Method for direct electro-catalytic synthesis of aromatic nitrile on graphite felt electrode

Abstract

The invention discloses a method for direct electro-catalytic synthesis of aromatic nitrile on a graphite felt electrode, which comprises the following steps: adding an electrolyte consisting of aromatic aldehyde as shown in a 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 performing electro-catalytic synthesis on the graphite felt electrode, performing constant-current electrolysis to generate aromatic nitrile as shown in a formula II; the solvent is prepared by mixing CH3CN or DMF (Dimethyl Formamide) and H2O according to the volume ratio of 70%: 30%-60%: 40%; the distance between the anode and the cathode is 8-26 mm; the conditions of the constant-current electrolysis are as follows: the room temperature, the current density is 5-15mA / cm < 2 >, and the rotating speed is 700-1000rpm; the reaction formula is as follows. The method has the advantages of no metal and low cost. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the field of organic electrochemical synthesis, and in particular relates to a method for directly electrocatalyzing the synthesis of aromatic nitrile. Background Art

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

[0003] The electrocatalytic synthesis of aromatic nitriles from aromatic aldehydes is a simple and easy-to-control method, but most of them require the use of expensive metal electrodes or media, and there are problems such as electrode contamination and corrosion (Chem J Chinese U. 2018, 39, 01, 78-84). Therefore, how to choose cheap electrodes and maintain a high yield is challenging. Yuan et al. used p-MeOBA as a substrate, NH4I as a medium, C as an anode, and Ni as a cathode to indirectly electrocatalyze the synthesis of p-MeOBN in DMSO with a yield of up to 99% (SciChina Chem. 2015, 15 (4), 747-750), but the corrosion of the cathode nickel occurred in the process. Hashem et al. used NH2OH·HCl as a nitrogen source on catalytic graphite, dehydrated under the action of MeSO2Cl, and converted a variety of aromatic aldehydes into aromatic nitriles at 60℃-120℃, with an overall yield of >80% (Synthesis (Stuttg), 2003, 2, 243-246).

[0004] Our research group studied the reaction of Cl with tetrabutylammonium perchlorate as supporting electrolyte, Pt as anode, Pb as cathode, in an undivided electrolytic cell at 60°C. - / ClO - As the medium, the indirect electrosynthesis method can effectively convert p-MeOBA into p-MeOBN with a yield of 99%. In this scheme, an inorganic medium with high chemical stability is used, and no additional oxidant is required. However, there are problems such as the use of expensive Pt electrodes, environmentally unfriendly Pb electrodes, and corrosion of electrodes by halogens in this reaction (J Electrochem Soc. 2024, 171, 085501). Summary of the invention

[0005] The purpose of the present invention is to provide a method for directly electrocatalytically synthesizing aromatic nitrile at room temperature, which has the advantages of being metal-free and low in cost.

[0006] To achieve the above object, the present invention adopts the following technical solution:

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

[0008]

[0009] Wherein, R is a C1-C4 straight chain or branched chain alkyl, a C1-C4 straight chain or branched chain alkoxy or a halogen;

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

[0011] The common graphite felt electrode described in the present invention refers to an unmodified graphite felt electrode.

[0012] Preferably, in the preparation of the nitrogen-doped graphite felt electrode, the ultrasonic treatment conditions are: treatment at 42 kHz and 210 W for 40 minutes.

[0013] Preferably, in the preparation of the nitrogen-doped graphite felt electrode, the high-temperature carbonization conditions are: heat treatment at 650-750°C in an argon atmosphere for 1-2 hours, more preferably heat treatment at 700°C in an argon atmosphere for 1 hour.

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

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

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

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

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

[0019] Preferably, the electrolysis temperature is 25°C.

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

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

[0022] The method is particularly preferred in the present invention as follows: an electrolyte consisting of p-MeOBA, a supporting electrolyte and a solvent is added to a membraneless electrolytic cell, wherein the anode and cathode electrode materials are GF and N06GF, respectively, and p-MeOBN is generated by constant current electrolysis; the solvent is a mixture of CH3CN and H2O in a volume ratio of 70%:30%, and the supporting electrolyte is TBAP; the constant current electrolysis conditions are: a temperature of 25°C and a current density of 10 mA / cm 2 , rotation speed 700 rpm, electrolysis for 6 h. Under this condition, p-MeOBA can be efficiently converted into the target product nitrile.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) Compared with the traditional chemical oxidation method, the present invention uses an electrochemical method, which does not require the addition of chemical oxidants (O2, H2O2 or metal oxides), avoids excessive oxidation, is safer, and is more in line with the standards of green chemistry.

[0025] (2) The present invention uses direct electrosynthesis, which has simple operating equipment and is carried out under normal temperature and pressure conditions; compared with the indirect electrosynthesis method, no medium needs to be added.

[0026] (3) The cathode and anode materials in the present invention 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 invention, the following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the protection scope of the present invention is not limited to these embodiments.

