A new process for the green synthesis of thiodicarb

Abstract

The application discloses a novel green synthesis process of thiodicarb, which uses chlorinated sulfur, methomyl and pyridine as raw materials to prepare thiodicarb, replaces sulfur dichloride in the traditional process with low-cost chlorinated sulfur, reduces the cost of raw materials, uses pyridine as alkalizing agent and solvent, dissolves methomyl in pyridine, makes the reactants in the liquid phase system, is beneficial to mass transfer, heat transfer and improves the reaction effect, removes the water washing process, uses methanol as a washing agent to wash the product, and avoids the problem of large amount of waste water in the conventional process. Under the process operation condition, the conversion rate of methomyl reaches 98.5%, the yield of thiodicarb reaches more than 92.1%, and no waste water is generated in the main process. The prepared thiodicarb is white powder, the colors of products of each batch are consistent, the content is greater than 97.6%, the thermal decomposition rate is less than 2.4%, and the appearance, content and thermal storage stability of the product meet the product standards.

Description

Technical Field

[0001] This invention relates to the field of compound synthesis technology, specifically a novel green synthesis process for thiodicarb. Background Technology

[0002] Dimethoate (abbreviated as dimethoate) is a dicarboxylate insecticide with high efficiency, broad spectrum, low toxicity, and systemic stomach poison action. It is one of the key insecticides used in large quantities both domestically and internationally in the past decade for controlling agricultural pests.

[0003] Currently, the industrial production of thiamethoxam generally employs a method of synthesizing thiamethoxam using methomyl, sulfur dichloride, and pyridine as raw materials in the presence of a solvent. Research focuses on reducing the impurity content in the finished product, improving product yield and purity, enhancing the product's thermal stability, reducing process wastewater generation, and addressing solvent recovery issues.

[0004] In their paper "Synthesis and Application Research of 4-Dimethylaminopyridine" published in the 10th issue of Chemical World in 1997, Sheng Yongli et al. proposed that by using 4-dimethylaminopyridine as a catalyst, the reaction time for synthesizing thiamethoxam was shortened from 20 hours to 10 hours and the yield of thiamethoxam was increased from 86% to 93.7% compared with the use of no catalyst.

[0005] In the first issue of Shaanxi Chemical Industry in 1998, Chai Shengyong et al. published a paper entitled "Study on Synthetic Route of Dimethoate". They conducted a comparative study on the synthetic routes of dimethoate and concluded that the synthetic route using pyridine as both an organic base and a solvent was better. Methanol washing can improve the purity of the product, but after washing with methanol four times, the yield of dimethoate was only 50%; while after washing with water four times, the yield of dimethoate was only 65%.

[0006] The publicly disclosed technical solutions have studied the synthesis process of thiocarbamate from multiple perspectives, including adjusting the solvent and catalyst. For example, patent CN108047106B proposes a method for synthesizing thiocarbamate by using pyridine (toluene, xylene, etc.) as a solvent, 4-dimethylaminopyridine as a catalyst, and separately adding sulfur dichloride and methomyl solutions containing solvent. Patent application CN112778179A proposes a method using pyridine as a solvent, 18-crown ether-6 as a catalyst, and under closed conditions, first adding a portion of sulfur dichloride to a pyridine solution of 18-crown ether-6, then adding the remaining sulfur dichloride and methomyl-pyridine solution to react, while simultaneously introducing chlorine gas; after the addition is complete, the reaction is continued at a constant temperature to obtain thiocarbamate. Patent application CN114031533A proposes using N-methylformamide and sulfur dichloride as raw materials to generate methylformamide thioamidine, which is then condensed with methomyl under the action of a catalyst to generate thiocarbamate.

[0007] Patent application CN114315672A proposes a method using methomyl, pyridine, and sulfur dichloride as raw materials, xylene and toluene as solvents, adding SCl2 dropwise to a reaction vessel at a temperature below 0°C, followed by the addition of methomyl, purging the vessel with nitrogen, and then raising the temperature to proceed with the reaction. After the reaction, centrifugation is performed to obtain a centrifuged liquid and a filter cake. The filter cake undergoes a first water washing and pressure filtration, a second water washing and centrifugation, followed by methanol washing and centrifugation. Finally, the obtained filter cake is vacuum dried to obtain the finished thiocarbamate product. Patent CN112479957A proposes a method using pyridine and sulfur dichloride as raw materials, xylene as solvent, adding SCl2 dropwise to a synthesis vessel containing pyridine and xylene at a temperature of -5 to 0°C to synthesize the ligand dipyridine hydrochloride sulfide; then adding methomyl and a trialkyl tertiary amine catalyst to synthesize thiocarbamate. This method increases the reaction pressure during thiocarbamate synthesis, shortening the synthesis time to 5 hours; it employs three-stage temperature control and gradient heating to avoid the side reactions caused by continuously reacting at high temperatures. In their paper "A New Production Process to Improve the Yield and Purity of Thionylcarbide," published in the 3rd issue of Shandong Chemical Industry in 2022, Zhao Wanxi et al. proposed a process using trialkyl tertiary amines as catalysts and xylene, dichloromethane, and chlorobenzene as solvents. The process involves first preparing ligands with sulfur dichloride and pyridine, and then synthesizing thiocarbide with methomyl under low pressure. The product purity is higher than 97% and the yield is higher than 90% (based on methomyl).

[0008] However, the above technologies still have problems such as large amounts of process wastewater, high costs, and difficulty in wastewater treatment. Furthermore, publicly available technologies have long used SCl2 as a reactant. One reason is that although S2Cl2 and SCl2 produce the same final product, SCl2 has a lower boiling point (60℃) and is easier to purify, therefore sulfur dichloride should be used (Chai Shengyong et al.: Research on the Synthetic Route of Methoxam, Shaanxi Chemical Industry, March 1998). Another reason is that S2Cl2 is generally considered an impurity in SCl2. If the SCl (S2Cl2) content in SCl2 is too high, it will react with pyridine to form dipyridine disulfide hydrochloride. When the ligand of this structure reacts with methomyl, elemental sulfur will be generated. If the elemental sulfur content in the finished product is too high, it will affect the product's thermal stability and other indicators, and may even cause spontaneous combustion (Zhao Wanxi et al.: New Process for Improving the Yield and Purity of Methoxam, Shandong Chemical Industry, Vol. 51, 2022).

