Preparation method of high-purity indoxacarb intermediate

Abstract

The invention discloses a preparation method of an indoxacarb high-purity intermediate, and belongs to the technical field of pesticide synthesis. Mixing chlorobenzene, 3-chloropropionyl chloride and the modified charcoal, stirring and reacting to obtain a first mixed solution; heating and stirring the first mixed solution for reaction to obtain a second mixed solution; adding dimethyl carbonate and anhydrous potassium carbonate into the second mixed solution, mixing and performing reflux reaction to obtain a third mixed solution; and sequentially carrying out reduced pressure distillation and ethanol recrystallization on the third mixed solution to obtain the high-purity indoxacarb intermediate. According to the invention, a molecular imprinting-coordination-sulfur doping synergistic catalysis system is constructed through three-step modification, so that precise recognition and efficient catalysis cooperation are realized, and the reaction selectivity and the product purity are improved. The modified charcoal has excellent stability and can be recycled, the production process is simplified, and the separation difficulty is reduced.

Description

Technical Field

[0001] This invention belongs to the field of pesticide synthesis technology, specifically relating to a method for preparing a high-purity intermediate of indoxacarb. Background Technology

[0002] Methyl 5-chloro-1-oxo-2,3-dihydroindene-2-carboxylate is a key intermediate in the synthesis of the highly effective and low-toxicity insecticide indoxacarb. Existing preparation techniques have significant drawbacks: First, traditional methods often use Lewis acids such as anhydrous aluminum trichloride as catalysts, resulting in strong corrosiveness, high emissions of waste, and difficulties in product separation. Second, while one-pot synthesis simplifies the process, the catalysts used lack selectivity, leading to low product purity that fails to meet the demands of high-end pesticide production. Third, some improved methods rely on precious metal catalysts, which are costly and lack prospects for industrial application.

[0003] Patent CN115807042A discloses a method for preparing an intermediate of indoxacarb, specifically a method for preparing (S)- or (R)-5-chloro-2,3-dihydro-2-hydroxy-1-oxo-1H-indene-2-carboxylic acid methyl ester. The method includes the following steps: 5-chloro-1-oxo-2,3-dihydro-1H-indene-2-carboxylic acid methyl ester undergoes an enzymatic reaction in the presence of Baeyer-Villiger monooxygenase and a cofactor to obtain (S)- or (R)-5-chloro-2,3-dihydro-2-hydroxy-1-oxo-1H-indene-2-carboxylic acid methyl ester. While this method exhibits good stereoselectivity and yield, it relies on a cofactor regeneration system, requires high control of reaction conditions, and limits enzyme stability and reusability, increasing the complexity and cost of industrial-scale production.

[0004] Patent CN109485568A discloses a method for preparing a high-optical-purity indoxacarb intermediate, comprising reacting 5-chloro-2-methoxycarbonyl-1-indanone ester with an oxidant in the presence of a chiral Zr-salen polymer to obtain the indoxacarb intermediate (2S)-5-chloro-2,3-dihydro-2-hydroxy-1-oxo-1H-indan-2-carboxylic acid methyl ester, with an S-body content as high as 99%. While this method significantly improves optical purity, the synthesis steps of the chiral Zr-salen polymer catalyst are cumbersome, the raw material cost is high, and the reaction must be carried out under strictly controlled anhydrous conditions, limiting its applicability in large-scale continuous production. Furthermore, this method does not provide a systematic solution for effectively suppressing byproducts such as epoxidized impurities, which may affect the purity and stability of the final intermediate. Summary of the Invention

[0005] One of the objectives of this invention is to provide a modified biochar for preparing high-purity indoxacarb intermediates, solving the problem of difficult product separation and low yield caused by the use of Lewis acid catalysts such as anhydrous aluminum trichloride in the prior art.

[0006] The second objective of this invention is to provide a method for preparing a high-purity indoxacarb intermediate based on the modified biochar, achieving a synthesis process with high yield, high purity, green technology, and recyclable catalyst.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing a high-purity indoxacarb intermediate includes the following steps: S1, chlorobenzene, 3-chloropropionyl chloride and modified biochar were mixed and stirred to obtain the first mixture; S2. The first mixture is heated and stirred to obtain the second mixture. S3. Dimethyl carbonate and anhydrous potassium carbonate are added to the second mixture and refluxed to obtain the third mixture. S4 and the third mixture were successively subjected to vacuum distillation and recrystallization with ethanol to obtain a high-purity intermediate of indoxacarb.

[0008] S1 involves Friedel-Crafts acylation, forming a key intermediate; S2 involves intramolecular cyclization, constructing the core framework of indoxacarb; and S3 involves esterification / methylation, introducing methyl ester groups. Modified biochar was used throughout the process as a multifunctional catalyst, simplifying the separation and purification steps and aiming to improve efficiency and purity.

