Metal hydroxide catalyst, preparation method thereof and pyroxasulfone synthesis method

Abstract

The invention provides a metal hydroxide catalyst, a preparation method thereof and a pyroxasulfone synthesis method. The metal hydroxide catalyst comprises monometal hydroxide or layered double-metal hydroxide; the general formula of the monometal hydroxide is M (OH) y, and the general formula of the layered bimetal hydroxide is [M < 2 + 1-x > (M < 3 + x > (OH) 2] < x + >. [A < n->] < x / n.mH2O or [M < 2 + 1-x > (M < 4 + x > (OH) 2] < 2x + >. [A < n->] < 2x / n.mH2O; the monometal hydroxide is prepared from metal salt through one of a hydrothermal / solvothermal method and a coprecipitation method; the layered double hydroxide is prepared from metal salt through a coprecipitation method. The metal hydroxide catalyst provided by the invention can efficiently and highly selectively activate H2O2 and oxidize thioether into sulfone, has excellent selectivity and catalytic efficiency, can be separated from a product through simple filtration or directly in a fixed bed after reaction, and is easy to recycle and reuse.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a metal hydroxide catalyst and its preparation method, as well as a method for synthesizing sulfonylpyrazine. Background Technology

[0002] Pyroxasulfone, chemically named 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazol-4-ylmethanesulfonyl]-4,5-dihydro-5,5-dimethyl-1,2-isoxaazole, is a new generation of highly effective, broad-spectrum, and low-toxicity pre-emergence soil-applied herbicide developed by Japan Combinatorial Chemicals Co., Ltd. Its unique mechanism of action involves inhibiting the synthesis of very long-chain fatty acids in plants, effectively controlling a variety of annual grasses and broadleaf weeds. Due to its excellent weed control effect at low dosages and high crop safety, demand for pyroxasulfone continues to grow rapidly in major agricultural markets worldwide, making it one of the most important herbicide products.

[0003] The synthesis of this compound is a multi-step process, the most critical and technical step of which is the highly selective oxidation of the thioether intermediate, 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylthio]-4,5-dihydro-5,5-dimethyl-1,2-isoxazole (Formula 1), to the corresponding sulfonylpyrazol. This conversion process directly determines the yield, purity, and production cost of the final product.

[0004]

[0005] Currently, the main technical routes for the oxidation of thioethers in sulfopyrazine involve a variety of catalyst systems. Common catalysts include tungsten metal catalysts, noble metal complexes, inorganic acids, and ionic liquids, each with its own advantages, but also revealing some technical bottlenecks in practical applications.

[0006] Currently, homogeneous catalytic systems are commonly used in industry, such as CN111393427A and CN118307533A, which utilize sodium tungstate, tungstic acid, and hydrogen peroxide. Although this system has a certain catalytic efficiency, it faces several insurmountable technical bottlenecks: the homogeneous tungsten catalyst is difficult to separate and recover from the complex reaction system after the reaction, which not only increases costs but also leads to tungsten metal residue in the product, affecting purity and generating wastewater containing heavy metals, resulting in significant environmental pressure; the selectivity for the target sulfone product is not ideal, and it is prone to producing over-oxidized byproducts; in batch reactors, the strong exothermic characteristics make temperature control difficult, posing a safety risk of hydrogen peroxide decomposition.

[0007] As described in patent CN114716429A, although functionalized ionic liquid technology can improve the oxidation efficiency of hydrogen peroxide, it has problems such as complex preparation process, high cost, difficulty in recycling and reuse, and may have special requirements for equipment.

[0008] Heterogeneous catalysts, including metal oxides (such as WO3, MoO3, TiO2, etc.), molecular sieves, and activated carbon, have solved the catalyst separation problem, but they share the following common issues: poor accessibility of active sites, with most active sites located in the internal pores of the catalyst, making it difficult for reactant molecules to diffuse to them; metal leaching problems, where active metal components easily dissolve in the oxidation reaction environment, leading to catalyst deactivation and product contamination; limited specific surface area, as metal oxides prepared by traditional methods typically have low specific surface areas; and difficulty in selectivity control, as the surface active sites are heterogeneous, resulting in poor selectivity for sulfide substrates with complex molecular structures.

[0009] While some technologies have improved the activity and increased the specific surface area of ​​heterogeneous catalysts through modification and loading, problems such as process complexity, high cost, and difficulty in recycling and reuse still exist. For example, the metal peroxide complex catalyst used in patent CN202511008992 has complex synthesis steps, high production costs, and the ligands may degrade during long-term operation, affecting the catalyst's lifespan. Similarly, the hybrid selenite catalyst used in patent CN202510842365 uses selenium, which is expensive and toxic. Furthermore, the supported metal oxide catalyst used in patent CN202510123724 suffers from complex support synthesis processes and high template agent costs.

