3-Methoxybenzaldehyde → 2-Bromo-5-methoxybenzaldehyde

A stirred solution of 3-methoxybenzaldehyde (27.23 g) in dichloromethane (150 mL) at 0° C. is treated with a solution of bromine (32 g) in dry dichloromethane (50 mL) over 30 minutes. The reaction mixture is stirred at room temperature for 4 hours, combined with a previous preparation carried out on the same scale, and washed with saturated sodium metabisulphite solution (400 mL), with water (400 mL), brine (400 mL) and dried over magnesium sulphate. Evaporation and recrystallisation of the residue from petroleum ether (b.p. 40-60° C.) gives 2-bromo-5-methoxybenzaldehyde (45.25 g) as a white solid, m.p. 73-74° C.