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Existing methods for the synthesis of 2-Picolinic acid include:
1. Oxidizing 2-methylpyridine with potassium permanganate to obtain 2-Picolinic acid, followed by solvent extraction. However, the reported yield is less than 70%.
2. Oxidizing 2-vinylpyridine with potassium permanganate to obtain 2-Picolinic acid, followed by extraction. Due to multiple side reactions, several recrystallizations are required to obtain a satisfactory product.
3. Oxidizing 2-methylpyridine with sulfuric acid can also yield 2-Picolinic acid, but this process generates a large amount of waste acid, making it difficult to handle.
Purification methods include benzene method, aqueous phase method, acetic acid method, and ethanol method. The benzene method consumes too much solvent, approximately 10 times that of the ethanol method. The aqueous phase method yields low purity products, while the acetic acid method, although producing high-quality products, corrodes equipment due to the strong acidity of acetic acid, making it unsuitable for safe production.
The purpose of this invention is to provide a method for synthesizing 2-Picolinic acid that is easy to operate and has a high yield.
The technical solution of this invention is a method for synthesizing 2-Picolinic acid, characterized by: hydrolyzing 2-cyanopyridine under alkaline conditions, followed by acid neutralization, and then extracting 2-Picolinic acid with ethanol. The method for synthesizing 2-Picolinic acid includes the following steps: adding reactants to a flask in a 1:2 ratio of 2-cyanopyridine to deionized water, stirring, heating to 50-70°C, adding 30% sodium hydroxide in a molar ratio of 1:1.0-1.3 of 2-cyanopyridine, continuing to heat and reflux for 4-12 hours, then distilling water with a mass ratio of 1:0.5-1.5 of 2-cyanopyridine to distilled water. After the water distillation, cooling the reaction mixture to 20-60°C, adding 30% hydrochloric acid to adjust the pH of the reaction mixture to 2.5-6.5, then heating with steam until the temperature of the reaction mixture reaches 100-160°C, evaporating the reaction mixture until dry, ending the water distillation, and finally adding 2-cyanopyridine to ethanol in a mass ratio of 1:1.0-3.0 to the flask, maintaining the temperature of the reaction mixture at 55-75°C, stirring and dissolving for 2-7 hours, followed by filtration, cooling the filtrate to crystallize, filtering, and drying to obtain solid 2-Picolinic acid.
This invention provides a simple and easy-to-operate process with high product yield.
Further explanation of this invention will be given through the following examples.
In a 500ml three-neck flask, 100g of 2-cyanopyridine and 200g of deionized water are added. The mixture is stirred and heated to 50°C, then 128.2g of 30% sodium hydroxide is added. After that, the mixture is further heated and refluxed for 4 hours. Then, 50g of water is distilled off, and the reaction mixture is cooled to 20°C. 30% hydrochloric acid is added to adjust the pH to 2.5. The mixture is then heated with steam until the temperature reaches 120°C, and the reaction mixture is evaporated until dry. After ending the water distillation, 300g of anhydrous ethanol is added to the flask, and the temperature of the reaction mixture is maintained at 55°C. After stirring and dissolving for 2 hours, the mixture is filtered, and the filtrate is cooled to crystallize. The solid 2-Picolinic acid is obtained by filtering and drying, with a yield of 106.0g, which is 89.6%.
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