[0010] Based on this, the development of a novel and highly efficient catalytic system to completely solve the technical bottleneck in the synthesis of sulfopyrazole has significant industrial application value and scientific significance. Summary of the Invention

[0011] This invention provides a metal hydroxide catalyst for the synthesis of sulfonylpyrazine, comprising a monometallic hydroxide or a layered bimetallic hydroxide; The general formula for the monometallic hydroxide is M(OH). y Where M is one of Ni, Co, Fe, Mn, Cu, Mg, Zn, Zr, Ti or Ce, and y is 2, 3 or 4, corresponding to the valence state of M; The layered bimetallic hydroxide has the general formula [M 2+ 1-x (M 3+ x (OH)2] x+ ·[A n- ] x / n ·mH2O or [M 2+ 1-x (M4 + x (OH)2] 2x+ ·[A n- ] 2x / n ·mH2O, Among them, M 2+ It is a divalent metal cation, selected from Ni 2+ Co 2+ Zn 2+ Mg 2+ At least one of them; M 3+ It is a trivalent metal cation, selected from Fe 3+ Al 3+ Cr 3+ At least one of them; M 4+ It is a tetravalent metal cation, selected from Zr. 4+ Ti 4+ Ce 4+ At least one of them; A n- It is an interlayer anion, selected from CO3. 2- NO3 - OH - At least one of them, where n corresponds to the valence state of the interlayer anion; x is M 3+ x Or M 4+ x The molar ratio of x to total metals is 0.05 ≤ x ≤ 0.3; m represents the amount of water of crystallization.

[0012] Furthermore, in the layered bimetallic hydroxide, M 2+ With M 3+ Or M 4+ The molar ratio is (3-19):1; the layered bimetallic hydroxide is preferably NiZr-LDH.

[0013] The present invention also provides a method for preparing the above-mentioned catalyst, wherein the single metal hydroxide is prepared by a metal salt by one of the following methods: hydrothermal / solvothermal method or coprecipitation method; The layered bimetallic hydroxide is prepared by co-precipitation of metal salts.

[0014] Furthermore, the specific steps of the hydrothermal / solvothermal method are as follows: (1) Dissolve the metal salt in an aqueous ethanol solution, add urea, and stir to dissolve; (2) After dissolution, transfer to a high-pressure reactor and react at 120-180℃ for 6-24 hours to obtain a monometallic hydroxide; In step (1), the volume ratio of water to ethanol in the ethanol-water solution is 1:(1-3). The preferred reaction conditions for step (2) are 150°C for 12 hours.

[0015] Furthermore, the specific steps for preparing monometallic hydroxides by the coprecipitation method are as follows: under vigorous stirring, the metal salt is rapidly mixed with an excess of sodium hydroxide solution, the pH value at the reaction endpoint is controlled between 10.5 and 11.5, the temperature is maintained at 25-60℃, and after the precipitate is formed, it is aged for another 1-3 hours to obtain the monometallic hydroxide.

[0016] Furthermore, the specific steps for preparing layered bimetallic hydroxides by the co-precipitation method are as follows: (1) Divalent metal ion salts and trivalent or tetravalent metal ion salt solutions are reacted according to M 2+ :(M 3+ Or M 4+ The molar ratio (3-19):1 is dissolved in water to prepare a mixed salt solution with a total metal ion concentration of 0.5-2.0 mol / L; Prepare a mixed alkaline solution containing NaOH and Na2CO3, wherein the concentration of NaOH is 1.0-3.0 mol / L and the concentration of Na2CO3 is 0.5-1.5 mol / L; (2) Add the mixed salt solution and the mixed alkali solution dropwise into the reactor, control the dropping rate to keep the pH value of the system stable in the range of 9.0-10.5, maintain the temperature at 60-80℃, and continue aging for 2-4 hours after the addition is completed to allow the precipitate to fully crystallize and obtain layered bimetallic hydroxide.