[0009] Furthermore, the conditions for the mixing and stirring reaction of chlorobenzene, 3-chloropropionyl chloride, and modified biochar include a temperature of 55-65°C and a time of 2-4 hours. This temperature range can activate the active sites of the modified biochar while avoiding high-temperature decomposition of 3-chloropropionyl chloride or polyacylation side reactions; the 2-4 hour time matches the Friedel-Crafts acylation kinetics rate, ensuring that chlorobenzene and 3-chloropropionyl chloride react fully, balancing reaction efficiency and intermediate stability.

[0010] Furthermore, the conditions for the first mixed liquid heating and stirring reaction include a temperature of 85~95℃ and a time of 2~4h. Temperatures higher than S1 can break the stable conformation of the intermediate and trigger intramolecular cyclization; the upper temperature limit matches the thermal stability of the modified biochar imprinted cavity to avoid cavity collapse; 2~4h ensures complete cyclization reaction and suppresses side reactions such as disproportionation and degradation of the intermediate at high temperatures.

[0011] Furthermore, the conditions for the reflux reaction of adding dimethyl carbonate and anhydrous potassium carbonate include a reaction temperature of 105-115°C and a reaction time of 3-5 hours. The reflux temperature is higher than the boiling point of dimethyl carbonate (90°C) to ensure a homogeneous reaction system and enhance the activity of the methylating agent; the weakly alkaline environment (anhydrous potassium carbonate) can activate the nucleophilic sites of the intermediate, and the 3-5 hour reaction time matches the nucleophilic addition reaction rate, ensuring complete methylation and avoiding over-substitution.

[0012] Furthermore, the weight ratio of chlorobenzene, 3-chloropropionyl chloride, modified biochar, dimethyl carbonate, and anhydrous potassium carbonate is (80~120):(10~15):(1.5~2.5):(12~18):(0.3~0.7). Excess chlorobenzene serves as both a solvent and reactant, enhancing the conversion rate of 3-chloropropionyl chloride; the amount of modified biochar is matched to the substrate concentration to ensure sufficient active sites and prevent aggregation; excess dimethyl carbonate provides sufficient methylation reagent; and the amount of anhydrous potassium carbonate is controlled within a weakly basic range to avoid intermediate hydrolysis. All ratios are optimized based on reaction stoichiometry and catalytic efficiency.

[0013] Furthermore, the conditions for vacuum distillation include a vacuum degree of 0.08~0.09 MPa, a temperature of 50~60℃, and a time of 4~6 h. A vacuum degree of 0.08~0.09 MPa lowers the boiling points of low-boiling-point components such as chlorobenzene and dimethyl carbonate; low-temperature distillation at 50~60℃ avoids the volatilization or thermal decomposition of the target intermediate; and 4~6 h ensures complete removal of low-boiling-point impurities, providing a high-purity crude product for subsequent recrystallization.

[0014] Furthermore, the conditions for ethanol recrystallization include heating to 60-70°C, cooling to 0-5°C at a rate of 1-2°C / min, and maintaining the temperature for crystallization for 12-18 hours. Ethanol exhibits the solubility characteristic of "dissolving at high temperatures and precipitating at low temperatures" for the target intermediate; slow cooling at 1-2°C / min avoids impurity encapsulation caused by rapid crystal growth; and maintaining the temperature at 0-5°C for 12-18 hours promotes complete crystal growth, improves purity and yield, and reduces crystal agglomeration.

[0015] Furthermore, in the S1 stage, chlorobenzene and 3-chloropropionyl chloride undergo a Friedel-Crafts acylation reaction catalyzed by modified biochar. The molecularly imprinted recognition cavity in the modified biochar has a specific adsorption effect on the generated 3,4'-dichlorophenylacetone intermediate, increasing its local concentration. The Zn-Schiff base coordination site acts as a Lewis acid to activate the carbonyl carbon of the acyl chloride, promoting electrophilic substitution. The sulfur doping site accelerates the Zn doping reaction through the electron bridge effect. 2+ Charge transfer between the substrate and the reaction lowers the activation energy.

[0016] Furthermore, the S2 stage does not require separation; the intramolecular cyclization is triggered directly by heating. The imprinted cavity of the modified biochar continuously captures and orients intermediates, enabling the cyclization reaction to proceed efficiently in a space-constrained environment and suppressing side reaction pathways.

[0017] Furthermore, dimethyl carbonate is introduced as a green methylating agent in the S3 stage, which completes the nucleophilic addition under weakly basic conditions, avoiding the use of highly toxic iodomethane or dimethyl sulfate.

[0018] Furthermore, the method for preparing the modified biochar includes the following steps: A1. Corn cob biochar is obtained by crushing corn cobs and then treating them at a first high temperature. A2. The first biochar was obtained by mixing and stirring corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide and azobisisobutyronitrile. A3. After the first biochar and salicylaldehyde are mixed and refluxed, zinc nitrate solution is added, mixed and stirred, and then subjected to a second high-temperature treatment to obtain the second biochar. A4. Modified biochar is obtained by grinding and mixing the second biochar and thiourea and then subjecting them to a third high-temperature treatment.

