Method for preparing sulfonyl compound by oxidizing sulfenyl compound in acidic electrolysis system

Abstract

The invention provides a method for preparing a sulfonyl compound by oxidizing a sulfur-based compound in an acidic electrolysis system, which is characterized in that the acidic electrolysis system is formed by adding an acidic aqueous solution into an organic solvent.

Description

Technical Field

[0001] The present invention relates to a method for preparing a sulfonyl compound by oxidizing a sulfur-based compound in an acidic electrolysis system. Background Art

[0002] Sulfonyl compounds are key intermediates in the synthesis of pesticides. They are usually obtained by oxidation of sulfur-based compounds and can be used to prepare HPPD inhibitor herbicides such as benzathine, cypermethrin and bispyribac. The use of hydrogen peroxide as an oxidant in the chemical method has certain safety issues, which limits its wide application in industry. The positive and negative electrodes of the electrochemical method can continuously provide electrons as a green redox agent, which can avoid the problems existing in the chemical method and will not pollute the environment.

[0003] Dávila's research group reported a method for synthesizing sulfones by electrochemical oxidation of thiophene compounds in acetonitrile-water mixed solutions (Journal of Electroanalytical Chemistry, 2019, 847: 113172). The experiment used dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as research substrates. The experimental results show that the electrochemical selective oxidation on the BDD anode to generate the corresponding sulfoxide or sulfone depends on the applied potential during the electrolysis of the system, the water content of the reaction medium and the concentration of sulfur compounds.

[0004] The Amri research group has developed a flow reactor device for the electrochemical synthesis of sulfoxides, sulfones and sulfoximines without the addition of electrolytes. The process uses anisole as the research substrate and reacts under the condition of acetonitrile and water volume ratio of 9:1 (The Journal of Organic Chemistry, 2021, 86(22): 15961-15972). With a Pt electrode as the anode and a Fe electrode as the cathode, a catalytic amount of Bu4NBF4 is added. When the current is 6F / mol, the conversion rate of anisole is 98% and the yield of anisole is 87%. Summary of the invention

[0005] In the existing electrochemical synthesis methods, the electrolysis system is mostly a mixed solution of organic solvent-water, and the proportion of organic solvent is high. Sulfur-based compounds are an oily organic substance that requires the use of organic solvents for dissolution and dispersion. On the one hand, the inventors of the present application screened suitable organic solvents to reduce the amount of organic solvents used; on the other hand, they tried to add an acidic aqueous solution to the electrolysis system and found that it not only enhanced the conductivity of the electrolysis system, but also reduced the occurrence of oxygen evolution side reactions. By controlling the concentration of acid in the electrolyte, the conversion of the intermediate sulfinyl compound to the sulfonyl compound is promoted to a certain extent, and the product yield obtained is higher.

[0006] Specifically, the present invention relates to:

[0007] (1) A method for preparing a sulfonyl compound by oxidizing a sulfur-based compound in an acidic electrolytic system, characterized in that the acidic electrolytic system is an organic solvent in which an acidic aqueous solution is added.

[0008] (2) The preparation method described in (1) above, wherein the sulfide compound represented by formula I is electrolytically oxidized in an acidic system to produce the sulfonyl compound represented by formula II,

[0009]

[0010] In the formula, R1 is H, halogen, C 1-6 Alkyl or halogenated C 1-6 alkyl;

[0011] R2 is H or C 1-6 alkyl;

[0012] R3 is halogen, preferably Br;

[0013] R3 is located at the ortho, meta or para position to the thio group.

[0014] (3) The preparation method according to (1) or (2) above, characterized in that the electrolytic oxidation of the sulfide compound to generate the sulfonyl compound in an acidic system is the following reaction:

[0015]

[0016] (4) The preparation method according to any one of (1) to (3) above, characterized in that the reaction of electrolytic oxidation of the sulfide compound to generate the sulfonyl compound in an acidic system is:

[0017]

[0018]

[0019] (5) The preparation method according to any one of (1) to (4) above is characterized in that the organic solvent is dichloromethane, dimethylacetamide, ethanol or acetonitrile, preferably acetonitrile, and further preferably, the amount of the organic solvent is 30-70% of the total volume of the electrolysis system, more preferably 40-60%.

