetroxide as the working electrode, a three-electrode system was used to electrocatalyze the preparation of brominated compounds from aromatic compounds. The method for preparing carbon paper with oxygen-rich defective cobalt tetroxide deposited includes: Carbon paper is immersed in a cobalt salt aqueous solution for electrodeposition, followed by a two-step calcination process to prepare the product. The electrodeposition occurs in a three-electrode system, with carbon paper as the working electrode. The two-step calcination process is as follows: the first step is calcination in an air atmosphere, at a calcination temperature of 200-400℃, and for a calcination time of 1-3 h; the second step is calcination in an argon atmosphere containing 2-10 vol% hydrogen, at a calcination temperature of 200-400℃, and for a calcination time of 5-30 min. The aromatic compound is selected from one or more of anisole, m-methyl anisole, 8-methoxypsoralen, gemfibrozil methyl ester, naproxen methyl ester, adapalene methyl ester, and δ-tocopherol methyl ester; The three-electrode system uses a platinum sheet as the counter electrode and Ag / AgCl as the reference electrode. The cyclic voltammetry scan range is 0 to -1.2V, the scan rate is 50 to 200mV / s, and the number of scan cycles is 20 to 200.

2. The method for electrochemical preparation of brominated products according to claim 1, characterized in that, In the method for preparing carbon paper with oxygen-rich defective cobalt tetroxide: The concentration of the cobalt salt aqueous solution is 0.05~0.5 M, and the cobalt salt is selected from one or more of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate.

3. The method for electrochemical preparation of brominated products according to claim 1, characterized in that, The second step is calcination, with a calcination temperature of 250~350℃.

4. The method for electrochemical preparation of brominated products according to claim 3, characterized in that, The second step is calcination, with a calcination temperature of 300~350℃ and a calcination time of 5~15min.

5. The method for electrochemical preparation of brominated products according to any one of claims 1 to 4, characterized in that, Specifically, it includes: An aqueous solution of alkali metal bromide and an organic solvent are added to a separable electrolytic cell, and an aromatic compound is added to the anode cell. Carbon paper with oxygen-rich cobalt tetroxide deposited on it is used as the working electrode, platinum foil as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction is carried out after energizing.

6. The method for electrochemical preparation of brominated products according to claim 5, characterized in that: The alkali metal bromide is selected from one or more of sodium bromide, potassium bromide, and lithium bromide; The concentration of the alkali metal bromide aqueous solution is 0.05~1M; The organic solvent is selected from one or more of acetonitrile, acetone, and N,N-dimethylformamide; The volume ratio of the alkali metal bromide aqueous solution to the organic solvent is 1:0.5~2.

0.

7. The method for electrochemical preparation of brominated products according to claim 5, characterized in that: The concentration of the aromatic compound in the anode tank is 10~100mM.

8. The method for electrochemical preparation of brominated products according to claim 5, characterized in that, The power is applied at a voltage of 1.0~2.0V for a duration of 0.5~4h.

9. The method for electrochemical preparation of brominated products according to any one of claims 6 to 8, characterized in that: The volume ratio of the alkali metal bromide aqueous solution to the organic solvent is 1:1; The power is applied at a voltage of 1.1~1.3V for a duration of 0.5~2h.

10. The method for electrochemical preparation of brominated products according to claim 9, characterized in that, The power was applied at a voltage of 1.1V for 2 hours.

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