Process for the preparation of sulfonyl compounds by oxidation of sulfenyl compounds in an acidic electrolytic system

Abstract

The present invention provides a method for preparing a sulfonyl compound by oxidizing a sulfenyl compound in an acidic electrolytic system, characterized in that the acidic electrolytic system is an acidic aqueous solution added to 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, typically obtained by oxidizing sulfur-based compounds. They can be used to prepare HPPD inhibitor herbicides such as fenpyrazone, tembotrione, and bispyribac. Chemical methods using hydrogen peroxide as an oxidant present safety concerns, limiting their widespread industrial application. Electrochemical methods, however, utilize a continuous supply of electrons from both the cathode and anode, acting as green redox agents. This avoids the challenges of chemical methods and poses no environmental risks.

[0003] The Dávila team reported a method for the electrochemical oxidation of thiophenes in an acetonitrile-water solution to synthesize sulfones (Journal of Electroanalytical Chemistry, 2019, 847:113172). The experiment used dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as substrates. The results showed that the electrochemical selective oxidation at the BDD anode to the corresponding sulfoxide or sulfone depends on the applied potential during electrolysis, the water content of the reaction medium, and the concentration of the sulfur compound.

[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 in an 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 an Fe electrode as the cathode, and a catalytic amount of Bu4NBF4 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 composed of a mixed solution of organic solvent and water, and the proportion of organic solvent is high. Sulfur-based compounds are oily organic substances that require the use of organic solvents for dissolution and dispersion. On the one hand, the inventors of this 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 was promoted to a certain extent, and the obtained product yield was 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 a method of adding an acidic aqueous solution to an organic solvent.

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

[0009]

[0010] Wherein, 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 of the thio group.

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

[0017]

[0018]

[0019] (5) The preparation method according to any one of (1) to (4) above, 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 (1) to (5) above 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) The method according to any one of (1) to (8) above, 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.

[0024] (10) The 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 sulfides to sulfones, 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 to prepare a sulfonyl compound by oxidizing a sulfur-based compound in an acidic electrolytic system. Specifically, the sulfur-based compound represented by Formula I is electrolytically oxidized in an acidic system to produce the sulfonyl compound represented by Formula II.

[0027]

[0028] Wherein, 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 of 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] wherein 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, with acetonitrile being a more specific example. The amount of organic solvent used can range from 30% to 70%, preferably 40% to 60%, of the total volume of the electrolytic system. If the amount of organic solvent used is too low, it may hinder the dissolution of the raw materials, thereby affecting the reaction rate; if the amount is too high, it may cause environmental pollution.

[0040] In some 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, aqueous sulfuric acid, aqueous hydrochloric acid, or aqueous nitric acid. 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, calculated as hydrogen ions. A low hydrogen ion concentration exacerbates the oxygen evolution side reaction, thereby reducing the selectivity of the target reaction; an excessively high hydrogen ion concentration increases the reaction cost and does not improve the reaction yield.

[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 reaction and cause excessive oxidation.

[0042] In some specific embodiments, the reaction temperature of the electrolytic oxidation is 5-55° C., preferably 20-40° 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 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, or a platinum electrode, preferably a manganese oxide electrode. 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. An appropriate distance between the plates can promote the mass transfer efficiency of the reactants to the electrode surface and increase the reaction rate. A distance greater than 6 cm will increase the 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 this 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 to pH 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 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of ethanol and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 77.5%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 18.8%.

[0053] Example 2

[0054] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of dichloromethane and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 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 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 50 mL of acetonitrile and 70 mL of 1.0 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 1.2%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 76.7%.

[0062] Example 5

[0063] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 60 mL of acetonitrile and 60 mL of 1.2 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 4.0%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 86.6%.

[0064] Example 6

[0065] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 80 mL of acetonitrile and 40 mL of 1.8 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 5.8%, 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 reaction yield.

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

[0069] Group 3: Investigation of sulfuric acid concentration

[0070] Example 7

[0071] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 60 mL of acetonitrile and 60 mL of 0.2 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 34.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 57.9%.

[0072] Example 8

[0073] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 60 mL of acetonitrile and 60 mL of 0.6 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 8.3%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.1%.

[0074] Example 9

[0075] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 60 mL of acetonitrile and 60 mL of 1.0 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 5.6%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.2%.

[0076] Example 10

[0077] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 60 mL of acetonitrile and 60 mL of 1.6 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 2.2%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 83.0%.

[0078] Conclusions of the third group of investigations:

[0079] The results of Examples 5 and 7-10 show that increasing the hydrogen ion concentration within a certain range can inhibit the occurrence of the oxygen evolution side reaction, promote the conversion of the intermediate 4-methylsulfinyl-2,3-dimethylbromobenzene to the product, and improve the yield. When the hydrogen ion concentration exceeds a certain range, the product yield decreases. This may be because the accumulation 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 resulting in a decrease in product yield.

[0080] Group 4: Investigation of current density

[0081] Example 11

[0082] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set to 100 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 20.1%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 75.6%.

[0083] Example 12

[0084] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set to 150 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 9.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 77.8%.

[0085] Example 13

[0086] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set at 250 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 4.3%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 82.5%.

[0087] Example 14

[0088] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 20 ° C, and the electrolysis current density is set to 300 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 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] Example 15

[0093] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 5 ° C, and the electrolysis current density is set to 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 8.5%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 84.4%.

[0094] Example 16

[0095] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 40 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 8.9%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene was 85.5%.

[0096] Example 17

[0097] Weigh 2.0 g (8.7 mmol) of 4-methylthio-2,3-dimethylbromobenzene and add it to a 150 mL single-chamber electrolytic cell. Add 70 mL of acetonitrile and 50 mL of 1.44 mol / 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 5 cm. The reaction temperature is kept constant at 55 ° C, and the electrolysis current density is set at 200 A / m 2 The power supply was turned on to conduct electrolysis. The electrolysis reaction was terminated when the current reached 5 F / 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 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 electrolysis system, characterized in that: The sulfonyl compound represented by formula I is electrolytically oxidized in an acidic system to generate the sulfonyl compound represented by formula II. Wherein, 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; R3 is located at the ortho, meta or para position of the thio group; The acidic electrolysis system is to add an acidic aqueous solution into an organic solvent; The organic solvent is dichloromethane or acetonitrile; Current density is 100A / m 2 ~300A / m 2 .

2. The method according to claim 1, characterized in that R3 is Br.

3. The 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 method according to claim 1 or 2, characterized in that in, The reaction of electrolytic oxidation of the sulfonyl compound to generate the sulfonyl compound in an acidic system is:

5. The method according to claim 1 or 2, characterized in that The organic solvent is acetonitrile, and the amount of the organic solvent used is 30-70% of the total volume of the electrolysis system.

6. The method according to claim 5, characterized in that The amount of organic solvent used is 40-60% of the total volume of the electrolysis system.

7. The method according to claim 1 or 2, characterized in that The acidic aqueous solution is a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution or a nitric acid aqueous solution.

8. The method according to claim 1 or 2, wherein the reaction temperature is 5 to 55°C.

9. The method according to claim 8, wherein the reaction temperature is 20-40°C.

10. The method according to claim 1 or 2, 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.

11. The method according to claim 1 or 2, wherein the distance between the anode and cathode plates is 1 cm to 6 cm.

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