反应详情

36.0 g (172.7 mmol) of 5-bromo-3-chloro-2-hydroxypyridine are stirred at 160° C. for 6 hours in 320 ml of phosphorus tribromide. The reaction mixture is cooled to room temperature and poured carefully into ice water. After 2 hours, the mixture is extracted three times with 500 ml of dichloromethane in each case. The combined organic phases are washed with sodium bicarbonate solution until neutral, dried over Na2SO4 and filtered, and the filtrate is evaporated to dryness. Chromatographic purification (silica gel/dichloromethane) gives 20.53 g of 3-chloro-2,5-dibromopyridine. ##STR14## m.p.: 40°-41° C.

1. extractionthe mixture is extracted three times with 500 ml of dichloromethane in each case
2. washThe combined organic phases are washed with sodium bicarbonate solution until neutral,
3. dry with materialdried over Na2SO4
4. filtrationfiltered
5. customthe filtrate is evaporated to dryness
6. customChromatographic purification (silica gel/dichloromethane)