New synthesis routes to 2-halopyridines. II. 2-bromopyridine

The use of bromine chloride (equilibrium mixture) in substitution reactions has been extended to heterocyclic substrates. The vapor phase bromination of pyridine (I) with bromine chloride at temperatures as low as 375° (carbon tetrachloride diluent) gave the following product distribution: 2-bromopyridine (IV) (75%) > 2-chloropyridine (VI) (21%) > 3-bromopyridine (II) (2.0%) ? 2,6-dibromopyridine (VI) (1.5%). In contrast, when bromine was employed in place of bromine chloride (450°; carbon tetrachloride diluent), product orientation was significantly altered to give nearly equal quantities of 3-bromopyridine (II) (17%) and 2-bromopyridine (IV) (22.7%).