[0017] Furthermore, the layered bimetallic hydroxide is prepared by co-precipitation and ion exchange methods, specifically through the following steps: (1) Divalent metal ion salts and trivalent or tetravalent metal ion salt solutions are reacted according to M 2+ :(M 3+ Or M 4+ The molar ratio (3-19):1 is dissolved in water to prepare a mixed salt solution with a total metal ion concentration of 0.5-2.0 mol / L; Prepare a mixed alkaline solution containing NaOH and Na2CO3, wherein the concentration of NaOH is 1.0-3.0 mol / L and the concentration of Na2CO3 is 0.5-1.5 mol / L; (2) Add the mixed salt solution and mixed alkali solution dropwise into the reactor, control the dropping rate to keep the pH value of the system stable in the range of 9.0-10.5, and maintain the temperature at 60-80℃. After the addition is completed, continue aging for 2-4 hours to allow the precipitate to fully crystallize. Then, after centrifugation, washing and drying, a layered bimetallic hydroxide precursor is obtained. (3) Disperse the precursor in water to prepare a suspension with a concentration of 20-50 g / L. Slowly add a solution containing the desired exchange ion X to the suspension. Stir and exchange at 60-80℃ for 12-24 hours. After centrifugation, washing and drying, the product is obtained as a layered bimetallic hydroxide. When X is Zr, ZrOCl2 solution is used, and the molar ratio of Zr to the precursor intermediate plate metal is controlled to be 1:(5-10).

[0018] This invention also provides a method for synthesizing sulfonylpyrazole, the specific steps of which are as follows: The thioether intermediate 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylthio]-4,5-dihydro-5,5-dimethyl-1,2-isooxazole was mixed with 30-50 wt% hydrogen peroxide solution and added to a reactor containing the above catalyst. Selective oxidation reaction was carried out at 35-60°C to synthesize sulfopyrazazole. The molar ratio of hydrogen peroxide to the sulfide intermediate is (2.0-2.5):1; The reactor is a batch reactor or a fixed-bed reactor; When the catalyst is a Zr-containing catalyst, the reaction temperature is 50-60℃; When the catalyst is Zr-free, the reaction temperature is 35-50℃.

[0019] Furthermore, the specific steps for synthesizing sulfonylpyrazine using a batch reactor are as follows: The catalyst and methanol were mixed at a mass ratio of 1:(20-40) and added to the reactor. The mixture was stirred and heated to 35-60°C. The sulfide intermediate was mixed with hydrogen peroxide solution and slowly added dropwise to the reactor. After the addition was complete, the reaction was continued for 30-90 minutes. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, concentrated under reduced pressure, crystallized, filtered again, washed, and dried to obtain sulfopyrazole product.

[0020] Furthermore, the specific steps for synthesizing sulfonylpyrazine using a fixed-bed reactor are as follows: (1) The catalyst is loaded into a fixed-bed reactor, heated to 35-60℃, and the back pressure is maintained at 0.2-0.5 MPa; (2) After mixing the sulfide intermediate methanol solution with the hydrogen peroxide solution, pump it into the reactor at a flow rate of 0.2-0.5 mL / min, control the residence time of the material in the reactor to be 60-90 minutes, and collect sulfopyrazine at the reactor outlet; The molar ratio of hydrogen peroxide to the sulfide intermediate is 2.2:1; The concentration of the thioether intermediate in the methanol solution is 0.4-0.6 g / mL.

[0021] The beneficial effects of this invention are as follows: The metal hydroxide catalyst provided by this invention, through the synergistic effect of its Lewis acid sites and surface hydroxyl groups, can efficiently and selectively activate H₂O₂ and oxidize sulfides to sulfones. After the reaction, the catalyst can be easily separated from the product by simple filtration or directly in a fixed bed, facilitating recovery and reuse. Using it as a catalyst for the oxidation of sulfides to sulfones exhibits excellent selectivity and catalytic efficiency. Its application in the synthesis of sulfonylpyrazol can effectively improve the reaction efficiency, selectivity, and safety of the oxidation reaction, thereby contributing to further reducing the preparation cost of sulfonylpyrazol. Detailed Implementation

[0022] The catalytic activity of single-metal hydroxides (such as Ni(OH)2 and Co(OH)2 nanosheets) mainly depends on the single type of Lewis acid sites and hydroxyl functional groups on their surface, and achieves catalytic cycling through a relatively direct dual activation and oxygen transfer pathway.

[0023] On the surface of a single metal hydroxide, the catalytic cycle begins with H2O2 at a single metal site (such as Ni). 2+ Coordination and activation at the metal center. This metal center, acting as a Lewis acid, attracts and polarizes the H₂O₂ molecule, causing its OO bond to elongate and weaken, leading to heterolytic cleavage, the removal of a water molecule, and the in-situ generation of a highly reactive metal-peroxide species (M₂O₂). + This process avoids homolytic cleavage of the OO bond, thus effectively suppressing the generation of non-selective hydroxyl radicals (·OH), laying the foundation for highly selective oxidation.

