Preparation method of phenylacetic acid

Abstract

The invention discloses a preparation method of phenylacetic acid, which comprises the following steps of: 1) heating benzyl cyanide to 50-100 DEG C, dropwise adding hydrochloric acid to the benzyl cyanide or dropwise adding the molten benzyl cyanide to hydrochloric acid, wherein the molar ratio of the hydrochloric acid to the benzyl cyanide is (1.2-5):1; after dropwise adding, performing a heat preservation reaction for 1-5 hours; and ending the reaction when the mass content of the benzyl cyanide in the reaction system is less than 5%; and 2) performing reduced-pressure distillation for recovering the unreacted benzyl cyanide in the reaction system of the step 1) until the mass content of the benzyl cyanide in the reaction system is less than 0.2%; adding water to the reaction system, and stirring and mixing; cooling for crystallization and performing suction filtration; and washing the obtained crystal with water, and drying to obtain a phenylacetic acid product. According to the preparation method disclosed by the invention, a technology of directly hydrolyzing benzyl cyanide with hydrochloric acid to prepare phenylacetic acid is adopted, few kinds of reactants are used, other organic matters except the raw material benzyl cyanide are not required, the consumption is low, the after-treatment is simple, and both the appearance and quality of the product meet requirements.

Description

technical field [0001] The invention relates to the technical field of synthesis of phenylacetic acid, in particular to a method for preparing phenylacetic acid by hydrolysis of phenylacetonitrile. Background technique [0002] The hydrolysis of phenylacetonitrile is a commonly used method for preparing phenylacetic acid. Its process conditions are relatively simple, and the reaction operation is simple and easy to control. It is the most researched and most mature industrial production method in China. The hydrolysis process is divided into two types: the first one uses strong alkali Such as sodium hydroxide or potassium hydroxide to make phenylacetonitrile into sodium phenylacetate, acidify and crystallize to obtain the product after decolorization; the second is directly hydrolyzed with acid and crystallized to obtain phenylacetic acid. The reaction equation is as follows: [0003] 1. Alkaline hydrolysis [0004] [0005] 2. Acid hydrolysis [0006] 1) Sulfuric ac...

AI Technical Summary

Problems solved by technology

[0013] 1) Alkaline hydrolysis consumes both alkali and acid, poor atom economy, and by-product ammonia and salt;

[0014] 2) Alkaline hydrolysis produces ammonia gas, which will bring out organic matter when the ammonia gas escapes, polluting the environment, no matter whether it is absorbed by water or acid, it cannot be used directly because the organic matter exceeds the standard;

[0015] 3) Sodium phenylacetate solution needs to be decolorized, resulting in solid waste, and the decolorization process releases odor, and the operating environment is poor;

[0016] 4) Using sulfuric acid hydrolysis, high temperature reaction will cause carbonization and coking of the reaction liquid, difficult post-processing, and also affect the appearance and quality of the product, resulting in a large amount of waste acid containing organic matter that is difficult to handle;

[0017] 5) Using hydrogen chloride / tetrahydrofuran for hydrolysis requires continuous feeding of hydrogen chloride gas. After the reaction, tetrahydrofuran needs to be separated and recovered. The operation process is cumbersome and the operating environment is poor;

[0018] 6) Hydrolysis using a mixture of propionic acid and concentrated hydrochloric acid consumes a large amount of organic acid, which is difficult to recycle and has little industrial value

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