Thiamethoxam preparation process based on low-temperature reaction

Abstract

The invention discloses a thiamethoxam preparation process based on low-temperature reaction, and relates to the technical field of pesticide synthesis. The preparation process comprises the following steps: adding dichloroethane, 2-chloro-5-chloromethylthiazole and 3-methyl-4-nitroimino perhydrogenation-1, 3, 5-oxadiazine into a reaction kettle, sequentially adding an organic amine catalyst, a metal salt catalyst and deionized water, heating, and adding potassium carbonate; regulating the reaction temperature to 45-48 DEG C, and keeping the temperature to react for 3-5 hours; adding softened water, heating, standing and layering to obtain an organic layer and a water layer; crystallizing the organic layer; carrying out centrifugal separation in a nitrogen protection atmosphere to obtain a thiamethoxam wet product; and drying the wet thiamethoxam product in vacuum, and crushing to obtain the thiamethoxam active compound. According to the method, the conversion rate of the 2-chloro-5-chloromethylthiazole can reach 99.3% or above, the yield of the thiamethoxam product is stabilized at 95.8% or above, the yield is greatly improved compared with that of an existing process, and the core defects that the conversion rate of raw materials is limited and many by-products are generated in the traditional process are thoroughly overcome.

Description

Technical Field

[0001] This invention relates to the field of pesticide synthesis technology, specifically to a thiamethoxam preparation process based on low-temperature reaction. Background Technology

[0002] Thiamethoxam, a representative neonicotinoid insecticide, has high efficiency, low toxicity, and broad-spectrum insecticidal activity. It has excellent control effects on a variety of agricultural pests such as aphids, planthoppers, and thrips, and is widely used for pest control in food crops, cash crops, and horticultural crops.

[0003] Currently, the mainstream industrial synthesis process for thiamethoxam is a one-step condensation method, using 2-chloro-5-chloromethylthiazole and 3-methyl-4-nitroimino-1,3,5-oxadiazine as core raw materials, undergoing a condensation reaction in the presence of a solvent and an acid-binding agent. Existing technologies mainly focus on optimizing the solvent system and simplifying post-processing. For example, CN115385904A discloses a composite solvent system using dimethyl carbonate and dichloroethane, with the reaction temperature controlled at 30-50℃. After the reaction, water is directly added, decolorized, and cooled to crystallize, which improves the product yield and content to some extent. However, this type of process still has the following significant shortcomings:

[0004] (1) The reaction temperature range is relatively wide (30-50℃), lacking precise control strategies. In actual production, side reactions are easily triggered by excessive local temperature, leading to increased product impurity content. Furthermore, the higher reaction temperature increases energy consumption and safety risks.

[0005] (2) The catalyst system is single or not clearly optimized, the reaction selectivity is insufficient, the conversion rate of 2-chloro-5-chloromethylthiazole is limited, the amount of by-products generated is large, and the purity of the product is affected.

[0006] (3) In the post-processing process, solvent recovery only adopts simple desolventizing, the purity of the recovered solvent is low, the recycling effect is poor, and resources are wasted; the washing wastewater is directly treated, and the efficient recovery of resources such as potassium chloride is not achieved, which does not meet the requirements of green chemical development.

[0007] (4) The crystallization process often adopts a single rate of cooling, resulting in uneven crystal growth and easy inclusion of impurities, making it difficult for the main content of the product to exceed 98%, and the appearance and color stability are insufficient.

[0008] To address the aforementioned shortcomings of existing technologies, this invention provides a thiamethoxam preparation process based on precise low-temperature control, achieving the technical goals of mild and efficient reaction, excellent product purity, and resource recycling. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-temperature reaction-based thiamethoxam preparation process that features mild reaction conditions, high product purity, high resource utilization, and good environmental friendliness.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A process for preparing thiamethoxam based on low-temperature reaction includes the following steps:

[0012] S1. Add dichloroethane to the reactor, start stirring and add 2-chloro-5-chloromethylthiazole and 3-methyl-4-nitroimino-1,3,5-oxadiazine. Then add organic amine catalyst, metal salt catalyst and deionized water in sequence. After heating, add potassium carbonate. During the feeding process, control the reactor temperature to not exceed 45°C.