[0019] Designed according to the functional requirements of "carrier construction - imprinted cavity formation - active site loading - electron transport bridge construction": corn cob biochar provides a high specific surface area carrier; step A2 constructs a specific imprinted cavity; step A3 loads Zn-Schiff base catalytic sites; step A4 uses sulfur doping to construct an electron transport pathway. Each step provides structural support for subsequent catalytic functions, achieving synergy between "recognition-catalysis-charge transfer".

[0020] Furthermore, the conditions for the first high-temperature treatment include a temperature of 500℃ and a time of 4 hours. 500℃ is a suitable temperature for biochar carbonization, which can remove impurities such as cellulose and hemicellulose from corn cobs and form a porous carbon skeleton (high specific surface area and porosity); 4 hours ensures complete carbonization and avoids residual organic impurities from affecting the subsequent imprint cavity construction and active site loading.

[0021] Furthermore, the weight ratio of the corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide, and azobisisobutyronitrile is 10:(1.2~1.8):(1.2~1.5):(4~6):(0.08~0.12). The amount of template molecule (3,4'-dichlorophenylacetone) is matched with the monomer (acrylamide) and crosslinking agent to ensure the number and structural integrity of the imprinted cavities; the amount of initiator (azobisisobutyronitrile) can fully initiate free radical polymerization, while avoiding excessive crosslinking of the polymer, thus ensuring the permeability of the imprinted cavities.

[0022] Furthermore, the reaction conditions for the corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide, and azobisisobutyronitrile (AIBN) include a reaction temperature of 55–65°C and a reaction time of 6–10 h. 55–65°C is the suitable temperature for the decomposition of AIBN to initiate free radicals; 6–10 h ensures complete monomer polymerization and crosslinking, forming a stable three-dimensional network structure, and avoids incomplete imprint cavity structure due to insufficient time.

[0023] Furthermore, the conditions for the reflux reaction of the first biochar and salicylaldehyde include a temperature of 65-75°C and a time of 3-5 hours. This temperature range promotes the Schiff base reaction between the salicylaldehyde groups and the amino groups on the biochar surface, forming an imine structure (Zn). 2+ Coordination provides sites); reflux ensures homogeneous reaction, and 3-5 hours ensures complete Schiff base reaction, avoiding the influence of unreacted groups on Zn. 2+ load.

[0024] Furthermore, the concentration of the zinc nitrate solution is 0.2 mol / L. This concentration is matched to the number of Schiff base sites to ensure Zn... 2+ Sufficiently coordinate the loading, while avoiding excessively high concentrations that could lead to Zn contamination. 2+ Agglomeration (reducing catalytic activity) or insufficient concentration leads to inadequate loading (affecting catalytic efficiency).

[0025] Furthermore, the conditions for adding zinc nitrate solution and mixing / stirring the reaction include a time of 4-6 hours. This ensures that Zn... 2+ The Zn group fully coordinates with the imine nitrogen and phenolic hydroxyl oxygen of the Schiff base to form a stable complex, avoiding insufficient coordination that could lead to Zn contamination. 2+ It is lost during subsequent high-temperature processing.

[0026] Furthermore, the weight ratio of the first biochar, salicylaldehyde, and zinc nitrate solution is 5:(1.0~1.4):(25~35). The amount of salicylaldehyde is matched to the number of amino groups on the surface of the first biochar to ensure sufficient Schiff base sites; the amount of zinc nitrate solution provides sufficient Zn. 2+ It forms a suitable coordination ratio with Schiff base sites to ensure the density of active sites.

[0027] Furthermore, the conditions for the second high-temperature treatment include a temperature of 480–520°C and a time of 2–4 hours. High-temperature curing of the Zn-Schiff base coordination structure enhances its stability in catalytic reactions (avoiding Zn...). 2+ (Shedding); at the same time, removing unreacted salicylaldehyde and zinc nitrate impurities, and avoiding damage to the imprint cavity structure and carbon skeleton stability within the temperature range.

[0028] Furthermore, the weight ratio of the second biochar to thiourea is 5:(1.5~2.5). The amount of thiourea used needs to provide sufficient active sulfur species (H2S, CS2) to ensure the number of sulfur doping sites; at the same time, excessive thiourea should be avoided to prevent sulfur atoms from over-covering active sites and affecting Zn. 2+ Catalytic activity.

[0029] Furthermore, the grinding and mixing conditions include a rotation speed of 300-500 r / min and a time of 10-15 min. This rotation speed and time allow the second biochar to come into full contact with thiourea, improving the uniformity of sulfur doping at high temperatures.

[0030] Furthermore, the conditions for the third high-temperature treatment include a temperature of 580–620°C and a time of 2.5–3.5 h. The high temperature activates the active sulfur species produced by the decomposition of thiourea, which react with the carbon skeleton to form CS bonds (sulfur doping).

[0031] Furthermore, in step A2, the amino group of acrylamide and the carbonyl group of 3,4'-dichlorophenylacetone form a specific bond through hydrogen bonding, constructing a three-dimensional network polymer structure around the template molecule during free radical polymerization and crosslinking reactions. After elution, an imprint recognition cavity is formed on the surface of biochar, and the cavity structure matches the diameter of the intermediate molecule dynamics.