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

[0029]

[0030] The structure of the corresponding prepared p-MeOBN is shown in Formula II-1:

[0031]

[0032] The expanded reaction substrates are:

[0033]

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

[0035] Embodiment 1:

[0036] A mixed solvent of 0.2042 g p-MeOBA (50 mmol / L), 0.3693 g hydroxylammonium sulfate, 0.4723 g TBAP, 21 mL CH3CN and 9 mL H2O was added to a 50 mL electrolytic cell at 25 °C. GF was used as anode and cathode respectively. The electrolysis was carried out at 700 rpm and 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 method. The reaction solution was purified by rotary evaporation, extraction, and column chromatography (petroleum ether / ethyl acetate = 10:1) for further structural characterization.

[0037] The p-MeOBN structure is characterized by: 1 H NMR (500MHz, CDCl3) δ: 7.59 (d, J = 8.9Hz, 2H), 6.95 (d, J = 8.9Hz, 2H), 3.86 (s, 3H), GC-MS (EI, 70eV) m / z: 133.15 [M + ]

[0038] Embodiment 2-9, comparative embodiment 1:

[0039] The electrolytic cells of Examples 2-9 are the same as those of Example 1, except that the cathode uses a nitrogen-doped graphite felt electrode, which is prepared by the following method: Graphite felt (GF) with a size of 2 cm*2 cm*0.5 cm is ultrasonically treated in deionized water and anhydrous ethanol for 10 minutes, then rinsed with deionized water, and dried in an oven at 100°C. The dried GF is placed in 100 ml of dopamine hydrochloride (C8H 11 The electrode was treated with ultrasound (42kHz, 210W) for 40 minutes in a methanol:Tris buffer (pH=8.5) solution (volume ratio, 1:1) of NO2·HCl, then rinsed 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 0.2mmol / L C8H 11 NO2·HCl doped graphite felt). The difference is that the cathode material is doped with C8H 11 The concentrations of NO2·HCl are 0.2mmol / L (Example 2), 0.4mmol / L (Example 3), 0.6mmol / L (Example 4), 0.8mmol / L (Example 5), 1.0mmol / L (Example 6), 1.5mmol / L (Example 7), 2.0mmol / L (Example 8), and 2.5mmol / L (Example 9).

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

[0041] Table 1 In different C8H 11 Results of electrosynthesis of p-MeOBA on cathode materials doped with NO2·HCl concentration

[0042]

[0043] It can be seen from Table 1 that when the concentration of the doped nitrogen source in the cathode material graphite felt is different, the yield of the product p-MeOBN is also different, among which the yield is the highest under the GF (0.6) condition, so the preferred cathode material is GF (0.6).

[0044] Embodiment 10-13:

[0045] The reaction steps 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), 15 mA / cm 2 (Example 13), the results of the direct electrolysis experiment are listed in Table 3.

[0046] Table 2 p-MeOBA electrosynthesis results at different current densities

[0047]

[0048]

[0049] It can be seen from Table 2 that when CH3CN / H2O is used as the reaction solvent, the yield of p-MeOBA to directly electrocatalyze p-MeOBN increases gradually with the increase of current density. 2 The yield of p-MeOBN is the highest when the current density is 10 mA / cm 2 .

[0050] Embodiment 14-15:

[0051] The reaction steps and reaction process are the same as in Example 4, except that the solvents are DMF:H2O=70%:30% (Example 14) and DMSO:H2O=70%:30% (Example 15). The results of the direct electrolysis experiment are listed in Table 4.

[0052] Table 3 p-MeOBA electrosynthesis results in 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. However, under the condition of CH3CN:H2O=7:3 (volume ratio), it is conducive to the formation of nitrile, so CH3CN:H2O=7:3 (volume ratio) is preferred.

[0055] Embodiment 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 direct electrolysis experimental results are listed in Table 5.

[0057] Table 4 Conversion of p-MeOBA to p-MeOBN at different reaction substrate concentrations

[0058]

[0059] It can be seen from Table 4 that different substrate concentrations in the reaction system have a great influence on the yield of p-MeOBN. This may be because when the electrode area is constant, when the reaction substrate concentration is high, side reactions are likely to occur. Therefore, the preferred substrate concentration is 25 mmol / L.

[0060] Embodiment 19-20:

[0061] The reaction steps and reaction process are the same as those in Example 17, except that the distances between the anode and cathode are different, namely 8 mm (Example 24) and 26 mm (Example 25), respectively. Direct electrolysis is carried out, and the experimental results are listed in Table 6.

[0062] Table 5 p-MeOBA electrosynthesis results at different interelectrode distances

[0063]

[0064] It can be seen from Table 5 that when the inter-electrode spacing is 16-26 mm, the p-MeOBN yield is higher, which may be because the electric field distribution in the solution is most conducive to the reaction at this spacing. In addition, the cell pressure is also lower when the inter-electrode spacing is 16-26 mm, which is more energy-saving.

[0065] Embodiment 21-26:

[0066] The reaction steps and reaction process are the same as those in Example 17, except that the reaction substrates are benzaldehyde (Example 21), m-methylbenzaldehyde (Example 22), 4-methylbenzaldehyde (Example 23), o-anisaldehyde (Example 24), 4-chlorobenzaldehyde (Example 25), and 4-tert-butylbenzaldehyde (Example 26). The direct electrolysis experimental results are listed in Table 7.