[0013] S2, after the feeding is completed, adjust the reaction temperature to 45-48℃ and maintain the temperature for 3-5 hours until the 2-chloro-5-chloromethylthiazole content is ≤0.5%;

[0014] S3, add softened water to the reacted material, heat it up and let it stand to separate the layers to obtain an organic layer and a water layer;

[0015] S4. Transfer the organic layer to the crystallization vessel, add sodium hypochlorite solution, adjust the pH to 5-6, first cool to 8-10℃ at a rate of 8-10℃ / h, then slowly cool to 2-3℃ at a rate of 3-5℃ / h, and hold for 0.5-0.8h.

[0016] S5, under a nitrogen protective atmosphere, centrifugation was used to obtain wet thiamethoxam. The mother liquor from centrifugation was desolventized under reduced pressure and then distilled to recover the solvent.

[0017] S6. After vacuum drying of the wet thiamethoxam, the product is pulverized to obtain the technical grade thiamethoxam.

[0018] S7, after the washing wastewater is filtered by plate and frame filter, the filtrate is evaporated and concentrated by double-effect evaporator to recover potassium chloride, and the residual liquid is discharged after biochemical treatment to meet the standards.

[0019] Furthermore, the volume of dichloroethane added is 5-8 times the mass of 2-chloro-5-chloromethylthiazole, and the molar ratio of 2-chloro-5-chloromethylthiazole to 3-methyl-4-nitroimino-perhydro-1,3,5-oxadiazine is 1:1.0~1.05.

[0020] Furthermore, the organic amine catalyst is selected from one or more of triethylamine, N,N-dimethylbenzylamine or tetramethylethylenediamine, and the amount used is 0.8-1.2% of the mass of 2-chloro-5-chloromethylthiazole; the metal salt catalyst is selected from one of zinc chloride, copper chloride or nickel chloride, and the amount used is 0.3-0.5% of the mass of 2-chloro-5-chloromethylthiazole.

[0021] Furthermore, the stirring rate is 300-400 r / min, the amount of deionized water added is 10-15% of the total mass of the reaction system, the heating rate is 2-3℃ / h, the potassium carbonate addition rate is 0.8-1.0 kg / min, the feeding time is 3.5-4 h, and the amount of potassium carbonate added is 1.05-1.15 times the molar number of 2-chloro-5-chloromethylthiazole.

[0022] Furthermore, the aqueous layer was subjected to a second extraction with dichloroethane, and the extract was combined with the organic layer.

[0023] Furthermore, the softened water is treated with ion exchange resin to remove impurities, and its conductivity is ≤50μS / cm. The amount added is 30-40% of the total mass of the reactants. After heating to 52-55℃, it is allowed to stand for 1-1.5 hours to separate into layers. The amount of dichloroethane added for the secondary extraction is 20-25% of the mass of the water layer.

[0024] Furthermore, the effective chlorine content of the sodium hypochlorite solution is 5-8%, the amount added is 0.5-0.8% of the total mass of the material, the stirring and decolorization time is 28-30 minutes, and the pH is adjusted to 5-6 with hydrochloric acid.

[0025] Furthermore, the nitrogen purity is ≥99.9%, the centrifugation rate is 3000-3500 r / min, and the desolvation temperature is 60-70℃ and the pressure is -0.07~-0.08 MPa.

[0026] Furthermore, the vacuum drying temperature is 60-70℃, the pressure is -0.08~-0.09MPa, the drying time is 4-6h, and the particle size of the pulverized material is 100-200 mesh.

[0027] Furthermore, the pressure of the plate and frame filter is 0.3-0.5 MPa, and the temperature of the double-effect evaporator is 80-90℃ and the pressure is -0.05~-0.06 MPa.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) This invention employs an "organic amine + metal salt" composite catalyst system. The organic amine catalyst enhances the nucleophilic substitution reaction activity of the raw materials, while the metal salt catalyst forms a synergistic effect, significantly improving reaction selectivity and effectively suppressing side reactions. Simultaneously, the reactor temperature is strictly controlled below 45℃ during the feeding stage and stabilized at 45-48℃ during the heat preservation stage, avoiding the localized high-temperature problem caused by the wide temperature range of existing technologies. With the support of these dual technologies, the conversion rate of 2-chloro-5-chloromethylthiazol can reach over 99.3%, and the yield of thiamethoxam is consistently above 95.8%, representing a yield increase of over 5 percentage points compared to existing processes. This completely solves the core defects of traditional processes, such as limited raw material conversion rate and numerous by-products.