[0032] Furthermore, in step A3, the imine nitrogen atom and the phenolic hydroxyl oxygen atom in the Schiff base structure react together with Zn. 2+ Formation of coordination complexes, Zn 2+ It is fixed inside the imprint recognition cavity to prevent metal aggregation.

[0033] Furthermore, in step A4, thiourea decomposes at high temperature to produce reactive sulfur species such as H2S and CS2, which undergo substitution reactions with the carbon skeleton of biochar. Simultaneously, sulfur atoms interact with Zn via lone pair electrons. 2+ It forms a weak coordination interaction and constructs a "carbon skeleton-sulfur-zinc" electron transport bridge.

[0034] The beneficial effects of this invention are: (1) This invention provides a highly efficient, green, and economical method for preparing high-purity indoxacarb intermediates. The core of this method lies in the use of a specialized biochar catalyst prepared through a three-step continuous modification process involving molecular imprinting, metal coordination, and sulfur doping. This catalyst integrates specific recognition, efficient catalysis, and rapid electron conduction. In the specific process, chlorobenzene, 3-chloropropionyl chloride, and the modified biochar are reacted in a specific weight ratio under mild conditions to initiate the reaction. Subsequently, the temperature is increased to complete the key cyclization. Then, dimethyl carbonate and anhydrous potassium carbonate are added and refluxed at a suitable temperature for methylation. Finally, high-purity products are obtained through vacuum distillation and programmed recrystallization with ethanol.

[0035] (2) The beneficial effects of the preparation method provided by this invention are reflected in multiple aspects. First, the modified biochar catalyst constitutes a synergistic "recognition-catalysis" microenvironment: its molecularly imprinted cavity can selectively adsorb and enrich key intermediates, improving the directionality and efficiency of subsequent cyclization and methylation reactions; the firmly anchored Zn-Schiff base sites provide stable Lewis acid active centers, while the electron transport bridge constructed by sulfur doping further enhances the overall catalytic efficiency. Second, the entire process design highlights the advantages of being green and simplified: the "one-pot two-step" continuous reaction from S1 to S3 avoids the separation and purification of intermediates, greatly simplifying the operation process; the use of dimethyl carbonate, a green methylation reagent, replaces the highly toxic traditional reagent, reducing safety and environmental risks from the source; the solid catalyst prepared from corn cob waste replaces the traditional homogeneous Lewis acid, making it easy to recycle and reuse, reducing production costs and emissions of waste. Detailed Implementation

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0037] During the Friedel-Crafts acylation reaction, when 3-chloropropionyl chloride and chlorobenzene are contacted with modified biochar at 60°C, Zn 2+ The active center coordinates with the carbonyl oxygen atom of 3-chloropropionyl chloride via its empty orbital, enhancing the positive charge of the carbonyl carbon and making it more susceptible to nucleophilic attack by the π electrons of the chlorobenzene aromatic ring. Simultaneously, the newly generated 3,4'-dichlorophenylacetone molecule is rapidly captured and localized to Zn because its geometry closely matches the peak pore size of the imprinted cavity on the modified biochar surface, and its ketone carbonyl group can form hydrogen bonds with the residual amide groups in the imprinted polymer network. 2+ The region adjacent to the coordination site. This confinement effect spatially fixes the intermediate molecule, effectively blocking its chance of secondary acylation with other chlorobenzene molecules in the system, while inhibiting the formation of aromatic ring chlorine substitution positional isomers due to free rotation or migration.

[0038] During the cyclization reaction stage, after the system is heated to 90℃, the C–H bond adjacent to the chlorine atom on the aromatic ring of the 3,4'-dichlorophenylacetone molecule anchored in the imprinted cavity, due to its relatively high electron cloud density, acts as a nucleophilic site to initiate intramolecular electrophilic attack on the carbonyl carbon of the activated side chain. In this process, the C–S–C formed by sulfur doping can interact with the adjacent Zn atoms due to their lone pair electrons. 2+ The d orbitals partially overlap, forming an electron bridge at the C–S–Zn interface, making it easier for aromatic ring π electrons to pass through sulfur atoms to Zn. 2+ The electron transfer weakens the electron density of the carbonyl C=O bond, reducing the energy barrier of the cyclization reaction. This electronic regulation mechanism allows the cyclization step to proceed efficiently under mild conditions, avoiding dechlorination or ring-opening side reactions caused by high temperatures.

[0039] In the catalyst separation stage, due to Zn 2+ Anchored to the biochar framework by the Schiff base structure, and with sulfur doping not compromising the mechanical strength of the carbon matrix, solid-liquid separation can be achieved by filtration after the reaction. During air calcination regeneration of the filter cake, organic residues are oxidized and decomposed, while Zn... 2+ Since it is in a coordinated stable state and has not volatilized or migrated, and the sulfur-doped structure has been carbonized and stabilized during the preparation of the inert precursor, the distribution of active centers did not change significantly after ten consecutive cycles.

