Step 3: 3-amino-4-methyl-5-nitrobenzoic acid (50 g, 254 mmol) was suspended in a mixture of concentrated hydrochloric acid (350 ml) and water (350 ml) at 0-5 °C. Subsequently, an aqueous solution of sodium nitrite (18.6 g, 270 mmol) (30 ml) was slowly added over 15 to 20 minutes. The reaction mixture was continued to be stirred at 0-5°C for 30 minutes. After that, the reaction mixture was slowly poured into a pre-cooled solution of concentrated hydrochloric acid (220 ml) of cuprous bromide (73.21 g, 516 mmol) and kept stirring at 0-5°C for 30 min followed by stirring at room temperature for 30 min. Finally, the reaction mixture was heated to 30-35 °C and stirred for 30 min, the precipitated solid was collected by filtration, washed with water (50 ml) and dried under vacuum to give 58 g of 3-bromo-4-methyl-5-nitrobenzoic acid as a pink solid in 88% yield.1H-NMR (CD3OD-d4) δppm: 2.6 (3H, s, CH3), 8.21 (1H, d , J = 1.4Hz, Ar-H), 8.27 (1H, d, J = 1.2Hz, Ar-H).