[0009] In addition, water washing is a necessary step in traditional synthesis methods, and it is generally performed twice. In the patent "A Method for Synthesizing Sulfadiazine with High Methomyl Conversion Rate" (Publication No.: CN114315672A), the molar ratio of each raw material converted to 100% purity is: Methomyl: Sulfur dichloride: Xylene: Toluene: Pyridine: Water: Methanol = 1:(0.53-0.58):(3.41-3.51):(0.17-0.19):(1.35-1.52):(55-56):(12) The washing water molar amount is 55 times that of methomyl; the patent "A Green Synthesis Process for Reducing Wastewater Generation" (Publication No.: CN115626886A) specifies the molar ratio of each material as methomyl:pyridine:SCl2:water:methanol = 1:(5.795~6.016):(0.516~0.545):(16.133~20.266):(8.886~9.035), reducing the washing water molar amount to methomyl ratio to 16~20. Based on the consumption of 1 kmol of methomyl (162.2 kg), at least 288 kg of water is required.

[0010] In summary, existing technologies for the synthesis of thiamethoxam have achieved product purity exceeding 97% and yield exceeding 90% through continuous advancements. The inventors believe that the key to thiamethoxam synthesis lies in reducing pollution caused by the synthesis process, minimizing wastewater discharge, and lowering production costs. While existing technologies also aim to reduce washing water consumption and wastewater production, the effectiveness still needs improvement. For example, the wastewater generated per ton of thiamethoxam production exceeds 5 cubic meters or even more, containing various organic compounds, making treatment difficult and requiring significant investment. Summary of the Invention

[0011] To address the aforementioned problems in existing technologies, this invention provides a novel green synthesis process for thiodicarb, which significantly reduces wastewater generation and discharge, streamlines preparation steps, lowers production costs, and eliminates potential environmental pollution risks while improving product quality.

[0012] First, this invention uses lower-cost sulfur chloride instead of sulfur dichloride, reducing raw material costs. Second, this invention eliminates the water washing process, further reducing material costs and wastewater treatment costs, as well as reducing wastewater discharge. Third, this invention uses excessive pyridine to dissolve elemental sulfur and pyridine hydrochloride produced by the sulfur chloride reaction, and then uses methanol washing to further reduce sulfur, pyridine, and pyridine hydrochloride in the product, simplifying the washing process of thiodicarb.

[0013] The above effects are achieved by the following technical solution:

[0014] A novel green synthesis process for thiodicarb uses sulfur chloride, pyridine, and methomyl as raw materials. The overall reaction equation is as follows:

[0015]

[0016] Methomyl was synthesized using excess pyridine as a solvent, with the molar ratio of raw materials being methomyl:disulfur dichloride:pyridine = 1:(0.6-0.8):(6-7).

[0017] First, dissolve methomyl in pyridine, then add sulfur chloride dropwise to the methomyl-pyridine solution to carry out the reaction;

[0018] After solid-liquid separation, the solid product obtained from the reaction is no longer washed with water, but directly washed with alcohol, and then dried to obtain the final product.

[0019] In traditional processes, catalysts such as organic bases like 4-dimethylaminopyridine (DMAP) and trialkyl tertiary amines are often added to shorten reaction time and ensure complete reaction. However, these catalysts need to be removed during subsequent product purification. Since pyridine itself is an organic base, the present invention provides a liquid environment for pyridine, which can also play a catalytic role in the reaction, avoiding the troublesome post-processing.

[0020] Includes the following steps:

[0021] Step 1, Preparation: Dissolve methomyl in pyridine to obtain a methomyl pyridine solution; place sulfur chloride in a balance funnel;

[0022] Step 2, Reaction: Place the reactor in a low-temperature constant-temperature reaction bath, add the methomyl pyridine solution, turn on the stirrer and control the stirrer speed to ≤160 rpm; turn on the circulating cold bath, adjust the temperature to -5~0℃, start adding sulfur chloride dropwise, control the dropping rate, and complete the addition of sulfur chloride within 20~30 minutes. The temperature of the sulfur chloride during the dropwise addition should not exceed 10℃. Continue to keep the temperature warm and stir for 20 minutes; after adjusting the temperature to 25~35℃, start timing and react at 25~35℃ for 4~6 hours. Adjust the temperature to below 16℃ and continue stirring for at least 1 hour. Low temperature can reduce the occurrence of some side reactions. By lowering the temperature and continuing to stir for a period of time, the reaction can be ensured to be complete.

[0023] Step 3, solid-liquid separation of the product: The reacted material is filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent recycling; the filter cake is transferred to a methanol washing tank.

[0024] Step 4, alcohol washing and filtration: Install a reflux condenser on the methanol washing vessel and circulate condensate. Add methanol to the vessel, start stirring, and control the stirrer speed to ≤240 rpm for the first alcohol washing. Adjust the temperature to 35-45℃, stir for 0.5-1 hour, and then cool to room temperature for filtration. Collect the filtrate and store it in a methanol washing liquid storage tank for subsequent methanol recovery. Transfer the filter cake to the methanol washing vessel for a second alcohol washing. The second alcohol washing is carried out at room temperature, and after stirring for at least 0.5 hours, cool to below 16℃ and filter. Send the filter cake for drying.

[0025] Step 5, Drying: Vacuum dry the filter cake obtained from filtration, controlling the drying temperature to ≤45℃ and the vacuum degree to ≥0.08MPa. After drying, the sulfadiazine product is obtained.

[0026] Step 6, Product Analysis and Testing: Weigh the obtained thiamethoxam finished product and calculate the yield based on methomyl. Analyze the content of thiamethoxam, methomyl, and elemental sulfur in the finished product using high-performance liquid chromatography (HPLC), and determine the melting point and pH value of the finished product. Conduct a heat storage stability test on thiamethoxam according to the standard GB / T19136-2003 "Determination of Heat Storage Stability of Pesticides" to determine the decomposition rate of the finished thiamethoxam. Verify that the obtained finished product meets the national standard requirements.

[0027] In step 3, the filtrate in the solvent recovery tank mainly consists of pyridine, pyridine hydrochloride, sulfur, and small amounts of methomyl and thiodicarb. The filtrate is first subjected to vacuum flash evaporation to recover approximately 80% of the pyridine. Then, the remaining material is filtered to remove solid impurities, including elemental sulfur. The filter cake is then sent to a sulfur recovery system. The filtrate is treated with sodium hydroxide solution to alkalize the pyridine hydrochloride, converting it to pyridine. Finally, azeotropic distillation is used to recover the pyridine.

