Preparation process of nicosulfuron intermediate 2-chloro-N, N-dimethyl nicotinamide

Abstract

The invention relates to the technical field of chemical synthesis, and particularly discloses a preparation process of a nicosulfuron intermediate 2-chloro-N, N-dimethyl nicotinamide. According to the invention, 2-chloronicotinic acid dimethyl ammonium salt is synthesized by a one-step method, and then the 2-chloro-N, N-dimethyl nicotinamide is prepared by an ammonium salt dehydration reaction. Compared with a traditional process, multiple steps of operation such as acyl chloride preparation and solvent recovery are omitted, equipment investment and energy consumption are reduced, and chlorine-containing wastewater and mixed salt are prevented from being generated; the dosage of dimethylamine is remarkably reduced, and dimethylamine residues are reduced, so that the raw material and three-waste treatment cost is remarkably reduced, the process is more energy-saving and environment-friendly, and the method is suitable for large-scale industrial production and has important significance in promoting sustainable development of the nicosulfuron industry.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and particularly relates to a preparation process of a nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide. Background Art

[0002] Nicosulfuron, also known as nicosulfuron, has the chemical name of 2-(4,6-dimethoxy-2-pyrimidinylcarbamoylsulfamoyl)-N,N-dimethylnicotinamide, and the CAS number is 111991-09-4. It is a sulfonylurea systemic herbicide that can be absorbed by the stems, leaves and roots of weeds, and can be used to control annual and perennial gramineous weeds, sedges and some broad-leaved weeds in corn fields. It has higher activity against narrow-leaved weeds than broad-leaved weeds and is safe for corn crops.

[0003] Nicosulfuron was first developed by Ishihara Sangyo Co., Ltd. in Japan and is synthesized from two main intermediates: 2-aminosulfonamide-N,N-dimethylpyridinecarboxamide (abbreviated as pyridinesulfonamide) and 2-amino-4,6-dimethoxypyrimidine. 2-Aminosulfonamide-N,N-dimethylpyridinecarboxamide is a crucial intermediate for the synthesis of nicosulfuron. Currently, the main industrial synthesis method of pyridinesulfonamide is as follows: Using -2-chloronicotinic acid and thionyl chloride as raw materials, dichloroethane as a solvent, carrying out an acyl chlorination reaction. After the reaction is completed, dimethylamine is added for an amidation reaction. After the intermediate control is qualified, water is added for liquid separation. After separating out the amination wastewater, the organic phase is distilled to remove dichloroethane to obtain Compound 1 (i.e., 2-chloro-N,N-dimethylnicotinamide). The amination wastewater needs to be added with alkali to distill out dimethylamine for recycling. Then, Compound 1 is slurried with water, sodium sulfide is added thereto, and a mercapto group reaction is carried out under reflux. After the intermediate control is qualified, it is acidified to obtain Compound 2. Compound 2 is then subjected to chlorination and amination reactions to obtain pyridinesulfonamide (Compound 4). The specific synthesis route is as follows.

[0004]

[0005] In the above synthesis process, although compound 1 with high content and yield can be obtained through acyl chlorination and amidation reactions, there are the following obvious defects: (1) The acyl chlorination reaction releases hydrogen chloride and sulfur dioxide, forming a mixed salt of sodium chloride and sodium sulfite at the tail gas absorption, which is difficult to separate, resulting in great environmental protection treatment pressure; (2) This process requires the use of the organic solvent dichloroethane, and it is necessary to raise the temperature to remove dichloroethane in the post-treatment, consuming a large amount of steam. The condensation process also requires a certain amount of cooling capacity, and the recovery rate of dichloroethane is low, polluting the environment; (3) Dimethylamine serves as both a reaction raw material and an acid-binding agent in the reaction process. 2.5 equivalents of dimethylamine need to be added. After the reaction, about 1 equivalent of dimethylamine exists in the wastewater in the form of hydrochloride, and liquid alkali needs to be added for recovery, increasing the amount of by-product sodium chloride; (4) The equipment for the chlorination and amidation reactions of 2-chloronicotinic acid is numerous, with high investment, large floor area, and a long process time. The total time for feeding and heat preservation is about 15 hours or more, and the time for solvent removal in the post-treatment is about 5 hours. Excluding wastewater treatment, a total of more than 20 hours is required, with too high time cost, low production efficiency, and high labor cost; (5) Most importantly, after the acyl chlorination reaction, a large amount of sulfur dioxide, hydrogen chloride, and thionyl chloride remain in the system, which will consume a large amount of dimethylamine, produce black impurities, affect the content of the intermediate, and even affect the appearance of the final nicosulfuron.

