A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid

Abstract

The present invention discloses a method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, which comprises the following steps: 1) Prepare an aqueous sulfuric acid solution, and add 2-nitro-4-methylsulfonyltoluene, a catalyst and a phase transfer agent into the aqueous sulfuric acid solution and mix them to obtain an electrolyte solution; 2) Add the electrolyte solution into the anode chamber of an H-type electrolytic cell, and separately take an aqueous sulfuric acid solution and add it into the cathode chamber, and conduct a constant voltage electrolysis reaction; 3) Extract, distill under reduced pressure and recrystallize the liquid in the anode chamber after the reaction to obtain 2-nitro-4-methylsulfonylbenzoic acid. By controlling the electrode potential, 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, is green and pollution-free; in an H-type electrolytic cell, an external DC power supply can be used to achieve the electrochemical oxidation of 2-nitro-4-methylsulfonyltoluene, and the reaction conditions are relatively mild and the catalytic activity is high.

Description

Technical Field

[0001] The present invention belongs to the field of organic chemical synthesis, and particularly relates to a method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid. Background Art

[0002] 2-nitro-4-methylsulfonylbenzoic acid, abbreviated as NMSBA, has a molecular formula of C8H7NO6S, and is a white or yellow powdery crystal with a melting point of 211-212 °C, a boiling point of 497.8 °C, slightly soluble in water, and soluble in organic solvents such as methanol. 2-nitro-4-methylsulfonylbenzoic acid is an important fine organic intermediate, widely used in the fields of medicine, dyes, and pesticides. Its main use is to prepare mesotrione. Mesotrione belongs to triketone herbicides and is a highly efficient corn field herbicide that has been widely used in developed countries. The domestic synthesis process of 2-nitro-4-methylsulfonylbenzoic acid is not yet mature, and the promotion of the herbicide mesotrione is limited. Therefore, its synthesis method is an urgent need for researchers.

[0003] There are two strong electron-withdrawing groups attached to 2-nitro-4-methylsulfonyltoluene. Therefore, 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 2-nitro-4-methylsulfonyltoluene to prepare 2-nitro-4-methylsulfonylbenzoic acid mainly include chemical oxidation method and liquid-phase air oxidation method. The chemical oxidation method has defects such as high production cost, large amount of three wastes treatment, dangerous operation process, and poor product quality. Patent US5424481 discloses a nitric acid oxidation method using vanadium pentoxide as a catalyst, which is the currently commonly used process in industry. However, this method generates a large amount of three wastes, is difficult to treat, and has serious nitrogen oxide pollution. The liquid-phase air oxidation method features using air or oxygen as an oxidizing agent. Patent document CN104557639A discloses a multi-component system oxidation method using air, oxygen-enriched air or oxygen as an oxidizing agent, sulfuric acid as a reaction medium, and transition metal oxide as a catalyst. During the reaction process, an oxidation reaction device with a self-priming stirrer is used to prepare the target product. This method has high requirements for equipment, high cost, and belongs to a gas-liquid phase reaction, which is not conducive to industrialization.

[0004] Currently, the existing oxidation synthesis methods of 2-nitro-4-methylsulfonylbenzoic acid have many drawbacks such as a large amount of three wastes treatment, poor operating conditions and safety, and high production cost. Therefore, the preparation process of 2-nitro-4-methylsulfonylbenzoic acid that is green and environmentally friendly, safe and efficient in synthesis method, and easy to prepare remains 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 2-nitro-4-methylsulfonylbenzoic acid with simple process, short cycle, mild conditions, and green environmental protection.

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

[0007] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0008] 1) Prepare a sulfuric acid aqueous solution by diluting analytical pure 98% sulfuric acid with triple-distilled water, and add 2-nitro-4-methylsulfonyltoluene, a catalyst, and a phase transfer agent to the sulfuric acid aqueous solution to obtain an electrolyte solution;

[0009] 2) Add the electrolyte solution to the anode chamber of an H-type electrolytic cell, and separately add the same sulfuric acid aqueous solution as in step 1) to the cathode chamber, and carry out a constant-voltage electrolysis reaction;

[0010] 3) Extract, distill under reduced pressure, and recrystallize the liquid in the anode chamber after the reaction to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0011] In step 1), the concentration of the sulfuric acid aqueous solution is preferably 1-2 mol / L.

