[OH:1][C:2]1[C:3]([Cl:13])=[C:4]([C:8]([Cl:12])=[CH:9][C:10]=1[Cl:11])[C:5]([NH2:7])=[O:6].[Na].C([O:17][C:18](=[O:21])[CH2:19]Br)C>CO>[C:5]([C:4]1[C:3]([Cl:13])=[C:2]([C:10]([Cl:11])=[CH:9][C:8]=1[Cl:12])[O:1][CH2:19][C:18]([OH:21])=[O:17])(=[O:6])[NH2:7]16 g (66.9 mmol) of 3-hydroxy-2,4,6-trichlorobenzamide is suspended in 100 ml of methanol and dissolved by adding 1.54 g (66.9 mmol) of sodium. After the addition of 16.8 g (66.9 mmol) of bromoacetic acid ethyl ester, the mixture is maintained under reflux until the reaction is complete (TLC control). The product is then concentrated to dryness under vacuum and the resultant 3-carbamoyl-2,4,6-trichlorophenoxyacetic acid methyl ester is suspended in 100 ml of water. The mixture is combined with 20 ml of concentrated sodium hydroxide solution and maintained for 3 hours at 60° C. for saponifying. The solution is filtered over active carbon, brought to pH 2 by adding concentrated hydrochloric acid, and the precipitate is vacuum-filtered after several hours of stirring in an ice bath. After washing with water and drying, 16.8 g (84% of theory) of 3-carbamoyl-2,4,6-trichlorophenoxyacetic acid is obtained as a white powder, mp 261°-262° C.
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