[0030] (2) The present invention is precisely designed for the crystallization process. Through a phased cooling strategy of "rapid nucleation followed by slow growth", combined with sodium hypochlorite decolorization and impurity removal and precise pH control of 5-6, the problem of crystal encapsulation of impurities caused by single-rate crystallization is effectively avoided, so that the main content of the product exceeds 99.0% and the main impurity content is controlled within 0.4%. At the same time, the dried product is a white and uniform crystal, which completely improves the shortcomings of the existing technology that the product purity is difficult to exceed 98% and the appearance is easy to turn yellow, and significantly enhances the product's market competitiveness.

[0031] (3) In the solvent recovery stage, the present invention adopts a combination process of "reduced pressure desolventizing + distillation" to recover solvents such as dichloroethane with a purity of ≥99.0% and a recovery rate of ≥95.9%, which can be directly recycled for feeding reaction, greatly reducing resource waste; in terms of wastewater treatment, through the resource utilization scheme of plate and frame filtration + double-effect evaporator concentration, the potassium chloride recovery rate is ≥90%, and the COD removal rate of the evaporation residue after biochemical treatment is ≥95.5%, realizing "wastewater reduction and resource recycling", which fully meets the requirements of green chemical development and solves the environmental pressure and resource waste problems caused by poor solvent recycling effect and direct discharge of wastewater in the existing technology.

[0032] (4) The present invention adopts a low-temperature reaction system throughout the process. The reaction temperature is more precise and lower than that of the existing process (30-50℃). With the control of steam condensate circulation, the energy consumption per unit product is reduced by more than 15% compared with the traditional process. At the same time, precise temperature control avoids side reactions and safety hazards caused by local high temperature. The slow feeding (3.5-4h) and optimized stirring and dispersion (300-400r / min) in the feeding stage further improve the stability of the reaction system, significantly reduce the safety risks in the production process, and take into account both economy and safety. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0034] This invention provides a process for preparing thiamethoxam based on a low-temperature reaction, comprising the following steps:

[0035] (1) Feeding reaction: First, add dichloroethane as a solvent to the jacketed reactor. The amount added should be sufficient to dissolve and disperse the subsequent solid raw materials, usually 5-8 times the mass of 2-chloro-5-chloromethylthiazole (volume-to-mass ratio, e.g., 1 kg of raw material corresponds to 5-8 L of solvent). Start stirring (stirring speed is 300-400 r / min), and add 2-chloro-5-chloromethylthiazole and 3-methyl-4-nitroimino-perhydro-1,3,5-oxadiazine to the solvent. The molar ratio of the two is 1:1.0~1.05. First, add the organic amine catalyst and stir for 15-20 minutes to ensure uniform dispersion. Then, add the metal salt catalyst and continue stirring for 10-15 minutes. Next, add deionized water (10-15% of the total mass of the reaction system). Heat the system slowly to 28-30℃ using steam condensate circulation (heating rate 2-3℃ / h). After naturally heating to 40℃, maintain the temperature. Then, slowly add potassium carbonate at a uniform rate of 0.8-1.0 kg / min, using a jacketed cooling system for real-time control to ensure the reactor temperature does not exceed 45℃ during the feeding process. The feeding time is 3.5-4 hours.

[0036] Among them, the organic amine catalyst is selected from one or more of triethylamine, N,N-dimethylbenzylamine or tetramethylethylenediamine, and the amount used is 0.8-1.2% of the mass of 2-chloro-5-chloromethylthiazole. The organic amine catalyst can promote the nucleophilic substitution reaction activity of the raw materials and increase the reaction rate. The metal salt catalyst is selected from one of zinc chloride, copper chloride or nickel chloride, and the amount used is 0.3-0.5% of the mass of 2-chloro-5-chloromethylthiazole. The metal salt catalyst and the organic amine catalyst form a synergistic effect, which significantly improves the reaction selectivity and inhibits the occurrence of side reactions. Potassium carbonate is used as an acid-binding agent, and its addition amount is 1.05-1.15 times the molar number of 2-chloro-5-chloromethylthiazole.

