Method for synthesizing dimethyl sulfoxide by taking dimethyl sulfide as raw material through electrooxidation

Abstract

The invention relates to a method for synthesizing DMSO (Dimethylsulfoxide) through electrooxidation of DMS (Dimethylsulfoxide), and belongs to the technical field of electrochemical synthesis. The method comprises the following steps: forming a two-phase electrolyte system by an organic solvent such as methylbenzene and dichloromethane and an acid aqueous solution such as sulfuric acid and methanesulfonic acid; pretreating the electrode; in a diaphragm-free electrolytic cell at the temperature of 5-35 DEG C, dimethyl sulfide, a cerium salt catalyst and a heteropolyacid cocatalyst are added into an electrolyte, and constant-current electrolytic oxidation is carried out at the current density of 50-500 mA / cm < 2 >; and separating liquid after reaction, drying an organic phase, recovering the solvent by atmospheric distillation, and collecting specific fractions by reduced pressure distillation to obtain the product. The reaction can be completed within 2-5 h, and the yield of dimethyl sulfoxide reaches 99.2%. According to the invention, Ce < 3 + > / Ce < 4 + > and heteropoly acid are driven by electric energy to form catalytic circulation, so that traditional hazardous oxidants such as nitric acid are completely abandoned, and NOx pollution is completely eradicated from the source. The method disclosed by the invention is simple and convenient to operate, mild in reaction condition, recyclable in electrolyte, high in selectivity and product yield and remarkable in industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical synthesis technology, specifically relating to a method for the electro-oxidation synthesis of dimethyl sulfoxide using dimethyl sulfide as a raw material. Background Technology

[0002] Dimethyl sulfoxide (DMSO), an important aprotic polar solvent and organic synthesis intermediate, has wide applications in pharmaceuticals, pesticides, petrochemicals, and electronics. Currently, the mainstream industrial methods for synthesizing DMSO, such as the nitric acid oxidation method and the nitrogen dioxide oxidation method, generally rely on highly corrosive and toxic strong oxidants. These methods not only require harsh reaction conditions and large equipment investments, but also generate large amounts of nitrogen oxides (NOx) during the production process. x The production of hydrogen peroxide and acidic wastewater leads to serious environmental pollution problems. For example, the hydrogen peroxide oxidation method involves expensive hydrogen peroxide, resulting in high production costs, and hydrogen peroxide requires high standards for production equipment and transportation safety. Another example is the dimethyl sulfate method, which generates large amounts of wastewater and waste gas, placing significant pressure on environmental protection; dimethyl sulfate is also highly toxic, posing safety hazards.

[0003] Therefore, it is necessary to invent a highly efficient method for synthesizing dimethyl sulfoxide that is safe and environmentally friendly, addressing the shortcomings of the above methods. Summary of the Invention

[0004] Based on the existing dimethyl sulfoxide production processes and their various drawbacks described in the background art, this invention provides a new environmentally friendly, efficient, and economical route for the synthesis of dimethyl sulfoxide. The method utilizes electrical energy as the driving force for electrochemical synthesis, supplemented by cerium salt catalysts and heteropolyacid co-catalysts. Under the action of the catalysts, an electro-oxidation reaction is carried out, thereby obtaining a high-yield dimethyl sulfoxide product.

[0005] The principle of this invention is mainly based on the reaction of dimethyl sulfide with Ce under the co-catalysis of heteropolyacids. 4+ Catalyst oxidizes to dimethyl sulfoxide, Ce 4+ The catalyst itself is reduced to Ce during the oxidation of dimethyl sulfide. 3+ This reduced Ce 3+ It is oxidized back to Ce on the anode surface. 4+ This forms a continuous redox cycle. Based on this principle, the present invention explored a series of reaction conditions, resulting in the following technical solution, thereby obtaining a method for synthesizing dimethyl sulfoxide with mild reaction conditions, high yield, and environmental friendliness. The specific steps are as follows: (1) Preparation of two-phase electrolyte system: Dissolve at least one electrolyte in deionized water, cool it and add an organic solvent that is immiscible with water to form a two-phase electrolyte system in which the aqueous phase and the organic phase coexist. (2) Electrode pretreatment: The anode and cathode are cleaned with detergent and deionized water in sequence. After surface cleaning, they are ultrasonically soaked in 0.5~1.5 mol / L hydrochloric acid solution for 10~20 min, and then washed with deionized water and anhydrous ethanol and dried. (3) Electrochemical oxidation reaction: The two-phase electrolyte system obtained in (1), raw material dimethyl sulfide, cerium salt catalyst and heteropoly acid co-catalyst are added to the diaphragmless electrolytic cell. The diaphragmless electrolytic cell is placed in a constant temperature water bath with magnetic stirring function. Stirring is carried out at constant temperature. Then, DC current is passed into the electrolytic cell to carry out constant current electrolytic oxidation reaction. (4) Product separation and purification: The reaction mixture obtained in (3) was allowed to stand and separate into layers. The aqueous phase was extracted with an organic solvent, and the organic phases were combined after separation. After drying with a desiccant, the organic solvent in the reaction mixture was first recovered by atmospheric distillation, and then the fraction at 75~77℃ was collected by vacuum distillation at a vacuum degree of 1.6 kPa.