[0006] There is a literature report on the process of reacting 2-chloro-3-trichloromethylpyridine with dimethylamine in water to obtain 2-chloro-N,N-dimethylnicotinamide. Although this route avoids the use of thionyl chloride, the synthesis process of 2-chloro-3-trichloromethylpyridine is complex, the raw material cost is extremely high, and it is necessary to continuously adjust the pH to 8 - 9 with dimethylamine solution during the reaction process, increasing the manual operation cost and time cost. Moreover, it has high requirements for the professional skills and experience of the operators. Once an operation error occurs, it may lead to fluctuations in the pH value, affecting the normal progress of the reaction, thereby reducing the purity and yield of the product, and it is not suitable for industrial application.

[0007] Therefore, developing a new process for preparing 2-chloro-N,N-dimethylnicotinamide that is environmentally friendly, has simple steps, high atom utilization rate, and good product purity and yield has important practical significance and market value, and has a profound impact on promoting the development of the nicosulfuron industry and enhancing the economic and environmental benefits of agricultural production. Summary of the Invention

[0008] Aiming at the problems of cumbersome operation, high production cost, and poor environmental friendliness existing in the synthesis method of the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide in the prior art, the present invention provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide.

[0009] To solve the above technical problems, the technical solution provided by the present invention is as follows:

[0010] A preparation process of nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, comprising the following steps:

[0011] S1, adding 2-chloronicotinic acid to an aqueous solution of dimethylamine, mixing evenly to obtain an aqueous solution of dimethylammonium 2-chloronicotinate;

[0012] S2, heating the aqueous solution of dimethylammonium 2-chloronicotinate to dehydrate to obtain dimethylammonium 2-chloronicotinate;

[0013] S3, adding a dehydration catalyst to the dimethylammonium dichloronicotinate, heating under an inert atmosphere for secondary dehydration to obtain 2-N,N-dimethylnicotinamide;

[0014] Among them, the dehydration catalyst is a Lewis acid. The specific reaction equation is as follows:

[0015]

[0016] Compared with the prior art, the preparation process of nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide provided by the present invention creatively adopts a one-step method to synthesize dimethylammonium 2-chloronicotinate, and then uses the ammonium salt dehydration reaction to prepare 2-chloro-N,N-dimethylnicotinamide. The new process provided by the present invention has the following advantages:

[0017] (1) The process route is simple, only using two raw materials, 2-chloronicotinic acid and dimethylamine. The raw material cost is low, and the amount of dimethylamine added is small. Dimethylamine is basically consumed completely during the reaction, and the residual amount in the wastewater is small, reducing the difficulty of wastewater treatment. The average cost of preparing each ton of 2-chloro-N,N-dimethylnicotinamide is saved by about 20%, significantly improving the atom utilization rate;

[0018] (2) Organic solvents are not used during the preparation process. Only water is generated during the whole process. Moreover, the process provided by the present invention is a one-step synthesis method, which does not involve an acyl chlorination process and there is no mixed salt of sodium sulfite and sodium chloride. It fundamentally solves the problems of high difficulty in treating three wastes and high energy consumption. In addition, the water generated during the reaction process can be used as a solvent for dissolving sulfur and sodium sulfide in the preparation of the next step of 2-mercapto-N,N-dimethylnicotinamide, saving water resources and more meeting the development requirements of green chemistry;

[0019] (3) The total time of the whole process is about 8h - 10h, which shortens the time cost by 50% compared with the traditional acyl chloride amidation process, and greatly improves the production efficiency. Since there is no organic solvent in the process, after the intermediate 2-chloro-N,N-dimethylnicotinamide is prepared, there is no need to switch the reaction device, and the next mercapto reaction can be directly fed, and the next intermediate 2-mercapto-N,N-dimethylnicotinamide can be prepared by one-pot method.