[0037] (2) Heat preservation reaction: After the feeding is completed, the reaction temperature is controlled at 45-48℃ through the steam condensate circulation system. This temperature range can effectively balance the reaction rate and inhibit side reactions. The heat preservation reaction is carried out for 3-5 hours. Every 1 hour, samples are taken to detect the content of 2-chloro-5-chloromethylthiazole until its content is ≤0.5% to be considered as qualified reaction.

[0038] (3) Water washing extraction: After the reaction is qualified, the material is transferred to the water washing extraction vessel, and softened water that has been pretreated (purified by ion exchange resin, conductivity ≤50μS / cm) is added (the amount added is 30-40% of the total mass of the reaction material). After heating to 52-55℃, the mixture is allowed to stand for 1-1.5h to separate into layers. The organic layer (containing thiamethoxam and dichloroethane) is transferred to the crystallization vessel. The aqueous layer (containing potassium chloride, unreacted potassium carbonate, etc.) is added with 20-25% of the aqueous layer mass of dichloroethane for secondary extraction. The extract is combined with the organic layer to improve the product yield.

[0039] (4) Staged crystallization: Add sodium hypochlorite solution with an effective chlorine content of 5-8% (the amount added is 0.5-0.8% of the total mass of the material) to the material in the crystallization vessel, stir for 28-30 min to remove color and impurities, and then add hydrochloric acid with a mass fraction of 10% at a rate of 0.5-1 mL / min to adjust the pH to 5-6. This pH range is conducive to crystal formation and reduces impurity encapsulation. First, cool down to 8-10℃ at a rate of 8-10℃ / h to promote the initial nucleation of crystals, and then slowly cool down to 2-3℃ at a rate of 3-5℃ / h, and keep warm for 0.5-0.8h to allow the crystals to grow fully and uniformly.

[0040] (5) Nitrogen-protected centrifugation and mother liquor distillation recovery: Under nitrogen protection atmosphere (nitrogen purity ≥ 99.9%), the crystallized material is sent to a centrifuge for centrifugation separation (centrifugation rate 3000-3500 r / min) to obtain thiamethoxam wet product; the centrifuged mother liquor is first desolventized under reduced pressure (temperature 60-70℃, pressure -0.07~-0.08MPa) to remove most of the water and light components, and then distilled through a distillation column (theoretical number of 20-30 plates, reflux ratio 2-3) to recover dichloroethane and methanol with a purity ≥ 99%, and the recovered solvent is directly recycled for the feeding reaction in step (1).

[0041] (6) Drying and packaging: The wet thiamethoxam product is sent into a vacuum drying oven and dried for 4-6 hours at a temperature of 60-70℃ and a pressure of -0.08~-0.09MPa. After drying, it is pulverized to 100-200 mesh by a pulverizing device to obtain white uniform crystalline thiamethoxam technical. After passing the inspection, it is packaged.

[0042] (7) Wastewater resource utilization treatment: The washing wastewater is first filtered by plate and frame filter to remove suspended solids (filtration pressure 0.3-0.5MPa). The filtrate enters a double-effect evaporator and is evaporated and concentrated under the conditions of temperature 80-90℃ and pressure -0.05~-0.06MPa to recover potassium chloride (recovery rate ≥90%). The evaporation residue is then treated by biochemical treatment (COD removal rate ≥95%) and discharged after meeting the standards.

[0043] The invention is further illustrated below with specific embodiments and comparative examples:

[0044] Example 1

[0045] This embodiment provides a thiamethoxam preparation process based on low-temperature reaction, as follows:

[0046] 1. Solvent: Dichloroethane (6 times the mass of 2-chloro-5-chloromethylthiazole, by volume).

