Preparation method of mesotrione

Abstract

The present invention discloses a preparation method of mesotrione, and the method steps are as follows: S1: Under the protection of an inert gas, 3-chloro-2-methylbenzenemethanethiol, phosphorus oxychloride, a composite catalyst and an organic solvent are mixed and reacted. After the reaction is completed, 2-chloro-3-methyl-4-methylthiophenylaldehyde is obtained through separation and vacuum distillation; 2-chloro-3-methyl-4-methylthiophenylaldehyde is mixed with sodium tungstate dihydrate and methanol, and hydrogen peroxide is added for reaction. After the reaction, 2-chloro-3-methyl-4-methylsulfonylbenzoic acid is obtained through filtration; S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid; S3: 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid is mixed and reacted with thionyl chloride and dichloroethane, and the reaction product is further reacted with 1,3-cyclohexanedione, triethylamine and samarium trichloride to prepare mesotrione. The present invention simplifies the preparation route of mesotrione, the preparation process is more green and safe, and the yield of mesotrione is higher.

Description

Technical Field

[0001] The present invention relates to the technical field of mesotrione, and particularly to a preparation method of mesotrione. Background Art

[0002] As a herbicide, mesotrione has a strong killing effect on various weeds. Moreover, mesotrione is not easily washed away by rainwater, so it exists on weeds for a longer time and has a better weeding effect.

[0003] After retrieval, the Chinese patent with the publication number CN104292137A discloses a synthesis method of mesotrione, which is prepared by reacting 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid 3-oxo-1-cyclohexene ester, cyanoacetone and triethylamine in an acetonitrile solvent; Yu Yu et al. published in the journal "Synthesis of the Corn Field Herbicide Mesotrione" proposed a preparation method of mesotrione. After synthesizing 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid, it is dissolved in dichloromethane, then thionyl chloride is added, the residual liquid is dissolved in acetonitrile, and finally 1,3-cyclohexanedione and acetone cyanohydrin are added for reaction.

[0004] For the existing synthesis of mesotrione, it is common to make 2-chloro-3-trifluoroethoxy-4-methylsulfonyl benzoic acid into an acyl chloride, then react it with 1,3-cyclohexanedione to obtain an ester, and finally react it with acetone cyanohydrin or cyanoacetone. However, the raw materials of the above-mentioned scheme are highly toxic, which will cause great harm to the environment and affect the physical health of personnel, and are not conducive to industrial production. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a preparation method of mesotrione, which simplifies the preparation route of mesotrione, the preparation process is more green and safe, and the yield of mesotrione is higher.

[0006] The preparation method of mesotrione proposed by the present invention comprises the following steps:

[0007] S1: Preparation of 2-chloro-3-methyl-4-methylsulfonyl benzoic acid;

[0008] S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid;

[0009] S3: Preparation of mesotrione

[0010] Mix 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid with thionyl chloride and dichloroethane for reaction, and then react the reaction product with 1,3-cyclohexanedione, triethylamine and samarium trichloride to obtain mesotrione.

[0011] Preferably, the method for preparing 2-chloro-3-methyl-4-methylsulfonylbenzoic acid in S1 is as follows:

[0012] S11: Under the protection of inert gas, 3-chloro-2-methylbenzenemethanethiol, phosphorus oxychloride, a composite catalyst and an organic solvent are mixed and reacted. After the reaction is completed, 2-chloro-3-methyl-4-methylthio benzaldehyde is obtained through separation and vacuum distillation;

[0013] S12: 2-chloro-3-methyl-4-methylthio benzaldehyde prepared in S11 is mixed with sodium tungstate dihydrate and methanol, and hydrogen peroxide is added for reaction. After the reaction, 2-chloro-3-methyl-4-methylsulfonylbenzoic acid is obtained through filtration.

[0014] Preferably, the mass-volume ratio of 3-chloro-2-methylbenzenemethanethiol, phosphorus oxychloride, the composite catalyst and the organic solvent in S11 is 100 g: 105-115 g: 1-10 g: 200-400 mL; the reaction conditions are: temperature 40-60 °C, time 8-12 h.

[0015] Preferably, the organic solvent is a mixture of DMF and ethylene glycol monoethyl ether in a ratio of 10: 1-3; the composite catalyst is a mixture of 3-amino-2-pyridineacetic acid and a metal oxide in a ratio of 1: 3-5; the metal oxide is one or more of alumina, ruthenium oxide, cobalt oxide and manganese oxide.

