CS240481B1 - Process for preparing 2-methyl-4-chlorophenoxyacetic acid - Google Patents

Abstract

The method for preparing 2-methyl-4-chlorophenoxyacetic acid is carried out by chlorination of sodium 2-methylphenoxyacetate with sodium hypochlorite in the presence of mineral acid. The solution of sodium 2-methyl-4-chlorophenoxyacetate obtained after chlorination of 2-methylphenoxyacetic acid with sodium hypochlorite is added to an excess of mineral acid and the precipitated 2-methyl-4-chlorophenoxyacetic acid is separated from the mother solution of mineral acids. The mother solution of mineral acids is used to prepare a dilute solution of mineral acids for the precipitation of 2-methyl-4-chlorophenoxyacetic acid. The method is also applicable in the production of pesticides.

Description

The present invention relates to the preparation of 2-methyl-4-chlorophenoxyacetic acid chloroacetate of 2-methylphenoxyacetic acid and its sodium salt with sodium hypochlorite.

2-Methyl-4-chlorophenoxyacetic acid and is ¹ ] salts are used as very effective herbicides. Most commonly, it is prepared by chlorination of 2-methylphenoxyacetic acid with chlorine gas at 95-105 ° C as described in CS Pat. no. 91160. A continuous method of chlorinating a sodium, di-potassium or sodium-potassium salt of 2-methylphenoxyacetic acid in an aqueous solution is described in CS Pat. No. 99 892, a continuous method of chlorination of free 2-methylphenoxyacetic acid with chlorine gas is described in CS Pat. no. The possibility of combining the chlorination of 2-methylphenoxyacetic acid with gaseous, chlorine and subsequent hypochlorite hypochlorite is disclosed in CS AO no. 172 186. Chlorination of 2-methylphenoxyacetic acid with chlorine gas at pH 4-6 is described in FR Pat. no. Chlorination with an aqueous solution of sodium hypochlorite prepared in advance or "in situ" in the reaction mixture at 50 ° C is described in GB Pat. No. 7212 625. The chlorination of suspended 2-methylphenoxyacetic acid at a pH equal to 1 heterogeneous phase in the presence of hydrochloric acid at 20 ° C is described in DAS No. 1,027,680. A method based on the action of sodium hydroxide or sodium carbonate on aqueous a solution of 2-methylphenoxyacetic acid sodium salt and chlorination chlorine is described in US Pat. no. Chlorination of 2-methylphenoxyacetic acid sodium salt with chlorine in the presence of bicarbonate is described in GB Pat. no. 8) 5-5, 504. Production of 2-methyl-4-chlorophenoxyacetic acid using sodium hypochlorite in the presence of a mineral or carboxylic acid and production of 2-methyl-4-chlorophenoxyacetic acid by chlorination of the sodium salt of 2-methylphenoxyacetic acid to give 2 of methyl-4-chlorophenoxyacetic acid by precipitation with an excess of an aqueous mineral acid solution is described in CS Pat. no. 179 200.

In the aforementioned references, in particular in CS AO no. No attention is paid to the use of parent mineral acids after the chlorination of 2-m-ethylphenoxyacetate with sodium hypochlorite and the precipitation of the sodium salt of 2-methyl-4-chlorophenoxyacetic acid in the mineral acid, followed by filtration of 2-methyl-4- chlorphenoxyacetic acid -from the mineral acid mother liquor solution. The suspension of 2-methyl-4-chlorophenoxyacetic acid is well filterable below the pH of the parent acid below 2.