[0028] Specifically, during the sodium hydroxide solution treatment process, a 30% sodium hydroxide solution is used to treat the solution until the pH reaches 9-12.

[0029] Specifically, in step 3, the pyridine-containing wastewater, after alkalization treatment, is first added to an azeotropic feed column for azeotropic distillation. An azeotrope (57% pyridine, 43% water) is obtained at the top of the column at a temperature of 92.6℃. After condensation, the reflux ratio is controlled within the range of 3-4. When the vapor temperature reaches 100℃ and the distillation rate is 25%-30%, the pyridine concentration in the distillate is approximately 50%, close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches over 98%, and the residue in the reactor contains almost no pyridine. This residue is then sent to the wastewater treatment system. Next, an appropriate amount of dehydrating agent, toluene, is added to the pyridine-water azeotrope for further azeotropic distillation. After dehydration, an azeotrope of toluene and water at 69.2℃~70℃ is obtained at the top of the column. After cooling, the toluene and water separate into layers. The toluene is recycled, while the water layer is sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration has a water content of approximately 2.0~3.0%. Finally, the crude pyridine is distilled to obtain pyridine. At a reflux ratio of 3~4, a small amount of the fore-fraction is first separated by distillation, and then the main fraction at 114℃~116℃ is collected. The pyridine content reaches more than 99.6%, and the water content is less than 0.04%. The purified recovered pyridine has reached the raw material quality specifications and can be used as a raw material for the production of thiamethoxam. The remaining residue after recovering pyridine is sent to the wastewater treatment system.

[0030] Furthermore, the filter cake obtained after filtering the remaining material after vacuum flash evaporation contains sulfur, a small amount of methomyl and thiodicarb, and other solid insoluble substances. It is recrystallized with CS2 or toluene to precipitate elemental sulfur crystals, and the remaining material is incinerated.

[0031] Furthermore, the wastewater generated during the pyridine recovery process includes the residue from azeotropic distillation to remove the pyridine-water azeotrope, the wastewater after the dehydrating agent and water separate in the azeotropic dehydration process, and the residue from the crude pyridine distillation process. The wastewater is treated by triple-effect evaporation. The condensate generated during the evaporation process can be reused or discharged after meeting the standards. The residue (waste salt) obtained after evaporation is treated as hazardous waste and entrusted to a qualified hazardous waste treatment unit for harmless treatment.

[0032] The single-solvent preparation method provided by this invention does not contain other solvents in the pyridine waste liquid obtained in step 3. High-purity pyridine can be recovered through vacuum flash evaporation, alkalization and azeotropic distillation. Unlike the prior art, which directly recycles pyridine in the pyridine waste liquid for subsequent thiodicarb synthesis in order to improve the utilization rate of pyridine, the pyridine recovered by this invention has higher purity, a wider range of uses, and lower processing costs.

[0033] In step 4, the filtrate in the methanol washing liquid storage tank mainly consists of methanol, and contains small amounts of pyridine, methomyl, sulfur, and organic compounds such as methomyl and thiodicarb. Methanol is recovered and recycled using a methanol distillation unit. The remaining waste liquid after methanol recovery undergoes further treatment to separate out sulfur and other substances.

[0034] Furthermore, the waste liquid after methanol recovery contains small amounts of pyridine, sulfur, methomyl, and thiodicarb. The solid phase obtained after filtration mainly contains sulfur, methomyl, and thiodicarb. It is recrystallized with CS2 or toluene to precipitate elemental sulfur crystals. The filtrate obtained from filtration is sent to the wastewater treatment system.

[0035] Step 4, during the alcohol washing process, the filtrate obtained from the second alcohol washing is used as the washing agent for the first alcohol washing, and fresh methanol is used for the second alcohol washing; the ratio of the total amount of fresh methanol used to methomyl is 230-280g of methanol added per mole of methomyl.

[0036] Unless otherwise stated, the above material ratios are calculated and given based on a raw material purity of 100%.

[0037] This invention, through scientific experimental design, uses excessive pyridine as both an alkalizing agent and a single solvent. This addresses the issue of sulfur chloride affecting product storage stability when used as a reactant, overcoming the preconceived notion that sulfur dichloride is superior to sulfur chloride in the preparation of thiamethoxam. Furthermore, it eliminates the need for water washing, significantly reducing production costs and shortening the time for material recovery after the reaction, thus reducing the overall production cycle and improving efficiency. Unexpectedly, the quality of the obtained product surpasses that of products obtained using existing technologies, providing a new research approach for the low-cost, green synthesis of thiamethoxam.

[0038] In traditional synthesis methods, water washing is a necessary step, and it is generally performed twice. In the patent "A Method for Synthesizing Sulfadiazine with High Methomyl Conversion Rate" (Publication No.: CN114315672A), the molar ratio of each raw material converted to 100% purity is: Methomyl: Sulfur Dichloride: Xylene: Toluene: Pyridine: Water: Methanol = 1:(0.53-0.58):(3.41-3.51):(0.17-0.19):(1.35-1.52):(55-56):(12.5) -14.3), the molar amount of washing water is 55 times that of methomyl; the patent "A green synthesis process of sulfadiazine to reduce wastewater generation" (publication number: CN115626886A) has a molar ratio of methomyl:pyridine:SCl2:water:methanol = 1:(5.795~6.016):(0.516~0.545):(16.133~20.266):(8.886~9.035), which reduces the molar ratio of washing water to methomyl to 16~20.

[0039] The purpose of water washing is to remove the byproduct pyridine hydrochloride. Pyridine is used as a solvent, and since the pyridine hydrochloride dissolves in pyridine, water washing is unnecessary. This invention eliminates the water washing process. Instead, by adding an excess of pyridine, the pyridine hydrochloride and elemental sulfur are dissolved in pyridine, thus eliminating the need for washing water. This significantly reduces water consumption and wastewater generation. The pyridine containing various dissolved substances undergoes simplified treatment; the pyridine hydrochloride is alkalized and converted back to pyridine, which is then recovered using azeotropic distillation.