[0024] Simultaneously, the thioether molecule coordinates with the same or adjacent Lewis acid sites of the same metal via the lone pair electrons on its sulfur atom. This coordination significantly reduces the electron cloud density of the sulfur atom, activating its electron-rich state and making it more susceptible to electrophilic attacks. Subsequently, the activated sulfur atom launches an electrophilic attack on the terminal oxygen atom in the neighboring metal-peroxide species. This process typically proceeds through an energy-favorable ternary cyclic transition state, ensuring efficient and precise transfer of oxygen atoms from the catalyst to the thioether, initially generating a sulfoxide intermediate. The sulfoxide intermediate undergoes a similar coordination activation and secondary oxygen transfer process, thereby selectively converting the thioether to sulfone in a stepwise manner.

[0025] After each oxygen transfer, a metal-hydroxy species (M-OH) is generated on the catalyst surface. Through proton transfer and rearrangement in the reaction medium (or with another molecule of H2O2), the initial metal-hydroxy active site is rapidly regenerated, completing the catalytic cycle.

[0026] The catalytic mechanism of layered bimetallic hydroxides is far more complex and efficient than that of monometallic systems. Their core advantages stem from the synergistic effect between different metal sites, tunable plate charges, and unique interlayer confinement environment.

[0027] In LDH, it is usually composed of a metal (such as Ni) 2+ Co 2+ As the primary redox center, it is responsible for the activation and electron transfer of H2O2; while another or more metals (such as Fe) 3+ Al 3+ Especially the introduction of Zr 4+ It acts as a strong Lewis acid center and structural stabilizer.

[0028] Among them, Zr 4+ The introduction of high-valence metals, due to their strong Lewis acidity, can more effectively polarize the OO bonds of H2O2, promoting the formation of more reactive metal-peroxide species.

[0029] At the same time, different metals interact through electronic coupling effects (e.g., Zr). 4+ The electron-withdrawing effect can modulate the adjacent Co 2 + The electron density at the site (making it more susceptible to redox cycles) together optimizes the reactivity of the active intermediate.

[0030] Multivalent metal pairs (such as Ni) exist within the LDH layer. 2+ / Ni 3+ Co 2+ / Co 3+ Fe 2+ / Fe 3+ This forms an efficient electron transfer channel, facilitating rapid electron transfer during the reaction. Furthermore, spontaneously formed surface oxygen vacancies (Ov) for charge balance play a crucial role in this process: firstly, as strong adsorption sites, they preferentially adsorb and activate H₂O₂ or oxygen molecules; secondly, as electron buffers, the electrons captured by oxygen vacancies can be transferred to adsorbed oxygen species, promoting their activation, or regulating the electron distribution on the catalyst surface, further enhancing substrate adsorption and activation.

[0031] LDH’s well-ordered layered structure and adjustable interlayer spacing (which can be controlled by introducing different ions) provide it with a unique nanoscale reaction space.

[0032] After sulfide molecules and H2O2 enter the interlayer domain, their molecular orientation and configuration are affected by the electrostatic potential and spatial constraints of the laminations, resulting in "pre-organization". This makes the reactive groups closer to the active sites, reduces the entropy barrier of the reaction, and significantly improves the reaction efficiency.

[0033] In the confined space between layers, after sulfoxides are oxidized to sulfoxides, due to spatial confinement and enrichment effects, they are more likely to remain in the interlayer and rapidly encounter the next reactive oxygen species, completing a second oxidation. This "relay" oxidation pathway greatly suppresses the possibility of sulfoxide intermediates desorbing from the catalyst surface and entering the bulk solution as byproducts, thus achieving a near-quantitative and highly efficient conversion from sulfoxides to sulfones.

[0034] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0035] Example 1 (1) Preparation of metal hydroxide catalysts 2.91 g of nickel nitrate hexahydrate, Ni(NO3)2·6H2O, was dissolved in a mixed solvent consisting of 40 ml of deionized water and 40 ml of anhydrous ethanol. 1.8 g of urea was added to the above solution, and the mixture was magnetically stirred for 30 minutes until completely dissolved, yielding a mixed solution. The mixed solution was transferred to a 100 ml stainless steel high-pressure reactor lined with polytetrafluoroethylene (PTFE). The reactor was placed in an oven and reacted at 150 °C for 12 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting green precipitate was washed three times each by centrifugation with deionized water and anhydrous ethanol. Finally, the precipitate was dried overnight in a vacuum drying oven at 80 °C to obtain the metal hydroxide catalyst.