[0040] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0041] Example 1

[0042] This embodiment provides a high-purity intermediate for indoxacarb, prepared through the following steps: A1. Take dried corn cobs and crush them to a particle size of 30 mesh. Wash them with deionized water four times to remove surface impurities. After drying at 115℃ for 16 hours, place them in a tube furnace and heat them to 500℃ in a nitrogen protective atmosphere for 4 hours. After cooling to 25℃, corn cob biochar is obtained. A2. 10 parts by weight of corn cob biochar were dispersed in 50 parts by weight of 95 wt% ethanol solution. 1.5 parts by weight of 3,4'-dichlorophenylacetone, 1.3 parts by weight of acrylamide, and 5 parts by weight of N,N'-methylenebisacrylamide were added. After ultrasonic dispersion at 250 W for 30 min, 0.10 parts by weight of azobisisobutyronitrile were added. Under a nitrogen protective atmosphere, the temperature was raised to 60 °C, and the mixture was stirred at 200 r / min for 8 h. After the reaction was completed, the precipitate was collected by filtration and placed in a Soxhlet extractor. 100 parts by weight of methanol-acetic acid mixed solution (volume ratio 9:1) were added, and the mixture was refluxed for 24 h. The solid was washed 5 times with deionized water and dried at 115 °C for 12 h to obtain the first biochar. A3. 5 parts by weight of the first biochar were dispersed in 50 parts by weight of 95 wt% ethanol solution, and 1.2 parts by weight of salicylaldehyde were added. The mixture was heated to 70°C under a nitrogen atmosphere and refluxed at 200 r / min for 5 h. After the reaction was completed, the mixture was cooled to 60°C, and 30 parts by weight of 0.2 mol / L zinc nitrate solution were slowly added dropwise. The mixture was stirred at 300 r / min for 5 h. After the reaction was completed, the precipitate was collected by filtration, washed three times with deionized water, dried at 115°C for 14 h, and then transferred to a tube furnace. Under a nitrogen atmosphere, the temperature was raised to 500°C at a rate of 5°C / min and held for 3 h. After cooling to 25°C, the second biochar was obtained. A4, 5 parts by weight of second biochar and 2.0 parts by weight of thiourea were mixed and ground at 400 r / min for 12 min. The mixture was then placed in a tube furnace and heated to 600℃ at a heating rate of 5℃ / min under a nitrogen protective atmosphere. After holding at this temperature for 3 h, the mixture was cooled to 25℃, washed 5 times with deionized water, and dried at 115℃ for 14 h to obtain modified biochar. S1, 100 parts by weight of chlorobenzene, 12 parts by weight of 3-chloropropionyl chloride and 2.0 parts by weight of modified biochar were placed in a three-necked flask and heated to 60°C under a nitrogen protective atmosphere. The mixture was stirred at 300 r / min for 3 h to obtain the first mixture. S2. The first mixture is heated to 90℃ and stirred at 300r / min for 3h. After the reaction is completed, it is cooled to 25℃, and the modified biochar is separated and recovered by filtration. The filter cake is washed twice with 8 parts by weight of chlorobenzene. The washing liquid and filtrate are combined to obtain the second mixture. The filter cake can be recycled after being dried at 115℃ for 8h. S3, 15 parts by weight of dimethyl carbonate and 0.5 parts by weight of anhydrous potassium carbonate were placed in the second mixture, heated to 110°C, and stirred under reflux at 300 r / min for 4 h. After the reaction was completed, the mixture was cooled to 25°C, 50 parts by weight of deionized water were added to the system, stirred for 15 min, and allowed to stand for 20 min to separate the organic phase. The aqueous phase was extracted twice with 30 parts by weight of ethyl acetate. The extracts and organic phases were combined, and 3 parts by weight of anhydrous magnesium sulfate were added to the combined organic phase. After standing and drying for 3 h, the anhydrous magnesium sulfate was removed by filtration to obtain the third mixture. S4. The third mixture was placed in a rotary evaporator and distilled under reduced pressure for 5 hours at a vacuum of 0.085 MPa and a water bath temperature of 55°C to obtain a crude product. 5 parts by weight of ethanol were added to the crude product, and the temperature was raised to 65°C. The mixture was then cooled to 4°C at a rate of 1.5°C / min and allowed to stand at a constant temperature for crystallization for 15 hours. After crystallization, the crystals were separated by filtration and washed twice with 1.5 parts by weight of cold ethanol (2°C). The crystals were then placed in a vacuum drying oven and dried for 7 hours at a temperature of 55°C and a vacuum of 0.085 MPa to obtain a high-purity intermediate of indoxacarb.

[0043] Example 2

[0044] The difference between this embodiment and Example 1 is that the ultrasonic power in step A2 is 200W and the stirring time is 6h; the reaction temperature in step S1 is 55℃ and the time is 2h, while the other raw materials and preparation process are the same as in Example 1.

[0045] Example 3

[0046] The difference between this embodiment and Example 1 is that the amount of salicylaldehyde used in step A3 is 1.0 part by weight and the amount of zinc nitrate solution used is 25 parts by weight; the reflux reaction temperature in step S3 is 105°C and the time is 3 hours; the other raw materials and preparation process are the same as in Example 1.

