Migration of halogen atoms in halogenoderivatives of 2,4‐dihydroxypyridine (I)

Abstract

When 3‐bromo‐2,4‐dihydroxypyridine is chlorinated in aqueous hydrochloric acid solution by adding hydrogen peroxide solution, 5‐bromo‐3‐chloro‐2,4‐dihydroxypyridine is formed. Hence the chlorine atom enters the 3‐position, the bromine atom being removed from this position and reintroduced at the 5‐position.5‐Bromo‐3‐chloro‐2,4‐dihydroxypyridine was also prepared by brominating 3‐chloro‐2,4‐dihydroxypyridine and chlorinating 5‐bromo‐2,4‐dihydroxypyridine. Its structure was established in different ways, i. e. by converting it into 3‐chloro‐2,4‐dihydroxypyridine on partial reduction, by converting it into 4‐amino‐2,3‐dichloro‐5‐bromopyridine and into 4‐amino‐2,5‐dibromo‐3‐chloropyridine. The structure of the two compounds last mentioned was proved by synthesis.