[0036] (2) Synthesis of sulfonylpyrazine Add 1.0 g of the above catalyst and 40 mL of methanol to a 250 mL three-necked flask, and stir to 40 °C. Mix 20.0 g of the thioether intermediate 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylthio]-4,5-dihydro-5,5-dimethyl-1,2-isoxazole with 9.8 g of 30% H2O2 solution, and slowly add the mixture dropwise to the reaction flask over 30 minutes. After the addition is complete, continue stirring at 40 °C for 60 minutes. Cool the reaction solution to room temperature, and separate the catalyst by filtration. Concentrate the filtrate under reduced pressure, add 50 mL of ice water to crystallize, filter, wash with cold water, and dry to obtain sulfopyrazol product.

[0037] Example 2 (1) Preparation of metal hydroxide catalysts Prepare 100 mL of a 0.5 mol / L Co(NO3)2·6H2O aqueous solution (solution A) and 100 mL of a 2.0 mol / L NaOH aqueous solution (solution B). Under vigorous stirring and at room temperature, add solution A dropwise to solution B. After the addition is complete, adjust and maintain the pH of the system at 11.0 with dilute NaOH solution, and control the temperature at 50 °C. Continue stirring and aging under these conditions for 2 hours. Filter the resulting pink precipitate, wash with deionized water until the filtrate is neutral, and then vacuum dry at 60 °C for 6 hours to obtain the metal hydroxide catalyst.

[0038] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 1 is that the catalyst is the catalyst prepared in Example 2.

[0039] Example 3 (1) Preparation of metal hydroxide catalysts The metal hydroxide catalyst obtained in step (1) of Example 1 was mixed with silicon dioxide (SiO2) at a mass ratio of 8:1, pressed into tablets, crushed, and sieved to obtain catalyst particles of 20-40 mesh.

[0040] (2) Synthesis of sulfonylpyrazine 20 mL of the above-mentioned catalyst particles were packed into a fixed-bed reactor (10 mm inner diameter). The system was heated to 45 °C and maintained at a back pressure of 0.3 MPa. A methanol solution of the sulfide intermediate (0.5 g / mL) and 30% H₂O₂ were mixed at a molar ratio of 2.2:1 and pumped into the reactor at a flow rate of 0.27 mL / min (residence time 75 ± 2 min). The clarified reaction liquid was collected directly and continuously from the reactor outlet without any catalyst separation step.

[0041] Example 4 (1) Preparation of metal hydroxide catalysts The metal hydroxide catalyst obtained in step (1) of Example 2 was uniformly mixed with silicon dioxide (SiO2) at a mass ratio of 8:1, pressed into tablets, crushed, and sieved to obtain catalyst particles of 20-40 mesh.

[0042] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 3 is that the catalyst particles are the catalyst particles prepared in Example 4.

[0043] Example 5 (1) Preparation of metal hydroxide catalysts Co(NO3)2·6H2O and Fe(NO3)3·9H2O were mixed according to Co 2+ :Fe 3+A mixed salt solution with a total metal ion concentration of 1.0 mol / L was prepared by dissolving NaOH and Na₂CO₃ in 100 ml of deionized water at a molar ratio of 4:1. A mixed alkali solution containing 2.0 mol / L NaOH and 1.0 mol / L Na₂CO₃ was prepared by dissolving NaOH and Na₂CO₃ in 100 ml of deionized water. Under vigorous stirring at 60 °C, the mixed salt and mixed alkali solutions were simultaneously and slowly added dropwise through a constant-pressure dropping funnel to a reaction flask containing 50 ml of deionized water, controlling the dropping rate to stabilize the pH of the reaction system at 10.0. After the addition was complete, the mixture was aged at 65 °C for 3 hours. The resulting suspension was centrifuged, washed with deionized water, and dried at 80 °C for 12 hours to obtain the metal hydroxide catalyst.

[0044] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 1 is that the catalyst is the catalyst prepared in Example 5.

[0045] Example 6 (1) Preparation of metal hydroxide catalysts Ni(NO3)2·6H2O and Al(NO3)3·9H2O are reacted according to Ni 2+ :Al 3+ A mixed salt solution with a total metal ion concentration of 1.0 mol / L was prepared by dissolving NaOH and Na₂CO₃ in 100 mL of deionized water at a molar ratio of 4:1. A mixed alkaline solution containing 2.0 mol / L NaOH and 1.0 mol / L Na₂CO₃ was prepared by dissolving NaOH and Na₂CO₃ in 100 mL of deionized water. Under vigorous stirring at 60 °C, both solutions were simultaneously and slowly added dropwise through a constant-pressure dropping funnel to a reaction flask containing 50 mL of deionized water, controlling the dropping rate to stabilize the pH of the reaction system at 10.0. After the addition was complete, the mixture was aged at 65 °C for 3 hours. The resulting suspension was centrifuged, washed several times with deionized water, and dried at 80 °C for 12 hours to obtain the NiAl-LDH precursor.