[0020] (4) The prepared 2-chloro-N,N-dimethylnicotinamide is white, which effectively improves the appearance and quality of the intermediate, and thus is conducive to improving the quality of the subsequent nicosulfuron product and enhancing the competitiveness of nicosulfuron in the market.

[0021] Further, the dehydration catalyst is at least one of iron salts or ferrous salts.

[0022] Preferably, the dehydration catalyst is at least one of iron sulfide, ferrous sulfide or ferric chloride.

[0023] More preferably, the dehydration catalyst is one or both of iron sulfide and ferrous sulfide.

[0024] The preferred catalyst can make the dehydration reaction of dimethylammonium 2-chloronicotinate proceed at a lower temperature, avoid decomposition or other side reactions at high temperature, and improve the yield and purity of the intermediate 2-chloro-N,N-dimethylnicotinamide.

[0025] Further, the addition amount of the dehydration catalyst is 1‰ - 5‰ of the mass of 2-chloronicotinic acid.

[0026] The addition amount of the preferred catalyst is conducive to reducing the introduction of impurities in the system and lowering the production cost on the premise of ensuring the efficient progress of the dehydration reaction.

[0027] Further, in S1, the mass concentration of the aqueous dimethylamine solution is 20% - 70%.

[0028] Further, in S1, the molar ratio of dimethylamine to 2-chloronicotinic acid in the aqueous dimethylamine solution is (1.0 - 1.2):1.

[0029] In the present invention, dimethylamine is only used as a reaction raw material. Therefore, only 1.0 - 1.2 equivalents of dimethylamine need to be added, which is not only conducive to reducing the material cost, but also avoids the problems of excessive dimethylamine residue in the reaction system, high difficulty in wastewater treatment, and the influence on the purity of the intermediate.

[0030] Further, in S2, the temperature for heating and dehydration is 100°C - 110°C, and dehydration is carried out until no distillate is collected.

[0031] Specifically, in S2, dehydration can be carried out under normal pressure or negative pressure, and dehydration under normal pressure is preferred.

[0032] It should be noted that after the dehydration in S2 is completed, the liquid material is in a viscous slurry state at this time, with some solids precipitated and the liquid level is relatively low. Therefore, stirring needs to be added during the dehydration process to avoid local overheating.

[0033] It should be noted that the secondary dehydration generally takes 4h to 5h to complete the dehydration.

[0034] Furthermore, in S3, the temperature of the secondary dehydration is 150°C to 200°C, and dehydration is carried out until no distillate is collected.

[0035] It should be noted that the secondary dehydration generally takes 2h to 4h to complete the dehydration. As the reaction progresses continuously, the liquid material becomes thinner and finally clear and transparent.

[0036] As a specific implementation manner of the present invention, the preparation process of the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide specifically includes the following steps:

[0037] Add the dimethylamine solution to 2-chloronicotinic acid, keep it warm at 0°C to 50°C for 0h to 5h, raise the temperature to 100°C to 110°C, dehydrate until no distillate is collected, add a dehydration catalyst, under an inert atmosphere, raise the temperature to 150°C to 200°C, carry out secondary dehydration until no distillate is collected, and cool down to obtain 2-chloro-N,N-dimethylnicotinamide.

[0038] It should be noted that during the reaction process, stirring is carried out throughout the whole process. The stirring is carried out by a double spiral ribbon stirrer, and the stirring rate is 50r / min to 100r / min.

[0039] Furthermore, the temperature of the cooling is 80°C to 100°C.

[0040] Since the next mercaptanization reaction needs to be carried out at about 100°C, therefore, in this step, only the temperature needs to be reduced to 80°C to 100°C to reduce energy consumption and save time.