[0016] Preferably, the mass-volume ratio of 2-chloro-3-methyl-4-methylthio benzaldehyde, sodium tungstate dihydrate, methanol and hydrogen peroxide in S12 is 100 g: 1-3 g: 80-120 mL: 200-400 g; the reaction conditions are: temperature 35-45 °C, time 10-20 h.

[0017] Preferably, the method for preparing 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid in S2 is as follows:

[0018] S21: 2-chloro-3-methyl-4-methylsulfonylbenzoic acid, p-toluenesulfonic acid and methanol are mixed and reacted. After the reaction, it is cooled, vacuum distilled and crystallized to obtain methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate;

[0019] S22: Methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate is dissolved in carbon tetrachloride, and then peroxybenzoic acid and bromine are added for reaction. After the reaction, it is neutralized, washed with water, concentrated and washed to obtain methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate;

[0020] S23: Mix methyl 2-chloro-3-(bromomethyl)-4-(methylsulfonyl)benzoate, sodium trifluoroethanolate and tetrahydrofuran for reaction, and then wash with water, concentrate, acidify, extract and dry to obtain 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-(methylsulfonyl)benzoic acid.

[0021] Preferably, in S21, the mass-to-volume ratio of 2-chloro-3-methyl-4-(methylsulfonyl)benzoic acid, p-toluenesulfonic acid and methanol is 100 g: 1-1.5 g: 400-600 mL.

[0022] Preferably, in S22, the mass-to-volume ratio of methyl 2-chloro-3-methyl-4-(methylsulfonyl)benzoate, carbon tetrachloride, peroxybenzoic acid and bromine is 100 g: 400-600 mL: 1-1.5 g: 80-120 g.

[0023] Preferably, in S23, the mass-to-volume ratio of methyl 2-chloro-3-(bromomethyl)-4-(methylsulfonyl)benzoate, sodium trifluoroethanolate and tetrahydrofuran is 5 g: 2-4 g: 8-12 mL.

[0024] Preferably, in S3, the mass-to-volume ratio of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-(methylsulfonyl)benzoic acid, thionyl chloride, dichloroethane, 1,3-cyclohexanedione, triethylamine and samarium trichloride is 1 g: 0.8-1.2 g: 4-6 mL: 0.3-0.5 g: 0.2-0.4 g: 0.01-0.1 g.

[0025] Advantageous technical effects of the present invention:

[0026] (1) By using the composite catalyst, the present invention can increase the yield of 2-chloro-3-methyl-4-(methylthio)benzaldehyde to over 98% with high purity, thereby increasing the yield of the subsequent intermediate of tefuryl, 2-chloro-3-methyl-4-(methylsulfonyl)benzoic acid. This is because the metal oxide in the composite catalyst of the present invention can promote the combination of phosphorus oxychloride and 3-chloro-2-methylbenzyl methyl sulfide, and while 3-amino-2-pyridineacetic acid promotes the combination of phosphorus oxychloride and 3-chloro-2-methylbenzyl methyl sulfide, it can also increase the activity of the third position of the benzene ring, making it easier to introduce the aldehyde group at the third position of the benzene ring, thus increasing the yield and purity of the preparation of 2-chloro-3-methyl-4-(methylthio)benzaldehyde. Compared with the existing method of first introducing an acetyl group at the third position of the benzene ring and then oxidizing the acetyl group to a carboxyl group, it is more conducive to industrial production with higher yield and purity.

[0027] (2) By adjusting the composition of the organic solvent and adding a certain amount of ethylene glycol monoethyl ether to DMF, the yield of 2-chloro-3-methyl-4-methylthio benzaldehyde can be further improved. In addition, the composite catalyst of the present invention is composed of 3-amino-2-pyridine acetic acid and metal oxide, which has a synergistic promoting effect on improving the yield of 2-chloro-3-methyl-4-methylthio benzaldehyde.

[0028] (3) The present invention uses samarium trichloride as a catalyst to synthesize mesotrione in one step. Compared with the existing method of first making 2-chloro-3-trifluoroethoxy-4-methylsulfonyl benzoic acid into acyl chloride, then reacting with 1,3-cyclohexanedione to obtain an ester, and finally rearranging with acetone cyanohydrin, the preparation method of the present invention simplifies the preparation route of mesotrione, the preparation process is more green and safe, and the yield of mesotrione is higher. Detailed implementation mode

[0029] The preparation method of 3-chloro-2-methyl benzyl mercaptan in the present invention is as follows: dissolve 1 mol of 3-chloro-2-methyl aniline in 5 mol of hydrochloric acid solution, then add 1 mol of sodium nitrite for diazotization reaction at a reaction temperature of 0 °C, and add the reaction product to an aqueous solution of sodium methyl mercaptide with a mass concentration of 20% for reaction to obtain 3-chloro-2-methyl benzyl mercaptan.