[0020] (6) The preparation method according to any one of the above (1) to (5) is characterized in that the acidic aqueous solution is an inorganic acid aqueous solution, preferably an aqueous sulfuric acid solution, an aqueous hydrochloric acid solution or an aqueous nitric acid solution, and further preferably the concentration of the acidic aqueous solution is 0.1 to 1.5 mol / L in terms of hydrogen ions, and more preferably 0.6 to 1.2 mol / L.

[0021] (7) The method according to any one of (1) to (6) above, wherein the current density is 50 A / m 2 ~500A / m 2 , preferably 100A / m 2 ~300A / m 2 .

[0022] (8) The method according to any one of (1) to (7) above, wherein the reaction temperature is 5 to 55°C, preferably 20 to 40°C.

[0023] (9) According to the method described in any one of (1) to (8) above, the anode is one selected from graphite, titanium, lead, ruthenium oxide, manganese oxide, lead dioxide, and platinum, and the cathode is one selected from platinum, nickel, stainless steel, and lead.

[0024] (10) A method according to any one of (1) to (9) above, wherein the distance between the anode and cathode plates is 1 cm to 6 cm.

[0025] Compared with the traditional process of oxidizing thioether to sulfone, the present invention provides a green process for oxidizing sulfur-based compounds to prepare sulfonyl compounds, which is simple to operate, low in reaction cost, mild and efficient. DETAILED DESCRIPTION

[0026] The method of the present invention can be used for preparing a sulfonyl compound by oxidizing a sulfonyl compound in an acidic electrolytic system. Specifically, the sulfonyl compound represented by formula I is electrolytically oxidized in an acidic system to generate a sulfonyl compound represented by formula II.

[0027]

[0028] In the formula, R1 is H, halogen, C 1-6 Alkyl or halogenated C 1-6 alkyl;

[0029] R2 is H or C 1-6 alkyl;

[0030] R3 is halogen, preferably Br;

[0031] R3 is located at the ortho, meta or para position to the thio group.

[0032] In a specific embodiment, R1 is H, Cl, methyl or trifluoromethyl.

[0033] In a specific embodiment, R2 is H or CH3.

[0034] In a specific embodiment, the preparation method of the present invention is used for the following reaction,

[0035]

[0036] In the formula, R1 and R2 are as defined above.

[0037] In a specific embodiment, the preparation method of the present invention includes but is not limited to the following reaction:

[0038]

[0039] In the electrolytic oxidation method of the present invention, specific examples of organic solvents include but are not limited to dichloromethane, dimethylacetamide, ethanol or acetonitrile, and a more specific example is acetonitrile. The amount of organic solvent used can be 30-70%, preferably 40-60% of the total volume of the electrolytic system. When the amount of organic solvent used is too low, it is not conducive to the dissolution of the raw materials, thereby affecting the reaction rate; when the amount is too high, it will cause pollution to the environment.

[0040] In some specific embodiments, the added acidic aqueous solution is an inorganic acid aqueous solution. Specific examples of inorganic acid aqueous solutions include, but are not limited to, sulfuric acid aqueous solution, hydrochloric acid aqueous solution or nitric acid aqueous solution. Preferably, at the start of the reaction, the concentration of the acidic aqueous solution in the electrolysis system is 0.1 to 1.5 mol / L, more preferably 0.6 to 1.2 mol / L, in terms of hydrogen ions. A low hydrogen ion concentration will aggravate the occurrence of the oxygen evolution side reaction, thereby reducing the selectivity of the target reaction; a high hydrogen ion concentration will increase the reaction cost, and the reaction yield will not increase.

[0041] In some embodiments, the current density during electrolytic oxidation is 50 A / m 2 ~500A / m 2 , preferably 100A / m 2 ~300A / m 2 A low current density will increase the reaction time, while a high current density will aggravate the side reactions and cause excessive oxidation.

[0042] In some specific embodiments, the reaction temperature of the electrolytic oxidation is 5 to 55° C., preferably 20 to 40° C. Low temperature affects the diffusion rate of reactants in the electrolytic system, while too high a temperature may lead to the occurrence of side reactions such as excessive oxidation.

