Hydrogen Bromide → 4-Bromo-3-iodotoluene

2-Iodo-4-methylaniline (100 g, 450 mmol) was suspended in the mixture of water (200 mL) and HBr (48%, 300 mL). The mixture was refluxed for 15 min. Then the mixture was cooled to 0° C., and NaNO2 (31.05 g, 0.45 mol) in water (150 ml) was added dropwise at such a rate that the temperature did not exceed 5° C. The diazonium solution wad stirred for a further 30 min at 0-5° C. and then added slowly to a stirred mixture of CuBr (64.5 g, 0.45 mol) in HBr (48%, 250 mL) and water (250 ml) at room temperature. The mixture was poured into ice and extracted with CH2Cl2 (500 ml×3). The methylene chloride layer was washed with brine, dried over Na2SO4, and evaporated in vacuum to give the crude product (109 g, yield 81.8%). It can be further purified by column chromatography eluting with petroleum ether. MS: 297 [M+1]+.