[0040] In addition, the inventors were pleasantly surprised to find that the product prepared by this method has a uniform particle size distribution, is a white solid powder, and the color of the product is consistent in multiple tests. The purity and yield of the product are also high, which significantly improves the quality and appearance of the product.

[0041] The reasons for this are twofold. First, using excess pyridine as the solvent, methomyl dissolves in pyridine, and the reaction system is in the liquid phase. After the addition of sulfur chloride, the intermediate product generated from the reaction of pyridine and sulfur chloride reacts with methomyl to obtain a uniformly dispersed solid thiodicarb in the liquid phase, resulting in a product with a uniform particle size distribution. In contrast, reaction systems using toluene or xylene as solvents have poorer reaction efficiency because the intermediate product from the reaction of pyridine and sulfur chloride is a solid, and methomyl, which has low solubility in toluene and xylene, is also a solid. Furthermore, experiments show that when toluene or xylene is used as a solvent, the color of subsequent batches of product is inconsistent. The reasons for this, besides factors such as temperature and the solubility of sulfur in the solvent, include the instability of the solid-liquid reaction system, which causes instability in product particle size and color. Therefore, using excess pyridine as the solvent, instead of toluene or xylene, yields better results! The product has a uniform particle size distribution, is a white solid powder, and the yield is improved. On the other hand, this invention eliminates the water washing process and uses methanol as the washing agent to wash the product, avoiding the problem of large wastewater volume in conventional processes. The filtrate obtained after alcohol washing is recycled by a methanol distillation unit, with a methanol recovery rate of more than 85.8%, reducing production costs. Because the residual sulfur, pyridine, pyridine hydrochloride, methomyl, and isomer byproducts in the product have a higher solubility in methanol than in water, washing with methanol results in a narrower melting range (melting points of various batches are between 165.2 and 169.6 °C, while the melting point of products obtained by traditional washing methods is between 155.6 and 166.9 °C) and higher purity than washing with water. Although it affects the yield, it improves the purity and thermal storage stability of the product and enhances its appearance consistency.

[0042] Furthermore, in this application, all the pyridine is used to dissolve methomyl. Since this application generates a large amount of solid sulfur, this method can dissolve elemental sulfur promptly. Simultaneously, any excess pyridine is recovered directly by flash evaporation and can be reused. This method avoids the drawbacks of extracting pyridine from the washing filtrate and simplifies the process.

[0043] However, it is important to understand that the above improvements cannot be achieved simply by adding an excessive amount of pyridine or changing a single condition in the water washing process. This invention removes most of the pyridine hydrochloride, sulfur, and small amounts of methomyl and thiocarbamate from the filter cake obtained from solid-liquid separation by adding an excessive amount of pyridine. Since there is no water washing process, this invention uses an increased amount of methanol for washing and a secondary alcohol washing method to remove the remaining small amount of impurities from the filter cake. Furthermore, because sulfur chloride is used as a solvent, more elemental sulfur is generated, making water washing less effective; the secondary alcohol washing method is more efficient at removing sulfur. This invention cleverly combines these four aspects, further improving product quality, simplifying the process, and reducing production costs without sacrificing product yield and purity.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. Thionyl carbide is prepared using sulfur chloride, methomyl, and pyridine as raw materials. The use of lower-cost sulfur chloride instead of sulfur dichloride in the traditional process reduces the cost of raw materials.

[0046] 2. Selecting a suitable solvent improves reaction efficiency. Since the intermediate complex formed by sulfur chloride and pyridine precipitates as a solid, and methomyl is also a solid, solid-phase reactions are difficult to transfer heat and have poor reaction efficiency. Therefore, a solvent must be added for dispersion. Methomyl is readily soluble in polar solvents such as pyridine. Using pyridine as both a solvent allows the reaction to proceed in a liquid-phase system, facilitating mass and heat transfer and improving reaction efficiency. The generated elemental sulfur also dissolves in pyridine, reducing the types of solvents added to the reaction system. Pyridine and the generated pyridine hydrochloride can be recycled in subsequent processing, with a pyridine recovery rate greater than 95%, reducing production costs.

[0047] 3. The washing process is eliminated, and methanol is used as the detergent to wash the product, avoiding the problems of large water consumption and large wastewater volume in conventional processes. Compared with patent CN115626886, based on the consumption of 1 kmol methomyl (162.2 kg), the solution of this application can save at least 288 kg of water.

[0048] The filtrate obtained after alcohol washing is recycled by methanol distillation, with a methanol recovery rate of more than 85.8%. No wastewater is generated in the main process, except for a small amount of wastewater generated during the alkalization treatment of the by-product pyridine hydrochloride. The production cost of the product is reduced by about 10% compared with the traditional process.

[0049] 4. The resulting product has a narrow melting range, more uniform particle size distribution, and is a white powder. The color of each batch of product is consistent, and the purity and thermal storage stability of the product are improved, with good appearance consistency.

[0050] 5. The saline wastewater after pyridine recovery is treated by triple-effect evaporation, and the wastewater can be reused or discharged in compliance with standards. The waste residue is handed over to a qualified unit for harmless treatment. The amount of "three wastes" generated in the entire production process is greatly reduced, avoiding environmental pollution. It is a green synthesis process that is relatively clean and environmentally friendly.

[0051] 6. This process employs a reasonable ratio of raw materials and solvents, and optimizes process conditions through orthogonal experiments. Under the optimized operating conditions, the conversion rate of methomyl reaches 98.5%, the yield of thiamethoxam exceeds 92.1%, wastewater volume is reduced by more than 80%, and the product production cost is reduced by approximately 10% compared to traditional processes. The prepared thiamethoxam is a white powder with a content greater than 97.6% and a thermal decomposition rate less than 2.4%. All product indicators, including appearance, content, and thermal storage stability, meet product standards. Attached Figure Description

[0052] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0053] Figure 1 A flowchart of the novel green synthesis process for thiamethoxam provided by this invention;

[0054] Figure 2 The graph shows the particle size distribution test results of the product in Example 1. Detailed Implementation

[0055] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0056] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0057] Example 1

[0058] (1) Preparation of materials. Weigh 52g of methomyl and dissolve it in 156g of pyridine to obtain a methomyl pyridine solution. Add 24.2g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0059] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 150 rpm. The circulating cold bath was turned on, and the temperature was adjusted to -4℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 20 min (the temperature during the dropping was ≤10℃). Stirring was continued for another 20 min. The temperature was adjusted to 25℃ and the timing was started. The reaction was carried out at 25℃ for 6 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0060] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0061] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 80g of the secondary alcohol washing filtrate. Stirring is started, and the stirrer speed is controlled to ≤220rpm. The temperature is adjusted to 45℃, and after stirring for 1.0h, it is cooled to room temperature and filtered. The filtrate obtained from the primary alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 80g of fresh methanol is added for the second alcohol washing, and after stirring at room temperature for about 0.5h, it is cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of primary alcohol washing; the filter cake is sent for drying.