[0006] Preferably, the electrolyte in (1) is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, nitric acid, acetic acid, and oxalic acid, and its concentration is 1~3 mol / L; The organic solvent is at least one of dichloromethane, chloroform, dichloroethane, ethyl acetate, butyl acetate, cyclohexane, n-hexane, methylcyclohexane, benzene, toluene, and xylene, and the volume ratio of the organic solvent to the acid solution is 1:1 to 1:2.

[0007] Preferably, in (2), the anode working electrode is selected from one of the following: platinum sheet electrode, titanium platinum-plated electrode, graphite electrode, DSA electrode (i.e., titanium-based iridium-tantalum coated electrode), lead dioxide electrode, and lead electrode; The cathode is selected from one of the following: lead electrode, platinum sheet electrode, stainless steel electrode, titanium electrode, titanium-plated platinum electrode, or conductive glass electrode.

[0008] Preferably, in (3), the amount of dimethyl sulfide used is 1% to 30% of the electrolyte mass; The catalyst is a cerium salt, selected from at least one of cerium methanesulfonate, cerium sulfate, cerium nitrate, cerium acetate, and cerium phosphate, and its amount is 5% to 15% of the electrolyte mass; The heteropolyacid cocatalyst is selected from at least one of phosphomolybdenum-vanadium heteropolyacid, phosphotungsten heteropolyacid, and phosphomolybdenum heteropolyacid, and its amount is 1% to 5% of the electrolyte mass.

[0009] Preferably, in (3), the temperature of the electrochemical oxidation reaction is 5℃~35℃; the current density of electrolysis is 50~500 mA / cm. 2 .

[0010] Preferably, the aqueous phase of the electrolyte separated in (4) can be recycled after separation and extraction; the organic phase of the electrolyte can be recycled by atmospheric distillation. During drying, the desiccant used is selected from at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate, or molecular sieve.

[0011] Compared with the prior art, the present invention has the following significant advantages: (1) Mild reaction conditions The reaction can be carried out at room temperature and pressure, without the need for high temperature and high pressure equipment, which significantly reduces energy consumption and the stringent requirements for reaction equipment, equipment investment and operational risks, and greatly improves operational safety. (2) It is environmentally friendly and enables the recycling of solvents. The electro-oxidation technique is employed to drive the cerium salt catalyst (Ce) with electrical energy. 3+ / Ce 4+ A cyclic catalytic system composed of a catalytic converter and a heteropolyacid co-catalyst replaces the highly corrosive and toxic chemical oxidants such as nitric acid or nitrogen dioxide used in traditional methods, eliminating the production of nitrogen oxides (NOx). x It reduces the generation of harmful gases such as ions and large amounts of acidic wastewater, achieving emission reduction at the source and demonstrating excellent environmental friendliness.

[0012] Furthermore, the aqueous phase of the electrolyte and the organic solvent after the reaction can be recovered and recycled, reducing waste emissions and production costs. The aqueous phase after the reaction can be treated and its concentration adjusted before recycling, and the recovered organic solvent can also be recovered and reused through atmospheric distillation. This internal material circulation mode greatly reduces the consumption of fresh electrolyte and organic solvent, while reducing the load and cost of waste treatment, making the entire process more economically competitive. At the same time, the reaction adopts a diaphragm-free electrolytic cell, which simplifies the structure of the electrolytic cell and significantly reduces equipment investment and maintenance costs.