[0043] In some specific embodiments, the anode of the electrolysis system is a graphite electrode, a titanium electrode, a lead electrode, a ruthenium oxide electrode, a manganese oxide electrode, a lead dioxide electrode, a platinum electrode, preferably a manganese oxide electrode, and the cathode is a platinum electrode, a nickel electrode, a stainless steel electrode, or a lead electrode, preferably a stainless steel electrode.

[0044] The distance between the anode and cathode plates can be, for example, 1 cm to 6 cm. Appropriate plate spacing can promote the mass transfer efficiency of reactants to the electrode surface and increase the reaction rate. A plate spacing greater than 6 cm will increase resistance and thus increase energy consumption.

[0045] Example

[0046] The method of the present invention is described in detail below with reference to specific embodiments.

[0047] In the examples of the present application, the HPLC detection conditions are as follows:

[0048] Liquid phase test conditions: the mobile phase was acetonitrile: water = 7:3 (V:V, formic acid adjusted the pH to 3.7-4.1); the chromatographic column was a C18 column, the detection wavelength for 4-methylthio-2,3-dimethylbromobenzene was 254 nm, and the injection volume was 5 μL; the detection wavelength for 4-methylsulfinyl-2,3-dimethylbromobenzene and 4-methylsulfonyl-2,3-dimethylbromobenzene was 235 nm, and the injection volume was 5 μL.

[0049]

[0050] Group 1: Investigation of solvents

[0051] Example 1

[0052] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of ethanol and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 77.5%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 18.8%.

[0053] Example 2

[0054] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2. Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current flow reached 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed using high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 5.7%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 91.7%.

[0055] Example 3

[0056] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of dichloromethane and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 33.6%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 62.9%.

[0057] Conclusions of the first group of investigations:

[0058] From the results, it can be seen that when acetonitrile is used as the solvent, the yield of the product 4-methylsulfonyl-2,3-dimethylbromobenzene is the highest.

[0059] Group 2: Investigation of acetonitrile volume

[0060] Example 4

[0061] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 50mL of acetonitrile and 70mL of 1.0mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current flow reached 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 1.2%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 76.7%.

[0062] Example 5

[0063] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 60mL of acetonitrile and 60mL of 1.2mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 4.0%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 86.6%.

[0064] Example 6

[0065] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 80mL of acetonitrile and 40mL of 1.8mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 5.8%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 90.0%.

[0066] Conclusions of the second group of investigations:

[0067] From the results of Example 2, Example 4, Example 5 and Example 6, it can be seen that as the volume of acetonitrile increases, the solubility of 4-methylthio-2,3-dimethylbromobenzene in the electrolysis system increases, thereby accelerating its diffusion rate from the electrolysis system to the electrode surface and improving the yield of the reaction.

[0068] When the volume of acetonitrile exceeded a certain level, the yield of the product showed a slightly decreasing trend, which may be caused by excessive oxidation.

[0069] Group 3: Investigation of sulfuric acid concentration

[0070] Example 7

[0071] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 60mL of acetonitrile and 60mL of 0.2mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 34.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 57.9%.

[0072] Example 8

[0073] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 60mL of acetonitrile and 60mL of 0.6mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 8.3%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.1%.

[0074] Example 9

[0075] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 60mL of acetonitrile and 60mL of 1.0mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 5.6%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.2%.

[0076] Example 10

[0077] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 60mL of acetonitrile and 60mL of 1.6mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 2.2%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 83.0%.

[0078] Conclusions of the third group of investigations:

[0079] From the results of Examples 5 and 7-10, it can be seen that increasing the concentration of hydrogen ions within a certain range can inhibit the occurrence of oxygen evolution side reactions, promote the conversion of the intermediate 4-methylsulfinyl-2,3-dimethylbromobenzene to products, and improve the yield. When the hydrogen ion concentration exceeds a certain range, the product yield decreases instead, which may be because the aggregation of anions on the anode surface affects the adsorption of 4-methylthio-2,3-dimethylbromobenzene and 4-methylsulfinyl-2,3-dimethylbromobenzene on the electrode surface, thereby causing a decrease in the product yield.