[0030] 3-chloro-2-methyl aniline and other raw materials are all commercially available.

[0031] Example 1

[0032] The preparation method of mesotrione proposed by the present invention is as follows:

[0033] S1: Preparation of 2-chloro-3-methyl-4-methylsulfonyl benzoic acid

[0034] Under the protection of an inert gas (nitrogen), mix 100 kg of 3-chloro-2-methyl benzyl mercaptan with 110 kg of phosphorus oxychloride, 5 kg of composite catalyst, and 300 L of organic solvent at 50 °C for 10 h. After the reaction, lower the temperature to 0 °C, then slowly add 150 kg of water and 150 kg of dichloroethane in sequence, stir for 30 min, separate the organic phase after standing, and obtain 2-chloro-3-methyl-4-methylthio benzaldehyde by vacuum distillation.

[0035]

[0036] Then mix 100 kg of 2-chloro-3-methyl-4-methylthio benzaldehyde with 2 kg of sodium tungstate dihydrate and 100 L of methanol, and add 300 kg of hydrogen peroxide (30%) to react at 40 °C for 15 h. After the reaction, add 1000 L of water to the reaction, stir and filter, and the filter cake is 2-chloro-3-methyl-4-methylsulfonyl benzoic acid.

[0037]

[0038] Wherein: the organic solvent is a mixture of DMF and ethylene glycol monoethyl ether in a ratio of 5:1; the composite catalyst is a mixture of 3-amino-2-pyridineacetic acid and alumina in a ratio of 1:4.

[0039] S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid

[0040] Mix 100 kg of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid, 1.2 kg of p-toluenesulfonic acid and 500 L of methanol, heat under reflux with stirring for 10 h, cool after the reaction, distill off methanol under reduced pressure, cool to precipitate a solid, and recrystallize with ethanol to obtain methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate.

[0041]

[0042] Dissolve 100 kg of methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate in 500 L of carbon tetrachloride, add 1.2 kg of peroxybenzoic acid and 100 kg of bromine, add bromine dropwise at room temperature, the dropping time is 30 min, after dropping, heat under reflux for 8 h; cool after the reaction, neutralize with saturated sodium carbonate, separate out the aqueous layer, wash the organic layer with water, concentrate to obtain a crude product, wash the crude product with ethyl acetate, and dry to obtain methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate.

[0043]

[0044] Mix 50 kg of methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate, 30 kg of sodium trifluoroethanolate and 100 L of tetrahydrofuran at room temperature and react for 4 h, then wash with water and concentrate to obtain methyl 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoate, add NaOH and water and reflux for 3 h, distill off the solvent tetrahydrofuran, cool, add hydrochloric acid for acidification, then add dichloromethane for extraction, wash with water, dry with magnesium sulfate, and concentrate to obtain 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid.

[0045]

[0046] S3: Preparation of mesotrione

[0047] 100 kg of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid is reacted with 100 kg of thionyl chloride by heating under reflux with stirring for 5 h. After the reaction, the solvent is distilled off, then 500 L of dichloromethane is added and cooled to room temperature. The product is then reacted with 40 kg of 1,3-cyclohexanedione, 30 kg of triethylamine, and 10 kg of samarium trichloride at room temperature for 8 h. The reaction mixture is washed with water, dried over magnesium sulfate, and concentrated to obtain mesotrione.

[0048]

[0049] Example 2

[0050] The preparation method of mesotrione proposed by the present invention is as follows:

[0051] S1: Preparation of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid

[0052] Under the protection of an inert gas, 100 kg of 3-chloro-2-methylbenzenemethanethiol is mixed with 105 kg of phosphorus oxychloride, 1 kg of a composite catalyst, and 200 L of an organic solvent at 40 °C and reacted for 8 h. After the reaction, the temperature is lowered to 0 °C, then 150 kg of water and 150 kg of dichloroethane are slowly added in sequence, stirred for 30 min, and after standing, the organic phase is separated out and distilled under reduced pressure to obtain 2-chloro-3-methyl-4-methylthio-benzaldehyde.