[0013] (3) High security The electro-oxidation reaction is carried out at room temperature or low temperature (5~35℃), avoiding the safety hazards caused by high temperature and high pressure, and significantly reducing the operational risks. (4) The reaction is highly efficient and rapid. By optimizing electrode materials, catalytic systems, and current densities, the reaction can be completed efficiently within 2–5 hours. (5) High yield The yield of dimethyl sulfoxide can reach over 98.5%; this is due to the synergistic effect of the cerium salt catalyst and the heteropolyacid co-catalyst, which improves the current efficiency and reaction rate. Combined with mild reaction conditions, the overall energy consumption is effectively controlled. A water / organic two-phase electrolyte system is used, and the reaction temperature is precisely controlled between 5 and 35 °C, and the current density between 50 and 500 mA / cm². 2Under isothermal conditions, this invention can effectively regulate the oxidation process; the system is conducive to the mass transfer of reactants and the dissipation of reaction heat; the catalyst and co-catalyst enable the oxidation reaction to selectively stop at the stage of generating dimethyl sulfoxide (DMSO), significantly inhibiting the over-oxidation of dimethyl sulfide to the byproduct dimethyl sulfone, thus laying a solid foundation for obtaining high-purity distillate products by simple vacuum distillation at 75~77℃ / 1.6 kPa.

[0014] (6) Simple post-processing The two-phase reaction system makes the products easy to separate, and the dimethyl sulfoxide product can be obtained by separation, extraction and distillation, which makes it easy to realize industrial production. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the continuous redox cycle reaction mechanism of the present invention. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0017] Example 1 (1) Electrolyte preparation: In an ice-water bath, 5g of 98% concentrated sulfuric acid was slowly added to 45ml of deionized water and stirred evenly. After the solution was cooled to 30℃, 50ml of cyclohexane was added to obtain a two-phase electrolyte system (hereinafter referred to as: two-phase electrolyte).

[0018] (2) Electrode pretreatment: Platinum sheet was selected as the anode (working electrode) and graphite sheet as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1 mol / L hydrochloric acid solution for 15 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0019] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3g cerium sulfate (catalyst), and 1g phosphomolybdic vanadium heteropolyacid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 10℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 0.6A (current density 200 mA / cm²). 2 Electrolysis begins and the reaction lasts for 2.5 hours.

[0020] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of cyclohexane. The upper organic phase was combined, dried with anhydrous magnesium sulfate, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 80-81°C was collected (to recover the solvent cyclohexane). When the temperature of the reactor reached above 82°C, heating was stopped, and the distillation was carried out under reduced pressure (1.6 kPa), collecting the fraction at 75-77°C. Finally, 6.1 g of dimethyl sulfoxide product was obtained, with a yield of 96.8%.

[0021] Example 2 (1) Electrolyte preparation: Take the aqueous electrolyte recovered after the reaction in Example 1, add 1g of deionized water, stir evenly, and add 50ml of 1,2-dichloroethane as the organic phase.

[0022] (2) Electrode pretreatment: Platinum sheet was selected as the anode and graphite sheet as the cathode, and pretreatment was carried out according to the method of Example 1.

[0023] (3) Electrochemical oxidation reaction: Add the above electrolyte, 5g of dimethyl sulfide and a magnetic stir bar to the electrolytic cell. Set the reaction temperature to 10℃, the current to 0.6A, and the electrolysis reaction to proceed for 2.5 h.

[0024] (4) Product post-processing and separation: After the reaction was completed, the product was allowed to stand and separate into layers. The aqueous phase was extracted three times with 50 ml of 1,2-dichloroethane, and the organic phases were combined, dried with anhydrous sodium sulfate, and filtered. The filtrate was distilled under normal pressure, and the fraction at 83-84 °C was collected (to recover the solvent 1,2-dichloroethane). Then, the distillation was carried out under reduced pressure, and the fraction at 75-77 °C was collected. Finally, 6.09 g of dimethyl sulfoxide was obtained, with a yield of 96.7%.

[0025] Conclusion: This embodiment demonstrates that the electrolyte and catalyst can be effectively recycled and reused, and no additional catalyst or co-catalyst needs to be added for subsequent experiments, while the reaction still maintains high activity.

[0026] Example 3 (1) Electrolyte preparation: In an ice-water bath, 4.9 g of methanesulfonic acid was slowly added to 45 ml of deionized water and stirred until homogeneous. After the solution was cooled to 25 °C, 50 ml of dichloromethane was added to obtain a two-phase electrolyte.