[0062] (5) Drying. The filter cake was placed in a vacuum dryer and dried under vacuum conditions, with the drying temperature controlled at ≤45℃ and the vacuum degree at ≥0.08MPa. After drying for 3 hours, 52.2g of a white powdery solid thiamethoxam with uniform particle size distribution was obtained. The thiamethoxam yield was calculated to be 91.8% based on methomyl.

[0063] The particle size distribution of the product was tested, and the results are as follows: Figure 2 As shown, D90 = 25.49 μm, indicating that the product particles are small and evenly distributed, and the product quality uniformity is good.

[0064] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 95.7% thiamethoxam, 0.24% methomyl, and 0.30% elemental sulfur. The melting point was 169℃ and the pH was 6.1. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the thiamethoxam was found to be 2.4%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0065] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction products is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. Then, the remaining material is filtered, and the filter cake is sent to the sulfur recovery system. The filtrate is treated with 30% sodium hydroxide solution to pH=10, and the hydrochloride in it is alkalized and converted into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 3. When the gas phase temperature reaches 100℃ and the distillation rate is 25%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%, and the residue in the kettle is almost negligible. The pyridine-containing residue was sent to the wastewater treatment system. Then, an appropriate amount of toluene, a dehydrating agent, was added to the pyridine-water azeotrope for azeotropic dehydration. An azeotrope of toluene and water at 69.2℃–70℃ was obtained at the top of the column. After cooling, the toluene and water were separated into layers. The toluene was recycled, and the water layer was sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration had a water content of approximately 3.0%. Finally, the dehydrated crude pyridine was distilled to obtain pyridine. Under a reflux ratio of 3, a small amount of the fore-fraction was first separated by distillation, and then the main fraction at 114℃–116℃ was collected. The pyridine content reached over 99.6%, and the water content was less than 0.04%. The remaining residue after pyridine recovery was sent to the wastewater treatment system. The pyridine obtained through the above recovery process met the raw material quality specifications and could be used as a raw material for the production of thiamethoxam. A total of 144.6g of final distillate was obtained, with a recovery rate of 92.2%.

[0066] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic compounds such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 86%. The waste liquid remaining after methanol recovery is recycled and treated.

[0067] (9) Wastewater treatment. The wastewater after pyridine recovery contains sulfur, sodium chloride and a small amount of other substances dissolved in water. The elemental sulfur is separated by filtration, and then the wastewater is treated by triple-effect evaporation. After the treated wastewater meets the standards, it can be reused or discharged. The residue (waste salt) obtained after evaporation is treated as hazardous waste and entrusted to a qualified hazardous waste treatment unit for harmless treatment.

[0068] (10) Waste liquid treatment. The waste liquid after methanol recovery contains small amounts of pyridine, methomyl, sulfur and thiodicarb, etc. After taking appropriate separation measures to recover the sulfur, methomyl and thiodicarb, the residue is treated as hazardous waste and entrusted to a qualified hazardous waste treatment unit for harmless treatment.

[0069] Example 2

[0070] (1) Preparation of materials. Weigh 81.2g of methomyl and dissolve it in 257g of pyridine to obtain a methomyl pyridine solution. Add 35.2g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0071] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 140 rpm. The circulating cold bath was turned on, and the temperature was adjusted to -3℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 25 min (the temperature during the dropping was ≤10℃). Stirring was continued for another 20 min. The temperature was adjusted to 30℃ and the timer was started. The reaction was carried out at 30℃ for 5 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0072] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0073] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 138g of the filtrate obtained from the second alcohol washing. Stirring is started, and the stirrer speed is controlled to be ≤230rpm. The temperature is adjusted to 40℃, and after stirring for 50min, it is cooled to room temperature and filtered. The filtrate obtained from the first alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 138g of fresh methanol is added for the second alcohol washing, and after stirring at room temperature for about 0.5h, it is cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of the first alcohol washing. The filter cake is sent for drying.

[0074] (5) Drying. The filter cake was placed in a vacuum dryer and dried under vacuum conditions, with the drying temperature controlled at ≤45℃ and the vacuum degree at ≥0.08MPa for 2.5h. After drying, 81.2g of a white powdery solid thiocarbamate with uniform particle size distribution was obtained. The yield of thiocarbamate was calculated to be 91.5% based on methomyl.

[0075] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 96.9% thiamethoxam, 0.30% methomyl, and 0.29% elemental sulfur. The melting point was measured to be 169.6℃ and the pH value to be 5.9. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the thiamethoxam was found to be 2.3%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0076] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction product is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. The residue is treated with 30% sodium hydroxide solution to pH 12 to alkalize the hydrochloride and convert it into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 3.5. When the vapor temperature reaches 100℃ and the distillation rate is 30%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%. The residue in the reactor contains almost no pyridine and is sent to the wastewater treatment plant. The system then processes the pyridine and water azeotrope; toluene, an appropriate amount of dehydrating agent, is added to the azeotropic dehydration agent to the pyridine and water azeotrope, resulting in a toluene-water azeotrope at 69.2℃~70℃ at the top of the column. After cooling, the toluene and water are separated, the toluene is recycled, and the aqueous layer is sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration has a water content of approximately 2.5%. Finally, the dehydrated crude pyridine is distilled to obtain pyridine. Under a reflux ratio of 3.5, a small amount of the fore-distillate is first separated, and then the main fraction at 114℃~116℃ is collected. The pyridine content reaches over 99.6%, and the water content is less than 0.04%. The remaining residue after pyridine recovery is sent to the wastewater treatment system. The pyridine obtained through the above recovery process meets the raw material quality specifications and can be used as a raw material for the production of thiamethoxam. A total of 240g of final distillate is obtained, with a recovery rate of 93.4%.

