A method for direct electrocatalytic synthesis of aromatic nitriles on graphite felt electrodes

Abstract

The application discloses a method for directly electrocatalytically synthesizing aromatic nitrile on a graphite felt electrode, which comprises the following steps: adding an electrolyte composed of aromatic aldehyde shown in formula I, a supporting electrolyte and a solvent into a diaphragm-free electrolytic cell, adopting a common graphite felt electrode or a nitrogen-doped graphite felt electrode as a cathode, adopting a graphite felt electrode as an anode, and generating aromatic nitrile shown in formula II through constant-current electrolysis; the solvent is CH3CN or DMF mixed with H2O at a volume ratio of 70%:30%-60%:40%; the distance between the anode and the cathode is 8-26 mm; and the constant-current electrolysis condition is that the room temperature is 5-15 mA / cm 2 , the current density is 700-1000 rpm, and the rotation speed is 700-1000 rpm; and the reaction formula is as follows. The application has the advantages of metal-free and low cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of organic electrochemical synthesis, and particularly relates to a method for directly electrocatalytically synthesizing aromatic nitrile. BACKGROUND

[0002] Aromatic nitrile compounds are widely used in the fields of pesticides, medicine, dyes and functional materials as an important chemical raw material and organic synthesis intermediate. For example, p-MeOBN (4-methoxybenzonitrile) can be used as a tyrosinase inhibitor in medical products (Thermochim. Acta. 2024, 731: 179653). p-MeOBN is synthesized from p-MeOBA (4-methoxybenzaldehyde) by a mature method, but in the traditional chemical catalytic method, an additional catalyst is often needed, which not only has harsh conditions, but also causes a certain degree of environmental pollution. Kumar et al. added sodium acetate as a catalyst in a methanol solvent, used hydroxylamine as a nitrogen source, reacted at room temperature for 1 h, converted aromatic aldehyde into aromatic aldehyde oxime, evaporated the methanol solvent, dissolved the remaining mixture in acetonitrile, added benzoyl chloride and potassium tert-butoxide, and continued to react at room temperature for 1 h to generate the corresponding nitrile compound (J Chem Sci. 2024, 136: 2). Wang et al. used ionic liquid 1-butyl-3-methylimidazolium chloride as a catalyst, reacted at 70℃ for 10 h, and converted aromatic aldehyde into the corresponding nitrile compound with a yield of 99% (ACS Sce. 2024, 12, 11338-11346). In these methods, the use of catalysts not only increases the cost of the preparation process, but also causes certain difficulties in subsequent separation.

[0003] Electrocatalytic synthesis of aromatic nitrile from aromatic aldehyde is a simple and easy-to-control method, but it often needs to use expensive metal electrodes or media, and has problems such as electrode pollution and corrosion (Chem J Chinese U. 2018, 39, 01, 78-84). Therefore, how to select a cheap electrode and maintain a high yield is a certain challenge. Yuan et al. used p-MeOBA as a substrate, NH4I as a medium, C as an anode, and Ni as a cathode to indirectly electrocatalytically synthesize p-MeOBN in DMSO, with a yield of 99% (Sci China Chem. 2015, 15(4), 747-750), but the cathode nickel was corroded in the process. Hashem et al. used NH2OH·HCl as a nitrogen source and MeSO2Cl for dehydration on graphite with catalytic properties, and converted various aromatic aldehydes into aromatic nitriles at 60℃-120℃, with an overall yield of >80% (Synthesis (Stuttg), 2003, 2, 243-246).

[0004] The present research group has studied the indirect electrochemical synthesis method in an organic-water mixed solvent using tetrabutylammonium perchlorate as a supporting electrolyte, Pt as an anode, Pb as a cathode, Cl - / ClO - as a medium at 60℃ in an unpartitioned electrolytic cell, which can effectively convert p-MeOBA to p-MeOBN with a yield of 99%. In this scheme, inorganic media with high chemical stability are used, and no additional oxidizing agent is needed. However, there are problems such as the use of expensive Pt electrodes, environmentally unfriendly Pb electrodes, and corrosion of halogen electrodes in the reaction (J Electrochem Soc.2024, 171, 085501). SUMMARY