[0027] (2) Electrode pretreatment: A DSA (titanium-based iridium-tantalum coating) was selected as the anode (working electrode), and a stainless steel sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1.5 mol / L hydrochloric acid solution for 20 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0028] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 4g cerium methanesulfonate (catalyst), and 1.2g phosphotungstic heteropoly acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 25℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 0.9A (current density 300 mA / cm²). 2 Electrolysis begins and the reaction lasts for 2 hours.

[0029] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of dichloromethane. The upper organic phase was combined, dried with a molecular sieve, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 39-40℃ was collected (to recover the solvent dichloromethane). Then, the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. Finally, 6.2 g of dimethyl sulfoxide product was obtained, with a yield of 98.4%.

[0030] Example 4 (1) Electrolyte preparation: In an ice-water bath, 7g of acetic acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of chloroform was added to obtain a two-phase electrolyte.

[0031] (2) Electrode pretreatment: Lead dioxide was selected as the anode (working electrode) and lead sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1.5 mol / L hydrochloric acid solution for 20 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0032] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 5.8g cerium acetate (catalyst), and 1.2g phosphomolybdic acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm², and set the constant current to 1.2A (current density 400 mA / cm²). 2 Electrolysis begins and the reaction lasts for 3 hours.

[0033] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of chloroform. The upper organic phase was combined, dried with a molecular sieve, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 61-62℃ was collected (to recover the solvent chloroform). Then, the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 5.9 g of dimethyl sulfoxide, with a yield of 93.6%.

[0034] Example 5 (1) Electrolyte preparation: In an ice-water bath, 8g of phosphoric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of n-hexane was added to obtain a two-phase electrolyte.

[0035] (2) Electrode pretreatment: Graphite sheet was selected as the anode (working electrode) and conductive glass sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1 mol / L hydrochloric acid solution for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0036] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g of dimethyl sulfide, 3.7g of cerium phosphate (catalyst), and 1.2g of phosphomolybdic acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 35℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm², and set a constant current of 0.9A (current density 300 mA / cm²). 2 Electrolysis begins and the reaction lasts for 4 hours.

[0037] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of n-hexane. The upper organic phase was combined, dried with a molecular sieve, and filtered. The filtrate was first distilled at atmospheric pressure, and the fraction at 68.5~69.5℃ was collected (to recover the solvent n-hexane). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75~77℃ was collected. Finally, 6.0 g of dimethyl sulfoxide product was obtained, with a yield of 95.3%.

[0038] Example 6 (1) Electrolyte preparation: In an ice-water bath, 10g of hydrochloric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of methylcyclohexane was added to obtain a two-phase electrolyte.

[0039] (2) Electrode pretreatment: A titanium-plated platinum sheet was selected as the anode (working electrode) and a titanium sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1 mol / L hydrochloric acid solution for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0040] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 31g cerium chloride (catalyst), and 1.2g phosphotungstic heteropoly acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 25℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 1.5A (current density 500 mA / cm²). 2 Electrolysis begins and the reaction lasts for 5 hours.

[0041] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of methylcyclohexane. The upper organic phase was combined, dried with magnesium sulfate, and filtered. The filtrate was first distilled at atmospheric pressure, and the fraction at 101~101.5℃ was collected (to recover the solvent methylcyclohexane). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75~77℃ was collected. Finally, 6.12 g of dimethyl sulfoxide product was obtained, with a yield of 97.1%.

[0042] Example 7 (1) Electrolyte preparation: In an ice-water bath, 5g of methanesulfonic acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 30℃, 50ml of cyclohexane was added to obtain a two-phase electrolyte.

[0043] (2) Electrode pretreatment: Platinum sheet was selected as the anode (working electrode) and lead sheet as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1 mol / L hydrochloric acid solution for 15 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0044] (3) Electrochemical oxidation reaction: Pour the electrolyte from (1) into a diaphragmless electrolytic cell, add 5.0 g of dimethyl sulfide, 3.5 g of cerium methanesulfonate (catalyst), and 1.3 g of phosphomolybdic vanadium heteropoly acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30°C. Connect a DC power supply, with the effective area of ​​both electrodes being 3 cm². 2 The constant current is set to 1.2A (current density 400mA / cm). 2Electrolysis begins and the reaction lasts for 2 hours.

