Method for preparing sulfonyl compounds by electrolytic oxidation of sulfur-based compounds

Abstract

The present invention provides a method for preparing sulfonyl compounds by electrolytic oxidation of sulfur-based compounds, which is characterized in that a surfactant is added to the electrolytic system.

Description

Technical Field

[0001] The present invention relates to a method for preparing sulfonyl compounds by electrolytic oxidation of sulfur-based compounds, and more specifically, to a method for preparing 4-(methylsulfonyl)-2,3-dimethylbromobenzene by electrolytic oxidation of 4-(methylthio)-2,3-dimethylbromobenzene. Background Art

[0002] 4-(Methylsulfonyl)-2,3-dimethylbromobenzene is a key intermediate for the synthesis of the herbicide tembotrione, and its structural formula is as follows:

[0003]

[0004] 4-(Methylsulfonyl)-2,3-dimethylbromobenzene is usually obtained by oxidizing 4-(methylthio)-2,3-dimethylbromobenzene. The oxidation often uses a hydrogen peroxide / metal catalyst system. However, this oxidation system has problems such as low utilization rate of hydrogen peroxide, high energy consumption, difficult recovery of metal catalysts, and easy environmental pollution.

[0005] Sodium hypochlorite, as a cheap and strong oxidizing agent, can effectively oxidize thioethers to sulfoxides or sulfones without a catalyst. The Li Jia research group reported a method of using droplet chemistry to rapidly oxidize organic sulfides to sulfoxides with sodium hypochlorite at room temperature (The Journal of Organic Chemistry 2021 86(7), 5011-5015). Under the catalysis of chloroauric acid, sodium hypochlorite can oxidize sulfides to sulfoxides in an extremely short time. At the same time, a series of substrates were studied in this system, and the sulfoxide yields were at a medium to good level. There are the following problems in the oxidation of thioethers to sulfones by sodium hypochlorite in chemical methods: the sodium hypochlorite solution is unstable, and the available chlorine will drop significantly after long-term storage. At the same time, the waste salts after the reaction are difficult to treat.

[0006] The Cecilia Bottecchia research group prepared hypochlorous acid by an electrochemical method in an acetonitrile-water system and oxidized 4-methyl-2-(methylthio)pyrimidine to 4-methyl-2-(methylsulfonyl)pyrimidine with hypochlorous acid (Organic Process Research & Development 2022 26(8), 2423-2437). In this system, the yield of 4-methyl-2-(methylsulfonyl)pyrimidine can still reach more than 90% at the kilogram-scale reaction. The advantage of the above electrochemical method is that there is no need to add an oxidant to the reaction system. Effective chlorine can be obtained by electrolytic oxidation of chloride ions, and the generated effective chlorine oxidizes thioethers to sulfoxides or sulfones, realizing the in-situ production and use of the oxidant. The chloride ions in the solution can be recycled, avoiding the post-treatment problem of chlorides. Summary of the Invention

[0007] At present, the electrolysis systems in electrochemical synthesis methods mainly use mixed solvents of organic solvents and water, with a relatively high proportion of organic solvents. The extensive use of organic solvents can lead to problems such as high voltage in the electrolysis system and environmental pollution. At the same time, in order to increase the conductivity of the organic solvent-water system, special supporting electrolytes for organic systems such as perchlorates and tetrabutylammonium hexafluorophosphate need to be added to the reaction system. Perchlorates are prone to react when heated and collided, and are also somewhat harmful to the human body. Such electrolytes are relatively expensive and are not conducive to practical applications.

[0008] The present invention aims to provide a method for preparing sulfonyl compounds by electrolytic oxidation of sulfide compounds. More specifically, it provides a method for preparing 4-methylsulfonyl-2,3-dimethylbromobenzene by electrolytic oxidation of 4-methylthio-2,3-dimethylbromobenzene. Further specifically, it provides a method for preparing 4-methylsulfonyl-2,3-dimethylbromobenzene by electrolytic oxidation of 4-methylthio-2,3-dimethylbromobenzene in an aqueous phase system.

[0009] 4-Methylthio-2,3-dimethylbromobenzene is an oily substance that is poorly soluble in water at room temperature. Therefore, an organic solvent needs to be used as the reaction solvent. One of the technical problems to be solved by the present invention is how to reduce the amount of organic solvent used to avoid the above problem of adding a supporting electrolyte to the electrolysis system. The present invention promotes the dispersion and dissolution of 4-methylthio-2,3-dimethylbromobenzene, which is an oily organic substance, in the aqueous phase by adding a water-soluble surfactant to the electrolysis system, so that it can be electrolytically oxidized into 4-methylsulfonyl-2,3-dimethylbromobenzene in the aqueous phase system.