[0005] The purpose of the present application is to provide a method for directly electrocatalytically synthesizing aromatic nitrile at room temperature, which has the advantages of no metal and low cost.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for directly electrocatalytically synthesizing aromatic nitrile on a graphite felt electrode, the method comprising: adding an electrolyte composed of an aromatic aldehyde represented by formula I, a supporting electrolyte and a solvent into an unpartitioned electrolytic cell, using a common graphite felt (GF) electrode or a nitrogen-doped graphite felt electrode as the cathode, and using a graphite felt (GF) electrode as the anode, and generating an aromatic nitrile represented by formula II through constant current electrolysis; the concentration of the substrate is 10-50mmol / L; the solvent is CH3CN or a mixture of DMF and H2O in a volume ratio of 70%:30%-60%:40%; the distance between the anode and the cathode is 8-26mm; the constant current electrolysis conditions are: room temperature, current density is 5~15mA / cm 2 , rotation speed is 700-1000rpm; the reaction formula is as follows:

[0008]

[0009] wherein R is C1-C4 linear or branched alkyl, C1-C4 linear or branched alkoxy or halogen;

[0010] The nitrogen-doped graphite felt electrode is prepared by the following method: after washing and drying, the common graphite felt electrode is placed in a dopamine hydrochloride solution with a concentration of 0.2-2.5mmol / L for ultrasonic treatment, and then washed and dried, and then high-temperature carbonization is carried out in an inert atmosphere to obtain a nitrogen-doped graphite felt electrode, which is denoted as NxxGF, wherein xx represents the concentration of dopamine hydrochloride, such as N02GF representing 0.2mmol / L C8H 11NO2·HCl doped graphite felt; the solvent of the dopamine hydrochloride solution is a mixed solvent obtained by mixing methanol and Tris buffer with pH of 8.5 at a volume ratio of 1:1.

[0011] The common graphite felt electrode according to the present application refers to an unmodified graphite felt electrode.

[0012] Preferably, in the preparation of the nitrogen-doped graphite felt electrode, the ultrasonic treatment condition is 42 kHz, 210 W for 40 minutes.

[0013] Preferably, in the preparation of the nitrogen-doped graphite felt electrode, the high-temperature carbonization condition is 650-750℃ heat treatment in argon atmosphere for 1-2h, more preferably 700℃ heat treatment in argon atmosphere for 1h.

[0014] Preferably, the substrate concentration is 25mmol / L.

[0015] Preferably, the solvent is CH3CN and H2O mixed at a volume ratio of 70%:30%.

[0016] Preferably, the cathode is a nitrogen-doped graphite felt electrode, and in the preparation of the nitrogen-doped graphite felt electrode, the dopamine hydrochloride solution has a concentration of 0.4-0.6mmol / L, and most preferably 0.6mmol / L, i.e. N06GF.

[0017] Preferably, the current density is 10mA / cm 2 .

[0018] Preferably, the electrode spacing is 16-26mm.

[0019] Preferably, the electrolysis temperature is 25℃.

[0020] Preferably, the electrolysis time is 6h.

[0021] Preferably, the supporting electrolyte is tetrabutylammonium perchlorate, and the concentration of the supporting electrolyte is 50mmol / L.

[0022] The present application particularly preferably provides a method comprising: adding an electrolyte composed of p-MeOBA, a supporting electrolyte and a solvent into a diaphragm-free electrolytic cell, and using GF and N06GF as the anode and cathode electrode materials, respectively, to generate p-MeOBN through constant current electrolysis; the solvent is CH3CN and H2O mixed at a volume ratio of 70%:30%, the supporting electrolyte is TBAP; the constant current electrolysis condition is: temperature 25℃, current density 10mA / cm 2 , rotation speed 700rpm, and electrolysis time 6h. Under this condition, p-MeOBA can be efficiently converted into the target product nitrile.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The present application uses an electrochemical method, which does not need to add chemical oxidants (O2, H2O2 or metal oxides) compared with the traditional chemical oxidation method, avoids excessive oxidation, is safer, and is more in line with the standards of green chemistry.

[0025] (2) The present application uses a direct electro-synthesis method, which is simple to operate and is carried out under normal temperature and pressure; compared with an indirect electro-synthesis method, it does not need to add a medium.

[0026] (3) In the present application, the cathode and anode materials are both graphite felt, which is low in cost and avoids the use of metal electrodes. DETAILED DESCRIPTION

[0027] In order to better understand the present application, the following are specific embodiments of the present application, which further describe the technical solutions of the present application, but the protection scope of the present application is not limited to these embodiments.

