A method for electrochemically synthesizing p-chlorobenzaldehyde

Abstract

The present invention discloses a method for electrochemically synthesizing p-chlorobenzaldehyde, and the steps are as follows: 1) Prepare a tetrabutylammonium perchlorate acetonitrile solution, add p-chlorotoluene, and mix to obtain an electrolyte solution; 2) Add the electrolyte solution into the anode chamber of an H-type electrolytic cell, add an aqueous alkali solution into the cathode chamber of the H-type electrolytic cell, clamp a catalyst with an electrode clip and place it into the anode chamber, and place a platinum plate electrode into the cathode chamber to carry out a constant current electrolysis reaction; 3) Subject the liquid in the anode chamber after the reaction to reduced pressure distillation and recrystallization to obtain p-chlorobenzaldehyde. By controlling the electrode current, the present invention enables the reaction to proceed according to a predetermined target, avoids the use of strong oxidants and harsh conditions such as high temperature and high pressure, and reduces 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 the electrochemical oxidation of p-chlorotoluene, 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 particularly relates to a method for electrochemically synthesizing p-chlorobenzaldehyde. Background Art

[0002] p-Chlorobenzaldehyde, abbreviated as PCAD, has the molecular formula C7H5ClO. It is a colorless to light yellow flaky crystal or powder, with a melting point of 48 °C and a boiling point of 214 °C. It is soluble in water and easily soluble in organic solvents such as ethanol. p-Chlorobenzaldehyde is an important fine organic intermediate and is widely used in fields such as medicine, dyes, and pesticides. In the pharmaceutical industry, p-chlorobenzaldehyde is used to produce phenobarbital through condensation and cyclization reactions with mercaptopropionic acid, and can also be used to synthesize drugs such as chlorobenzamine acid, the sedative aminobutyric acid, and the veterinary drug chlorpheniramine maleate. In the pesticide industry, p-chlorobenzaldehyde is an important intermediate for synthesizing plant growth regulators such as uniconazole, paclobutrazol, chlorocinnamyl alcohol, and the herbicide methidathion. In the dye industry, triphenylmethane-based acid dyes with p-chlorobenzaldehyde as an intermediate have good brightness and high coloring degree, and are widely used in industries such as wool and silk printing and dyeing. The domestic synthesis process of p-chlorobenzaldehyde is not yet mature, and the production capacity is relatively low, far from meeting the broad market demand. Therefore, its synthesis method is an urgent need for researchers.

[0003] There is a strong electron-withdrawing group attached to p-chlorotoluene, so the oxidation of the methyl group on the benzene ring is difficult and requires a strong oxidizing agent and catalyst. Currently reported methods for oxidizing p-chlorotoluene to prepare p-chlorobenzaldehyde mainly include chemical oxidation methods and liquid-phase air oxidation methods. Chemical oxidation methods have defects such as high production costs, large amounts of three wastes treatment, dangerous operation processes, and poor product quality. Patent CN101138729 discloses a liquid-phase oxidation method using alumina as a carrier and cobalt and manganese as catalysts. This method is the process commonly used in industry at present, but this method requires high temperature and high pressure and a long reaction time. Patent CN109651111A discloses a multi-component system oxidation method using air, oxygen-enriched air, or oxygen as an oxidizing agent, an organic solvent as a reaction medium, and a transition metal chloride as a catalyst. During the reaction process, bromine is used as a catalyst for the substitution reaction. This method has strict requirements for reaction conditions, high costs, and low selectivity.

[0004] Currently existing methods for oxidizing and synthesizing p-chlorobenzaldehyde have many drawbacks such as low selectivity, poor operating conditions and safety, high production costs, and long synthesis time. Therefore, realizing a preparation process for p-chlorobenzaldehyde with high purity, safe and efficient synthesis method, and easy preparation is still the focus of research. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for electrochemically synthesizing p-chlorobenzaldehyde with simple process, short cycle, mild conditions, and high selectivity.

[0006] The technical solution of the present invention is outlined as follows:

[0007] A method for electrochemically synthesizing p-chlorobenzaldehyde, comprising the following steps:

[0008] 1) Prepare a tetrabutylammonium perchlorate acetonitrile solution, add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution, and mix to obtain an electrolyte solution;

[0009] 2) Add the electrolyte solution to the anode chamber of an H-type electrolytic cell, add an aqueous alkali solution to the cathode chamber of the H-type electrolytic cell, clamp the catalyst with an electrode clip and place it in the anode chamber, and place a platinum plate electrode in the cathode chamber, and perform a constant current electrolysis reaction for 3 hours;

[0010] 3) Subject the liquid in the anode chamber after the reaction to reduced pressure distillation and recrystallization to obtain p-chlorobenzaldehyde.