[0010] Specifically, the present invention relates to a method for preparing sulfonyl compounds by electrolytic oxidation of sulfide compounds, characterized in that a surfactant is added to the electrolysis system.

[0011] Preferably, the electrolytic oxidation reaction of the present invention is carried out in an aqueous phase system.

[0012] Compared with the traditional process of oxidizing thioether to sulfone, the present invention solves the problems of high energy consumption and serious environmental pollution, and provides an environmentally friendly, mild and efficient green process for oxidizing 4-methylthio-2,3-dimethylbromobenzene to prepare 4-methylsulfonyl-2,3-dimethylbromobenzene. Specific Embodiments

[0013] In some embodiments, in the electrolytic oxidation method of the present invention, the surfactant used is a quaternary ammonium salt surfactant. More specific examples include, but are not limited to, dodecyldimethylbenzylammonium chloride, dodecyltrimethylammonium chloride, etc. The amount of the surfactant can be 0.1-10% of the total mass of the reaction materials, preferably 0.5-5%, and more preferably 0.5-2.5%.

[0014] In some embodiments, an aqueous solution of a chloride salt catalyst is further added to the electrolysis system. Specific examples of the chloride salt catalyst include, but are not limited to, sodium chloride, potassium chloride, etc. Preferably, at the start of the reaction, the chloride salt concentration in the electrolysis system is 1 mol / L or less, preferably 0.1 mol / L or less, in terms of chloride ions.

[0015] In some embodiments, the method of the present invention is a method for preparing 4-(methylsulfonyl)-2,3-dimethylbromobenzene by electrooxidizing 4-(methylthio)-2,3-dimethylbromobenzene.

[0016] In some embodiments, the anode in the electrolysis system is a titanium-based lead dioxide electrode or a titanium-based ruthenium dioxide / iridium dioxide composite electrode, and the cathode is a stainless steel electrode, a nickel electrode, or a platinum electrode. Preferably, both the anode and the cathode are plate-shaped electrodes. The distance between the anode and cathode plates can be, for example, 1 to 4 cm.

[0017] In some embodiments, the electrooxidation reaction temperature is 10 to 60 °C, preferably 10 to 40 °C, and more preferably 20 °C.

[0018] In some embodiments, the current density during electrooxidation is 100 A / m 2 ~1000 A / m 2 and preferably 100 A / m 2 ~300 A / m 2 .

[0019] Examples

[0020] The method of the present invention will be described in detail below with reference to specific examples.

[0021] In the examples and comparative examples of this application, the high-performance liquid chromatography detection conditions are as follows:

[0022] Liquid phase test conditions: The mobile phase is acetonitrile: water = 4:1, and the pH is adjusted to 3.7 - 4.1 with formic acid; The chromatographic column uses a C18 column. The detection wavelength for 4-(methylthio)-2,3-dimethylbromobenzene is 254 nm, and the injection volume is 5 μL; The detection wavelength for 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 235 nm, and the injection volume is 5 μL.

[0023] Group 1: Investigation of surfactants

[0024] Example 1

[0025] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.3 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L aqueous NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 74%.

[0026] Example 2

[0027] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.9 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L aqueous NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 77.2%.

[0028] Example 3

[0029] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L aqueous NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol. Qualitative and quantitative analysis of the reaction solution is carried out using high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 84%.

[0030] Example 4

[0031] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 1.5 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and add 60 mL of 0.1 mol / L aqueous NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite as the anode and a plate-shaped stainless steel electrode as the cathode, and the distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol. Qualitative and quantitative analysis of the reaction solution is carried out using high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 81.1%.

[0032] Example 5

[0033] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 0.77 g of dodecyldimethylbenzylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and add 60 mL of 0.1 mol / L aqueous NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, and the distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol. Qualitative and quantitative analysis of the reaction solution is carried out using high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 79.5%.

[0034] Comparative Example 1

[0035] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene. Without adding a surfactant, add it to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 60 mL of 0.1 mol / L aqueous NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant-temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high-performance liquid chromatography to conduct qualitative and quantitative analysis of the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 2%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 0.24%.

[0036] Comparative Example 2

[0037] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1 g of sodium dodecylbenzenesulfonate, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 60 mL of 0.1 mol / L aqueous NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant-temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high-performance liquid chromatography to conduct qualitative and quantitative analysis of the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 71.3%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 18.1%.

