Hydrogen Peroxide → 3-Bromo-5-chlorobenzene-1,2-diol

To a stirred suspension of 3-bromo-5-chloro-2-hydroxybenzaldehyde (49.5 g, 0.21 mol) in 0.5N aqueous NaOH (500 ml, 250 mmol) at 40° C. was added dropwise hydrogen peroxide (21.4 g of a 35% aqueous solution, 220 mmol) over 15 minutes and the resultant mixture stirred for 16 hours. The mixture was cooled to room temperature, diluted with 1N aqueous NaOH (200 ml) and washed with diethyl ether (3×300 ml). The aqueous layer was acidified with concentrated HCl to pH 2 and extracted with diethyl ether (3×200 ml). The organic extracts were combined, washed with brine, dried over Na2SO4, filtered and concentrated in vacuo to afford the title compound as a red/brown solid (46.0 g, 99% yield).