[0046] 2.0 g of NiAl-LDH precursor was dispersed in 80 ml of deionized water to form a suspension. A 0.1 mol / L ZrOCl2 aqueous solution was prepared. The ZrOCl2 solution was slowly added dropwise to the NiAl-LDH precursor suspension, controlling the molar ratio of Zr to the total metal in the NiAl-LDH precursor middle layer to be 1:8. The reaction was stirred at 70 °C for 18 hours to carry out ion exchange (Al2O3). 3+ Zr 4+ (Substitution). After the reaction is complete, centrifugation, washing, and drying are performed to obtain the metal hydroxide catalyst.

[0047] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 1 is that the catalyst is the catalyst prepared in Example 6 and the reaction temperature is 55°C.

[0048] Example 7 (1) Preparation of metal hydroxide catalysts Co(NO3)2·6H2O and Al(NO3)3·9H2O were reacted according to Co 2+ :Al 3+ A mixed salt solution with a total metal ion concentration of 1.0 mol / L was prepared by dissolving NaOH and Na₂CO₃ in 100 mL of deionized water at a molar ratio of 3:1. A mixed alkaline solution containing 2.0 mol / L NaOH and 1.0 mol / L Na₂CO₃ was prepared by dissolving NaOH and Na₂CO₃ in 100 mL of deionized water. Under vigorous stirring and constant pressure, both solutions were simultaneously and slowly added dropwise through a constant-pressure dropping funnel to a reaction flask containing 50 mL of deionized water, controlling the dropping rate to stabilize the pH of the reaction system at 10.0. After the addition was complete, the mixture was aged at 65°C for 3 hours. The resulting suspension was centrifuged, washed several times with deionized water, and dried at 80°C for 12 hours to obtain the CoAl-LDH precursor.

[0049] 2.0 g of CoAl-LDH precursor was dispersed in 100 mL of deionized water. A 0.05 mol / L ZrOCl₂ solution was slowly added dropwise, controlling the molar ratio of Zr to the total metal in the middle layer of the CoAl-LDH precursor to be 1:10. Ion exchange was performed at 75 °C for 24 hours (Al 3+ Zr 4+ (Substitution). The product was centrifuged, washed, and dried to obtain a metal hydroxide catalyst.

[0050] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 1 is that the catalyst is the catalyst prepared in Example 7 and the reaction temperature is 55°C.

[0051] Example 8 (1) Preparation of metal hydroxide catalysts The metal hydroxide catalyst obtained in step (1) of Example 5 was mixed with silicon dioxide (SiO2) at a mass ratio of 8:1, pressed into tablets, crushed, and sieved to obtain catalyst particles of 20-40 mesh.

[0052] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 3 is that the catalyst particles are the catalyst particles prepared in Example 8 and the reaction temperature is 40°C.

[0053] Example 9 (1) Preparation of metal hydroxide catalysts The metal hydroxide catalyst obtained in step (1) of Example 6 was mixed with silicon dioxide (SiO2) at a mass ratio of 8:1, pressed into tablets, crushed, and sieved to obtain catalyst particles of 20-40 mesh.

[0054] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 3 is that the catalyst particles are the catalyst particles obtained in Example 9 and the reaction temperature is 55°C.

[0055] Example 10 (1) Preparation of metal hydroxide catalysts The metal hydroxide catalyst obtained in step (1) of Example 7 was uniformly mixed with silicon dioxide (SiO2) at a mass ratio of 8:1, pressed into tablets, crushed, and sieved to obtain catalyst particles of 20-40 mesh.

[0056] (2) Synthesis of sulfonylpyrazine The only difference from step (2) of Example 3 is that the catalyst particles are the catalyst particles obtained in Example 10 and the reaction temperature is 55°C.

[0057] Comparative Example 1 Add 1.0 g of sodium tungstate and 40 mL of methanol to a 250 mL three-necked flask, and stir to 40 °C. Mix 20.0 g of the thioether intermediate with 9.8 g of 30% H₂O₂ solution, and slowly add the mixture dropwise to the reaction flask over 30 minutes. After the addition is complete, continue stirring at 40 °C for 60 minutes. Cool the reaction solution to room temperature, add 50 mL of ice water to crystallize, filter, wash with cold water, and dry to obtain sulfopyrazole product.