[0053] Then 100 kg of 2-chloro-3-methyl-4-methylthio-benzaldehyde is mixed with 1 kg of sodium tungstate dihydrate and methanol, and 200 kg of hydrogen peroxide is added and reacted at 35 °C for 10 h. After the reaction, 1000 L of water is added to the reaction, stirred and filtered, and the filter cake is 2-chloro-3-methyl-4-methylsulfonylbenzoic acid.

[0054] Among them: the organic solvent is a mixture of DMF and ethylene glycol monoethyl ether in a ratio of 10:1; the composite catalyst is a mixture of 3-amino-2-pyridineacetic acid and ruthenium oxide in a ratio of 1:3.

[0055] S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid

[0056] 100 kg of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid, 1 kg of p-toluenesulfonic acid, and 400 L of methanol are mixed and heated under reflux with stirring for 10 h. After the reaction, methanol is distilled off under reduced pressure after cooling, and a solid precipitates out upon cooling. It is recrystallized with ethanol to obtain methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate.

[0057] Dissolve 100 kg of methyl 2-chloro-3-methyl-4-(methylsulfonyl)benzoate in 400 L of carbon tetrachloride, then add 1 kg of peroxybenzoic acid and 80 kg of bromine. The bromine is added dropwise at room temperature, and the dropping time is 30 min. After the dropping is completed, the temperature is raised to reflux for 8 h. After the reaction, it is cooled, neutralized with saturated sodium carbonate, the aqueous layer is separated out, the organic layer is washed with water, concentrated to obtain the crude product, and the crude product is washed with ethyl acetate, dried to obtain methyl 2-chloro-3-(bromomethyl)-4-(methylsulfonyl)benzoate.

[0058] Mix 50 kg of methyl 2-chloro-3-(bromomethyl)-4-(methylsulfonyl)benzoate, 20 kg of sodium trifluoroethoxide and 80 L of tetrahydrofuran at room temperature and react for 4 h. Then, after washing with water and concentrating, methyl 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-(methylsulfonyl)benzoate is obtained. Then, add NaOH and water and reflux for 3 h, then distill off the solvent tetrahydrofuran. After cooling, add hydrochloric acid for acidification, then add dichloromethane for extraction, wash with water, dry with magnesium sulfate, and concentrate to obtain 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-(methylsulfonyl)benzoic acid.

[0059] S3: Preparation of mesotrione

[0060] React 100 kg of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-(methylsulfonyl)benzoic acid with 80 kg of thionyl chloride under heating and reflux with stirring for 5 h. After the reaction, distill off the solvent, then add 500 L of dichloromethane and cool to room temperature. The product is then reacted with 30 kg of 1,3-cyclohexanedione, 20 kg of triethylamine and 5 kg of samarium trichloride at room temperature for 8 h. The reactant is washed with water, dried with magnesium sulfate, and concentrated to obtain mesotrione.

[0061] Example 3

[0062] The preparation method of mesotrione proposed by the present invention has the following steps:

[0063] S1: Preparation of 2-chloro-3-methyl-4-(methylsulfonyl)benzoic acid

[0064] Under the protection of inert gas, mix 100 kg of 3-chloro-2-methylbenzenemethanethiol with 115 kg of phosphorus oxychloride, 10 kg of composite catalyst and 400 L of organic solvent at 60 °C and react for 12 h. After the reaction, lower the temperature to 0 °C, then slowly add 150 kg of water and 150 kg of dichloroethane in sequence, stir for 30 min, stand still, separate out the organic phase, and obtain 2-chloro-3-methyl-4-(methylthio)benzaldehyde by vacuum distillation.

[0065] Then, 100 kg of 2-chloro-3-methyl-4-methylthio benzaldehyde is mixed with 3 kg of sodium tungstate dihydrate and methanol, and 400 kg of hydrogen peroxide is added, followed by reacting at 45 °C for 20 h. After the reaction, 1000 L of water is added to the reaction mixture. After stirring, filtration is carried out, and the filter cake is 2-chloro-3-methyl-4-methylsulfonyl benzoic acid.

[0066] Among them: the organic solvent is a mixture of DMF and ethylene glycol monoethyl ether in a ratio of 10:3; the composite catalyst is a mixture of 3-amino-2-pyridine acetic acid and manganese oxide in a ratio of 1:5.

[0067] S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid

[0068] 100 kg of 2-chloro-3-methyl-4-methylsulfonyl benzoic acid, 1.5 kg of p-toluenesulfonic acid and 600 L of methanol are mixed and heated under reflux with stirring for 10 h. After the reaction, it is cooled, and methanol is distilled off under reduced pressure. The solid is precipitated upon cooling and recrystallized with ethanol to obtain methyl 2-chloro-3-methyl-4-methylsulfonyl benzoate.