[0067] Table 6 Electrolytic synthesis of different aromatic nitriles

[0068]

[0069] It can be seen from Table 6 that when the benzene ring contains different electron-withdrawing groups and electron-donating groups at different positions, the yields of the corresponding nitriles are also different. The ortho and meta positions may be limited by steric hindrance, and the yields of the corresponding nitrile products are 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] Embodiment 27-31:

[0071] The electrolytic cells of Examples 27-31 are the same as those of Example 1, except that the anode is a nitrogen-doped graphite felt electrode, which is prepared by the following method: Graphite felt (GF) with a size of 2 cm*2 cm*0.5 cm is ultrasonically treated in deionized water and anhydrous ethanol for 10 minutes, then rinsed with deionized water, and dried in an oven at 100°C. The dried GF is placed in 100 ml of dopamine hydrochloride (C8H 11 The electrode was treated with ultrasound (42kHz, 210W) for 40 minutes in a methanol:Tris buffer (pH=8.5) solution (volume ratio, 1:1) of NO2·HCl, then rinsed 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 0.2mmol / L C8H 11 NO2·HCl doped graphite felt). The difference is that the anode material is doped with C8H 11 The concentrations of NO2·HCl are 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 electrolysis reaction steps and reaction processes of Examples 27-31 are the same as those of Example 1, and direct electrolysis is carried out. The experimental results are listed in Table 7.

[0073] Table 7 Different C8H 11 Results of electrosynthesis of p-MeOBA on NO2·HCl doped anode materials

[0074]

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

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for directly electrocatalytically synthesizing aromatic nitrile on a graphite felt electrode, characterized in that: The method comprises: adding an electrolyte consisting of an aromatic aldehyde shown in Formula I, a supporting electrolyte and a solvent into a membrane-free electrolytic cell; using an ordinary graphite felt electrode or a nitrogen-doped graphite felt electrode as a cathode and a graphite felt electrode as an anode; and generating an aromatic nitrile shown in Formula II by constant current electrolysis; the substrate concentration is 10-50 mmol / L; the solvent is a mixture of CH3CN or DMF and H2O in 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 conditions are: room temperature, current density of 5-15 mA / cm 2 , the rotation speed is 700-1000rpm; the reaction formula is as follows: Wherein, R is a C1-C4 straight chain or branched chain alkyl, a C1-C4 straight chain or branched chain alkoxy or a halogen; The nitrogen-doped graphite felt electrode is prepared by the following method: after washing and drying, an ordinary graphite felt electrode is placed in a dopamine hydrochloride solution with a concentration of 0.2-2.5 mmol / L for ultrasonic treatment, and then washed and dried and then subjected to high-temperature carbonization in an inert atmosphere to obtain a nitrogen-doped graphite felt electrode; the solvent of the dopamine hydrochloride solution is a mixed solvent obtained by a volume ratio of 1:1 with methanol and a Tris buffer solution with a pH of 8.

5.

2. The method according to claim 1, characterized in that: In the preparation of the nitrogen-doped graphite felt electrode, the high-temperature carbonization conditions are: heat treatment at 650-750° C. in an argon atmosphere for 1-2 hours.

3. The method according to claim 1, characterized in that: The substrate concentration is 25 mmol / L.

4. The method according to claim 1, characterized in that: The solvent is a mixture of CH3CN and H2O in a volume ratio of 70%:30%.

5. The method according to claim 1, characterized in that: The cathode is a nitrogen-doped graphite felt electrode. During the preparation of the nitrogen-doped graphite felt electrode, the concentration of the dopamine hydrochloride solution is 0.4-0.6 mmol / L, preferably 0.6 mmol / L.

6. The method according to claim 1, characterized in that: The current density is 10 mA / cm 2 .

7. The method according to claim 1, characterized in that: The electrode spacing is 16-26 mm.

8. The method according to claim 1, characterized in that: The electrolysis temperature was 25°C and the electrolysis time was 6 h.

9. The method according to claim 1, characterized in that: The supporting electrolyte is tetrabutylammonium perchlorate, and the supporting electrolyte concentration is 50 mmol / L.

10. The method according to claim 1, characterized in that: The method comprises: adding an electrolyte consisting of p-MeOBA, a supporting electrolyte and a solvent into a membrane-free electrolytic cell, wherein the anode and cathode electrode materials are respectively a common graphite felt electrode and a nitrogen-doped graphite felt electrode prepared by using a 0.6 mmol / L dopamine hydrochloride solution, and generating p-MeOBN by constant current electrolysis; the solvent is a mixture of CH3CN and H2O in a volume ratio of 70%:30%, and the supporting electrolyte is tetrabutylammonium perchlorate; the constant current electrolysis conditions are: a temperature of 25°C and a current density of 10 mA / cm 2 , rotation speed 700rpm, electrolysis 6h.

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