[0077] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic matter such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 84.5%. The waste liquid remaining after methanol recovery is recycled and treated.

[0078] (9) Wastewater treatment and (10) waste liquid treatment were carried out using the same methods as in Example 1.

[0079] Example 3

[0080] (1) Preparation of materials. Weigh 162.3g of methomyl and dissolve it in 554g of pyridine to obtain a methomyl pyridine solution. Add 72.9g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0081] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 160 rpm. The circulating cold bath was turned on, and the temperature was adjusted to -4℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 30 min (the temperature during the dropping was ≤10℃). Stirring was continued for another 20 min. The temperature was adjusted to 28℃ and the timing was started. The reaction was carried out at 28℃ for 6 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0082] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0083] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 280g of the filtrate obtained from the second alcohol washing. Stirring is started, and the stirrer speed is controlled to ≤240rpm. The temperature is adjusted to 35℃, and after stirring for 1 hour, it is cooled to room temperature and filtered. The filtrate obtained from the first alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 280g of fresh methanol is added for the second alcohol washing, and the mixture is stirred at room temperature for about 0.5 hours, then cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of first alcohol washing. The filter cake is sent for drying.

[0084] (5) Drying. The product was vacuum dried at a temperature ≤45℃ and a vacuum degree ≥0.08MPa for 3 hours to obtain 163.4g of a white powdery solid thiocarbamate with uniform particle size distribution. The yield of thiocarbamate was calculated to be 92.1% based on methomyl.

[0085] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 98.0% thiamethoxam, 0.31% methomyl, and 0.21% elemental sulfur. The melting point was 167.0℃ and the pH was 6.5. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the thiamethoxam was found to be 2.1%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0086] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction products is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. Then, the remaining material is filtered, and the filter cake is sent to the sulfur recovery system. The filtrate is treated with a 30% sodium hydroxide solution to a pH of about 11, and the hydrochloride in it is alkalized and converted into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 4. When the gas phase temperature reaches 100℃ and the distillation rate is 28%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%, and the residue in the kettle is almost completely recovered. The pyridine-free fraction was sent to the sulfur recovery system. Then, an appropriate amount of toluene was added to the pyridine-water azeotrope for azeotropic dehydration. An azeotrope of toluene and water at 69.2℃–70℃ was obtained at the top of the column. After cooling, the toluene and water were separated into layers. The toluene was recycled, and the water layer was sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration had a water content of approximately 2.0%. Finally, the dehydrated crude pyridine was distilled to obtain pyridine. Under a reflux ratio of 3.0, a small amount of the fore-fraction was first separated, and then the main fraction at 114℃–116℃ was collected. The pyridine content reached over 99.6%, and the water content was less than 0.04%. The remaining residue after pyridine recovery was sent to the wastewater treatment system. The pyridine obtained through the above recovery process met the raw material quality specifications and could be used as a raw material for the production of thiodicarb. A total of 525.2g of final distillate was obtained, with a recovery rate of 94.8%.

[0087] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic compounds such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 85.2%. The waste liquid remaining after methanol recovery is recycled and treated.

[0088] (9) Wastewater treatment and (10) waste liquid treatment were carried out using the same methods as in Example 1.

[0089] Example 4

[0090] (1) Preparation of materials. Weigh 243.5g of methomyl and dissolve it in 730g of pyridine to obtain a methomyl pyridine solution. Add 113.4g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0091] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 130 rpm. The circulating cold bath was turned on, and the temperature was adjusted to -2℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 25 min (the temperature during the dropping was ≤10℃). Stirring was continued for another 20 min. The temperature was adjusted to 32℃ and the timing was started. The reaction was carried out at 32℃ for 6 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0092] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0093] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 405g of the filtrate obtained from the second alcohol washing. Stirring is started, and the stirrer speed is controlled to be ≤220rpm. The temperature is adjusted to 35℃, and after stirring for 1 hour, it is cooled to room temperature and filtered. The filtrate obtained from the first alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 405g of fresh methanol is added for the second alcohol washing, and after stirring at room temperature for about 0.5 hours, it is cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of first alcohol washing; the filter cake is sent for drying.

[0094] (5) Drying. The product was vacuum dried at a temperature ≤45℃ and a vacuum degree ≥0.08MPa for 3 hours to obtain 485.3g of a white powdery solid thiamethoxam with uniform particle size distribution. The yield of thiamethoxam was calculated to be 91.2% based on methomyl.

[0095] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 96.7% thiamethoxam, 0.33% methomyl, and 0.38% elemental sulfur. The melting point was measured to be 165.2℃ and the pH value to be 6.6. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the thiamethoxam was found to be 2.6%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0096] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction products is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. Then, the remaining material is filtered, and the filter cake is sent to the sulfur recovery system. The filtrate is treated with 30% sodium hydroxide solution to pH=10 to alkalize the hydrochloride and convert it into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 3. When the vapor temperature reaches 100℃ and the distillation rate is 30%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%, and the residue in the kettle contains almost no pyridine. Pyridine and residual liquid were sent to the wastewater treatment system. Then, an appropriate amount of toluene, a dehydrating agent, was added to the azeotrope of pyridine and water for azeotropic dehydration. An azeotrope of toluene and water at 69.2℃–70℃ was obtained at the top of the column. After cooling, the toluene and water were separated; the toluene was recycled, and the aqueous layer was sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration had a water content of approximately 2.2%. Finally, the dehydrated crude pyridine was distilled to obtain pyridine. Under a reflux ratio of 3.5, a small amount of fore-fraction was first separated by distillation, and then the main fraction at 114℃–116℃ was collected. The pyridine content reached over 99.6%, and the water content was less than 0.04%. The remaining residual liquid after pyridine recovery was sent to the wastewater treatment system. The pyridine obtained through the above recovery process met the raw material quality specifications and could be used as a raw material for the production of thiamethoxam. A total of 689.8g of final distillate was obtained, with a recovery rate of 94.1%.

[0097] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic matter such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 84.6%. The waste liquid remaining after methanol recovery is recycled and treated.

[0098] (9) Wastewater treatment and (10) waste liquid treatment were carried out using the same methods as in Example 1.