[0047] Example 4

[0048] The difference between this embodiment and Example 1 is that the amount of thiourea used in step A4 is 1.5 parts by weight and the grinding speed is 300 r / min; the vacuum distillation temperature in step S4 is 50℃ and the time is 4h. The other raw materials and preparation process are the same as in Example 1.

[0049] Example 5

[0050] The difference between this embodiment and Example 1 is that the amount of 3,4'-dichlorophenylacetone used in step A2 is 1.2 parts by weight; the reaction temperature in S2 is 85°C and the time is 4 hours; the other raw materials and preparation process are the same as in Example 1.

[0051] Example 6

[0052] The difference between this embodiment and Example 1 is that the ultrasonic power in step A2 is 300W and the stirring time is 10h; the stirring reaction time of the zinc nitrate solution in step A3 is 6h; and the reaction time of S1 is 4h. The remaining raw materials and preparation process are the same as in Example 1.

[0053] Example 7

[0054] The difference between this embodiment and Example 1 is that in step A2, the amount of 3,4'-dichlorophenylacetone is 1.8 parts by weight and the amount of acrylamide is 1.5 parts by weight; in step A4, the grinding speed is 500 r / min and the holding time is 3.5 h; and in step S3, the reflux reaction time is 5 h. The remaining raw materials and preparation process are the same as in Example 1.

[0055] Example 8

[0056] The difference between this embodiment and Example 1 is that the amount of salicylaldehyde used in step A3 is 1.4 parts by weight and the reflux reaction temperature is 75°C; the amount of thiourea used in step A4 is 2.5 parts by weight and the heating rate is 6°C / min; the vacuum distillation time in step S4 is 6 hours and the crystallization temperature is 0°C. The remaining raw materials and preparation process are the same as in Example 1.

[0057] Example 9

[0058] The difference between this embodiment and Example 1 is that the amount of azobisisobutyronitrile used in step A2 is 0.08 parts by weight and the reaction temperature is 55°C; the stirring reaction time in step A3 is 4 hours; the reaction time in step S2 is 2 hours, and the remaining raw materials and preparation process are the same as in Example 1.

[0059] Example 10

[0060] The difference between this embodiment and Example 1 is that the amount of N,N'-methylenebisacrylamide used in step A2 is 4 parts by weight; the heating rate in step A4 is 4℃ / min; the reaction temperature in step S3 is 105℃; and the remaining raw materials and preparation process are the same as in Example 1.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that in step A2 of the modified biochar preparation, 3,4'-dichlorophenylacetone is not added; only acrylamide, N,N'-methylenebisacrylamide and corn cob biochar are polymerized. The remaining raw materials and preparation process are the same as in Example 1.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that salicylaldehyde is not added in step A3 of the modified biochar preparation, and zinc nitrate solution is replaced with an equimolar amount of zinc chloride solution. The other raw materials and preparation process are the same as in Example 1.

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is that in step A4 of the preparation of modified biochar, thiourea is not added, and the second biochar is directly kept at 600°C in a nitrogen atmosphere for 3 hours. The remaining raw materials and preparation process are the same as in Example 1.

[0067] Comparative Example 4

[0068] The difference between this comparative example and Example 1 is that, in step A1 of the modified biochar preparation, 30-mesh commercial activated carbon was used instead of corn cob biochar, while the other raw materials and preparation process remained the same as in Example 1.

[0069] Comparative Example 5

[0070] The difference between this comparative example and Example 1 is that, in step S1 of intermediate synthesis, 2.0 parts by weight of anhydrous aluminum trichloride is used to replace the modified biochar, while the other raw materials and preparation process remain the same as in Example 1.

[0071] Comparative Example 6

[0072] The difference between this comparative example and Example 1 is that the modified biochar of this invention is not used; instead, commercially available activated carbon loaded with 5 wt% Zn is used. 2+ (Prepared by conventional impregnation method) As a catalyst, the other raw materials and preparation process are the same as in Example 1.

[0073] Comparative Example 7

[0074] The difference between this comparative example and Example 1 is that 3,4'-dichlorophenylacetone is not added in step A2 of the modified biochar preparation and thiourea is not added in step A4. The remaining raw materials and preparation process are the same as in Example 1.

[0075] Comparative Example 8

[0076] The difference between this comparative example and Example 1 is that, in step S3 of the intermediate synthesis, 15 parts by weight of iodomethane were used to replace dimethyl carbonate, while the remaining raw materials and preparation process remained the same as in Example 1.

[0077] Performance testing

[0078] The following performance tests were performed on the high-purity indoxacarb intermediates obtained in Examples 1-10 and Comparative Examples 1-8: 1. Yield determination: Accurately weigh the pure product of indoxacarb high-purity intermediate after final drying, and calculate the theoretical yield according to the stoichiometric ratio based on the amount of 3-chloropropionyl chloride added. Yield = (actual yield / theoretical yield) × 100%.