[0045] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of cyclohexane. The upper organic phase was combined, dried with anhydrous magnesium sulfate, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 80-81°C was collected (to recover the solvent cyclohexane). When the temperature of the reactor reached above 82°C, heating was stopped, and the distillation was carried out under reduced pressure (1.6 kPa), collecting the fraction at 75-77°C. Finally, 6.25 g of dimethyl sulfoxide product was obtained, with a yield of 99.2%.

[0046] Comparative Example 1 (without catalyst) The difference from Example 1 is that (3) the electrochemical oxidation reaction: The above electrolyte was poured into a diaphragm-free electrolytic cell, 5g of dimethyl sulfide and 4g of phosphomolybdic vanadium heteropoly acid (co-catalyst, the amount of co-catalyst was increased to 4g) were added, and a magnetic stir bar was placed in the cell. The electrolytic cell was placed in a constant temperature water bath and the reaction temperature was set to 10°C. A DC power supply was connected, and the effective area of ​​both electrodes was 3cm². 2 The constant current is set to 0.6A (current density 200mA / cm). 2 Electrolysis begins, and the reaction lasts for 10 hours (a significantly longer reaction time compared to Example 1). The other steps are exactly the same.

[0047] The final product obtained was 2.5g of dimethyl sulfoxide, with a yield of 39.7%.

[0048] Conclusion: The product yield in Comparative Example 1 was much lower than that in Example 1, indicating that the heteropolyacid co-catalyst of the cerium salt catalyst played a catalytic role, which improved the product yield.

[0049] Comparative Example 2 (without co-catalyst) The difference from Example 1 is that (3) the electrochemical oxidation reaction: The above electrolyte was poured into a diaphragmless electrolytic cell, 5g of dimethyl sulfide and 4g of cerium sulfate (catalyst) were added, and a magnetic stir bar was placed in the cell. The electrolytic cell was placed in a constant temperature water bath, and the reaction temperature was set to 10°C. A DC power supply was connected, and the effective area of ​​both electrodes was 3cm². 2 The constant current is set to 0.6A (current density 200mA / cm). 2 Electrolysis was initiated, and the reaction lasted for 15 hours (a significantly longer reaction time compared to Example 1). The other steps were exactly the same as in Example 1.

[0050] The final product yielded 6.05 g of dimethyl sulfoxide, with a yield of 96%.

[0051] Conclusion: Compared with Example 1, Comparative Example 2 did not use a co-catalyst, resulting in a significant decrease in reaction rate and a substantial increase in reaction time. The yield of the obtained product was similar to that of Example 1, but the reaction time was 6 times that of Example 1. This indicates that the use of a co-catalyst plays a role in accelerating the reaction and shortening the reaction time in the reaction of the present invention.

[0052] Comparative Example 3 (Examining the effect of catalyst dosage on the product) The difference from Example 7 is that the amount of catalyst used in (3) is different from that in Example 7, specifically as follows: Pour the electrolyte from (1) into a membraneless electrolytic cell, add 5g of dimethyl sulfide, 1g of cerium methanesulfonate (catalyst) and 1.3g of phosphomolybdic vanadium heteropoly acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30°C. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 1.2A (current density 400mA / cm). 2 Electrolysis begins and the reaction lasts for 4.5 hours.

[0053] The final product yielded 6.22 g of dimethyl sulfoxide, with a yield of 98.7%.

[0054] Compared to Example 7, the amount of catalyst used was reduced, resulting in a decrease in the reaction rate and an increase in the reaction time. A longer reaction time was required to obtain dimethyl sulfoxide with a yield close to that of Example 7.

[0055] Comparative Example 4 (Catalyst dosage varied) The difference from Example 7 is that, in (3), the amount of catalyst was adjusted to 8g of cerium methanesulfonate, and the constant current was set to 1.2A (current density 400 mA / cm²). 2 The electrolysis reaction lasted for 2 hours.

[0056] The final product yielded 6.24 g of dimethyl sulfoxide, with a yield of 99%.

[0057] Compared to Example 7, the product yield remained almost unchanged when the amount of catalyst was increased. This indicates that once the amount of catalyst reaches a certain proportion, further increases in its amount have virtually no impact on the final product yield. The catalyst dosage proportion in Example 7 is already an optimized value.

[0058] Example 8 (1) Electrolyte preparation: In an ice-water bath, 15g of oxalic acid was slowly added to 50ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 60ml of dichloroethane was added to obtain a two-phase electrolyte.

