SU118508A1 - The method of obtaining 2,4-dichlorophenoxyacetic acid - Google Patents

Description

2,4-dichlorophenoxyacetic acid is a highly physiologically active substance and is used in agricultural practice as a stimulator of growth and increase in the yield of many important crops and as a means of weed control (herbicide).

The known method of producing 2,4-dichlorophenoxyacetic acid by alkali on an alloy of 2,4-dichlorophenol with chloroacetic acid gives small yields of the product in the order of 20-30% of the theoretical.

The proposed method for producing 2,4-dichlorophenoxyacetic acid eliminates this drawback and increases the yield of the product to 78% of the theoretical value, calculated as dichlorophenol. This is achieved by maintaining the temperature of the reaction mixture within 40-60 ° during the addition of alkali, after which the heating is continued at a temperature of 60-65 ° and then at 100 °.

Example. Take the following source materials:

2,4-dichlorophenol (fraction 206-209 °, mp. 41-43 °). . 80 g;

monochloroacetic acid technical (90-92%). 10 g;

soda in the form of a 40% solution ... / ... 156 g

2,4-dichlorophenol and chloroacetic acid are placed in the reaction flask and the mixture is heated to melt 2,4-dichlorophenol, after which it is cooled to 20-25 ° and, under stirring, in a mixture of sodium hydroxide solution is added dropwise, maintaining the within 40-60 °. After adding sodium hydroxide solution, the mixture is heated with stirring to a temperature of 60-65 ° for 2 hours. The mixture, thickens as a result of the formation of 2,4-dichlorophenoxyacetic acid sodium salt. To end the reaction, the mixture is heated for an additional 3-4 hours in a boiling water bath. 150-200 ml of hot water is added to the hot semi-solid mass, and the mixture is thoroughly stirred while heating in a water bath for 1 hour. After cooling to

No. 118508-2 room temperature, the mixture is transferred to a Buchner funnel and the mother liquor is carefully sucked off. . The resulting white crystalline mass for final washing 1 and from 2,4-dichlorophene is washed with dilute alkali. The mixture is heated on a boiling water bath with stirring for 1 hour, after which the hot condition (60) is sucked off from the washing liquid in a Büchner funnel and then washed twice on the filter with a small amount of water. The obtained white finely crystalline salt of 2,4-dichlorophenoxyacetic acid is dried (in a steam flasher); 103 g of salt or 84.79 og of theoretical yield are obtained (calculated as 2,4-dichlorophenol).

Next, the sodium salt of 2,4-dichlorophenoxyacetic acid is dissolved in boiling water based on I weight. h. salt 15 wt. h of water. The hot solution is filtered, and to a clear filter heated to 50-60 °, 15% hydrochloric acid is gradually added with stirring until acidic to Congo. After precipitation the mixture is cooled to room temperature, the precipitate is settled, thoroughly washed with water until the hydrochloric acid is removed and dried in a steam dryer (70-90 °). A white or slightly yellowish fine crystalline powder of 2,4-dichlorophenoxyacetic acid having a m.p. 138-139 °. The yield is 84.5 g or 78% of the theoretical (based on 2,4-dichlo, rphenol). For final purification, the product is recrystallized from 35% acetic acid. The final purified product is white crystals with m.p. 139-140 ° without any smell.

Subject invention

The method of producing 2,4-dichlorophenoxyacetic acid by the action of alkali on an alloy of 2,4-dichlorophenol with chloroacetic acid, characterized in that during the addition of alkali the temperature of the reaction mixture is maintained at 40-60 °, after which the heating is continued at 60-65 ° and finally at 100 °.