Pyridines Hydroxypyridines, Nitropyridines

Nitropyridines exhibit substituent reductions including through-nitrogen (azo/azoxy) coupling. Amino-pyridines have been found to be unreducible when using voltammetry. Hydroxypyridines and pyri-dones generally yield mixtures of piperidines and 1,2,5,6-tetrahydropyridines. Halogenated derivatives... 

Certain other reactions differ from those discussed in being brought about by acid rather than alkali. Thus, although 2-aminopyridine is unaffected by acid 8 , 2,6-diaminopyridine is converted by hot 10 per cent hydrochloric acid into 2-amino-6-hydroxypyridine 0. The second step, to 2,6-dihydroxypyridine, is more difficult889, 89i, 2,6-Diamino-3-nitroso-pyridine can be converted into the dihydroxy compound with acid or alkali, but with 2,6-diamino-3-nitropyridine alkali is essential s a, The not very convincing explanation usually given for the difference in behaviour between... 

The formation of hydroxypyridines from nitropyridines is not a well-explored aspect of pyridine chemistry, though 2-hydroxypyridines have been obtained from 2-nitropyridines both by the action of acid and of alkali237, 7i3b. Whilst 4-nitropyridine exposed to the atmosphere is slowly converted by autoquaternization and hydrolysis into 4-hydroxypyridine and... 

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