[0038] Conclusion of the first group of investigations:

[0039] When no surfactant is added, yellow droplets adhere to the wall of the electrolytic cell after electrolysis. Initially, it is observed that the amount of raw material reacted is small. Through liquid-phase detection, it is confirmed that the reaction of the raw material is small and the product yield is also very low, indicating that the reaction effect of the oil-water two-phase is extremely poor without the action of a surfactant. Adding a surfactant can promote the dissolution and reaction of the raw material. The preferred dosage of the surfactant is 0.1-10% of the total mass of the reaction materials, preferably 0.5-5%, and more preferably 0.5-2.5%.

[0040] In addition, compared with sodium dodecylbenzenesulfonate, when using dodecyltrimethylammonium chloride or dodecyl dimethyl benzyl ammonium chloride as surfactants, the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is higher. The reason may be that these two surfactants have better emulsifying and reaction-promoting effects. At the same time, they are cationic surfactants and can avoid migrating to the anode under the attraction of the electric field and undergoing oxidation.

[0041] Group 2: Electrode investigation

[0042] Example 6

[0043] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L NaCl aqueous solution to it. Use a reticulated titanium-based ruthenium dioxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and then use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 78.7%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 4.49%.

[0044] Example 7

[0045] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L NaCl aqueous solution to it. Use a reticulated titanium-based lead dioxide electrode as the anode and a plate-shaped stainless steel electrode as the cathode. The distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 36.7%.

[0046] Example 8

[0047] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L aqueous NaCl solution to it. Use a reticulated titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 ². After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 66.1%.

[0048] Example 9

[0049] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L aqueous NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 ². After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 77.1%.

[0050] Conclusion of the second group of investigations:

[0051] The ruthenium-iridium-titanium composite electrode has a better chlorine evolution effect, generates more active chlorine, promotes electrolytic oxidation, and thus improves the yield. The yield is higher when the anode is a plate-shaped ruthenium-iridium-titanium electrode, probably because the plate shape is more conducive to preventing the adsorption of intermediates or products on the electrode and causing side reactions.

[0052] The third group: Investigation of chlorides

[0053] Example 10

[0054] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 60 mL of pure water thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to conduct qualitative and quantitative analysis of the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 80%.

[0055] Example 11

[0056] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 0.05 mol / L NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to conduct qualitative and quantitative analysis of the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 81.2%.

[0057] Example 12

[0058] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 0.2 mol / L NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2After the temperature of the reaction solution reaches the set temperature, turn on the power supply and perform electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol, and the reaction solution is qualitatively and quantitatively analyzed by high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 78.1%.

[0059] Example 13

[0060] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 0.25 mol / L NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m2. After the temperature of the reaction solution reaches the set temperature, turn on the power supply and perform electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol, and the reaction solution is qualitatively and quantitatively analyzed by high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 75.5%.

[0061] Example 14

[0062] Weigh 0.2 g (0.87 mmol) of 4-methylthio-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device, and then add 1 mol / L NaCl solution thereto. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 After the temperature of the reaction solution reaches the set temperature, turn on the power supply and perform electrolysis. The electrolysis reaction ends when the electricity consumption reaches 6 F / mol, and the reaction solution is qualitatively and quantitatively analyzed by high performance liquid chromatography. The results show that the conversion rate of 4-methylthio-2,3-dimethylbromobenzene is 100%, and the yield of 4-methylsulfonyl-2,3-dimethylbromobenzene is 74.5%.

[0063] Example 15

[0064] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L KCl aqueous solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, and the distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity consumption is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 78.7%.

[0065] Example 16

[0066] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 0.6 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 60 mL of 0.1 mol / L NH4Cl aqueous solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, and the distance between the anode and cathode plates is 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 30 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity consumption is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 84.7%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 36%.

[0067] Conclusion of the third group of investigations:

[0068] When using dodecyltrimethylammonium chloride or dodecyldimethylbenzylammonium chloride as the surfactant, it is also possible not to add a chloride salt as the catalyst because dodecyltrimethylammonium chloride or dodecyldimethylbenzylammonium chloride can ionize chloride ions.

[0069] When adding a chloride salt as the catalyst, the effects of potassium chloride and sodium chloride are equivalent, while the effect of ammonium chloride is relatively poor.

[0070] Increasing the chloride ion concentration within a certain range can effectively inhibit the occurrence of side reactions, thereby increasing the product yield. However, when the concentration of chloride salts exceeds a certain range, the product yield shows a downward trend instead. The reason may be that the faster the chlorine production rate, the more likely the active chlorine reacts with intermediate products or products to form by-products such as chlorosulfone or chlorosulfoxide. Excess hypochlorous acid will also react with the product, resulting in a decrease in the product yield.

