General procedure: A diazonium salt solution was prepared by dissolving 1 mole of 2-bromo-4,6-difluoroaniline hydrobromide in aqueous HCl with 1.1-1.10 moles of NaNO2 at 0°C to 5°C. The solution was then slowly warmed to 15°C, during which time the release of nitrogen was observed. To this solution, 1.5 moles of hypophosphorous acid was added at a temperature below 5°C, followed by a slow warming to 15°C, during which the release of nitrogen was observed. The reaction mixture is stirred for 1 hour, decanted and extracted with a suitable organic solvent to give 1-bromo-3,5-difluorobenzene in 75% molar yield. The target product with purity higher than 99% was obtained by distillation. This method is also applicable to the synthesis of other 1-bromo-3,5-dihalobenzenes.