[0099] Example 5

[0100] (1) Preparation of materials. Weigh 325g of methomyl and dissolve it in 975g of pyridine to obtain a methomyl pyridine solution. Add 149.3g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0101] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 160 rpm. The circulating cold bath was turned on, and the temperature was adjusted to -1℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 30 min (the temperature during the dropping was ≤10℃). Stirring was continued for another 20 min. The temperature was adjusted to 34℃ and the timing was started. The reaction was carried out at 34℃ for 6 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0102] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0103] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 550g of the filtrate obtained from the second alcohol washing. Stirring is started, and the stirrer speed is controlled to ≤240rpm. The temperature is adjusted to 38℃, and after stirring for 1 hour, it is cooled to room temperature and filtered. The filtrate obtained from the first alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 550g of fresh methanol is added for the second alcohol washing, and the mixture is stirred at room temperature for about 0.5 hours, then cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of first alcohol washing. The filter cake is sent for drying.

[0104] (5) Drying. The product was vacuum dried at a temperature ≤45℃ and a vacuum degree ≥0.08MPa for 3 hours to obtain 648.2g of a white powdery solid thiocarbamate with uniform particle size distribution. The yield of thiocarbamate was calculated to be 91.4% based on methomyl.

[0105] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 96.6% thiamethoxam, 0.34% methomyl, and 0.23% elemental sulfur. The melting point was measured to be 164.9℃ and the pH value to be 6.4. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the finished thiamethoxam was found to be 2.7%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0106] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction products is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. Then, the remaining material is filtered, and the filter cake is sent to the sulfur recovery system. The filtrate is treated with 30% sodium hydroxide solution to pH=10, and the hydrochloride in it is alkalized and converted into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 3.5. When the gas phase temperature reaches 100℃ and the distillation rate is 27%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%, and the residue in the reactor is almost completely recovered. The residue, free of pyridine, was sent to the wastewater treatment system. Then, an appropriate amount of toluene, a dehydrating agent, was added to the pyridine-water azeotrope for azeotropic dehydration. An azeotrope of toluene and water at 69.2℃–70℃ was obtained at the top of the column. After cooling, the toluene and water were separated; the toluene was recycled, and the aqueous layer was sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration had a water content of approximately 2.5%. Finally, the dehydrated crude pyridine was distilled to obtain pyridine. With a reflux ratio of 4, a small amount of the fore fraction was first distilled off, and then the main fraction at 114℃–116℃ was collected. The pyridine content reached over 99.6%, and the water content was less than 0.04%. The remaining residue after pyridine recovery was sent to the wastewater treatment system. The pyridine obtained through the above recovery process met the raw material quality specifications and could be used as a raw material for the production of thiamethoxam. A total of 928.2g of final distillate was obtained, with a recovery rate of 94.7%.

[0107] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic matter such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 84.8%. The waste liquid remaining after methanol recovery is recycled and treated.

[0108] (9) Wastewater treatment and (10) waste liquid treatment were carried out using the same methods as in Example 1.

[0109] Example 6

[0110] (1) Preparation of materials. Weigh 163.0g of methomyl and dissolve it in 489g of pyridine to obtain a methomyl pyridine solution. Add 75.3g of S2Cl2 to the equilibrium dropper and place the dropper on the reaction vessel.

[0111] (2) Reaction process. The reactor was placed in a low-temperature constant-temperature reaction bath, and a pyridine solution of methomyl was added. Stirring was started, and the stirrer speed was controlled at 140 rpm. The circulating cold bath was turned on, and the temperature was adjusted to 0℃. S2Cl2 was added dropwise, and the dropping rate was controlled. Sulfur chloride was added dropwise within 24 min (temperature ≤10℃ during dropping). Stirring was continued for another 20 min. The temperature was adjusted to 29℃ and the timer was started. The reaction was carried out at 29℃ for 5 h. Then the temperature was adjusted to below 16℃ and stirring was continued for 1 h.

[0112] (3) Solid-liquid separation of products. The reacted materials are filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent solvent recycling. The filter cake is transferred to a methanol washing tank.

[0113] (4) Alcohol washing and filtration. A reflux condenser is installed on the methanol washing vessel and circulating cooling water is introduced. The filter cake obtained after solid-liquid separation is added to the vessel, along with 250g of the filtrate obtained from the second alcohol washing. Stirring is started, and the stirrer speed is controlled to be ≤240rpm. The temperature is adjusted to 42℃, and after stirring for 40min, it is cooled to room temperature and filtered. The filtrate obtained from the first alcohol washing is collected and stored in a methanol washing liquid storage tank for subsequent methanol recovery. The filter cake is transferred to the methanol washing vessel for a second alcohol washing. 250g of fresh methanol is added for the second alcohol washing, and after stirring at room temperature for about 0.5h, it is cooled to below 16℃ and filtered. The filtrate obtained from the second alcohol washing is used as the washing liquid for the next batch of first alcohol washing; the filter cake is sent for drying.

[0114] (5) Drying. The product was vacuum dried at a temperature ≤45℃ and a vacuum degree ≥0.08MPa for 3 hours to obtain 161.3g of a white powdery solid thiocarbamate with uniform particle size distribution. The yield of thiocarbamate was calculated to be 91.0% based on methomyl.

[0115] (6) Product Analysis and Testing. High-performance liquid chromatography (HPLC) analysis revealed that the finished product contained 97.8% thiamethoxam, 0.32% methomyl, and 0.36% elemental sulfur. The melting point was 167.2℃, and the pH was 6.0. A thermal storage stability test was conducted according to the standard GB / T19136-2003 "Determination of Thermal Storage Stability of Pesticides." The decomposition rate of the thiamethoxam was found to be 2.4%, lower than the national standard requirement of 5%. All indicators of the obtained thiamethoxam finished product met the national standard requirements.