[0071] Group 4: Investigation of reaction temperature

[0072] Example 17

[0073] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 0.1 mol / L NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 10 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity consumption reaches 6 F / mol, and use high-performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 77.3%.

[0074] Example 18

[0075] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 0.1 mol / L NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 20 °C, and set the electrolysis current density to 200 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity consumption reaches 6 F / mol, and use high-performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 90.7%.

[0076] Example 19

[0077] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 0.1 mol / L NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, and keep the reaction temperature constant at 40 °C. Set the electrolysis current density to 200 A / m 2 ². After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 79.1%.

[0078] Conclusion of the fourth group of investigations:

[0079] As the reaction temperature rises from 20 °C to 40 °C, the product yield shows a downward trend. The reason may be that as the reaction temperature increases, the solubility of chlorine in water decreases, and the amount of chlorine gas overflowing from the solution increases. At the same time, as the temperature rises, hypochlorous acid will further react to form chloric acid.

[0080] Fifth group: Investigation of current density

[0081] Example 20

[0082] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 0.1 mol / L NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, and keep the reaction temperature constant at 20 °C. Set the electrolysis current density to 100 A / m 2 ². After the temperature of the reaction solution reaches the set temperature, turn on the power supply and carry out electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to qualitatively and quantitatively analyze the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 81.8%.

[0083] Example 21

[0084] Weigh 0.2 g (0.87 mmol) of 4-(methylthio)-2,3-dimethylbromobenzene and 1.2 g of dodecyltrimethylammonium chloride, and add them to a 100 mL single-chamber electrolytic cell equipped with a stirring device. Then add 0.1 mol / L NaCl solution to it. Use a plate-shaped titanium-based ruthenium dioxide / iridium dioxide composite electrode as the anode and a plate-shaped stainless steel electrode as the cathode, with the distance between the anode and cathode plates being 3 cm. Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature constant at 20 °C, and set the electrolysis current density to 300 A / m 2 . After the temperature of the reaction solution reaches the set temperature, turn on the power supply and conduct electrolysis. End the electrolysis reaction when the electricity passed is 6 F / mol, and use high performance liquid chromatography to conduct qualitative and quantitative analysis of the reaction solution. The results show that the conversion rate of 4-(methylthio)-2,3-dimethylbromobenzene is 100%, and the yield of 4-(methylsulfonyl)-2,3-dimethylbromobenzene is 82.5%.

[0085] Conclusion of the fifth group of investigations:

[0086] As can be seen from Examples 18, 20, and 21, when the current density is 200 A / m 2 , the yield of the product 4-(methylsulfonyl)-2,3-dimethylbromobenzene is the highest.

Claims

1. A method for preparing 4-(methylsulfonyl)-2,3-dimethylbromobenzene by electrooxidizing 4-(methylthio)-2,3-dimethylbromobenzene, characterized in that, A quaternary ammonium salt surfactant is added to the electrolysis system, and the electrolytic oxidation is carried out in an aqueous phase system. The quaternary ammonium salt surfactant is one or two selected from dodecyldimethylbenzylammonium chloride and dodecyltrimethylammonium chloride.

2. The method according to claim 1, wherein the dosage of the surfactant is 0.5-5% of the total mass of the reaction materials.

3. The method according to claim 2, wherein the dosage of the surfactant is 0.5-2.5% of the total mass of the reaction materials.

4. The method according to any one of claims 1 to 3, wherein an aqueous solution of a chloride salt catalyst is further added to the electrolysis system.

5. The method according to claim 4, wherein the chloride salt catalyst is sodium chloride or potassium chloride.

6. The method according to claim 5, wherein the chloride salt concentration in the electrolysis system is 1 mol / L or less in terms of chloride ions.

7. The method according to claim 6, wherein the chloride salt concentration in the electrolysis system is 0.1 mol / L or less in terms of chloride ions.

8. The method according to any one of claims 1 to 3, wherein the anode is a titanium-based lead dioxide electrode or a titanium-based ruthenium dioxide / iridium dioxide composite electrode, and the cathode is a stainless steel electrode, a nickel electrode, or a platinum electrode.

9. The method according to any one of claims 1 to 3, wherein both the anode and the cathode are plate-shaped electrodes.

10. The method according to any one of claims 1 to 3, wherein the distance between the anode and cathode plates is 1-4 cm.

11. The method according to any one of claims 1 to 3, wherein the reaction temperature is 10-40 °C.

12. The method according to claim 11, wherein the reaction temperature is 20 °C.

13. The method according to any one of claims 1 to 3, wherein the current density is 100 A / m 2 to 300 A / m 2 .

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