[0080] Group 4: Investigation of current density

[0081] Embodiment 11

[0082] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 100A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 20.1%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 75.6%.

[0083] Example 12

[0084] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 150A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 9.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 77.8%.

[0085] Example 13

[0086] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 250A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 4.3%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 82.5%.

[0087] Embodiment 14

[0088] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 20℃ and set the electrolysis current density at 300A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 4.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 84.3%.

[0089] Conclusions of the fourth group of investigation:

[0090] From Example 2 and Examples 11-14, it can be seen that when the current density is 200A / m 2 When , the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was the highest.

[0091] Group 5: Investigation of reaction temperature

[0092] Embodiment 15

[0093] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 5℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current flow reached 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 8.5%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 84.4%.

[0094] Example 16

[0095] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 40℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current flow reached 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 8.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.5%.

[0096] Embodiment 17

[0097] Weigh 2.0g (8.7mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150mL single-chamber electrolytic cell. Add 70mL of acetonitrile and 50mL of 1.44mol / L H2SO4 aqueous solution. Use a manganese oxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 5cm. Keep the reaction temperature at 55℃ and set the electrolysis current density at 200A / m 2 . Turn on the power supply to perform electrolysis. The electrolysis reaction was terminated when the current was 5F / mol, and the reaction solution was qualitatively and quantitatively analyzed by high performance liquid chromatography. The results showed that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene was 100%, the yield of 4-methylsulfinyl-2,3-dimethylbromobenzene was 14.6%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 80.8%.

[0098] Conclusions of the fifth group of investigation:

[0099] From the results of Example 2 and Examples 15-17, it can be seen that the reaction temperature is preferably below 40°C.

Claims

1. A method for preparing a sulfonyl compound by oxidizing a sulfur-based compound in an acidic electrolytic system, characterized in that: The acidic electrolysis system is prepared by adding an acidic aqueous solution into an organic solvent.

2. The preparation method according to claim 1, wherein The sulfonyl compound represented by formula I is electrolytically oxidized in an acidic system to generate the sulfonyl compound represented by formula II. In the formula, R1 is H, halogen, C 1-6 Alkyl or halogenated C 1-6 alkyl; R2 is H or C 1-6 alkyl; R3 is halogen, preferably Br; R3 is located at the ortho, meta or para position to the thio group.

3. The preparation method according to claim 1 or 2, characterized in that: in, The electrolytic oxidation of the sulfonyl compound in an acidic system to generate a sulfonyl compound is as follows: wherein R1 and R2 are as defined in claim 1.

4. The preparation method according to any one of claims 1 to 3, characterized in that: in, The reaction of electrolytic oxidation of the sulfonyl compound in an acidic system to generate a sulfonyl compound is:

5. The preparation method according to any one of claims 1 to 4, characterized in that: The organic solvent is dichloromethane, dimethylacetamide, ethanol or acetonitrile, preferably acetonitrile, and more preferably the amount of the organic solvent is 30-70% of the total volume of the electrolysis system, more preferably 40-60%.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The acidic aqueous solution is an inorganic acid aqueous solution, preferably a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution or a nitric acid aqueous solution, and more preferably the acidic aqueous solution has a concentration of 0.1 to 1.5 mol / L in terms of hydrogen ions, and more preferably 0.6 to 1.2 mol / L.

7. The method according to any one of claims 1 to 6, wherein the current density is 50 A / m 2 ~500A / m 2 , preferably 100A / m 2 ~300A / m 2 .

8. The method according to any one of claims 1 to 7, wherein the reaction temperature is 5 to 55°C, preferably 20 to 40°C.

9. The method according to any one of claims 1 to 8, wherein the anode is one selected from graphite, titanium, lead, ruthenium oxide, manganese oxide, lead dioxide, and platinum, and the cathode is one selected from platinum, nickel, stainless steel, and lead.

10. The method according to any one of claims 1 to 9, wherein the distance between the cathode and anode plates is 1 cm to 6 cm.

Images