[0047] 2. Raw material molar ratio: 2-chloro-5-chloromethylthiazole: 3-methyl-4-nitroimino-perhydro-1,3,5-oxadiazine = 1:1.02;

[0048] 3. Catalyst: Triethylamine (1.0% of raw material mass) + Zinc chloride (0.4% of raw material mass);

[0049] 4. Reaction temperature: ≤45℃ during the feeding stage, 46℃ during the heat preservation stage, and heat preservation time of 4h;

[0050] 5. Crystallization process: First, cool down to 10℃ at 8℃ / h, then cool down to 2℃ at 4℃ / h, and hold for 0.6h;

[0051] 6. Solvent recovery: The distillation column has 25 theoretical plates and a reflux ratio of 2.5;

[0052] 7. Wastewater treatment: Double-effect evaporator temperature 85℃, pressure -0.055MPa.

[0053] Example 2

[0054] This embodiment provides a thiamethoxam preparation process based on low-temperature reaction, as follows:

[0055] 1. Solvent: Dichloroethane (7 times the mass of raw material);

[0056] 2. Raw material molar ratio: 1:1.04;

[0057] 3. Catalyst: Triethylamine + N,N-dimethylbenzylamine (mass ratio 1:1, total amount 1.1%) + copper chloride (0.35%).

[0058] 4. Reaction temperature: 47℃ during the heat preservation stage, for 3.5 hours;

[0059] 5. Crystallization process: First, cool down to 9℃ at a rate of 9℃ / h, then cool down to 3℃ at a rate of 3℃ / h, and hold at that temperature for 0.7h;

[0060] The remaining parameters are the same as in Example 1.

[0061] Example 3

[0062] This embodiment provides a thiamethoxam preparation process based on low-temperature reaction, as follows:

[0063] 1. Solvent: Dichloroethane (5 times the mass of the raw material);

[0064] 2. Raw material molar ratio: 1:1.01;

[0065] 3. Catalyst: Tetramethylethylenediamine (0.8%) + Nickel chloride (0.3%);

[0066] 4. Reaction temperature: 45℃ during the heat preservation stage, for 5 hours;

[0067] 5. Crystallization process: First, cool down to 8℃ at a rate of 10℃ / h, then cool down to 2℃ at a rate of 5℃ / h, and hold for 0.5h.

[0068] The remaining parameters are the same as in Example 1.

[0069] Comparative Example 1

[0070] This comparative example represents the existing mainstream process, as detailed in invention patent application CN115385904A:

[0071] 1. Solvent: Dimethyl carbonate + dichloroethane (volume ratio 1:1), the amount used is 6 times the mass of the raw materials;

[0072] 2. Raw material molar ratio: 1:1.05;

[0073] 3. Catalyst: Triethylamine (1.2%), no metal salt catalyst;

[0074] 4. Reaction temperature: 30-50℃ (no precise control, natural heating), holding time: 5 hours;

[0075] 5. Crystallization process: Cool down to 5℃ at a single rate of 5℃ / h, and hold for 1 hour;

[0076] 6. Solvent recovery: Desolventization only (temperature 70℃, pressure -0.07MPa), no distillation;

[0077] 7. Wastewater treatment: direct biochemical treatment, potassium chloride is not recovered.

[0078] Comparative Example 2

[0079] 1. The solvent and raw material molar ratios are the same as in Example 1;

[0080] 2. Catalyst: Triethylamine only (1.0%), no metal salts;

[0081] 3. Reaction temperature: 30-50℃ during the feeding stage (precise temperature control without jacket), 48℃ during the heat preservation stage, and heat preservation time for 5 hours;

[0082] 4. Crystallization process: Cooling at a single rate of 6℃ / h to 5℃;

[0083] 5. Solvent recovery and wastewater treatment are the same as in Comparative Example 1.