[0011] The concentration of the tetrabutylammonium perchlorate acetonitrile solution is preferably 0.1 mol / L.

[0012] Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 - 0.03 mol / L.

[0013] The aqueous alkali solution is preferably a 1 mol / L potassium hydroxide aqueous solution or a 1 mol / L sodium hydroxide aqueous solution.

[0014] The current of the constant current electrolysis reaction is 0.01 A.

[0015] Preferably, the catalyst is prepared by the following method: In proportion, mix 250 mg of polyvinylpyrrolidone with 10 mL of an N,N-dimethylformamide solution of molybdenum chloride with a concentration of 0.4 - 0.6 mol / L to obtain a mixed solution; immerse the carbon cloth in the mixed solution for 5 s, take it out, dry it, and place it in a tubular furnace with argon flowing through and sodium hypophosphite placed upstream, and heat it at 600 °C for 2 hours.

[0016] Preferably, the average molecular weight of polyvinylpyrrolidone is 58000.

[0017] The size of the carbon cloth is 2.5 cm × 2.5 cm.

[0018] The mass of sodium hypophosphite is 1 g.

[0019] The present invention controls the electrode current to make the reaction proceed according to a predetermined target, avoids the use of strong oxidants and harsh conditions such as high temperature and high pressure, and reduces resource waste and environmental pollution. The method of the present invention is simple, has a short cycle, is green and pollution-free; in an H-type electrolytic cell, an external DC power supply can realize the electrochemical oxidation of p-chlorotoluene, and the reaction conditions are mild and the catalytic activity is high. Detailed implementation mode

[0020] The following embodiments are provided to enable those skilled in the art to better understand the present invention, but do not limit the present invention in any way.

[0021] The H-type electrolytic cell used in each of the following embodiments is commercially available, and its model is preferably C007-1. Other models of H-type electrolytic cells can also be used in the present invention.

[0022] Example 1

[0023] The catalyst was prepared by the following method:

[0024] 250 mg of polyvinylpyrrolidone with an average molecular weight of 58,000 was mixed with 10 mL of an N,N-dimethylformamide solution of molybdenum chloride with a concentration of 0.6 mol / L to obtain a mixed solution; a 2.5 cm × 2.5 cm carbon cloth was immersed in the mixed solution for 5 s, taken out, dried, and placed in a tubular furnace with argon flowing through it and 1 g of sodium hypophosphite placed upstream, and heated at 600 °C for 2 hours.

[0025] Example 2

[0026] The catalyst was prepared by the following method:

[0027] 250 mg of polyvinylpyrrolidone with an average molecular weight of 58,000 was mixed with 10 mL of an N,N-dimethylformamide solution of molybdenum chloride with a concentration of 0.4 mol / L to obtain a mixed solution; a 2.5 cm × 2.5 cm carbon cloth was immersed in the mixed solution for 5 s, taken out, dried, and placed in a tubular furnace with argon flowing through it and 1 g of sodium hypophosphite placed upstream, and heated at 600 °C for 2 hours.

[0028] Example 3

[0029] A method for electrochemically synthesizing p-chlorobenzaldehyde includes the following steps:

[0030] 1) Analytical pure tetrabutylammonium perchlorate was dissolved in acetonitrile to prepare a tetrabutylammonium perchlorate acetonitrile solution with a concentration of 0.1 mol / L. p-Chlorotoluene was added to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 mol / L, and mixed to obtain an electrolyte solution;

[0031] 2) 25 mL of the electrolyte solution was added to the anode chamber of the H-type electrolytic cell, and 25 mL of a KOH aqueous solution with a concentration of 1 mol / L was added to the cathode chamber of the H-type electrolytic cell. The proton exchange membrane in the middle of the H-type electrolytic cell was a Nafion 117 proton membrane. The catalyst prepared in Example 2 was clamped with an electrode clip and placed in the anode chamber, and a platinum sheet electrode was placed in the cathode chamber. Constant current electrolysis reactions were carried out at currents of 5 mA, 10 mA, and 15 mA for 3 hours;

[0032] 3) Analyze the liquid in the anode chamber after the reaction by gas chromatography. According to the current sequence, the following results are obtained successively:

[0033] The conversion rate of p-chlorotoluene is 39.7%, and the selectivity of p-chlorobenzaldehyde is 50%;

[0034] The conversion rate of p-chlorotoluene is 75.6%, and the selectivity of p-chlorobenzaldehyde is 91.4%;

[0035] The conversion rate of p-chlorotoluene is 88.4%, and the selectivity of p-chlorobenzaldehyde is 66.4%.

