CS262625B1 - Method of 2-methyl-4-chlorophenyl acetic acid's dimethyl amine salts preparation - Google Patents

Abstract

The neutralization of 2-methyl-4-chlorophenoxytoic acid with an aqueous solution of dimethylamine is solved. Mineral acid-contaminated 2-methyl-4-chlorophenoxyacetic acid is neutralized with an aqueous solution of dimethyl amine containing sodium hydroxide to form 2-methyl-4-chlorophenoxy-ootonic acid dimethylamine salt. The solution will find application in the production of dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid which

Description

262625 2

The invention relates to the production of dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid.

2-Methyl-4-chlorophenoxyacetic acid and its salts are used as very effective herbicides. It is most commonly prepared by chlorine of 2-methylphenoxyacetic acid with chlorine gas at a temperature of 95-105 ° C as described in U.S. Pat. No. 91,160. The continuous mode of chloroacid, potassium or sodium potassium 2-methylphenoxyacetic acid in aqueous solution is described in MS. No. 99,892, the continuous chlorination process of free 2-methylphenoxyacetic acid with chlorine gas is described by MS. patent 107 807. The possibility of combining the chlorination of 2-methyl-phenoxyacetic acid with gaseous chlorine followed by chlorochlorine chlorination is reported by MS. Chlorination of 2-methylphenoxyacetic acid with chlorine gas at pH 4-6 is described in French Patent 1,116,266. Chlorination with an aqueous solution of sodium hypochlorite prepared in advance or "in situ" in the reaction mixture at 50 ° C is described in U.S. Patent 722,625. Chlorination of suspended 2-methylphenoxyacetic acid at a pH equal to 1 in the heterogeneous phase in the presence of hydrochloric acid with sodium hypochlorite at 20 ° C is described in DAS 1,027,680. Of 2-methyl-4-chlorophenoxyacetic acid with sodium hypochlorite in the presence of a mineral butocarboxylic acid, producing 2-methyl-4-chlorophenoxyacetic acid by chlorination of 2-methylphenoxyacetic acid sodium salt and obtaining 2-methyl-4-chlorophenoxyacetic acid by precipitation with excess aqueous mineral acid solution described čs . AO 179 200. The disadvantage of preparing MS. AO 179 200 is that 2-methyl-4-chlorophenoxyacetic acid is recovered from the solution by chlorination by precipitation from excess mineral acid, followed by filtration of 2-methyl-4-chlorophenoxyacetic acid from the mother liquor of the mineral acids.

The filter cake contains 30 to 80 wt. % of phenoxyacetic acids, with a residue of up to 100% by weight. it consists predominantly of a mother liquor of mineral acids with a concentration of 0.2 to 2% by weight. mineral acid. The concentration of mineral acids in the mother liquor is maintained in the above range because the suspension of 2-methyl-4-chlorophenoxyacetic acid is well filterable in this range. Washing the filter cake is not due to the fact that 2-methyl-4-chlorophenoxyacetic acid is soluble in water at 2 to 10 g / l (by temperature), which can cause product loss. In the neutralization of the filter cake, the neutralizing agent, in addition to neutralizing 2-methyl-4-chlorophenoxyacetic acid, neutralizes preferably the mineral acid, thereby causing its loss. This is particularly disadvantageous in the use of expensive neutralizing agents such as dimethylamine.

The aforementioned drawbacks are alleviated by the preparation of the dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid by neutralizing the 2-methyl-4-chlorophenoxyacetic acid contaminated with the mineral acid with an aqueous solution of dimethylamine containing 0 %, 01 to 5 wt. sodium hydroxide. An advantage of the process of the invention is that a much cheaper neutralizing agent, sodium hydroxide, is used to neutralize the mineral acids from the filter cake and 2-methyl-4-chlorophenoxyacetic acid, with a substantial zinc product. Dimethylamine is used to neutralize 2-methyl-4-chlorophenoxyacetic acid. There is practically no change in the herbicidal properties of the dimethyl amine salt of 2-methyl-4-chlorophenoxyacetic acid. The embodiment of the invention is simple and undemanding, wherein the amount of sodium hydroxide in the aqueous dimethylamine is determined based on the mineral acid content of the 2-methyl-4-chlorophenoxyacetic acid filter cake. Example 1

2-methyl-4-chlorophenoxyacetic acid filter cake prepared by MS. AO 179 200 contained 43.1 wt. 2-methyl-4-chlorophenoxyacetic acids, of which 92.6 wt. 2-methyl-4-chlorophenoxyacetic acid, further containing 1.2 wt. hydrochloric acid.

The filter cake was neutralized with 38.2 wt. dimethylamine aqueous solution containing 5.6 wt. sodium hydroxide. The resulting pH of the solution was 7.2.

Claims (1)

EXAMPLE 2 The procedure of Example 1 was followed except that the filter cake contained 46.2 wt. of phenoxytoic acids, of which 0.01 wt. 2-methyl-4-chlorophenoxyacetic acids and contained 0.8 wt. hydrochloric acid. 35.7 wt% was used for neutralization. dimethylamine aqueous solution containing 3.8 wt. sodium hydroxide. The resulting pH value of the solution after neutralization was 7.5. The invention is applicable to the production of the dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid, which is used as a herbicide in agriculture. OBJECT OF THE INVENTION A process for the preparation of dimethylamine salt of 2-methyl-4-chlorophenoxyacetic acid by neutralization of 2-methyl-4-chlorophenoxyacetic acid contaminated with mineral acid with dimethylamine, characterized in that the neutralization of 2-methyl-4-chlorophenoxyacetic acid is performed with a dimethylamine aqueous solution containing 0.1 to 5 wt. sodium hydroxide.