[0028] The structural formula of p-MeOBA used in the following examples is shown as formula I-1:

[0029]

[0030] The structure of the prepared p-MeOBN is shown as formula II-1:

[0031]

[0032] The expanded reaction substrate is:

[0033]

[0034] The electrolysis steps and results of generating p-MeOBN from p-MeOBA are as follows:

[0035] Example 1:

[0036] In a 50 mL electrolytic cell, 0.2042 g of p-MeOBA (50 mmol / L), 0.3693 g of hydroxylammonium sulfate, 0.4723 g of TBAP, 21 mL of a mixed solvent of CH3CN and H2O, and 9 mL of H2O were added, the temperature was 25°C, GF was used as the anode and cathode, the rotation speed was 700 rpm, and the current density was 10 mA / cm 2 The target product p-MeOBN was obtained by direct electrochemical catalysis after electrolysis for 6 h. The electrolysis product was analyzed by gas chromatography-mass spectrometry and quantified by area normalization. The reaction solution was purified by rotary evaporation, extraction, and column chromatography (petroleum ether / ethyl acetate = 10:1), and then further structure characterization was performed.

[0037] The structure of p-MeOBN was characterized as: 1 H NMR (500 MHz, CDC13) δ: 7.59 (d, J = 8.9 Hz, 2H), 6.95 (d, J = 8.9 Hz, 2H), 3.86 (s, 3H), GC-MS (EI, 70 eV) m / z: 133.15 [M + ]

[0038] Examples 2-9, Comparative Example 1:

[0039] The electrolytic cells of Examples 2-9 were the same as Example 1, except that the cathode was a nitrogen-doped graphite felt electrode, which was prepared by the following method: 2 cm*2 cm*0.5 cm size of graphite felt (GF) was ultrasonicated in deionized water and anhydrous ethanol for 10 minutes, respectively, then washed with deionized water and dried in an oven at 100 °C. The dried GF was put into 100 ml of methanol: Tris buffer (pH = 8.5) solution (volume ratio, 1:1) dissolved with different concentrations of dopamine hydrochloride (C8H 11 NO2·HCl) and ultrasonicated (42 kHz, 210 W) for 40 minutes, then washed with deionized water and dried in an oven at 80 °C. Finally, it was heat-treated at 700 °C in an argon atmosphere for 1 hour to obtain a nitrogen-doped graphite felt electrode (denoted as NxxGF, xx represents the concentration of dopamine hydrochloride; for example, N02GF represents graphite felt doped with 0.2 mmol / L C8H 11 NO2·HCl). The only difference was the concentration of C8H 11 NO2·HCl doped in the cathode material, which was 0.2 mmol / L (Example 2), 0.4 mmol / L (Example 3), 0.6 mmol / L (Example 4), 0.8 mmol / L (Example 5), 1.0 mmol / L (Example 6), 1.5 mmol / L (Example 7), 2.0 mmol / L (Example 8), and 2.5 mmol / L (Example 9), respectively.

[0040] The electrolysis reaction steps and reaction processes of Examples 2-9 were the same as Example 1, and direct electrolysis was performed. The experimental results are listed in Table 1.

[0041] Table 1. p-MeOBA electro-synthesis results on cathode materials doped with different concentrations of C8H 11 NO2·HCl

[0042]

[0043] As shown in Table 1, the yield of product p-MeOBN is different when the concentration of nitrogen source doped in cathode material graphite felt is different, wherein the yield is the highest under the condition of GF(0.6), thus the cathode material is preferably GF(0.6).

[0044] Examples 10-13:

[0045] The reaction step and reaction process are the same as those in Example 4, except that the current density is 5 mA / cm 2 (Example 10), 7.5 mA / cm 2 (Example 11), 12.5 mA / cm 2 (Example 12), and 15 mA / cm 2 (Example 13), and the results of direct electrolysis experiment are shown in Table 3.

[0046] Table 2 Results of direct electrocatalysis of p-MeOBA to p-MeOBN under different current densities

[0047]

[0048]

[0049] As shown in Table 2, when CH3CN / H2O is used as the reaction solvent, the yield of p-MeOBN directly electrocatalyzed from p-MeOBA gradually increases with the current density, and the yield of p-MeOBN is the highest when the current density is 10 mA / cm 2 , thus the current density is preferably 10 mA / cm 2 .