[0041] The preparation process of 2-chloro-N,N-dimethylnicotinamide provided by the present invention has high production efficiency, low production cost, and the whole process does not need to use organic solvents, without the generation of three wastes, and the process is more green and environmentally friendly, with high economic and environmental benefits, and has important significance for promoting the sustainable development of the nicosulfuron industry.

[0042] It should be noted that in S3, after sampling in the central control until the reaction is qualified, the temperature is reduced. The sampling and monitoring in the central control adopt high performance liquid chromatography, and the specific detection conditions are as follows:

[0043] Chromatographic column: C18, 5μm, 4.6mm×250mm;

[0044] Mobile phase: acetonitrile: water: acetic acid = 300:700:3.5;

[0045] Flow rate: 1.0 mL / min;

[0046] Column temperature: 25 °C;

[0047] Detection wavelength: 270 nm.

[0048] Among them, the retention times of 2-chloro-N,N-dimethylnicotinamide and 2-chloronicotinic acid are approximately 6.08 min and 3.39 min, respectively.

[0049] In the one-step synthesis method of the present invention, 2-chloro-N,N-dimethylnicotinamide is prepared by dehydrating the ammonium salt. Compared with the traditional process, multiple steps such as the preparation of acyl chloride and solvent recovery are omitted, reducing equipment investment and energy consumption, and avoiding the generation of chlorine-containing wastewater and mixed salts. Moreover, the dosage of dimethylamine is significantly reduced, reducing the dimethylamine residue, thereby significantly reducing the raw material and three-waste treatment costs. The process is more energy-saving and environmentally friendly, suitable for large-scale industrial production, and is of great significance to the sustainable development of nicosulfuron. Specific Embodiments

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] To better illustrate the present invention, further examples are given below through embodiments.

[0052] The conditions for on-line detection of 2-chloro-N,N-dimethylnicotinamide and 2-chloronicotinic acid in the following examples and comparative examples are as follows:

[0053] Chromatographic column: C18, 5 μm, 4.6 mm × 250 mm;

[0054] Mobile phase: acetonitrile: water: acetic acid = 300:700:3.5;

[0055] Flow rate: 1.0 mL / min;

[0056] Column temperature: 25 °C;

[0057] Detection wavelength: 270 nm.

[0058] Among them, the retention times of 2-chloro-N,N-dimethylnicotinamide and 2-chloronicotinic acid are approximately 6.08 min and 3.39 min, respectively.

[0059] In the following examples and comparative examples, room temperature refers to 25 ± 5°C.

[0060] Example 1

[0061] This example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, and the specific steps are as follows:

[0062] At room temperature, add 200 g of 2-chloronicotinic acid to a reactor equipped with a double helical ribbon agitator, and then add 157.37 g of a 40% by mass aqueous solution of dimethylamine in one portion. Start stirring, set the stirring rate at 80 r / min, stir at room temperature for 2 h, then continue to heat up to 105°C, dehydrate under normal pressure until no distillate is collected, add 0.4 g of ferrous sulfide, displace with nitrogen, continue to heat up and dehydrate to 170°C, and no distillate is collected. Take a sample for in-process control, and detect by HPLC that the remaining 2-chloronicotinic acid is 0.304%. Cool down to 100°C to await the next mercaptation reaction.

[0063] Obtain 235.81 g of 2-chloro-N,N-dimethylnicotinamide, with a content of 98.7%, a yield of 99.3%, and a whiteness of 95.5.

[0064] Example 2

[0065] This example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, and the specific steps are as follows:

[0066] Under the condition of 0°C, add 200 g of 2-chloronicotinic acid to a reactor equipped with a double helical ribbon agitator, and then add 286.62 g of a 20% by mass aqueous solution of dimethylamine in one portion. Start stirring, set the stirring rate at 50 r / min, stir at room temperature for 2 h, then continue to heat up to 100°C, dehydrate under normal pressure until no distillate is collected, add 0.2 g of ferrous sulfide, displace with nitrogen, continue to heat up and dehydrate to 150°C, and no distillate is collected. Take a sample for in-process control, and detect by HPLC that the remaining 2-chloronicotinic acid is 0.58%. Cool down to 80°C to await the next mercaptation reaction.