[0059] (2) Electrode pretreatment: A titanium-based iridium-tantalum coated electrode was selected as the anode (working electrode) and a titanium sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1.5 mol / L hydrochloric acid solution for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0060] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 9.6g cerium acetate (catalyst), and 1.4g phosphotungstic acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 35℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm², and set the constant current to 1.5A (current density 500 mA / cm²). 2 Electrolysis begins and the reaction lasts for 4 hours.

[0061] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of dichloroethane. The organic phases were combined, dried with magnesium sulfate, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 83-84℃ was collected (to recover the solvent dichloroethane). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 5.75 g of dimethyl sulfoxide, with a yield of 91.2%.

[0062] Example 9 (1) Electrolyte preparation: In an ice-water bath, 9g of nitric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of benzene was added to obtain a two-phase electrolyte.

[0063] (2) Electrode pretreatment: A titanium-based iridium-tantalum coated electrode was selected as the anode (working electrode) and a titanium sheet was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1.5 mol / L hydrochloric acid solution for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0064] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3.7g cerium nitrate (catalyst), and 1.4g phosphomolybdic vanadium heteropolyacid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 1.0A (current density 333 mA / cm²). 2 Electrolysis begins and the reaction lasts for 3 hours.

[0065] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of benzene. The organic phases were combined, dried with magnesium sulfate, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 80-81℃ was collected (to recover the solvent benzene). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 6.03 g of dimethyl sulfoxide, with a yield of 95.7%.

[0066] Example 10 (1) Electrolyte preparation: In an ice-water bath, 9g of concentrated sulfuric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of toluene was added to obtain a two-phase electrolyte.

[0067] (2) Electrode pretreatment: A titanium-based platinum-coated electrode was selected as the anode (working electrode) and conductive glass was selected as the cathode (counter electrode). The electrode was cleaned with detergent, placed in a 1.5 mol / L hydrochloric acid solution and sonicated for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0068] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3.7g cerium sulfate (catalyst), and 1.4g phosphomolybdic acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 35℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 1.2A (current density 400mA / cm). 2 Electrolysis begins and the reaction lasts for 2.5 hours.

[0069] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of toluene. The organic phases were combined, dried with magnesium sulfate, and filtered. The filtrate was first distilled at atmospheric pressure, and the fraction at 110-111℃ was collected (toluene solvent was recovered). Then the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 6.15 g of dimethyl sulfoxide, with a yield of 97.6%.

[0070] Example 11 (1) Electrolyte preparation: In an ice-water bath, 9g of nitric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 50ml of xylene was added to obtain a two-phase electrolyte.

[0071] (2) Electrode pretreatment: A lead electrode was selected as the anode (working electrode) and a graphite electrode as the cathode (counter electrode). The electrodes were cleaned with detergent, ultrasonically treated in 1 mol / L hydrochloric acid solution for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0072] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3.7g cerium nitrate (catalyst), and 1.3g phosphotungstic heteropoly acid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 25℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm², and set the constant current to 1.2A (current density 400mA / cm²). 2 Electrolysis begins and the reaction lasts for 3.5 hours.

[0073] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml xylene. The organic phases were combined, dried with magnesium sulfate, and filtered. The filtrate was first distilled at atmospheric pressure, and the fraction at 137-140℃ was collected (to recover the solvent xylene). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 6.01 g of dimethyl sulfoxide, with a yield of 95.5%.

[0074] Example 12 (1) Electrolyte preparation: In an ice-water bath, 13g of methanesulfonic acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 60ml of ethyl acetate was added to obtain a two-phase electrolyte.

[0075] (2) Electrode pretreatment: A lead dioxide electrode was selected as the anode (working electrode) and a lead electrode was selected as the cathode (counter electrode). The electrodes were cleaned with detergent, placed in a 1 mol / L hydrochloric acid solution and sonicated for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0076] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3.7g cerium methanesulfonate (catalyst), and 1.3g phosphomolybdic vanadium heteropolyacid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 0.75A (current density 250mA / cm). 2 Electrolysis begins and the reaction lasts for 4 hours.

[0077] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of ethyl acetate. The organic phases were combined, dried with a molecular sieve, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 76-76℃ was collected (to recover the solvent ethyl acetate). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 6.19 g of dimethyl sulfoxide, with a yield of 98.3%.