[0036] Obtain p-chlorobenzaldehyde by vacuum distillation and recrystallization.

[0037] Experiments prove that when 1 mol / L sodium hydroxide aqueous solution is used to replace 1 mol / L KOH aqueous solution in this example, the current is 10 mA, and the constant current electrolysis reaction is carried out for 3 hours; other conditions are the same as those in this example, and the conversion rate of p-chlorotoluene and the selectivity of p-chlorobenzaldehyde are similar to the results under the same conditions.

[0038] Example 4

[0039] A method for electrochemically synthesizing p-chlorobenzaldehyde, comprising the following steps:

[0040] 1) Dissolve analytical pure tetrabutylammonium perchlorate in acetonitrile to prepare tetrabutylammonium perchlorate acetonitrile solutions with concentrations of 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L. Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 mol / L, and mix to obtain the electrolyte solution;

[0041] 2) Add 25 mL of the electrolyte solution to the anode chamber of the H-type electrolytic cell, add 25 mL of 1 mol / L KOH aqueous solution to the cathode chamber of the H-type electrolytic cell. The proton exchange membrane in the middle of the H-type electrolytic cell is Nafion 117 proton membrane. Clamp the catalyst prepared in Example 2 with an electrode clip and place it in the anode chamber, and place the platinum sheet electrode in the cathode chamber. Carry out a constant current electrolysis reaction at a current of 10 mA for 3 hours;

[0042] 3) Analyze the liquid in the anode chamber after the reaction by gas chromatography. According to the electrolyte concentration sequence, the following results are obtained successively:

[0043] The conversion rate of p-chlorotoluene is 75.6%, and the selectivity of p-chlorobenzaldehyde is 91.4%.

[0044] The conversion rate of p-chlorotoluene is 60.8%, and the selectivity of p-chlorobenzaldehyde is 60.1%.

[0045] The conversion rate of p-chlorotoluene is 43.9%, and the selectivity of p-chlorobenzaldehyde is 55.6%.

[0046] Through vacuum distillation and recrystallization, p-chlorobenzaldehyde is obtained.

[0047] Example 5

[0048] A method for electrochemically synthesizing p-chlorobenzaldehyde, comprising the following steps:

[0049] 1) Dissolve analytically pure tetrabutylammonium perchlorate in acetonitrile to prepare a tetrabutylammonium perchlorate acetonitrile solution with a concentration of 0.1 mol / L. Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentrations 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, mix to obtain an electrolyte solution;

[0050] 2) Add 25 mL of the electrolyte solution to the anodic chamber of an H-type electrolytic cell. Add 25 mL of a 1 mol / L aqueous KOH solution to the cathodic chamber of the H-type electrolytic cell. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane. Clamp the catalyst prepared in Example 2 with an electrode clip and place it in the anodic chamber, and place a platinum sheet electrode in the cathodic chamber. Carry out a constant current electrolysis reaction at a current of 10 mA for 3 hours;

[0051] 3) Analyze the liquid in the anodic chamber after the reaction by gas chromatography. In the order of the p-chlorotoluene concentration, the following are obtained successively:

[0052] A conversion rate of 92.9% of p-chlorotoluene and a selectivity of 21.7% of p-chlorobenzaldehyde.

[0053] A conversion rate of 75.6% of p-chlorotoluene and a selectivity of 91.4% of p-chlorobenzaldehyde.

[0054] A conversion rate of 58.3% of p-chlorotoluene and a selectivity of 89.1% of p-chlorobenzaldehyde.

[0055] A conversion rate of 40.8% of p-chlorotoluene and a selectivity of 88.7% of p-chlorobenzaldehyde.

[0056] A conversion rate of 33% of p-chlorotoluene and a selectivity of 88.4% of p-chlorobenzaldehyde.

[0057] Through vacuum distillation and recrystallization, p-chlorobenzaldehyde is obtained.

[0058] Example 6

[0059] A method for electrochemically synthesizing p-chlorobenzaldehyde, comprising the following steps:

[0060] 1) Dissolve analytical pure tetrabutylammonium perchlorate in acetonitrile to prepare a tetrabutylammonium perchlorate acetonitrile solution with a concentration of 0.1 mol / L. Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 mol / L, and mix to obtain the electrolyte solution;

[0061] 2) Add 25 mL of the electrolyte solution to the anode chamber of the H-type electrolytic cell. Add 25 mL of a 1 mol / L KOH aqueous solution to the cathode chamber of the H-type electrolytic cell. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane. Clamp the catalyst prepared in Example 2 with an electrode clip and place it in the anode chamber, and place the platinum sheet electrode in the cathode chamber. Perform a constant current electrolysis reaction at a current of 10 mA for 1 h, 2 h, 3 h, 4 h, and 5 h;

[0062] 3) Analyze the liquid in the anode chamber after the reaction by gas chromatography. In the order of electrolysis time, the following results are obtained successively:

[0063] The conversion rate of p-chlorotoluene is 7.9%, and the selectivity for p-chlorobenzaldehyde is 0%.