[0058] Comparative Example 2 20 mL of catalyst particles were packed into a fixed-bed reactor (10 mm inner diameter). The system was heated to 45 °C and maintained at a back pressure of 0.3 MPa. A methanol solution of the sulfide intermediate (0.5 g / mL) was mixed with 30% H₂O₂ at a molar ratio of 2.2:1 and pumped into the reactor at a flow rate of 0.27 mL / min (residence time 75 ± 2 min). The clarified reaction liquid was collected directly and continuously from the reactor outlet without any catalyst separation step. The catalyst particles were WO₃ / TiO₂ catalyst (WO₃ 10 wt% loading).

[0059] The sulfopyrazole products prepared in the above examples and comparative examples were analyzed by liquid chromatography, and the results are shown in Table 1.

[0060] Table 1

[0061] As can be seen from Examples 1 to 10, the metal hydroxide catalyst provided by the present invention, through the construction of nanosheet and layered bimetallic hydroxide structures, achieves high exposure, stability, and multifunctional synergy at its active sites (Lewis acid sites and hydroxyl groups) (such as Ni). 2+ With Zr 4+ (The synergy of the two); the unique interlayer confinement effect is more like a "nanoreactor", which precisely controls the conversion from sulfide to sulfone through a "step-by-step" oxidation pathway.

[0062] As can be seen from Comparative Examples 1 and 2, the use of sodium tungstate or WO3 / TiO2 as catalysts in the synthesis of sulfonylpyrazole from sulfide intermediates results in poor selectivity for the production of sulfonylpyrazole products.

[0063] In summary, the metal hydroxide catalyst system provided by this invention successfully and systematically solves the core bottlenecks of existing technologies in terms of high selectivity, catalyst separation and recovery, metal residue, and environmental impact. It combines the high efficiency of homogeneous catalysts with the ease of handling of heterogeneous catalysts, providing a breakthrough solution for the green, low-cost, and continuous industrial production of sulfopyrazine.

Claims

1. A metal hydroxide catalyst for the synthesis of sulfonylpyrazine, characterized in that, Including monometallic hydroxides or layered bimetallic hydroxides; The general formula for the monometallic hydroxide is M(OH). y Where M is one of Ni, Co, Fe, Mn, Cu, Mg, Zn, Zr, Ti or Ce, and y is 2, 3 or 4, corresponding to the valence state of M; The layered bimetallic hydroxide has the general formula [M 2+ 1-x (M 3+ x (OH)2] x+ ·[A n- ] x / n ·mH2O or [M 2+ 1-x (M 4+ x (OH)2] 2x+ ·[A n- ] 2x / n ·mH2O, Among them, M 2+ It is a divalent metal cation, selected from Ni 2+ Co 2+ Zn 2+ Mg 2+ At least one of them; M 3+ It is a trivalent metal cation, selected from Fe 3+ Al 3+ Cr 3+ At least one of them; M 4+ It is a tetravalent metal cation, selected from Zr. 4+ Ti 4+ Ce 4+ At least one of them; A n- It is an interlayer anion, selected from CO3. 2- NO3 - OH - At least one of them, where n corresponds to the valence state of the interlayer anion; x is M 3+ x Or M 4+ x The molar ratio of x to total metals is 0.05 ≤ x ≤ 0.3; m represents the amount of water of crystallization.

2. A metal hydroxide catalyst for the synthesis of sulfonylpyrazine according to claim 1, characterized in that, In the layered bimetallic hydroxide, M 2+ With M 3+ Or M 4+ The molar ratio is (3-19):1; the layered bimetallic hydroxide is preferably NiZr-LDH.

3. The method for preparing the catalyst according to any one of claims 1-2, characterized in that, The monometallic hydroxide is prepared from a metal salt by one of the following methods: hydrothermal / solvothermal method or coprecipitation method; The layered bimetallic hydroxide is prepared by co-precipitation of metal salts.

4. The preparation method according to claim 3, characterized in that, The specific steps of the hydrothermal / solvothermal method are as follows: (1) Dissolve the metal salt in an aqueous ethanol solution, add urea, and stir to dissolve; (2) After dissolution, transfer to a high-pressure reactor and react at 120-180℃ for 6-24 hours to obtain a monometallic hydroxide; In step (1), the volume ratio of water to ethanol in the ethanol-water solution is 1:(1-3). The preferred reaction conditions for step (2) are 150°C for 12 hours.

5. The preparation method according to claim 3, characterized in that, The specific steps for preparing monometallic hydroxides by the coprecipitation method are as follows: under vigorous stirring, the metal salt is rapidly mixed with an excess of sodium hydroxide solution, the pH value at the reaction endpoint is controlled between 10.5 and 11.5, the temperature is maintained at 25-60℃, and after the precipitate is formed, it is aged for another 1-3 hours to obtain the monometallic hydroxide.