[0116] (7) Solvent recovery and recycling. The filtrate obtained from filtering the reaction products is placed in a solvent recovery tank. The main components are pyridine, pyridine hydrochloride, sulfur, and a small amount of methomyl. The filtrate is first subjected to vacuum flash evaporation to recover about 80% of the pyridine. Then, the remaining material is filtered, and the filter cake is sent to the sulfur recovery system. The filtrate is treated with 30% sodium hydroxide solution to pH=10, and the hydrochloride in it is alkalized and converted into pyridine. The pyridine-containing wastewater after alkalization is subjected to azeotropic distillation. An azeotrope (57% pyridine and 43% water) is obtained at the top of the column at a temperature of 92.6℃. The reflux ratio is controlled at about 4. When the gas phase temperature reaches 100℃ and the distillation rate is 25%, the pyridine concentration in the distillate is about 50%, which is close to the equilibrium concentration of azeotropic distillation. The pyridine recovery rate reaches more than 98%, and the residue in the kettle is almost negligible. The pyridine-containing residue was sent to the wastewater treatment system. Then, an appropriate amount of toluene, a dehydrating agent, was added to the pyridine-water azeotrope for azeotropic dehydration. An azeotrope of toluene and water at 69.2℃–70℃ was obtained at the top of the column. After cooling, the toluene and water were separated; the toluene was recycled, and the aqueous layer was sent to the wastewater treatment system. The crude pyridine obtained after azeotropic dehydration had a water content of approximately 2.8%. Finally, the dehydrated crude pyridine was distilled to obtain pyridine. Under a reflux ratio of 3, a small amount of the fore fraction was first distilled off, and then the main fraction at 114℃–116℃ was collected. The pyridine content reached over 99.6%, and the water content was less than 0.04%. The remaining residue after pyridine recovery was sent to the wastewater treatment system. The pyridine obtained through the above recovery process met the raw material quality specifications and could be used as a raw material for the production of thiamethoxam. A total of 465.5g of final distillate was obtained, with a recovery rate of 94.8%.

[0117] (8) Methanol recovery and recycling. The filtrate obtained after methanol washing and filtration is collected and stored in a methanol washing liquid storage tank. The main component is methanol, and it also contains small amounts of organic matter such as pyridine, methomyl, sulfur and the product thiodicarb. Methanol is recovered and recycled using a methanol distillation unit, with a methanol recovery rate of approximately 83.8%. The waste liquid remaining after methanol recovery is recycled and treated.

[0118] (9) Wastewater treatment and (10) waste liquid treatment were carried out using the same methods as in Example 1.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A novel green synthesis process for thiodicarb, characterized in that, Using sulfur chloride, pyridine, and methomyl as raw materials, the overall reaction equation is: The molar ratio of the raw materials is methomyl: disulfur dichloride: pyridine = 1:0.6~0.8:6~7; Includes the following steps: Step 1, Preparation: Dissolve methomyl in pyridine to obtain a methomyl pyridine solution; place sulfur chloride in a balance funnel; Step 2, reaction: Place the reaction vessel in a low-temperature constant temperature reaction bath, add the pyridine solution of methomyl, turn on the stirrer, and control the stirrer speed to ≤160 rpm; Turn on the circulating cold bath and adjust the temperature to -5~0℃. Start adding sulfur chloride dropwise, controlling the dropping rate, and complete the addition of sulfur chloride within 20~30 minutes. The temperature of the sulfur chloride during the addition should not exceed 10℃. Continue to keep the temperature warm and stir the reaction for 20 minutes. After adjusting the temperature to 25~35℃, start timing and react at 25~35℃ for 4~6 hours. After the reaction is completed, adjust the temperature to below 16℃ and continue stirring for at least 1 hour. Step 3, solid-liquid separation of the product: The reacted material is filtered, and the filtrate is collected and stored in a solvent recovery tank for subsequent recycling; the filter cake is transferred to a methanol washing tank. Step 4, alcohol washing and filtration: Install a reflux condenser on the methanol washing tank and circulate condensate. Add methanol to the tank, start stirring, and control the stirrer speed to ≤240 rpm for the first alcohol washing. Adjust the temperature to 35~45℃, stir for 0.5~1h, and then cool to room temperature for filtration. Collect the filtrate and store it in a methanol washing liquid storage tank for subsequent methanol recovery. Transfer the filter cake to the methanol washing tank for a second alcohol washing. The second alcohol washing is carried out at room temperature, and after stirring for at least 0.5h, cool to below 16℃ and then filter. The filter cake is sent to dry; Step 5, Drying: The filter cake obtained by filtration is vacuum dried, and the drying temperature of the vacuum dryer is controlled to be ≤45℃ and the vacuum degree is ≥0.08MPa. After drying, the sulfadiazine product is obtained. In step 3, the filtrate in the solvent recovery tank is first subjected to vacuum flash evaporation to recover pyridine; then the remaining material is filtered to remove solid impurities including elemental sulfur, the filtrate is treated with sodium hydroxide solution to alkalize the pyridine hydrochloride and convert it into pyridine, and finally pyridine is recovered by azeotropic distillation. In step 3, the pyridine-containing wastewater after alkalization is first subjected to azeotropic distillation to obtain an azeotrope of pyridine and water; then, a dehydrating agent is added to the azeotrope of pyridine and water for azeotropic dehydration; finally, the dehydrated crude pyridine is distilled to obtain pyridine; and the wastewater generated in the pyridine recovery process is sent to the wastewater treatment system.

2. The novel green synthesis process for thiodicarb according to claim 1, characterized in that, The filter cake obtained after filtering the remaining material after vacuum flash evaporation is recrystallized with CS2 or toluene to precipitate elemental sulfur crystals, and the remaining material is incinerated.

3. The novel green synthesis process for thiodicarb according to claim 1, characterized in that, Wastewater generated during the pyridine recovery process is treated by triple-effect evaporation. The condensate produced during the evaporation process can be reused or discharged after meeting the standards. The residue obtained after evaporation is treated as hazardous waste.

4. The novel green synthesis process for thiodicarb according to claim 1, characterized in that, In step 4, the filtrate in the methanol washing liquid storage tank is used to recover methanol and recycle it using a methanol distillation unit. The remaining waste liquid after methanol recovery is recycled and treated to separate sulfur and other substances.

5. A novel green synthesis process for thiodicarb according to claim 4, characterized in that, After recovering methanol, the waste liquid is separated and the sulfur, methomyl, and thiodicarb are recovered. The residue is then treated as hazardous waste.

6. The novel green synthesis process for thiodicarb according to claim 1, characterized in that, In step 4, during the alcohol washing process, the filtrate obtained from the second alcohol washing is used as the washing agent for the first alcohol washing, while fresh methanol is used for the second alcohol washing.

7. A novel green synthesis process for thiodicarb according to claim 6, characterized in that, The ratio of fresh methanol to methomyl is 230-280g of methanol per mole of methomyl.

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