[0064] The conversion rate of p-chlorotoluene is 41.6%, and the selectivity for p-chlorobenzaldehyde is 90.1%.

[0065] The conversion rate of p-chlorotoluene is 75.6%, and the selectivity for p-chlorobenzaldehyde is 91.4%.

[0066] The conversion rate of p-chlorotoluene is 94.3%, and the selectivity for p-chlorobenzaldehyde is 67.1%.

[0067] The conversion rate of p-chlorotoluene is 100%, and the selectivity for p-chlorobenzaldehyde is 65.9%.

[0068] Perform vacuum distillation and recrystallization to obtain p-chlorobenzaldehyde.

[0069] Example 7

[0070] A method for electrochemically synthesizing p-chlorobenzaldehyde, comprising the following steps:

[0071] 1) Dissolve analytical pure tetrabutylammonium perchlorate in acetonitrile to prepare a tetrabutylammonium perchlorate acetonitrile solution with a concentration of 0.1 mol / L. Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 mol / L, and mix to obtain the electrolyte solution;

[0072] 2) Add 25 mL of electrolyte into the anode chamber of the H-type electrolytic cell, and add 25 mL of 1 mol / L KOH aqueous solution into the cathode chamber of the H-type electrolytic cell. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane. Clamp the catalysts prepared in Example 1 and Example 2 with electrode clamps and place them in the anode chamber, and place the platinum sheet electrode in the cathode chamber. Carry out a constant current electrolysis reaction for 3 h at a current of 10 mA respectively;

[0073] 3) Analyze the liquid in the anode chamber after the reaction by gas chromatography, and obtain the order of the molybdenum chloride concentration in the prepared catalyst as follows:

[0074] For p-chlorotoluene, the conversion rate is 73.6%, and the selectivity for p-chlorobenzaldehyde is 89.8%.

[0075] For p-chlorotoluene, the conversion rate is 75.6%, and the selectivity for p-chlorobenzaldehyde is 91.4%.

[0076] Through vacuum distillation and recrystallization, p-chlorobenzaldehyde is obtained.

Claims

1. A method for electrochemically synthesizing p-chlorobenzaldehyde, characterized in that It includes the following steps: 1) Prepare a tetrabutylammonium perchlorate acetonitrile solution, add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution, and mix to obtain an electrolyte solution; 2) Add the electrolyte solution to the anode chamber of an H-type electrolytic cell, add an aqueous alkali solution to the cathode chamber of the H-type electrolytic cell, clamp the catalyst with an electrode clip and place it in the anode chamber, and place a platinum sheet electrode in the cathode chamber, and perform a constant current electrolysis reaction for 3 hours; 3) Subject the liquid in the anode chamber after the reaction to reduced pressure distillation and recrystallization to obtain p-chlorobenzaldehyde; the catalyst is prepared by the following method: In proportion, mix 250 mg of polyvinylpyrrolidone with 10 mL of an N,N-dimethylformamide solution of molybdenum chloride with a concentration of 0.4 - 0.6 mol / L to obtain a mixed solution; Immerse the carbon cloth in the mixed solution for 5 s, take it out, dry it, and place it in a tube furnace with argon flowing through and sodium hypophosphite placed upstream, and heat it at 600 °C for 2 hours; The concentration of the tetrabutylammonium perchlorate acetonitrile solution is 0.1 mol / L; Add p-chlorotoluene to the tetrabutylammonium perchlorate acetonitrile solution to make the final concentration 0.02 - 0.03 mol / L; The current of the constant current electrolysis reaction is 0.01 A.

2. The method according to claim 1, characterized in that The aqueous alkali solution is a 1 mol / L potassium hydroxide aqueous solution or a 1 mol / L sodium hydroxide aqueous solution.

3. The method according to claim 1, characterized in that The average molecular weight of the polyvinylpyrrolidone is 58000.

4. The method according to claim 1, wherein The size of the carbon cloth is 2.5 cm × 2.5 cm.

5. The method according to claim 1, wherein The mass of the sodium hypophosphite is 1 g.