[0012] The final concentration of the 2-nitro-4-methylsulfonyltoluene in the electrolyte solution is preferably 0.01-0.02 mol / L.

[0013] The final concentration of the catalyst in the electrolyte solution is preferably 0.07-0.12 mol / L.

[0014] The catalyst is preferably sodium molybdate or ammonium molybdate.

[0015] The final mass percentage of the phase transfer agent in the electrolyte solution is preferably 0.07%-0.12%.

[0016] The phase transfer agent is preferably tetrabutylammonium chloride or tetrabutylammonium bromide.

[0017] The proton exchange membrane in the middle of the H-type electrolytic cell is preferably a Nafion 115 proton membrane or a Nafion 117 proton membrane.

[0018] The electrode in the anode chamber is preferably a graphite rod electrode, a carbon cloth electrode, or a carbon paper electrode; the electrode in the cathode chamber is preferably a platinum sheet electrode.

[0019] The conditions for the constant-voltage electrolysis reaction are: the voltage is preferably 2.1-2.5 V, the temperature is preferably 15-30 °C; the electrolysis time is preferably 4-6 h.

[0020] By controlling the electrode potential, the present invention enables the reaction to proceed according to a predetermined target, avoiding the use of strong oxidants and harsh conditions such as high temperature and high pressure, and 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 the electrochemical oxidation of 2-nitro-4-methylsulfonyltoluene, and the reaction conditions are relatively mild with high catalytic activity. Description of the Drawings

[0021] Figure 1 It is a graph of the oxidation results of Example 1 at different temperatures;

[0022] Figure 2 It is a graph of the oxidation results of Example 2 at different constant voltage electrolysis times;

[0023] Figure 3 It is a graph of the oxidation results of Example 3 at different final concentrations of sodium molybdate;

[0024] Figure 4 It is a graph of the oxidation results of Example 4 at different final concentrations of sulfuric acid;

[0025] Figure 5 It is a graph of the oxidation results of Example 5 at different final concentrations of 2-nitro-4-methylsulfonyltoluene;

[0026] Figure 6 It is a graph of the oxidation results of Example 6 at different final mass percentages of tetrabutylammonium chloride;

[0027] Figure 7 It is a graph of the oxidation results of Example 7 at different constant voltages. Detailed Embodiments

[0028] The following examples 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.

[0029] Example 1

[0030] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0031] 1) Prepare a 2 mol / L sulfuric acid aqueous solution by diluting analytical pure 98% sulfuric acid with triple-distilled water, add 2-nitro-4-methylsulfonyltoluene to make the final concentration 0.02 mol / L, add the catalyst sodium molybdate to make the final concentration 0.1 mol / L, and add the phase transfer agent tetrabutylammonium chloride to make the final mass percentage in the electrolyte 0.12%, and mix to obtain the electrolyte;

[0032] 2) Add 25 mL of the electrolyte solution to the anodic chamber of the H-type electrolytic cell. Separately, take another 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a graphite rod electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; electrolyze at a constant voltage of 2.3 V and temperatures of 15 °C, 20 °C, 30 °C, 40 °C, and 60 °C for 6 h.

[0033] 3) Extract the liquid in the anodic chamber after the reaction with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anodic chamber is 1:2. After standing for complete stratification, analyze it by liquid chromatography. In the order of temperature, the following are obtained successively:

[0034] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 58.48%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 95.03%.

[0035] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.37%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 95.16%.

[0036] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 55.99%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 94.01%.

[0037] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 49.7%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 83.29%.