[0050] Examples 14-15:

[0051] The reaction step and reaction process are the same as those in Example 4, except that the solvent is DMF:H2O=70:30 (Example 14) and DMSO:H2O=70:30 (Example 15), and the results of direct electrolysis experiment are shown in Table 4.

[0052] Table 3 Results of direct electrocatalysis of p-MeOBA under different solvents

[0053]

[0054] As shown in Table 3, the organic solvent in the mixed solution has a great influence on the reaction results. When DMSO is used as the solvent, the electrolyte cannot be completely dissolved. When CH3CN:H2O=7:3 (volume ratio) is used as the solvent, it is beneficial to the generation of nitrile, thus CH3CN:H2O=7:3 (volume ratio) is preferred.

[0055] Examples 16-18:

[0056] The reaction steps and reaction process are the same as in Example 4, except that the concentration of the reaction substrate p-MeOBA is 35 mmol / L (Example 16), 25 mmol / L (Example 17), and 10 mmol / L (Example 18), respectively. The results of the direct electrolysis experiments are shown in Table 5.

[0057] Table 4 p-MeOBA conversion to p-MeOBN at different substrate concentrations

[0058]

[0059] As shown in Table 4, the substrate concentration in the reaction system has a great influence on the yield of p-MeOBN. This is probably because when the substrate concentration is high, side reactions are more likely to occur under the same electrode area. Therefore, the substrate concentration is preferably 25 mmol / L.

[0060] Examples 19-20:

[0061] The reaction steps and reaction process are the same as in Example 17, except that the distance between the anode and the cathode is 8 mm (Example 24) and 26 mm (Example 25), respectively. The results of the direct electrolysis experiments are shown in Table 6.

[0062] Table 5 p-MeOBA electro-synthesis results at different electrode distances

[0063]

[0064] As shown in Table 5, when the electrode distance is 16-26 mm, the yield of p-MeOBN is higher. This is probably because the electric field distribution in the solution is most conducive to the reaction at this distance. In addition, the cell voltage is also lower at this distance, which is more energy-efficient.

[0065] Examples 21-26:

[0066] The reaction steps and reaction process are the same as in Example 17, except that the reaction substrate is benzaldehyde (Example 21), m-methylbenzaldehyde (Example 22), 4-methylbenzaldehyde (Example 23), o-methoxybenzaldehyde (Example 24), 4-chlorobenzaldehyde (Example 25), and 4-tert-butylbenzaldehyde (Example 26), respectively. The results of the direct electrolysis experiments are shown in Table 7.

[0067] Table 6 Electrolytic synthesis of different aromatic nitriles

[0068]

[0069] From Table 6, it can be seen that when different electron-withdrawing groups and electron-donating groups are substituted on the benzene ring, the yield of the corresponding nitrile is also different. The ortho and meta positions may be limited by steric hindrance, and the yield of the corresponding nitrile product is not high. The yield of the electron-donating group is higher than that of the electron-withdrawing group, which may be because the electron-donating group is more conducive to the formation of stable carbon cations.

[0070] Examples 27-31:

[0071] The electrolytic cells of Examples 27-31 are the same as Example 1, except that the anode is a nitrogen-doped graphite felt electrode, which is prepared by the following method: 2 cm * 2 cm * 0.5 cm size graphite felt (Graphite Felt, abbreviated as GF) is ultrasonically treated in deionized water and anhydrous ethanol for 10 minutes respectively, then washed with deionized water and dried in an oven at 100°C. The dried GF is placed in a 100 ml methanol: Tris buffer solution (pH = 8.5) solution (volume ratio, 1:1) containing different concentrations of hydrochloric acid dopamine (C8H 11 NO2·HCl) and ultrasonically treated (42 kHz, 210 W) for 40 minutes, then washed with deionized water and dried in an oven at 80°C. Finally, heat treatment at 700°C in an argon atmosphere for 1 hour to obtain a nitrogen-doped graphite felt electrode (denoted as NxxGF, xx represents the concentration of hydrochloric acid dopamine; for example, N02GF represents 0.2 mmol / L C8H 11 NO2·HCl doped graphite felt). The difference is that the concentration of C8H 11 NO2·HCl doped in the anode material is 0.2 mmol / L (Example 27), 0.6 mmol / L (Example 28), 1.0 mmol / L (Example 29), 1.5 mmol / L (Example 30), and 2.0 mmol / L (Example 31), respectively.

