CS242170B1 - Process for preparing 2-methyl-4-chlorophenoxyacetic acid - Google Patents

Abstract

The method provides for the preparation of 2-methyl-4-chlorophenoxyacetic acid by chlorination of 2-methylphenoxyacetic acid and/or its sodium salt and subsequent chlorination of the reaction mixture with sodium hypochlorite. 2-methyl-4-chlorophenoxyacetic acid is obtained from the reaction mixture by precipitation in excess of mineral acid. The molar ratio of chlorine to 2-methylphenoxyacetic acid and/or its sodium salt is 0.01 to 0.59 : : 1 and the chlorine is used in the form of off-gas from the decomposition of alkali hypochlorites. The method can be used in the production of herbicide preparations.

Description

242170

The present invention relates to chlorination of 2-methylphenoxyacetic acid with chlorine and chlorinating with sodium hypochlorite.

Chlorination of the sodium salt of 2-methylphenoxyacetic acid with chlorine, the molar ratio of 2-methylphenoxyacetic acid to chlorine being 1: 0.6 to 1.25, treated with NaOH and freed from unreacted 2-methylphenoxyacetic acid sodium salt. post-chlorinating impurities with aqueous NaClO solution at 10 to 50 ° C. A drawback is that chlorine waste is not used for chlorination and, after chlorination with chlorine, the reaction mixture must be introduced into the alkaline region with NaOH and the chlorination with NaCl is more preferably carried out in the presence of mineral acid.Chlorination of 2-methylphenoxyacetic acid with chlorine gas at pH 4-6, FR Pat. No. 1,116,266. Chlorination with an aqueous solution of NaClO prepared in advance or "in situ" in the reaction mixture at 50 ° C is described in GB Pat. No. 722,625. Chloroacid-suspended 2-methylphenoxyacetic acid at pH 1 in the heterogeneous phase of the presence of hydrochloric acid with sodium chloride at 20 ° C is described by DAS No. 1,027,687. A process based on sodium hydroxide or carbonate sodium hydroxide U.S. Pat. No. 4,766,596 to the aqueous solution of 2-methylphenoxyacetic acid sodium chloride and chlorine chlorination. No. 2,770,651. The chlorination sodium salt in the presence of sodium bicarbonate is described in GB Pat. No. 855,504. Production of 2-methyl-4-chlorophenoxyacetic acid by chlorination with an aqueous solution of 2-methylphenoxyacetic acid sodium hypochlorite in the presence of a mineral butyrocarboxylic acid, while the reaction mixture is poured into an excess of aqueous mineral acid and precipitated with 2-methyl- The 4-chlorophenoxyacetic acid is separated from the mother acids by filtration and subsequently dried at 105 ° C to describe CSA No.179,200.

The aforementioned drawbacks are alleviated by the process according to the invention, characterized in that the 2-methylphenoxyacetic acid and its sodium chloride is chlorinated, the chlorine to 2-methylphenoxyacetic acid ratio and / or sodium salt is 0.01-0.59: 1, and the resulting reaction mixture is made up of an aqueous sodium hypochlorite solution and 2-methyl-4-chlorophenoxyacetic acid is obtained by introducing the reaction mixture into an excess of mineral acid. From the reaction mixture, the non-chlorine formed by the reaction of excess sodium hypochlorite in the form of a flue gas. From the suspension, 2-methyl-4-chlorophenoxyacetic acid was removed by filtration. Dochorination of the reaction mixture with sodium hypochlorite takes place in a mineral and / or organic acid medium. For chlorination with chlorine, chlorine is used as the off-gas from the decomposition of alkaline chlorates. This decomposition takes place self-loosely, e.g. in containers, eventually excess sodium hypochlorite is decomposed by introducing the reaction mixture after chlorinating with NaClO excess mineral acid. It is an advantage of the present invention that a chlorine gas is used which has so far escaped and has not been used. Compared to MS. NO.179,200 reduces the consumption of NaClO as well as the mineral acid. Due to the fact that sachlor will not be discharged into the air, the formation of exhalates from the plant is prevented. At the same time, by reducing the mineral acid consumption, the amount of mineral salts in the wastewater. Part of the mineral acids are substituted by 2-methyl-4-chlorophenoxyacetic acid formed by chlorination with chlorine. O-against MS. No. 172,188,18 is the preferred method according to the invention, since at a molar ratio of chlorine to 2-methylphenoxyacetic acid and / or its sodium salt, adjusting the pH by adding the alkali hydroxide to the reaction mixture is not necessary before with NaClO. We will make the invention simple and simple. It consists in connecting the NaClO reservoirs and the degassing of 2-methyl-4-chlorophenoxyacetic acid with an excess of mineral acid to an absorption column in which 2-methylphenoxyacetic acid and / or its sodium salt will circulate. In addition to the decomposition of the NaClO decomposition, waste chlorine from other processes such as chlorine liquefaction, waste chlorine after chlorination of the organic substances after purification and impurities, especially from hydrogen chloride, can be used. Example 1

To 950 g of an aqueous solution containing 13.3 wt. 2-methylphenoxyacetate sodium was injected with gas containing 3.4% by volume of chlorine. After 1 hour, the blowing was stopped and the reaction mixture found to contain 3.1% by weight. 2-methyl-4-chlorophenoxyacetic acid and 0.8% wt. other 2-methylphenoxyacetic acid chloro derivatives. Then, 525 g of an aqueous solution of 12.5 wt% was added to the reaction mixture. NaClO and 112 g 35.6 wt. sulfuric acid. The mixture was stirred for 2 hours. It was then poured into 600 g of 8.1% wt H2SO4 and the precipitated 2-methyl-4-chlorophenoxyacetic acid was filtered off, washed with water and dried. 137.2 g of product were obtained with a content of 87.2% by weight. 2-methyl-4-chlorophenoxyacetic acid, 5.8 wt. 2-methyl-6-chlorophenoxyacetic acid, 2.2% by weight of 2-methylphenoxyacetic acid, 1.2% by weight of 2-methyl-4,6-dichlorophenoxyacetic acid. Example 2

The procedure of Example 1 was followed, except that 940 g of an aqueous solution containing 12.4% by weight of chlorine was used for chlorination. Of 2-methyl-4-chlorophenoxyacetic acid and 0.9 wt. 2-methyl-4-chlorophenoxyacetic acid. The chlorine pH was 6.1. 2-Methyl-4-

Claims (5)

SUBJECT Process for the preparation of 2-methyl-4-chlorophenoxyacetic acid by chlorination of 2-methylphenoxyacetic acid and / or its sodium salt with chlorine and chlorination with sodium hypochlorite, preferably in a medium of mineral acid or organic acid, followed by precipitation of 2-methyl-4-chlorophenoxyacetic acid % of the reaction mixture to an excess of mineral acid, characterized in that the molar ratio of chlorine to 2-methylphenoxyacetic acid and / or its sodium salt is 0.01 to 0.59: 1 and that chlorine is used as a off-gas from the decomposition of alkaline hypochlorites.