[0069] 100 kg of methyl 2-chloro-3-methyl-4-methylsulfonyl benzoate is dissolved in 600 L of carbon tetrachloride, and then 1.5 kg of perbenzoic acid and 120 kg of bromine are added. Bromine is added dropwise at room temperature, and the dropping time is 30 min. After the dropping is completed, the temperature is raised to reflux for 8 h; after the reaction, it is cooled, neutralized with saturated sodium carbonate, the aqueous layer is separated, the organic layer is washed with water, concentrated to obtain a crude product, and the crude product is washed with ethyl acetate and dried to obtain methyl 2-chloro-3-bromomethyl-4-methylsulfonyl benzoate.

[0070] 50 kg of methyl 2-chloro-3-bromomethyl-4-methylsulfonyl benzoate, 40 kg of sodium trifluoroethanolate and 120 L of tetrahydrofuran are mixed and reacted at room temperature for 4 h, and then washed with water and concentrated to obtain methyl 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoate. Then, NaOH and water are added and refluxed for 3 h, the solvent tetrahydrofuran is distilled off, hydrochloric acid is added for acidification after cooling, and then dichloromethane is added for extraction. After washing with water, it is dried with magnesium sulfate and concentrated to obtain 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonyl benzoic acid.

[0071] S3: Preparation of mesotrione

[0072] React 100 kg of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid with 120 kg of thionyl chloride under heating and reflux with stirring for 5 h. After the reaction, remove the solvent by evaporation, then add 500 L of dichloromethane and cool to room temperature. The product is then reacted with 50 kg of 1,3-cyclohexanedione, 40 kg of triethylamine, and 15 kg of samarium trichloride at room temperature for 8 h. Wash the reaction mixture with water, dry it over magnesium sulfate, and concentrate to obtain mesotrione.

[0073] Example 4

[0074] In "S3: Preparation of mesotrione" of this scheme, the addition amount of samarium trichloride is 5 kg, and the other conditions are the same as those in Example 1.

[0075] Example 5

[0076] In "S3: Preparation of mesotrione" of this scheme, the addition amount of samarium trichloride is 15 kg, and the other conditions are the same as those in Example 1.

[0077] Example 6

[0078] In "S3: Preparation of mesotrione" of this scheme, the addition amount of 1,3-cyclohexanedione is 30 kg, and the other conditions are the same as those in Example 1.

[0079] Example 7

[0080] In "S3: Preparation of mesotrione" of this scheme, the addition amount of 1,3-cyclohexanedione is 50 kg, and the other conditions are the same as those in Example 1.

[0081] Comparative Example 1

[0082] The organic solvent in this scheme is DMF, and the other conditions are the same as those in Example 1.

[0083] Comparative Example 2

[0084] The catalyst in "S1: Preparation of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid" of this scheme is alumina, and the other conditions are the same as those in Example 1.

[0085] Comparative Example 3

[0086] The catalyst in "S1: Preparation of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid" of this scheme is 3-amino-2-pyridineacetic acid, and the other conditions are the same as those in Example 1.

[0087] Detect the yields and purities of 2-chloro-3-methyl-4-methylthio benzaldehyde and mesotrione prepared in Examples 1-7 and Comparative Examples 1-3. The results are shown in Table 1.

[0088] Table 1 Product Detection Results

[0089]

[0090]

[0091] From the test results of Examples 1-7, it can be seen that the present invention improves the yield of 2-chloro-3-methyl-4-methylthio benzaldehyde through the composite catalyst, and the purity is high, thereby improving the yield of the subsequent intermediate of mesotrione, 2-chloro-3-methyl-4-methylsulfonyl benzoic acid; in addition, using samarium trichloride as the catalyst, mesotrione is synthesized in one step. Compared with the existing method of first making 2-chloro-3-trifluoroethoxy-4-methylsulfonyl benzoic acid into acyl chloride, then reacting with 1,3-cyclohexanedione to obtain an ester, and finally rearranging with acetone cyanohydrin, the preparation method of the present invention simplifies the preparation route of mesotrione, the preparation process is more environmentally friendly and safe, and the yield of mesotrione is as high as over 98%.