[0067] Obtain 235.58 g of 2-chloro-N,N-dimethylnicotinamide, with a content of 98.5%, a yield of 99.0%, and a whiteness of 95.4.

[0068] Example 3

[0069] This example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, and the specific steps are as follows:

[0070] At 50 °C, 200 g of 2-chloronicotinic acid was added to a reactor equipped with a double-helical ribbon agitator, and then 98.15 g of an aqueous dimethylamine solution with a mass concentration of 70% was added all at once. Stirring was started, and the stirring rate was set at 100 r / min. Stirring was carried out at room temperature for 2 h, and then the temperature was raised to 110 °C. Atmospheric dehydration was carried out until no distillate was collected. 1 g of ferric chloride was added, and nitrogen replacement was carried out. The temperature was raised and dehydration was continued to 200 °C, and no distillate was collected. Samples were taken for in-process control, and HPLC detection showed that 0.35% of 2-chloronicotinic acid remained. The temperature was lowered to 80 °C for the next thiolation reaction.

[0071] 235.58 g of 2-chloro-N,N-dimethylnicotinamide was obtained, with a content of 98.5%, a yield of 99.0%, and a whiteness of 95.6.

[0072] Comparative Example 1

[0073] This comparative example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, and the specific steps are as follows:

[0074] (1) Preparation of 2-chloronicotinoyl chloride

[0075] At 20 - 35 °C, 100 g of 2-chloronicotinic acid, 300 g of toluene, and 91 g of thionyl chloride were successively added to a reaction flask. Under nitrogen protection, the mixture was stirred and heated to 85 - 95 °C, and the reaction was carried out for 4 h. Then, vacuum distillation was carried out to obtain 2-chloronicotinoyl chloride;

[0076] (2) Preparation of 2-chloro-N,N-dimethylnicotinamide

[0077] Under nitrogen protection, 300 g of toluene was added to the 2-chloronicotinoyl chloride prepared in step (1), and the mixture was stirred evenly. The temperature was lowered to -3 °C to 3 °C, and then 62 g of dimethylamine hydrochloride was added. 141 g of triethylamine was added dropwise with stirring. After the addition was completed, the reaction was continued at -3 °C to 3 °C for 1 h. Samples were taken for HPLC detection, and the remaining amount of 2-chloronicotinoyl chloride was <0.3%. The reaction was stopped, and the temperature of the reaction solution was controlled at 25 - 30 °C. Water was added to the reaction solution for extraction and liquid separation. The organic phase was vacuum distilled to dryness, and the temperature of the dried product was controlled at 95 °C. The material was discharged and cooled, and dried to obtain 119.12 g of 2-chloro-N,N-dimethylnicotinamide, with a content of 97.5%, a yield of 99.1%, and a whiteness of 85.9.

[0078] Comparative Example 2

[0079] This comparative example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide. The only difference from Example 1 is that the dehydration catalyst ferrous sulfide is not added. The specific steps are as follows:

[0080] At room temperature, 200 g of 2-chloronicotinic acid was added to a reactor equipped with a double-ribbon agitator, and then 157.37 g of an aqueous dimethylamine solution with a mass concentration of 40% was added all at once. Stirring was started, and the stirring rate was set at 80 r / min. Stirring was carried out at room temperature for 2 h, then the temperature was raised to 105 °C, and dehydration was carried out under normal pressure until no distillate was collected. Nitrogen replacement was carried out, and the temperature was raised to continue dehydration to 170 °C, and no distillate was collected. Samples were taken for in-process control, and HPLC detection showed that 0.31% of 2-chloronicotinic acid remained. The temperature was lowered to 100 °C for the next mercapto reaction.

[0081] 200.26 g of 2-chloro-N,N-dimethylnicotinamide was obtained, with a content of 92.7% and a yield of 79.2%. The appearance was gray.