[0079] 2. Purity determination: High performance liquid chromatography: The chromatographic column was a C18 reversed-phase column (250 mm × 4.6 mm, 5 μm), the mobile phase was methanol-water (70:30, v / v), the flow rate was 1.0 mL / min, the detection wavelength was 254 nm, the column temperature was 30 ℃, the injection volume was 20 μL, and the purity was calculated as (target peak area / total peak area) × 100%.

[0080] 3. Cyclic Stability Test of Modified Biochar: The modified biochar from Examples 1-10 and Comparative Examples 1-8 was recovered and the following regeneration-use cycle was repeated 10 times: ① Modified Biochar Recovery: After the reaction, the modified biochar was separated by filtration and washed twice with 8 parts by weight of chlorobenzene to remove residual reactants on the surface; ② Modified Biochar Regeneration: The washed modified biochar was placed in a tube furnace and heated to 500°C at 5°C / min under a nitrogen protective atmosphere, held at that temperature for 2 hours, and cooled to 25°C to complete the regeneration; ③ Recycling: The regenerated modified biochar was fed into the next round of reaction according to the original intermediate synthesis process. The product yield was measured after each cycle, and the ratio of the yield of the 10th cycle to the yield of the 1st cycle (yield retention rate) was calculated to evaluate the cyclic stability of the catalyst.

[0081] 4. Byproduct content and assessment of waste discharge: Gas chromatography-mass spectrometry (GC-MS) was used to determine the types of byproducts and the proportion of peak areas; the amount of waste residue (excluding modified biochar) generated after the reaction was determined by gravimetric method, and the acid / alkali content in the wastewater was determined by titration method to assess the level of waste discharge.

[0082] The results are shown in Table 1: Table 1

[0083] The test results in Table 1 show that Examples 1-10 of the present invention have good performance, while the yield, purity and stability of Comparative Examples 1-8 are lower than those of Example 1, and the content of by-products and the amount of waste generated are higher. This proves the inventiveness of the "molecular imprinting-coordination-sulfur doping" synergistic system of the present invention, as well as the advanced nature of the green process design.

[0084] Comparative Example 1, lacking the template molecule 3,4'-dichlorophenylacetone, failed to form a specific recognition cavity on the modified biochar surface that matched the intermediate molecular structure. This prevented the specific enrichment of the substrate and intermediate to increase local concentration, and also hindered the directional arrangement of intermediate molecules through spatial confinement. Consequently, reaction efficiency decreased, and non-target side reactions significantly increased, ultimately resulting in reduced product yield and purity. Catalyst cycle stability also declined due to the lack of spatial protection at the active site. Comparative Example 2 omitted salicylaldehyde, preventing the formation of a Schiff base structure. Furthermore, the zinc source was replaced, and Zn... Unable to achieve stable coordination fixation through the synergistic effect of imine nitrogen and phenolic hydroxyl oxygen, severe aggregation occurs, leading not only to a reduction in the number of Lewis acid active centers and a significant decrease in catalytic activity, but also to the aggregation of Zn. It is also prone to detachment from the support surface, causing a sharp deterioration in the catalyst's cycle stability and a subsequent decrease in reaction selectivity. Comparative Example 3, without sulfur doping modification, could not construct a "carbon framework-sulfur-zinc" electron transport bridge, and Zn... The charge transfer efficiency between the active site and the substrate is significantly reduced, the activation energy of the reaction cannot be effectively reduced, and the catalytic efficiency is directly affected; at the same time, the sulfur atom's position on Zn... The lack of weak coordination stabilization also exacerbates the aggregation and loss of active centers to some extent, further reducing product yield and catalyst cycle stability.

[0085] Comparative Example 4 used commercial activated carbon instead of corn cob biochar. Its pore structure and pore size distribution differed significantly from the hierarchical pores of corn cob biochar, failing to meet the mass transfer requirements of the substrate, intermediates, and products in the reaction system, leading to reduced mass transfer efficiency. Simultaneously, the surface chemistry of commercial activated carbon differed, resulting in an incompatible number and distribution of active sites for subsequent modification, affecting the modification effects of molecular imprinting, Schiff base coordination, and sulfur doping. Ultimately, this disrupted the structural integrity of the synergistic system, leading to a comprehensive decline in overall performance. Comparative Example 5 used traditional anhydrous aluminum trichloride instead of modified biochar. As a homogeneous Lewis acid, it not only exhibited extremely poor catalytic selectivity and easily triggered numerous side reactions, but also formed complexes with products and intermediates, resulting in extremely difficult product separation and high loss rates. Furthermore, it possessed inherent defects such as strong corrosivity, inability to be recycled, and high emissions of waste gas, wastewater, and solid waste, completely contradicting the green and efficient concept of this invention. Comparative Example 6 used activated carbon prepared by a conventional impregnation method to support Zn. 2+ The catalyst, lacking both a molecularly imprinted recognition cavity and a Schiff base coordination structure, Zn 2+ Precise fixation and uniform dispersion are impossible, leading to easy aggregation and a significant reduction in the number and activity of active sites. Furthermore, the lack of specific recognition and directional catalysis results in poor reaction selectivity, increased byproducts, and reduced Zn activity. 2+ The catalyst is also prone to detachment during cycling, resulting in extremely poor catalyst stability. Comparative Example 7 lacks both the molecularly imprinted template molecule and the sulfur-doped reagent, completely losing the core three-dimensional synergistic system of this invention. It has neither enrichment and orientation capabilities nor efficient electron transport pathways. The superposition of these two defects reduces the reaction efficiency and selectivity to an extremely low level, and the aggregation and loss of active centers are also more severe, ultimately making it the worst performing group among all comparative samples. Although Comparative Example 8 retains the synergistic system, it uses highly toxic iodomethane instead of green dimethyl carbonate as the methylating agent. Iodomethane itself has poor reaction selectivity and is prone to triggering non-target side reactions, resulting in a slight decrease in product purity. At the same time, its highly toxic properties and the high difficulty of subsequent waste treatment also violate the green process design concept of this invention, and its overall performance is inferior to that of the examples.

