General Steps:
Part A-Preparation of copper (I) bromide solution: dissolve copper (I) bromide (72.5 g, 505 mmol) in 37% hydrochloric acid (150 mL) and heat to 80°C until a clarified solution is formed.
Part B-Diazotization and Sandmeyer bromination: to a concentrated hydrochloric acid solution (150 mL) of 2,5-dimethyl-4-nitroaniline (21 g, 126 mmol), a mixture of saturated sodium nitrite solution (1.7 g, 253 mmol) and water (20 mL) was added slowly and dropwise at 0°C with continuous stirring for 30 min. Subsequently, copper (I) bromide solution prepared in part A was added slowly and dropwise at the same temperature. After addition, the reaction mixture was warmed up to 80 °C and maintained for 1 hour. After completion of the reaction, the reaction mixture was diluted with water and extracted with ethyl acetate. The organic layers were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure. Finally, the target product 1-bromo-2,5-dimethyl-4-nitrobenzene (22 g, 76% yield) was purified by column chromatography (eluent: hexane/ethyl acetate, 8:2).