[0038] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 56.53%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.21%. See Figure 1 . Then, perform vacuum distillation and recrystallization separately to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0039] Example 2

[0040] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0041] 1) Prepare a 2 mol / L sulfuric acid aqueous solution by diluting analytical grade 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro-4-methylsulfonyltoluene to make the final concentration 0.02 mol / L, add the catalyst sodium molybdate to make the final concentration 0.1 mol / L, and add the phase transfer agent tetrabutylammonium chloride to make the final mass percentage in the electrolyte solution 0.12%. Mix to obtain the electrolyte solution;

[0042] 2) Add 25 mL of the electrolyte solution to the anodic chamber of the H-shaped electrolytic cell. Separately, take another 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-shaped electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a graphite rod electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; perform constant voltage electrolysis at a voltage of 2.3 V and a temperature of 20 °C for 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h.

[0043] 3) Extract the liquid in the anodic chamber after the reaction with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anodic chamber is 1:2. After standing for complete stratification, analyze it by liquid chromatography. In chronological order, the following are obtained successively:

[0044] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 42.2%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 82.16%.

[0045] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 44.11%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 90.27%.

[0046] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 49.77%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.79%.

[0047] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 51.4%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 98.63%.

[0048] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 54.57%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.3%.

[0049] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.37%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 95.16%. See Figure 2 Then, perform vacuum distillation and recrystallization respectively to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0050] Example 3

[0051] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0052] 1) Prepare a 2 mol / L sulfuric acid aqueous solution by diluting analytical pure 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro-4-methylsulfonyltoluene to make the final concentration 0.02 mol / L, add sodium molybdate as a catalyst to make the final concentrations 0.03, 0.05, 0.07, 0.1, 0.12, 0.16, and 0.2 mol / L respectively, and add tetrabutylammonium chloride as a phase transfer agent to make the final mass percentage in the electrolyte solution 0.12%, and mix to obtain the electrolyte solution;

[0053] 2) Add 25 mL of electrolyte solution to the anodic chamber of the H-shaped electrolytic cell. Separately, take another 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-shaped electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a graphite rod electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; electrolyze at a constant voltage of 2.3 V and a temperature of 20 °C for 6 h.

[0054] 3) Extract the liquid in the anodic chamber after the reaction with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anodic chamber is 1:2. After standing for complete stratification, analyze it by liquid chromatography. In the order of the final concentration of sodium molybdate, the following results are obtained successively:

[0055] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 49.65%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 86.27%.

[0056] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 53.36%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 97.22%.

[0057] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 56.9%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 96.41%.

[0058] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.37%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 95.16%.

[0059] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.35%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 90.55%.

[0060] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 56.67%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 92.1%.

[0061] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 58.56%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 97.31%. See Figure 3 ... Then, perform vacuum distillation and recrystallization separately to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0062] Experiments prove that when ammonium molybdate is used to replace sodium molybdate in this example, and other conditions are the same as in this example, the conversion rate and selectivity of 2-nitro-4-methylsulfonyltoluene are similar to those in this example.

[0063] Example 4

[0064] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0065] 1) Prepare 0.5, 1, 1.5, and 2 mol / L sulfuric acid aqueous solutions by diluting analytical pure 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro

[0066] -4-methylsulfonyltoluene to a final concentration of 0.02 mol / L, add the catalyst sodium molybdate to a final concentration of 0.1 mol / L, and add the phase transfer agent tetrabutylammonium chloride to a final mass percentage of 0.12% in the electrolyte solution. Mix to obtain the electrolyte solution;

[0067] 2) Add 25 mL of each electrolyte solution to the anodic chamber of an H-type electrolytic cell. Separately, take 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a graphite rod electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; electrolyze at a voltage of 2.3 V and a temperature of 20 °C for 6 h under a constant voltage.

[0068] 3) Extract the liquid in the anodic chamber after the reaction with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anodic chamber is 1:2. After standing for complete stratification, analyze by liquid chromatography. In the order of sulfuric acid aqueous solution concentration, the following results are obtained:

[0069] A conversion rate of 34.92% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 30.22% of 2-nitro-4-methylsulfonylbenzoic acid.

