反应详情

The product from (a) (145 g) was dissolved in concentrated hydrochloric acid (750 ml) and water (450 ml) and the solution cooled to -10° C. Sodium nitrite (54 g) in cold water (450 ml) was added dropwise with stirring over a period of 90 minutes while the mixture was kept at -5° C. The solution was stirred for a further 2 hours, and then basified with concentrated ammonia, keeping the temperature below 20° C. The solid which separated was washed with water, dried, dissolved in ether (1500 ml) and washed with cold sodium hydroxide solution (1 M; 1 liter). The ether solution was washed twice with water (1 liter portions), dried, and evaporated to give the required 3-bromo-2-chloro-5-methylpyridine.

1. customwas kept at -5° C
2. stirringThe solution was stirred for a further 2 hours
3. customthe temperature below 20° C
4. customThe solid which separated
5. washwas washed with water
6. customdried
7. dissolutiondissolved in ether (1500 ml)
8. washwashed with cold sodium hydroxide solution (1 M; 1 liter)
9. washThe ether solution was washed twice with water (1 liter portions)
10. customdried
11. customevaporated