[0078] Example 13 (1) Electrolyte preparation: In an ice-water bath, 15g of hydrochloric acid was slowly added to 45ml of deionized water and stirred until homogeneous. After the solution was cooled to 20℃, 80ml of butyl acetate was added to obtain a two-phase electrolyte.

[0079] (2) Electrode pretreatment: A platinum sheet electrode was selected as the anode (working electrode) and a lead electrode as the cathode (counter electrode). The electrodes were cleaned with detergent, placed in a 1 mol / L hydrochloric acid solution and sonicated for 25 min, then rinsed with deionized water and anhydrous ethanol, and dried for later use.

[0080] (3) Electrochemical oxidation reaction: Pour the above electrolyte into a diaphragm-free electrolytic cell, add 5g dimethyl sulfide, 3.3g cerium chloride (catalyst), and 1.7g phosphomolybdic vanadium heteropolyacid (co-catalyst), and place a magnetic stir bar. Place the electrolytic cell in a constant temperature water bath and set the reaction temperature to 30℃. Connect a DC power supply, with the effective area of ​​both electrodes being 3cm². 2 The constant current is set to 0.75A (current density 250mA / cm). 2 Electrolysis begins and the reaction lasts for 4.5 hours.

[0081] (4) Product post-processing and separation: After the reaction was completed, the mixture was poured into a separatory funnel and allowed to stand for separation. The lower aqueous phase was separated, and the aqueous phase was extracted three times with 50 ml of ethyl acetate. The organic phases were combined, dried with a molecular sieve, and filtered. The filtrate was first distilled under normal pressure, and the fraction at 126-127℃ was collected (to recover the solvent ethyl acetate). Then, the temperature was lowered and the distillation was carried out under reduced pressure (1.6 kPa), and the fraction at 75-77℃ was collected. The final product obtained was 6.08 g of dimethyl sulfoxide, with a yield of 96.5%.

[0082] Table 1 Comparison of reaction conditions and yields between the examples and comparative examples

[0083] Experimental results show that the synergistic effect of catalyst and co-catalyst can significantly improve reaction efficiency. For example, comparing Example 1, Comparative Examples 1 and 2, the difference lies in whether the catalyst and co-catalyst are used together. Obviously, the product yield in Comparative Example 1 is much lower than that in Example 1, which shows that the catalyst makes a very significant contribution to improving the product yield in this application. In Comparative Example 2, without the use of co-catalyst, the reaction time is greatly increased, which shows that using co-catalyst in conjunction with catalyst can shorten the reaction time.

[0084] The comparison between Example 7 and Comparative Examples 3 and 4 shows that reducing the amount of catalyst also affects the product yield. However, when the amount of catalyst is increased to a certain extent, the yield does not increase.

[0085] In other embodiments, the type or amount of catalyst was different compared to Example 7, and the reaction parameters were fine-tuned. The results showed that the product yield was not significantly different, which indicates that the method of the present invention has good stability and the product yield does not fluctuate significantly.

[0086] The experiments and results in Table 1 demonstrate that, in this invention, using dimethyl sulfide as a raw material, and with the aid of a cerium salt catalyst and a heteropolyacid co-catalyst, a high-yield dimethyl sulfoxide product can be obtained through an electro-oxidation reaction (the yield can reach up to 99.2%, Example 7). Furthermore, the method of this invention is environmentally friendly, has mild reaction conditions (can be carried out at room temperature), is highly safe, has high efficiency and speed, and is simple to process afterward, making it easy for industrial production.

Claims

1. A method for the electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide, characterized in that, The steps are as follows: (1) Preparation of two-phase electrolyte system: an acid solution is used as the electrolyte and dissolved in deionized water, and then an organic solvent is added to form a two-phase electrolyte system in which the aqueous phase and the organic phase coexist; the organic solvent is immiscible with water; (2) Electrode pretreatment: Take the anode and cathode, and clean them with detergent and deionized water respectively. Then, place them in 0.5~1.5 mol / L hydrochloric acid solution and ultrasonically soak for 10~20 min. Then wash them with deionized water and anhydrous ethanol respectively and dry them. (3) Electrochemical oxidation reaction: Dimethyl sulfide, cerium salt catalyst, heteropoly acid co-catalyst and the two-phase electrolyte system obtained in (1) are added to the diaphragmless electrolytic cell. The diaphragmless electrolytic cell is then placed in a constant temperature water bath with magnetic stirring function and stirred at 5℃~35℃. Then, DC current is passed through the electrolytic cell and electrochemical oxidation reaction is carried out under constant current electrolysis to obtain the reaction mixture. (4) Product separation and purification: The reaction mixture obtained in (3) was allowed to stand and separate into layers. The aqueous phase was separated, and the organic phases were extracted with organic solvents, separated, and then combined. After drying, the organic solvent in the reaction mixture was first recovered by atmospheric distillation, and then the fraction at 75~77℃ was collected by vacuum distillation at a vacuum degree of 1.6 kPa to obtain dimethyl sulfoxide.

2. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, (1) The acid solution is selected from any one of sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, nitric acid, acetic acid, and oxalic acid, and its concentration is 1~3 mol / L; The organic solvent is selected from any one of dichloromethane, chloroform, dichloroethane, ethyl acetate, butyl acetate, cyclohexane, n-hexane, methylcyclohexane, benzene, toluene, and xylene, and the volume ratio of the organic solvent to the acid solution is (0.5~2):

1.

3. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, (2) The anode is selected from any one of the following: platinum sheet electrode, titanium platinum electrode, graphite electrode, titanium-based iridium-tantalum coated electrode, lead dioxide electrode, and lead electrode; The cathode is selected from any one of the following: lead electrode, platinum sheet electrode, stainless steel electrode, titanium electrode, titanium-plated platinum electrode, or conductive glass electrode.

4. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, (3) The mass of dimethyl sulfide is 1% to 30% of the mass of the two-phase electrolyte system; The cerium salt catalyst is selected from any one of cerium methanesulfonate, cerium sulfate, cerium nitrate, cerium acetate, and cerium phosphate, and its mass is 5% to 15% of the mass of the two-phase electrolyte system; The heteropolyacid cocatalyst is selected from any one of phosphomolybdenum-vanadium heteropolyacid, phosphotungsten heteropolyacid, and phosphomolybdenum heteropolyacid, and its mass is 1% to 5% of the two-phase electrolyte system.

5. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, (3) The temperature of the electrochemical oxidation reaction is 5℃~35℃; the current density of electrolysis is 50~500 mA / cm².

6. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, During drying, any one of anhydrous sodium sulfate, anhydrous magnesium sulfate, or molecular sieves can be used as a desiccant.

7. The method for electro-oxidative synthesis of dimethyl sulfoxide from dimethyl sulfide as described in claim 1, characterized in that, The steps include the following: (1) Preparation of two-phase electrolyte system: In an ice-water bath, 5g of methanesulfonic acid was slowly added to 45ml of deionized water and stirred evenly. After the solution was cooled to 30℃, 50ml of cyclohexane was added to form a two-phase electrolyte system in which the aqueous phase and the organic phase coexist. (2) Electrode pretreatment: platinum sheet electrode is used as anode and lead electrode is used as cathode. They are cleaned with detergent and deionized water in turn. Then they are placed in 1 mol / L hydrochloric acid solution and ultrasonically soaked for 15 min. Then they are washed with deionized water and anhydrous ethanol in turn and then dried. (3) Electrochemical oxidation reaction: 5g of dimethyl sulfide, 3.5g of cerium methanesulfonate, 1.3g of phosphomolybdic vanadium heteropoly acid and the two-phase electrolyte system obtained in (1) were added to a diaphragmless electrolytic cell. The diaphragmless electrolytic cell was placed in a constant temperature water bath with magnetic stirring function and stirred at 30°C. Then, DC power was passed through the electrolytic cell to carry out the electrochemical oxidation reaction and obtain the reaction mixture. (4) Product separation and purification: The reaction mixture obtained in (3) was allowed to stand and separate into layers. The aqueous phase was extracted multiple times with organic solvents, and the organic phases were combined after separation. After drying, the organic solvent in the reaction mixture was first recovered by atmospheric distillation, and then the fraction at 75~77℃ was collected by vacuum distillation at 1.6 kPa to obtain dimethyl sulfoxide.

8. The application of cerium salt catalysts and heteropolyacid co-catalysts in the electro-oxidative synthesis of dimethyl sulfoxide, characterized in that, The cerium salt catalyst is selected from any one of cerium methanesulfonate, cerium sulfate, cerium nitrate, cerium acetate, cerium phosphate, and cerium chloride; The heteropolyacid cocatalyst is selected from any one of phosphomolybdenum-vanadium heteropolyacid, phosphotungsten heteropolyacid, and phosphomolybdenum heteropolyacid.

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