[0070] A conversion rate of 51.2% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 99.06% of 2-nitro-4-methylsulfonylbenzoic acid.

[0071] A conversion rate of 55.7% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 91.8% of 2-nitro-4-methylsulfonylbenzoic acid.

[0072] A conversion rate of 57.37% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 95.16% of 2-nitro-4-methylsulfonylbenzoic acid. See Figure 4 ... Then, carry out vacuum distillation and recrystallization respectively to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0073] Example 5

[0074] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0075] 1) Prepare a 2 mol / L sulfuric acid aqueous solution by diluting analytical pure 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro-4-methylsulfonyltoluene to final concentrations of 0.01, 0.02, 0.03, and 0.04 mol / L respectively, add the catalyst sodium molybdate to a final concentration of 0.1 mol / L, and add the phase transfer agent tetrabutylammonium chloride to a final mass percentage of 0.12% in the electrolyte solution. Mix to obtain the electrolyte solution;

[0076] 2) Add 25 mL of the electrolyte solution to the anodic chamber of the H-type electrolytic cell. Separately, take another 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a graphite rod electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; electrolyze at a constant voltage of 2.3 V and a temperature of 20 °C for 6 h.

[0077] 3) Extract the liquid in the anodic chamber after the reaction with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anodic chamber is 1:2. After standing for complete stratification, analyze it by liquid chromatography. In the order of the final concentration of 2-nitro-4-methylsulfonyltoluene, the following are obtained successively:

[0078] A conversion rate of 56.08% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 93.06% of 2-nitro-4-methylsulfonylbenzoic acid.

[0079] A conversion rate of 57.37% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 95.16% of 2-nitro-4-methylsulfonylbenzoic acid.

[0080] A conversion rate of 40.89% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 95.38% of 2-nitro-4-methylsulfonylbenzoic acid.

[0081] A conversion rate of 33.17% of 2-nitro-4-methylsulfonyltoluene and a selectivity of 94.34% of 2-nitro-4-methylsulfonylbenzoic acid. See Figure 5 Then, carry out vacuum distillation and recrystallization respectively to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0082] Example 6

[0083] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0084] 1) Prepare a 2 mol / L sulfuric acid aqueous solution by diluting analytical pure 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro-4-methylsulfonyltoluene to make the final concentration 0.02 mol / L, add sodium molybdate as a catalyst to make the final concentration 0.1 mol / L, and add tetrabutylammonium chloride as a phase transfer agent to make the final mass percentages in the electrolyte solution 0.02%, 0.07%, 0.12%, and 0.2% in sequence, and mix to obtain the electrolyte solution;

[0085] 2) Add 25 mL of the electrolyte solution to the anodic chamber of the H-type electrolytic cell. Separately, take another 25 mL of the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 117 proton membrane; the electrode in the anodic chamber is a carbon paper electrode, and the electrode in the cathodic chamber is a platinum sheet electrode; electrolyze at a constant voltage of 2.3 V and a temperature of 20 °C for 6 h.

[0086] 3) The liquid in the anode chamber after the reaction is extracted with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anode chamber is 1:2. After standing for complete stratification, it is analyzed by liquid chromatography. In the order of the final mass percentage of tetrabutylammonium chloride, the following are obtained successively:

[0087] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.26%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 59.04%.

[0088] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 56.58%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 98.09%.

[0089] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.37%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 95.16%.

[0090] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 41.01%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.14%. See Figure 6 Then, vacuum distillation and recrystallization are carried out separately to obtain 2-nitro-4-methylsulfonylbenzoic acid.