[0092] From the test results of Example 1 and Comparative Example 1, it can be seen that by adjusting the composition of the organic solvent and adding a certain amount of ethylene glycol monoethyl ether to DMF, the yield of the intermediate of mesotrione, 2-chloro-3-methyl-4-methylthio benzaldehyde, can be further improved; from the test results of Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that the composite catalyst added in the present invention has a synergistic promoting effect on improving the yield and purity of 2-chloro-3-methyl-4-methylthio benzaldehyde.

[0093] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of mesotrione, characterized in that, The method steps are as follows: S1: Preparation of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid; S2: Preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid; S3: Preparation of mesotrione Mix 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid with thionyl chloride and dichloroethane for reaction, and then react the reaction product with 1,3-cyclohexanedione, triethylamine and samarium trichloride to obtain mesotrione; The method steps for the preparation of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid in S1 are as follows: S11: Under the protection of an inert gas, mix 3-chloro-2-methylbenzenemethanethiol, phosphorus oxychloride, a composite catalyst and an organic solvent for reaction. After the reaction is completed, separate and distill under reduced pressure to obtain 2-chloro-3-methyl-4-methylthiophenylaldehyde; S12: Mix the 2-chloro-3-methyl-4-methylthiophenylaldehyde prepared in S11 with sodium tungstate dihydrate and methanol, and add hydrogen peroxide for reaction. After the reaction, filter to obtain 2-chloro-3-methyl-4-methylsulfonylbenzoic acid; The organic solvent is a mixture of DMF and ethylene glycol monoethyl ether in a ratio of 10:1 - 3; the composite catalyst is a mixture of 3-amino-2-pyridineacetic acid and a metal oxide in a ratio of 1:3 - 5; the metal oxide is one or more of alumina, ruthenium oxide and manganese oxide.

2. The preparation method of topramezone according to claim 1, characterized in that, The mass-to-volume ratio of 3-chloro-2-methylbenzenemethanethiol, phosphorus oxychloride, the composite catalyst and the organic solvent in S11 is 100 g:105 - 115 g:1 - 10 g:200 - 400 mL; the reaction conditions are: temperature 40 - 60 °C, time 8 - 12 h.

3. The preparation method of mesotrione according to claim 1, characterized in that, The mass-to-volume ratio of 2-chloro-3-methyl-4-methylthiophenylaldehyde, sodium tungstate dihydrate, methanol and hydrogen peroxide in S12 is 100 g:1 - 3 g:80 - 120 mL:200 - 400 g; the reaction conditions are: temperature 35 - 45 °C, time 10 - 20 h.

4. The preparation method of topramezone according to claim 1, characterized in that, The method steps for the preparation of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid in S2 are as follows: S21: Mix 2-chloro-3-methyl-4-methylsulfonylbenzoic acid, p-toluenesulfonic acid and methanol for reaction. After the reaction, cool, distill under reduced pressure and crystallize to obtain methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate; S22: Dissolve methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate in carbon tetrachloride, add peroxybenzoic acid and bromine for reaction. After the reaction, neutralize, wash with water, concentrate and wash to obtain methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate; S23: Mix methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate, sodium trifluoroethoxide and tetrahydrofuran for reaction, and then wash with water, concentrate, acidify, extract and dry to obtain 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid.

5. The preparation method of topramezone according to claim 4, characterized in that, The mass-to-volume ratio of 2-chloro-3-methyl-4-methylsulfonylbenzoic acid, p-toluenesulfonic acid and methanol in S21 is 100 g:1 - 1.5 g:400 - 600 mL.

6. The preparation method of topramezone according to claim 4, characterized in that, In S22, the mass-volume ratio of methyl 2-chloro-3-methyl-4-methylsulfonylbenzoate, carbon tetrachloride, perbenzoic acid, and bromine is 100 g: 400 - 600 mL: 1 - 1.5 g: 80 - 120 g.

7. The preparation method of topramezone according to claim 4, characterized in that, In S23, the mass-volume ratio of methyl 2-chloro-3-bromomethyl-4-methylsulfonylbenzoate, sodium trifluoroethoxide, and tetrahydrofuran is 5 g: 2 - 4 g: 8 - 12 mL.

8. The preparation method of topramezone according to claim 1, characterized in that In S3, the mass-volume ratio of 2-chloro-3-(2,2,2-trifluoroethoxy)methyl-4-methylsulfonylbenzoic acid, thionyl chloride, dichloroethane, 1,3-cyclohexanedione, triethylamine, and samarium(III) chloride is 1 g: 0.8 - 1.2 g: 4 - 6 mL: 0.3 - 0.5 g: 0.2 - 0.4 g: 0.01 - 0.1 g.

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