[0072] The electrolytic reaction steps and reaction processes of Examples 27-31 are the same as Example 1, and direct electrolysis is performed. The experimental results are listed in Table 7.

[0073] Table 7 p-MeOBA electro-synthesis results on anode materials doped with different concentrations of C8H 11 NO2·HCl

[0074]

[0075] From the above results, it can be seen that the graphite felt anode material doped with a lower concentration of nitrogen source has little effect on the yield of p-MeOBN. However, when the doping concentration is higher, it is not conducive to the formation of nitrile, which may be because after N-doping, the hydrophilicity of the graphite felt electrode increases (Mater Chem Phys. 2019, 237, 121873), affecting the adsorption of organic matter on the anode, so the anode material is GF.

[0076] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Any modification, equivalent replacement, and improvement of the above embodiment made by any person skilled in the art without departing from the technical solution of the present application, and according to the technical essence of the present application, are still within the protection scope of the present application.

Claims

1. A method for the direct electrocatalytic synthesis of aromatic nitriles on a graphite felt electrode, characterized in that: The method is: in diaphragmless electrolytic cell is added by formula I shows aromatic aldehyde, supporting electrolyte, hydroxyl ammonium sulfate and solvent composition electrolyte, cathode uses ordinary graphite felt electrode or nitrogen doped graphite felt electrode, anode uses graphite felt electrode, through constant current electrolysis generates formula II shows aromatic nitrile; The concentration of the substrate is 10-50mmol / L; The solvent is CH3CN or DMF and H2O is mixed at volume ratio 70%:30%-60%:40%; The distance between the anode and the cathode is 8-26mm; The constant current electrolysis condition is: room temperature, current density is 5-15mA / cm 2 , rotation speed is 700-1000rpm; Reaction formula is as follows: R is C1-C4 linear or branched alkyl, C1-C4 linear or branched alkoxy or halogen; The nitrogen-doped graphite felt electrode is prepared by the following method: after washing and drying, the common graphite felt electrode is put into a dopamine hydrochloride solution with a concentration of 0.2-2.5 mmol / L for ultrasonic treatment, and then after washing and drying, high-temperature carbonization is carried out in an inert atmosphere to obtain the nitrogen-doped graphite felt electrode; the solvent of the dopamine hydrochloride solution is a mixed solvent obtained by mixing methanol and Tris buffer solution with a pH of 8.5 at a volume ratio of 1:

1. In the preparation of the nitrogen-doped graphite felt electrode, the high-temperature carbonization conditions are: heat treatment in an argon atmosphere at 650-750℃ for 1-2h.

2. The method of claim 1, wherein: The substrate concentration is 25mmol / L.

3. The method of claim 1, wherein: The solvent is a mixture of CH3CN and H2O at a volume ratio of 70%:30%.

4. The method of claim 1, wherein: The cathode is a nitrogen-doped graphite felt electrode, and in the preparation process of the nitrogen-doped graphite felt electrode, the concentration of the dopamine hydrochloride solution is 0.4-0.6mmol / L.

5. The method of claim 1, wherein: The cathode is a nitrogen-doped graphite felt electrode, and in the preparation process of the nitrogen-doped graphite felt electrode, the concentration of the dopamine hydrochloride solution is 0.6mmol / L.

6. The method of claim 5, wherein: The electrode spacing is 16-26mm.

7. The method of claim 1, wherein: The current density is 10 mA / cm 2 .

8. The method of claim 1, wherein: The electrolysis temperature is 25℃, and the electrolysis time is 6h.

9. The method of claim 1, wherein: The supporting electrolyte is tetrabutylammonium perchlorate, and the concentration of the supporting electrolyte is 50mmol / L.

10. The method of claim 1, wherein: ​ 11. The method of claim 1, wherein: The method is: adding p -MeOBA, a supporting electrolyte, hydroxylammonium sulfate and a solvent to form an electrolyte, and the anode and cathode electrode materials are ordinary graphite felt electrode and nitrogen-doped graphite felt electrode prepared using 0.6 mmol / L dopamine hydrochloride solution respectively, and MeOBN is generated by constant current electrolysis p -MeOBN; the solvent is CH3CN and H2O mixed at a volume ratio of 70%:30%, the supporting electrolyte is tetrabutylammonium perchlorate; and the constant current electrolysis conditions are: temperature 25℃, current density 10mA / cm 2 , rotation speed 700rpm, and electrolysis time 6h.

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