[0091] Example 7

[0092] A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, comprising the following steps:

[0093] 1) Analytical pure 98% concentrated sulfuric acid is prepared into a 2 mol / L sulfuric acid aqueous solution with triple-distilled water. 2-nitro-4-methylsulfonyltoluene is added to make the final concentration 0.02 mol / L, sodium molybdate as a catalyst is added to make the final concentration 0.1 mol / L, and tetrabutylammonium bromide as a phase transfer agent is added to make the final mass percentage in the electrolyte 0.12%. The mixture is obtained as the electrolyte.

[0094] 2) 25 mL of the electrolyte is added to the anode chamber of an H-type electrolytic cell, and another 25 mL of the same sulfuric acid aqueous solution as in step 1) is added to the cathode chamber. The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 115 proton membrane; the electrode in the anode chamber is a carbon cloth electrode, and the electrode in the cathode chamber is a platinum sheet electrode; electrolysis is carried out at voltages of 2.0 V, 2.1 V, 2.2 V, 2.3 V, 2.4 V, 2.5 V, 2.6 V in sequence, at a temperature of 20 °C, and a constant voltage for 6 h.

[0095] 3) The liquid in the anode chamber after the reaction is extracted with ethyl acetate. The volume ratio of ethyl acetate to the liquid taken from the anode chamber is 1:2. After standing for complete stratification, it is analyzed by liquid chromatography. In the order of the voltage, the following are obtained successively:

[0096] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 41.01%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.14%.

[0097] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 51.11%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 96.24%.

[0098] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 52.74%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 93.6%.

[0099] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 55.06%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 99.68%.

[0100] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 56.87%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 98.28%.

[0101] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 57.64%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 93.7%.

[0102] The conversion rate of 2-nitro-4-methylsulfonyltoluene is 69.63%, and the selectivity of 2-nitro-4-methylsulfonylbenzoic acid is 83.76%. See Figure 7 . Then, vacuum distillation and recrystallization are carried out separately to obtain 2-nitro-4-methylsulfonylbenzoic acid.

Claims

1. A method for electrochemically synthesizing 2-nitro-4-methylsulfonylbenzoic acid, characterized in that It includes the following steps: 1) Prepare a sulfuric acid aqueous solution by diluting analytical pure 98% concentrated sulfuric acid with triple-distilled water. Add 2-nitro-4-methylsulfonyltoluene, a catalyst, and a phase transfer agent to the sulfuric acid aqueous solution and mix to obtain an electrolyte solution; 2) Add the electrolyte solution to the anodic chamber of an H-type electrolytic cell. Separately, take the same sulfuric acid aqueous solution as in step 1) and add it to the cathodic chamber, and conduct a constant-voltage electrolysis reaction; 3) Extract, distill under reduced pressure, and recrystallize the liquid in the anodic chamber after the reaction to obtain 2-nitro-4-methylsulfonylbenzoic acid; The catalyst is sodium molybdate or ammonium molybdate; the phase transfer agent is tetrabutylammonium chloride or tetrabutylammonium bromide.

2. The method according to claim 1, characterized in that In step 1), the concentration of the sulfuric acid aqueous solution is 1 - 2 mol / L.

3. The method according to claim 1, characterized in that The final concentration of 2-nitro-4-methylsulfonyltoluene in the electrolyte solution is 0.01 - 0.02 mol / L.

4. The method according to claim 1, characterized in that The final concentration of the catalyst in the electrolyte solution is 0.07 - 0.12 mol / L.

5. The method according to claim 1, wherein The final mass percentage of the phase transfer agent in the electrolyte solution is 0.07% - 0.12%.

6. The method according to claim 1, wherein The proton exchange membrane in the middle of the H-type electrolytic cell is a Nafion 115 proton membrane or a Nafion 117 proton membrane.

7. The method according to claim 1, wherein The electrode in the anodic chamber is a graphite rod electrode, a carbon cloth electrode, or a carbon paper electrode; the electrode in the cathodic chamber is a platinum sheet electrode.

8. The method according to claim 1, wherein The conditions for the constant-voltage electrolysis reaction are: voltage is 2.1 - 2.5 V, temperature is 15 - 30 °C; time is 4 - 6 h.

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