[0084] The data from Examples 1, 2, 3 and the comparative examples are summarized in the following table:

[0085] index Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 2-Chloro-5-chloromethylthiazole conversion rate (%) 99.7 99.6 99.3 95.2 96.8 99.5 Thiamethoxam product yield (%) 96.5 96.2 95.8 90.3 91.5 94.2 Product main content (purity, %) 99.3 99.2 99.0 97.8 98.0 98.5 Content of major impurities (%) 0.32 0.35 0.41 1.68 1.45 0.89 Dichloroethane recovery rate (%) 96.8 96.5 95.9 81.2 80.5 82.3 Purity of recovered solvent (%) 99.2 99.1 99.0 88.7 89.3 87.9 Potassium chloride recovery rate (%) 92.5 91.8 90.6 - (Not recycled) - (Not recycled) - (Not recycled) Wastewater COD removal rate (%) 96.3 95.9 95.5 82.6 83.1 82.8 Energy consumption per unit product (kWh / t) 860 875 890 1120 1080 990 Product Appearance White, uniform crystals White, uniform crystals White, uniform crystals pale yellow crystals pale yellow crystals White crystals with a slight yellow tinge

[0086] In terms of reaction efficiency and raw material utilization, Examples 1-3 achieved a conversion rate of over 99.3% for 2-chloro-5-chloromethylthiazol, thanks to the synergistic effect of the "organic amine + metal salt" composite catalyst and the low-temperature control strategy. The yield of thiamethoxam was stable at 95.8%-96.5%. In contrast, Comparative Example 1, which used a single catalyst and had a crude temperature control, had a conversion rate of only 95.2% and a yield of 90.3%. Comparative Example 2, lacking a metal salt catalyst, also had a conversion rate and yield of only 96.8% and 91.5%, respectively, which were significantly lower than the levels of the Examples. This fully demonstrates the key role of the composite catalyst system and precise temperature control in improving reaction selectivity and reducing side reactions.

[0087] In terms of product quality, the embodiments achieved a product main content exceeding 99.0% through a staged crystallization process combined with decolorization, impurity removal, and pH control. The main impurity content was controlled at 0.32%-0.41%, and the product exhibited a uniform white crystal appearance. This solved the problem of existing technologies where product purity was difficult to exceed 98% and the color was yellowish. In contrast, Comparative Examples 1-2, which used a single-rate cooling crystallization, had a purity of only 97.8%-98.0% and an impurity content as high as 1.45%-1.68%. Although Comparative Example 3 retained the composite catalyst and temperature control, the single crystallization rate still resulted in a purity of 98.5% and an impurity content of 0.89%, highlighting the importance of staged crystallization in optimizing crystal morphology and reducing impurity encapsulation.

[0088] In terms of resource recycling and environmental performance, the example uses a distillation column to recover solvent, achieving a dichloroethane recovery rate of 95.9%-96.8%, with a recovered solvent purity of ≥99.0% that can be directly recycled and reused. Simultaneously, the washing wastewater is treated by a double-effect evaporator, achieving a potassium chloride recovery rate of ≥90.6% and a wastewater COD removal rate of ≥95.5%, meeting the requirements of green chemical development. In contrast, the comparative examples only use simple vacuum desolventizing, resulting in a solvent recovery rate of less than 83% and a purity of less than 89.3%, making efficient recycling impossible. Furthermore, potassium chloride is not recovered, and the wastewater COD removal rate is only 82%-83%, causing serious resource waste and environmental pressure.

[0089] In terms of energy consumption and safety, the example controlled the energy consumption per unit product to 860-890 kWh / t through low temperature control (≤45℃ during feeding stage and 45-48℃ during heat preservation stage), which reduced energy consumption and avoided safety risks caused by local high temperatures. In contrast, Comparative Examples 1-2 had a wide temperature range (30-50℃) and lacked precise control, resulting in energy consumption per unit product as high as 1080-1120 kWh / t. This not only significantly increased energy consumption but also increased the probability of side reactions and production safety hazards.

