A method for electrochemically synthesizing benzaldehyde

Abstract

The present invention discloses a method for electrochemically synthesizing benzaldehyde. The steps are as follows: 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H 3+n PMo 12‑ n V n O 40 in an ethanol aqueous solution with a volume concentration of 20%-80%, and uniformly drop it on a carbon carrier to obtain an anode, where n = 1-3; dissolve toluene in a tetrabutylammonium perchlorate-acetonitrile solution to obtain an anolyte. 2) Add the anolyte to the anode chamber of an H-type electrolytic cell, add a sulfuric acid aqueous solution to the cathode chamber, place the anode in the anode chamber, and place a platinum sheet as the cathode in the cathode chamber to carry out a constant voltage electrolysis reaction. The present invention avoids the use of strong oxidants and harsh conditions such as high temperature and high pressure, reducing resource waste and environmental pollution. The method of the present invention is simple, has a short cycle, and is green and pollution-free; in an H-type electrolytic cell, an external DC power supply can achieve selective electrochemical oxidation of toluene, and the reaction conditions are relatively mild with high catalytic activity.

Description

Technical Field

[0001] The present invention belongs to the field of organic chemical synthesis, and specifically relates to a method for electrochemically synthesizing benzaldehyde. Background Art

[0002] The selective oxidation of benzylic C-H bonds to produce high-value-added chemical products and intermediates has always been a research hotspot. The aromatic aldehydes, ketones and carboxylic acids produced by this method are widely used in the fields of energy, medicine, agriculture, etc. As an important chemical intermediate, benzaldehyde is usually synthesized by the toluene side-chain chlorination hydrolysis method or the toluene direct oxidation method. The toluene side-chain chlorination hydrolysis method is to replace the hydrogen atom on the methyl group of toluene with a chlorine atom under light, and then the mixture is hydrolyzed and rectified to obtain benzaldehyde [Nature Communications, 10(2019), 1-9]. This method will cause serious corrosion of equipment, and the toxic component chlorine contained in the product will limit the application of benzaldehyde. The toluene direct oxidation method is to directly oxidize toluene to benzaldehyde in the presence of a catalyst and an oxidant [Angewandte Chemie-International Edition, 56(2017), 5912-5915]. This method uses dangerous oxidants under high temperature and high pressure, which will cause environmental pollution and huge energy consumption; in addition, since the oxidation ability of toluene is much higher than that of benzaldehyde, benzaldehyde is prone to peroxidation to form benzoic acid or CO2. As a green synthesis method, electrochemical oxidation has received extensive attention due to its mild reaction conditions and environmental friendliness. However, there are few reports on the electrocatalytic selective oxidation of toluene to prepare benzaldehyde at present. Therefore, it is of great practical significance to develop an energy-saving and environment-friendly method for electrochemically synthesizing benzaldehyde. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for electrochemically synthesizing benzaldehyde with mild conditions, green environmental protection and high product selectivity.

[0004] The technical solution of the present invention is outlined as follows:

[0005] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0006] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H 3+n PMo 12-n V n O 40 in an ethanol aqueous solution with a volume concentration of 20%-80%, and uniformly drop it on a carbon carrier to obtain an anode, where n = 1-3; dissolve toluene in a tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 15-50 mM to obtain an anolyte,

[0007] 2) Add the anolyte into the anode chamber of the H-type electrolytic cell, add 0.3 - 1 M sulfuric acid aqueous solution into the cathode chamber of the H-type electrolytic cell, place the anode into the anode chamber, and place a platinum sheet as the cathode into the cathode chamber to conduct a constant voltage electrolysis reaction.

[0008] In step 1), the concentration of the ethanol aqueous solution is preferably 50%.

[0009] In the said step 1), n = 1, 2 or 3.

[0010] The carbon support is preferably carbon paper or graphite rod.

[0011] The concentration of tetrabutylammonium perchlorate - acetonitrile is 0.1 - 0.3 M.

[0012] The voltage is 3.2 - 5.2 V, and the electrolysis reaction time is 4 - 10 h.

[0013] The proton exchange membrane disposed in the middle of the H-type electrolytic cell is preferably Nafion 115 proton membrane, and Nafion 117 proton membrane can also be selected.

[0014] The present invention avoids the use of strong oxidants and harsh conditions such as high temperature and high pressure, reducing resource waste and environmental pollution. The method of the present invention is simple, has a short cycle, is green and pollution-free; in the H-type electrolytic cell, an external DC power supply can realize the selective electrochemical oxidation of toluene, and the reaction conditions are mild and the catalytic activity is high. Specific embodiments

[0015] The following examples are to enable those skilled in the art to better understand the present invention, but do not limit the present invention in any way.