The above drawbacks are alleviated by the preparation of 2-methyl-4-chlorophenoxyacetic acid by chlorination of 2-methylphenoxyacetic acid with sodium hypochlorite in the presence of a mineral acid. After chlorination, the 2-methyl-4-chlorophenoxyacetic acid is precipitated with the mineral acid from the solution obtained and the 2-methyl-4-chlorophenoxyacetic acid is separated from the mother acid mineral solution. SUMMARY OF THE INVENTION The present invention is characterized in that for the preparation of a dilute mineral acid, a concentration of 1 to 60% by weight, which is used to precipitate 2-methyl-4-chlorophenoxyacetic acid after chlorination, is used a mineral acid concentration solution of 0.01 to 5 wt. after filtering 2-methyl-4-chlorophenoxyacetic acid from the previous batch, to dilute the concentrated mineral acid at a concentration of 10 to 99 wt.

Compared to CS AO no. 179 200 produces less waste water, reducing its acidity and the amount of 2-methyl-4-chlorophenoxyacetic acid therein. 2 to 15 g / l of 2-methyl-4-chloro-phenoxyacetic acid (depending on temperature, pH, mineral acid, etc.) are found in the recirculating mother acids. Part of the mineral acids are also used in the process from the recirculating mother liquors of the mineral acids, higher yields of 2-methyl-4-chlorophenoxyacetic acid are achieved compared to CS AO No. 179 200, lowering the yield of 2-methyl-4-chlorophenoxyacetic acid. the consumption of mineral acids and the quality of the waste water is improved.

EXAMPLE

To 940 g of an aqueous solution of 13.2% w / w. Sodium 2-methylphenoxyacetate 620 g of 13.2 wt. NaOCl and 750 g 8.5 wt. H2SO4 such that the temperature of the solution does not exceed 45 ° C during the addition. After the addition, the mixture was stirred for 1 h. The resulting solution was poured into 285 g of 23.2 wt. H2SO4.

The precipitated 2-methyl-4-chlorophenoxyacetic acid was filtered off, washed with water and dried. 138.2 g of a product containing 91.6 wt. 2-methyl-4-chlóirfenoxyoctovej acid of 2.3 / ₀ by weight. 2-methyl-6-chlórfenoxyloctovej acid and 1.9% of ^{2-metyl.-4,6-dichloro-l} lórfeno xyoctovej acid and 0.8% by weight. Of 2-methylphenoxyacetic acid. The H2SO4 mother liquor contained 5.3 g / l phenoxyacetic acids (a mixture of 2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4-6-dichlorophenoxyacetic acid, and 2-methylphenoxyacetic acid).

Example 1 and d 2

The procedure of Example 1 was followed except that 23.2% wt. The sulfuric acid mother liquors of Example 1 were used to dilute 96 wt. H2SO4. 142.1 g and 911.9 wt. Of 2-methyl-4-phenoxyacetic acid.

Example 3

The procedure of Example 2 was followed except that 54 wt. H2SO4 which was used to precipitate 2-methyl-4-chlorophenoxyacetic acid. 143.1 g of product with a content of 92.4% by weight were obtained. % Of 2-methyl-4-chlorophenoxyacetic acid, 1.9 wt. 2-methyl-6-chlorophenoxyacetic acid,

1.6% Of 2-methyl-4,6-dichlorophenoxyacetic acid. .

Example 1 and d 4

The procedure of Example 2 was followed except that 24.2 wt. H 2 SO 4, mother liquors of mineral acids were used, containing 0.09 wt. H2SO4 a

5.7 g / l phenoxyactoacids. 140.9 g of a product containing 93.1 wt. % of phenoxyacetic acids and 1.2 wt. water.

Example 1 a d 5 i

The procedure of Example 4 was followed except that 1.8 percent by weight was prepared for precipitation. sulfuric acid. 13.8.9 g of a product containing 92.8 wt. % Of 2-methyl-4-chlorophenoxyacetic acids and 1.8 wt. water.