[0090] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A process for preparing thiamethoxam based on low-temperature reaction, characterized in that, Includes the following steps: S1. Add dichloroethane to the reactor, start stirring and add 2-chloro-5-chloromethylthiazole and 3-methyl-4-nitroimino-1,3,5-oxadiazine. Then add organic amine catalyst, metal salt catalyst and deionized water in sequence. After heating, add potassium carbonate. During the feeding process, control the reactor temperature to not exceed 45°C. S2, after the feeding is completed, adjust the reaction temperature to 45-48℃ and maintain the temperature for 3-5 hours until the 2-chloro-5-chloromethylthiazole content is ≤0.5%; S3, add softened water to the reacted material, heat it up and let it stand to separate the layers, obtaining an organic layer and a water layer; S4. Transfer the organic layer to the crystallization vessel, add sodium hypochlorite solution, adjust the pH to 5-6, first cool to 8-10℃ at a rate of 8-10℃ / h, then slowly cool to 2-3℃ at a rate of 3-5℃ / h, and hold for 0.5-0.8h. S5, under a nitrogen protective atmosphere, centrifugation was used to obtain wet thiamethoxam. The mother liquor from centrifugation was desolventized under reduced pressure and then distilled to recover the solvent. S6. After vacuum drying of the wet thiamethoxam, the product is pulverized to obtain the technical grade thiamethoxam. S7, after the washing wastewater is filtered by plate and frame filter, the filtrate is evaporated and concentrated by double-effect evaporator to recover potassium chloride, and the residual liquid is discharged after biochemical treatment to meet the standards.

2. The thiamethoxam preparation process based on low-temperature reaction according to claim 1, characterized in that, In step S1, the volume of dichloroethane added is 5-8 times the mass of 2-chloro-5-chloromethylthiazole, and the molar ratio of 2-chloro-5-chloromethylthiazole to 3-methyl-4-nitroimino-perhydro-1,3,5-oxadiazine is 1:1.0~1.

05.

3. The thiamethoxam preparation process based on low-temperature reaction according to claim 2, characterized in that, In step S1, the organic amine catalyst is selected from one or more of triethylamine, N,N-dimethylbenzylamine or tetramethylethylenediamine, and the amount used is 0.8-1.2% of the mass of 2-chloro-5-chloromethylthiazole; the metal salt catalyst is selected from one of zinc chloride, copper chloride or nickel chloride, and the amount used is 0.3-0.5% of the mass of 2-chloro-5-chloromethylthiazole.

4. The thiamethoxam preparation process based on low-temperature reaction according to claim 3, characterized in that, In step S1, the stirring rate is 300-400 r / min, the amount of deionized water added is 10-15% of the total mass of the reaction system, the heating rate is 2-3℃ / h, the potassium carbonate addition rate is 0.8-1.0 kg / min, the feeding time is 3.5-4 h, and the amount of potassium carbonate added is 1.05-1.15 times the molar number of 2-chloro-5-chloromethylthiazole.

5. The thiamethoxam preparation process based on low-temperature reaction according to claim 4, characterized in that, In step S3, dichloroethane is added to the aqueous layer for a second extraction, and the extract is combined with the organic layer.

6. The thiamethoxam preparation process based on low-temperature reaction according to claim 5, characterized in that, In step S3, the softened water is treated with ion exchange resin to remove impurities, and the conductivity is ≤50μS / cm. The amount added is 30-40% of the total mass of the reactants. After heating to 52-55℃, the water is allowed to stand for 1-1.5 hours to separate into layers. The amount of dichloroethane added for the secondary extraction is 20-25% of the mass of the water layer.

7. The thiamethoxam preparation process based on low-temperature reaction according to claim 6, characterized in that, In step S4, the effective chlorine content of the sodium hypochlorite solution is 5-8%, the amount added is 0.5-0.8% of the total mass of the material, and the stirring and decolorization time is 28-30 min; the pH is adjusted to 5-6 with hydrochloric acid.

8. The thiamethoxam preparation process based on low-temperature reaction according to claim 7, characterized in that, In step S5, the nitrogen purity is ≥99.9%, the centrifugation rate is 3000-3500 r / min, the desolvation temperature is 60-70℃, and the pressure is -0.07~-0.08 MPa.

9. The thiamethoxam preparation process based on low-temperature reaction according to claim 8, characterized in that, In step S6, the vacuum drying temperature is 60-70℃, the pressure is -0.08~-0.09MPa, the drying time is 4-6h, and the particle size of the pulverized material is 100-200 mesh.

10. The thiamethoxam preparation process based on low-temperature reaction according to claim 9, characterized in that, In step S7, the pressure of the plate and frame filter is 0.3-0.5 MPa, and the temperature of the double-effect evaporator is 80-90℃ and the pressure is -0.05~-0.06 MPa.