Preparation method of 2-methyl-3-methoxybenzoic acid

Abstract

The invention relates to a preparation method of 2-methyl-3-methoxybenzoic acid, which comprises the following steps: (1) respectively feeding a sodium phenolate solution formed by 2-methyl-3-hydroxybenzoic acid, sodium hydroxide and water and dimethyl sulfate into an alkylation reaction unit through different conveying units, and carrying out alkylation reaction at 50-90 DEG C, an alkylation reaction solution is obtained; and (2) an alkylation reaction liquid flowing out of the alkylation reaction unit enters a hydrolysis reaction unit for a hydrolysis reaction, and a hydrolysate containing 2-methyl-3-methoxybenzoic acid sodium is obtained. According to the preparation method carried out in the continuous production device, the production process is simplified, refining steps such as recrystallization are avoided, the production cost is reduced, and the scheme is actually feasible after industrial production application, and the preparation method can be applied to industrial continuous production.

Description

Technical field [0001] The present disclosure relates to the field of compound preparation techniques, in particular to a method of preparing 2- methyl-3-methoxybenzoic acid. Background [0002] 2-Methyl-3-methoxybenzoic acid is an important intermediate in pharmaceutical and pesticide chemicals, especially the key intermediate of methoxenylhydrazide, and the minimum content standard for this product is currently available at 98.5%, and the content standard for most enterprises is 99%. [0003] CN107778167A discloses a method of obtaining 2-methyl-3-methoxybenzoic acid by a two-step reaction of 2,6-dichlorotoluene as raw material, The purity of the obtained 2-methyl-3-methoxybenzoic acid can reach up to 99.6%, but the first step of the disclosed two-step reaction has a reaction time of up to ten hours and involves the treatment of copper salts and the distillation recovery of solvents, the second step reaction conditions are harsh and the reaction time is long, if used for indus...

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Problems solved by technology

[0003] CN107778167A discloses taking 2,6-dichlorotoluene as raw material to obtain the method for 2-methyl-3-methoxybenzoic acid through two-step reaction, the purity of the 2-methyl-3-methoxybenzoic acid that obtains is the highest can It can reach 99.6%, but the reaction time of the first step in the disclosed two-step reaction is as long as ten hours and involves the treatment of copper salt and rectification and recovery of the solvent. The second step reaction conditions are harsh and the reaction time is longer. For industrial production, there are problems of low production efficiency and high equipment input costs

CN111018693A discloses a kind of reaction with solid sodium methylate, dimethyl sulfoxide and 2,6-dichlorotoluene, drips methyl substituting agent, makes intermediate 2-methyl-3-chloroanisole, and then React with toluene, tetrahydrofuran and magnesium chips, and pass in carbon dioxide gas to prepare 2-methyl-3-methoxybenzoic acid, with a yield of about 88% and a purity of up to 99.6%, but the synthesis process is complex and involves many Sub-distillation, the process takes a long time, the production efficiency is low, and the energy consumption is high

CN106946685A discloses a method for preparing 2-methyl-3-methoxybenzoic acid using 3-chloro-o-xylene as a starting material through oxidation and alkylation. The purity of the product can reach up to 99%. However, the first step of oxidation involves the recovery and reuse of catalysts and the rectification and recovery of solvents, and the risk factor of oxygen oxidation is high. The second step of alkylation involves the treatment of copper salts and the rectification and recovery of solvents. The process is complicated. , high energy consumption

[0004] Although the above-mentioned patent applications can all obtain 2-methyl-3-methoxybenzoic acid of higher purity, due to the complex process flow, high energy consumption, low production efficiency and other shortcomings, industrialized production cannot be realized. Currently, the commonly used industrialized The method used in the production is to produce 2-methyl-3-methoxybenzoic acid by hydroxylation and hydrolysis of 2-methyl-3-hydroxybenzoic acid as raw material. In "Synthesis of Methoxyfenozide" The method for preparing 2-methyl-3-methoxybenzoic acid by alkylation and hydrolysis of 2-methyl-3-methoxybenzoic acid is mentioned in , and 7.9g (0.05mol) 3-hydroxyl -2-Methylbenzoic acid and 13.4g (0.1mol) 30% sodium hydroxide solution, stirred for 0.5h, then 15.8g (0.125mol) dimethyl sulfate was added dropwise, while 6.7g (0.05mol) 30% Sodium hydroxide solution, control the drop rate, keep the alkaline system, and the reaction temperature is 40-45 ° C. After the dropwise addition, keep the temperature for 1h, then add 6.7g (0.05mol) 30% sodium hydroxide solution to the system, and heat up to 60°C, stir for 0.5h, cool to room temperature, add dropwise an appropriate amount of hydrochloric acid, adjust pH = 1-2, then cool to 5-10°C, keep stirring for 0.5h, filter, wash the filter cake twice with cold water, and dry to obtain a solid Product 3-methoxy-2-methylbenzoic acid 8.3g, HPLC purity 96.1%, yield 96.1%

[0005] The above-mentioned 2-methyl-3-hydroxybenzoic acid is used as a raw material, and dimethyl sulfate is an alkylating agent, and the method for preparing 2-methyl-3-methoxybenzoic acid through alkylation hydrolysis is widely used in industry. Products with higher purity cannot be directly obtained, and further purification through recrystallization and other post-treatment processes is required. Even simple recrystallization as a post-treatment method still cannot obtain products with a purity that meets the requirements. Solvents also increase energy consumption

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