Example 1 and d 6

The reaction kettle was charged with 1 940 grams of 15.0 wt. % Sodium 2-methylphenoxyacetate and 1320 g. NaOCl. Then 500 g 10.1% were added to the mixture. wt. HC1. After the addition, the kettle contents were stirred for 1 hour. Then the solution was poured to 1500 g

6.8 wt. HC1. The precipitated 2-methyl-4-chlorophenoxyacetic acid was filtered from the hydrochloric acid mother liquor. Drying gave 303.7 g of 92.1 wt. Of 2-methyl-chlorophenoxyacetic acid. The parent hydrochloric acid contained 4.2 g / l of phenoxyacetic acids.

Example?

The procedure of Example 3 was followed except that 6.8 wt. HCl was prepared by dilution with 32 wt. HCl with the hydrochloric acid mother liquor of Example 6 was obtained by drying 312.1 g of 92.6 wt. Of 2-methyl-4-chlorophenoxyacetic acid. The mother liquor contained 1.9 g / l phenoxyacetic acids.

The invention is applicable to the preparation of 2-methyl-4-chlorophenoxyacetic acids which are used in the manufacture of herbicidal compositions.

Claims (2)

240481, except that 54% by weight of H2SO4 was prepared, which was used to precipitate 2-methyl-4-chlorophenoxyacetic acid. The yield was 143.1 g of 92.4% by weight of 2-methyl-4-chlorophenoxyacetic acid, 1.9% by weight. 2-methyl-6-chlorophenoxyacetic acid, 1.6 wt. 2-methyl-4,6-dichlorophenoxyacetic acid. . EXAMPLE 4 Example 2 was followed with the difference that mineral acid mother liquors containing 0.09% by weight were used to prepare 24.2% by weight of H2SO4. H2SO4 and 5.7 g / l of phenoxyacetic acids. 140.9 g of product was obtained, which contained 93.1 wt. phenoxyacetic acids and 1.2% w / w. EXAMPLE 5 Example 4 was followed with the difference that 1.8 percent by weight of the precipitate was prepared. sulfuric acid. 138.9 g of product was obtained, which contained 92.8 wt. 2-methyl-4-chlorophenoxyacetic acid and 1.8 wt. water. EXAMPLE 6 1 940 g / ml of 15.0% by weight were added to the reaction vessel. 2-methylphenoxyacetate and 1320 g 13.9 wt. NaOCl. Thereafter, 500 g of 10.1% was added to the mixture. wt.HCl. After the addition, the contents of the kettle were stirred for 1 hour. Then the solution was poured into 1500 g of 6.8% by weight. HCl. The precipitated 2-methyl-4-chlorophenoxyacetic acid was filtered off from the mother solution of hydrochloric acid]. Drying gave 303.7 g 92.1% by weight. 2-Methyl-chlorophenoxyacetic acid. The mother hydrochloric acid contained 4.2 g / l of phenoxyacetic acid. Example? The procedure of Example 3 was followed with a difference of 6.8% by weight. HCl by dilution with 32 wt. HCl with the parent hydrochloric acid solution of Example 6. Drying gave 312.1 g of 92.6% by weight. 2-methyl-4-chlorophenoxyacetic acid. The mother liquor contained 1.9 g / l of phenoxyacetic acids. The invention is applicable to the preparation of 2-methyl-4-chlorophenoxyacetic acids which are used in the preparation of herbicidal compositions. SUBJECT A method of preparing 2-methyl-4-chlorophenoxyacetic acid by chlorination of sodium 2-methylphenoxyacetate with sodium hypochlorite in the presence of dilute mineral acid, liberating 2-methyl-4-chlorophenoxyacetic acid from the resulting solution after chlorination. by precipitation in excess of an aqueous solution of the mineral acid and 2-methyl-4-chloro-phenoxyacetic acid is separated from the mother liquor solution, characterized in that the 2-methyl-4-chlorophenoxyacetic acid - the mineral acid solution used, prepared by diluting a mineral acid concentration of 10 to 99% by weight. with a mineral acid master solution concentration of 0.01 to 5% by weight. to a final mineral acid concentration of 1-60%! wt.