The directive influence of the n‐oxide group during the nitration of derivatives of pyridine‐n‐oxide (II)

Abstract 3,5‐Dibromopyridine‐N‐oxide, when heated with a mixture of fuming nitric acid and sulphuric acid, just like 3‐bromo‐ and 3‐ethoxypyridine‐N‐oxide, yields the 4‐nitro‐derivative. In 3,5‐diethoxypyridine‐N‐oxide, however, the nitro‐group enters the 2‐position. 3,5‐Dibromo‐4‐nitropyridine‐N‐oxide and 3,5‐diethoxy‐2‐nitropyridine‐N‐oxide are found to be phototropic substances.