[0086] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-purity intermediate of indoxacarb, characterized in that, The preparation method includes the following steps: S1, chlorobenzene, 3-chloropropionyl chloride and modified biochar were mixed and stirred to obtain the first mixture; S2. The first mixture is heated and stirred to react, resulting in the second mixture. S3. Dimethyl carbonate and anhydrous potassium carbonate are added to the second mixture and refluxed to obtain the third mixture. S4 and the third mixture were successively subjected to vacuum distillation and recrystallization with ethanol to obtain a high-purity intermediate of indoxacarb.

2. The method for preparing a high-purity indoxacarb intermediate as described in claim 1, characterized in that, The conditions for the mixed stirring reaction of chlorobenzene, 3-chloropropionyl chloride and modified biochar include a temperature of 55-65℃ and a time of 2-4h; the conditions for the first mixed solution to be heated and stirred include a temperature of 85-95℃ and a time of 2-4h; the conditions for the mixed reflux reaction of adding dimethyl carbonate and anhydrous potassium carbonate include a reaction temperature of 105-115℃ and a reaction time of 3-5h.

3. The method for preparing a high-purity indoxacarb intermediate as described in claim 1, characterized in that, The weight ratio of chlorobenzene, 3-chloropropionyl chloride, modified biochar, dimethyl carbonate and anhydrous potassium carbonate is (80~120):(10~15):(1.5~2.5):(12~18):(0.3~0.7).

4. The method for preparing a high-purity indoxacarb intermediate as described in claim 1, characterized in that, The conditions for recrystallizing the ethanol include heating to 60-70°C, cooling to 0-5°C at a rate of 1-2°C / min, and then maintaining the temperature for crystallization for 12-18 hours.

5. The method for preparing a high-purity indoxacarb intermediate as described in claim 1, characterized in that, The method for preparing the modified biochar includes the following steps: A1. Corn cob biochar is obtained by crushing corn cobs and then treating them at a first high temperature. A2. The first biochar was obtained by mixing and stirring corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide and azobisisobutyronitrile. A3. After the first biochar and salicylaldehyde are mixed and refluxed, zinc nitrate solution is added, mixed and stirred, and then subjected to a second high-temperature treatment to obtain the second biochar. A4. Modified biochar is obtained by grinding and mixing the second biochar and thiourea and then subjecting them to a third high-temperature treatment.

6. The method for preparing a high-purity indoxacarb intermediate as described in claim 5, characterized in that, The weight ratio of corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide, and azobisisobutyronitrile is 10:(1.2~1.8):(1.2~1.5):(4~6):(0.08~0.12).

7. The method for preparing a high-purity indoxacarb intermediate as described in claim 5, characterized in that, The conditions for the reaction of corn cob biochar, 3,4'-dichlorophenylacetone, acrylamide, N,N'-methylenebisacrylamide, and azobisisobutyronitrile include a reaction temperature of 55-65°C and a reaction time of 6-10 h; the conditions for the reflux reaction of the first biochar and salicylaldehyde include a temperature of 65-75°C and a time of 3-5 h.

8. The method for preparing a high-purity indoxacarb intermediate as described in claim 5, characterized in that, The concentration of the zinc nitrate solution is 0.2 mol / L; the conditions for adding the zinc nitrate solution and mixing and stirring the reaction include a time of 4 to 6 hours.

9. The method for preparing a high-purity indoxacarb intermediate as described in claim 5, characterized in that, The weight ratio of the first biochar, salicylaldehyde, and zinc nitrate solution is 5:(1.0~1.4):(25~35); the conditions for the second high-temperature treatment include a temperature of 480~520℃ and a time of 2~4h.

10. The method for preparing a high-purity indoxacarb intermediate as described in claim 5, characterized in that, The weight ratio of the second biochar to thiourea is 5:(1.5~2.5); the grinding and mixing conditions include a rotation speed of 300~500 r / min and a time of 10~15 min; the conditions for the third high-temperature treatment include a temperature of 580~620℃ and a time of 2.5~3.5 h.

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