[0016] Example 1

[0017] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0018] 1) Respectively dissolve Keggin-type molybdenum-containing heteropolyacids H3PMo 12 O 40 , H4PMo 11 V1O 40 , H5PMo 10 V2O 40 , H6PMo9V3O 40 in an ethanol aqueous solution with a volume concentration of 50%, uniformly drop it on carbon paper to obtain the anode; dissolve toluene in a 0.3 M tetrabutylammonium perchlorate - acetonitrile solution to make the final concentration 20 mM to obtain the anolyte.

[0019] 2) Add the anolyte to the anodic chamber of an H-type electrolytic cell, add a 0.5 M sulfuric acid aqueous solution to the cathodic chamber of the H-type electrolytic cell, place the anode in the anodic chamber, place a platinum sheet as the cathode in the cathodic chamber, and electrolyze at a constant voltage of 4.2 V for 6 h.

[0020] The products were analyzed by gas chromatography, and in the order of the types of heteropolyacids, the following were obtained successively:

[0021] The conversion rate of toluene was 90.4%, and the selectivity of benzaldehyde was 28.4%.

[0022] The conversion rate of toluene was 85.8%, and the selectivity of benzaldehyde was 52.2%.

[0023] The conversion rate of toluene was 83.4%, and the selectivity of benzaldehyde was 83.5%.

[0024] The conversion rate of toluene was 77.7%, and the selectivity of benzaldehyde was 45.4%.

[0025] Example 2

[0026] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0027] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drop it on carbon paper, carbon cloth, and graphite rods to obtain an anode; dissolve toluene in a 0.3 M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 20 mM to obtain an anolyte.

[0028] 2) Add the anolyte to the anodic chamber of an H-type electrolytic cell, add a 0.5 M sulfuric acid aqueous solution to the cathodic chamber of the H-type electrolytic cell, place the anode in the anodic chamber, place a platinum sheet as the cathode in the cathodic chamber, and electrolyze at a constant voltage of 4.2 V for 6 h.

[0029] The products were analyzed by gas chromatography, and in the order of the types of carbon carriers, the following were obtained successively:

[0030] The conversion rate of toluene was 83.4%, and the selectivity of benzaldehyde was 83.5%.

[0031] The conversion rate of toluene was 34.9%, and the selectivity of benzaldehyde was 68.5%.

[0032] The conversion rate of toluene was 64.6%, and the selectivity of benzaldehyde was 45.1%.

[0033] Example 3

[0034] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0035] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drop it on carbon paper to obtain the anode; dissolve toluene in 0.1M, 0.3M, 0.5M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 20 mM to obtain the anolyte,

[0036] 2) Add the above anolyte to the anode chamber of an H-type electrolytic cell, add 0.5M sulfuric acid aqueous solution to the cathode chamber of the H-type electrolytic cell, place the anode in the anode chamber, place a platinum sheet as the cathode in the cathode chamber, and electrolyze at a constant voltage of 4.2V for 6h.

[0037] The product is analyzed by gas chromatography, and in the order of tetrabutylammonium perchlorate concentration, the following are obtained in sequence:

[0038] The conversion rate of toluene is 47.5%, and the selectivity of benzaldehyde is 60.0%.

[0039] The conversion rate of toluene is 83.4%, and the selectivity of benzaldehyde is 83.5%.

[0040] The conversion rate of toluene is 54.0%, and the selectivity of benzaldehyde is 50.7%.

[0041] Example 4

[0042] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0043] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drop it on carbon paper to obtain the anode; dissolve toluene in 0.3M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 15 mM, 20 mM, 50 mM to obtain the anolyte,

[0044] 2) Add the above anolyte to the anode chamber of an H-type electrolytic cell, add 0.5M sulfuric acid aqueous solution to the cathode chamber of the H-type electrolytic cell, place the anode in the anode chamber, place a platinum sheet as the cathode in the cathode chamber, and electrolyze at a constant voltage of 4.2V for 6h.

[0045] The product is analyzed by gas chromatography, and in the order of the final concentration of toluene, the following are obtained in sequence:

[0046] The conversion rate of toluene is 90.5%, and the selectivity of benzaldehyde is 75.6%.

[0047] The conversion rate of toluene is 83.4%, and the selectivity of benzaldehyde is 83.5%.

[0048] Conversion rate of toluene: 55.2%, selectivity of benzaldehyde: 81.9%.

[0049] Example 5

[0050] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0051] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drip it onto carbon paper to obtain an anode; dissolve toluene in a 0.3M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 20 mM to obtain an anolyte.