6. The preparation method according to claim 3, characterized in that, The specific steps for preparing layered bimetallic hydroxides by the co-precipitation method are as follows: (1) Divalent metal ion salts and trivalent or tetravalent metal ion salt solutions are reacted according to M 2+ :(M 3+ Or M 4+ The molar ratio (3-19):1 is dissolved in water to prepare a mixed salt solution with a total metal ion concentration of 0.5-2.0 mol / L; Prepare a mixed alkaline solution containing NaOH and Na2CO3, wherein the concentration of NaOH is 1.0-3.0 mol / L and the concentration of Na2CO3 is 0.5-1.5 mol / L; (2) Add the mixed salt solution and the mixed alkali solution dropwise into the reactor, control the dropping rate to keep the pH value of the system stable in the range of 9.0-10.5, maintain the temperature at 60-80℃, and continue aging for 2-4 hours after the addition is completed to allow the precipitate to fully crystallize and obtain layered bimetallic hydroxide.

7. The preparation method according to claim 3, characterized in that, The layered bimetallic hydroxide was prepared by co-precipitation and ion exchange methods, with the specific steps as follows: (1) Divalent metal ion salts and trivalent or tetravalent metal ion salt solutions are reacted according to M 2+ :(M 3+ Or M 4+ The molar ratio (3-19):1 is dissolved in water to prepare a mixed salt solution with a total metal ion concentration of 0.5-2.0 mol / L; Prepare a mixed alkaline solution containing NaOH and Na2CO3, wherein the concentration of NaOH is 1.0-3.0 mol / L and the concentration of Na2CO3 is 0.5-1.5 mol / L; (2) Add the mixed salt solution and mixed alkali solution dropwise into the reactor, control the dropping rate to keep the pH value of the system stable in the range of 9.0-10.5, and maintain the temperature at 60-80℃. After the addition is completed, continue aging for 2-4 hours to allow the precipitate to fully crystallize. Then, after centrifugation, washing and drying, a layered bimetallic hydroxide precursor is obtained. (3) Disperse the precursor in water to prepare a suspension with a concentration of 20-50 g / L. Slowly add a solution containing the desired exchange ion X to the suspension. Stir and exchange at 60-80℃ for 12-24 hours. After centrifugation, washing and drying, the product is obtained as a layered bimetallic hydroxide. When X is Zr, ZrOCl2 solution is used, and the molar ratio of Zr to the precursor intermediate plate metal is controlled to be 1:(5-10).

8. A method for synthesizing sulfonylpyrazole, characterized in that, The specific steps are as follows: The thioether intermediate 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylthio]-4,5-dihydro-5,5-dimethyl-1,2-isooxazole was mixed with 30-50 wt% hydrogen peroxide solution and added to a reactor containing the catalyst according to any one of claims 1-2. Selective oxidation reaction was carried out at 35-60°C to synthesize sulfopyrazazole. The molar ratio of hydrogen peroxide to the sulfide intermediate is (2.0-2.5):1; The reactor is a batch reactor or a fixed-bed reactor; When the catalyst is a Zr-containing catalyst, the reaction temperature is 50-60℃; When the catalyst is Zr-free, the reaction temperature is 35-50℃.

9. The method for synthesizing sulfonylpyrazole according to claim 8, characterized in that, The specific steps for synthesizing sulfopyrazole using a batch reactor are as follows: The catalyst and methanol were mixed at a mass ratio of 1:(20-40) and added to the reactor. The mixture was stirred and heated to 35-60°C. The sulfide intermediate was mixed with hydrogen peroxide solution and slowly added dropwise to the reactor. After the addition was complete, the reaction was continued for 30-90 minutes. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, concentrated under reduced pressure, crystallized, filtered again, washed, and dried to obtain sulfopyrazole product.

10. The method for synthesizing sulfonylpyrazole according to claim 8, characterized in that, The specific steps for synthesizing sulfopyrazole using a fixed-bed reactor are as follows: (1) The catalyst is loaded into a fixed-bed reactor, heated to 35-60℃, and the back pressure is maintained at 0.2-0.5 MPa; (2) After mixing the sulfide intermediate methanol solution with the hydrogen peroxide solution, pump it into the reactor at a flow rate of 0.2-0.5 mL / min, control the residence time of the material in the reactor to be 60-90 minutes, and collect sulfopyrazine at the reactor outlet; The molar ratio of hydrogen peroxide to the sulfide intermediate is 2.2:1; The concentration of the thioether intermediate in the methanol solution is 0.4-0.6 g / mL.

Images