[0082] Comparative Example 3

[0083] This comparative example provides a preparation process for the nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide. The only difference from Example 1 is that the dehydration catalyst was replaced with concentrated sulfuric acid. The specific steps are as follows:

[0084] At room temperature, 200 g of 2-chloronicotinic acid was added to a reactor equipped with a double-ribbon agitator, and then 157.37 g of an aqueous dimethylamine solution with a mass concentration of 40% was added all at once. Stirring was started, and the stirring rate was set at 80 r / min. Stirring was carried out at room temperature for 2 h, then the temperature was raised to 105 °C, and dehydration was carried out under normal pressure until no distillate was collected. 1 g of 98% concentrated sulfuric acid was added, nitrogen replacement was carried out, and the temperature was raised to continue dehydration to 170 °C, and no distillate was collected. Samples were taken for in-process control, and HPLC detection showed that 0.90% of 2-chloronicotinic acid remained. The temperature was lowered to 100 °C for the next mercapto reaction.

[0085] 204.94 g of 2-chloro-N,N-dimethylnicotinamide was obtained, with a content of 96.5% and a yield of 84.38%. The appearance was gray.

[0086] In the examples of the present invention, using 2-chloronicotinic acid and dimethylamine as raw materials and a Lewis acid as the dehydration catalyst, 2-chloro-N,N-dimethylnicotinamide with a yield of over 99%, a purity of 98%, and a whiteness of over 95 was prepared by a one-pot dehydration reaction, and there was no production of three wastes. The process safety, economy, and environmental protection were significantly improved, and it had high practical value.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide, characterized in that: The steps include: S1, adding 2-chloronicotinic acid to the dimethylamine aqueous solution, mixing evenly, to obtain a 2-chloronicotinic acid dimethylammonium salt aqueous solution; S2, heating the 2-chloronicotinic acid dimethylammonium salt aqueous solution and dehydrating it to obtain 2-chloronicotinic acid dimethylammonium salt; S3, adding a dehydration catalyst to the dimethylammonium dichloronicotinic acid salt, and heating the mixture under an inert atmosphere for secondary dehydration to obtain 2-N,N-dimethylnicotinamide; Wherein, the dehydration catalyst is a Lewis acid.

2. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 1, characterized in that: The dehydration catalyst is at least one of a ferric salt or a ferrous salt.

3. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 2, characterized in that: The dehydration catalyst is at least one of iron sulfide, ferrous sulfide or ferric chloride.

4. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 3, characterized in that: The dehydration catalyst is one or both of iron sulfide and ferrous sulfide.

5. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 1, characterized in that: The added amount of the dehydration catalyst is 1‰ to 5‰ of the mass of 2-chloronicotinic acid.

6. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 1, characterized in that: In S1, the mass concentration of the dimethylamine aqueous solution is 20% to 70%; and / or In S1, the molar ratio of dimethylamine to 2-chloronicotinic acid in the dimethylamine aqueous solution is (1.0-1.2):

1.

7. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 1, characterized in that: In S2, the temperature of the heating dehydration is 100°C to 110°C, and the dehydration is performed until no fraction is extracted.

8. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 1, characterized in that: In S3, the temperature of the secondary dehydration is 150°C to 200°C, and the dehydration is performed until no fraction is extracted.

9. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to any one of claims 1 to 8, characterized in that: The specific steps include: Add dimethylamine solution to 2-chloronicotinic acid, keep the temperature at 0°C to 50°C for 0h to 5h, raise the temperature to 100°C to 110°C, dehydrate until no fraction is produced, add a dehydration catalyst, raise the temperature to 150°C to 200°C under an inert atmosphere, perform secondary dehydration until no fraction is produced, and cool to obtain 2-chloro-N,N-dimethylnicotinamide.

10. The process for preparing nicosulfuron intermediate 2-chloro-N,N-dimethylnicotinamide according to claim 9, characterized in that: During the reaction, stirring is performed throughout the process, and a double-screw stirrer is used for stirring at a stirring rate of 50 r / min to 100 r / min; and / or The cooling temperature is 80°C to 100°C.

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