[0052] 2) Add the anolyte to the anode chamber of an H-type electrolytic cell, add 0.3M, 0.5M, 1M sulfuric acid aqueous solution to the cathode chamber of the H-type electrolytic cell, place the anode in the anode chamber, place a platinum sheet as the cathode in the cathode chamber, and electrolyze at a constant voltage of 4.2V for 6h.

[0053] The product is analyzed by gas chromatography. In the order of the final concentration of sulfuric acid aqueous solution, the following results are obtained in sequence:

[0054] Conversion rate of toluene: 45.6%, selectivity of benzaldehyde: 64.3%.

[0055] Conversion rate of toluene: 83.4%, selectivity of benzaldehyde: 83.5%.

[0056] Conversion rate of toluene: 88.4%, selectivity of benzaldehyde: 73.2%.

[0057] Example 6

[0058] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0059] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drip it onto carbon paper to obtain an anode; dissolve toluene in a 0.3M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 20 mM to obtain an anolyte.

[0060] 2) Add the anolyte to the anode chamber of an H-type electrolytic cell, add 0.5M sulfuric acid aqueous solution to the cathode chamber of the H-type electrolytic cell, place the anode in the anode chamber, place a platinum sheet as the cathode in the cathode chamber, and electrolyze at constant voltages of 3.2V, 4.2V, and 5.2V for 6h.

[0061] The product is analyzed by gas chromatography. In the order of voltage, the following results are obtained in sequence:

[0062] The conversion rate of toluene is 39.7%, and the selectivity of benzaldehyde is 84.6%.

[0063] The conversion rate of toluene is 83.4%, and the selectivity of benzaldehyde is 83.5%.

[0064] The conversion rate of toluene is 91.6%, and the selectivity of benzaldehyde is 43.2%.

[0065] Example 7

[0066] A method for electrochemically synthesizing benzaldehyde, comprising the following steps:

[0067] 1) Dissolve Keggin-type molybdenum-containing heteropolyacid H5PMo 10 V2O 40 in an aqueous ethanol solution with a volume concentration of 50%, and uniformly drop it on carbon paper to obtain the anode; dissolve toluene in a 0.3M tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 20 mM to obtain the anolyte,

[0068] 2) Add the anolyte to the anode chamber of an H-type electrolytic cell, add a 0.5M sulfuric acid aqueous solution to the cathode chamber of the H-type electrolytic cell, place the anode in the anode chamber, place a platinum sheet as the cathode in the cathode chamber, and electrolyze at a constant voltage of 4.2V for 2h, 4h, 6h, 8h, 10h.

[0069] The product is analyzed by gas chromatography. In the order of electrolysis time, the following are obtained in turn:

[0070] The conversion rate of toluene is 40.8%, and the selectivity of benzaldehyde is 61.1%.

[0071] The conversion rate of toluene is 72.7%, and the selectivity of benzaldehyde is 62.5%.

[0072] The conversion rate of toluene is 83.4%, and the selectivity of benzaldehyde is 83.5%.

[0073] The conversion rate of toluene is 87.2%, and the selectivity of benzaldehyde is 74.5%.

[0074] The conversion rate of toluene is 89.5%, and the selectivity of benzaldehyde is 64.6%.

[0075] Replace the aqueous ethanol solution with a volume concentration of 50% in this example with an aqueous ethanol solution with a volume concentration of 20% or an aqueous ethanol solution with a volume concentration of 80%, and select an electrolysis time of 2h. Other conditions are the same as in this example. The conversion rate of toluene and the selectivity of benzaldehyde are similar to those of toluene with an electrolysis time of 2h in this example.

Claims

1. A method for electrochemically synthesizing benzaldehyde, characterized in that It includes the following steps: 1) Dissolve the Keggin-type molybdenum-containing heteropolyacid H 3+n PMo 12-n V n O 40 in an ethanol aqueous solution with a volume concentration of 20%-80%, and uniformly drop it on a carbon carrier to obtain an anode, where n = 2; dissolve toluene in a tetrabutylammonium perchlorate-acetonitrile solution to make the final concentration 15-50 mM to obtain an anolyte, and the carbon carrier is carbon paper; 2) Add the anolyte into the anode chamber of the H-type electrolytic cell, add a 0.3-1M sulfuric acid aqueous solution into the cathode chamber of the H-type electrolytic cell, place the anode into the anode chamber, and place a platinum sheet as the cathode into the cathode chamber to conduct a constant voltage electrolysis reaction.

2. The method according to claim 1, characterized in that In the step 1), the concentration of the ethanol aqueous solution is 50%.

3. The method according to claim 1, wherein The concentration of the tetrabutylammonium perchlorate-acetonitrile is 0.1-0.3M.

4. The method according to claim 1, characterized in that The constant voltage is