The general procedure for the synthesis of 2-amino-4,5-dichlorobenzoic acid from 5,6-dichloroisoindoline-1,3-dione was as follows: 25% aqueous sodium hydroxide solution (75 mL) was cooled to 0°C, bromine (16.0 g, 0.1 mol) was added slowly and the mixture was stirred until a yellow NaOBr solution was formed. 4,5-Dichlorophthalimide (21.6 g, 0.1 mol) was dissolved in 5% aqueous sodium hydroxide solution (170 mL), cooled to 0°C, and then the solution was slowly added to the above cold NaOBr solution. The reaction mixture was reacted under vigorous stirring for 5 minutes and subsequently heated to 80°C and held for 2 minutes. After completion of the reaction, the mixture was cooled and neutralized with concentrated hydrochloric acid to pH neutral. The precipitate was collected by filtration and washed with ice water. The crude product was purified by solvent recrystallization from a mixture of methanol and water to give 14.8 g (72% yield) of 2-amino-4,5-dichlorobenzoic acid with a melting point of 196-203° C. The crude product was purified by solvent recrystallization from a mixture of methanol and water.
