Azoxypyridines

The catalytic effect of tetra-n-butylammonium fluoride in the homogeneous reduction of heterocyclic A-oxides and nitroarenes by hexamethyldisilane in tetra-hydrofuran can occur with EXPLOSIVE violence, but can be controlled by the slow addition of the disilane to the A-oxide (or nitroarene) and tetra-n-butylammonium fluoride to yield the parent heterocycle (>70%) (or azobenzene 84%). In a similar manner, azoxybenzene is converted into azobenzene (95%), and 4-nitropyridine-l-oxide, is reduced to azoxypyridine-l,l -dioxide (78%), with minor amounts of azopyridine-1, l -dioxide and azopyridine-1-oxide [5,6]. 

In 2-propanol solutions, acidified with hydrogen chloride, 7 is photoreduced quantitatively to 4-hydroxylaminopyridine 3) as determined by following the spectral changes during irradiation and workup under alkaline or neutral conditions to yield 4,4 -azo- or 4,4 -azoxypyridine 77). 

Oxidation of aminopyridines with Caro s acid gives nitropyridines the use of peroxy-trifluoroacetic acid leads to nitropyridine JV-oxides (60JOC1716). Oxidation with alkaline hypochlorite converts aminopyridines into symmetrical azopyridines, and azoxypyridines are formed by oxidation with persulfate (59YZ549). 

TABLE VIII-10. Preparation and Properties of Azoxypyridines and Derivatives... 

Nitraminopyridines that normally do not rearrange when heated with sulfuric acid give azopyridines (XII-391 R = 6-Cl, 2-CI, 5-Cl, 4-Cl, 5-COOH) or azoxypyridines (XI-392, R = 6-COOH) in addition to 3-pyridinols(XII-393 R = 5-Cl, S-OCjHs, 4-CH3, S-CH3, 2-S02 0H). 5-Nitramino-2-pyridinesulfonic acid gives 3-pyridinol. °... 

The reduction of azo- to hydrazo-pyridines has been carried out with zinc and alkali4546 sodium sulphide442e-3 and stannous chloride i, 443 Azoxy compounds have been reduced to azo compounds by zinc and alkali454, 46ia and by arsenite o and to hydrazo compounds by stannous chloride d, 457 With azoxypyridine 1-oxides the possibilities are more complicated, as illustrated36 ... 

Zinc and acetic acid convert 4,4 -azoxypyridine l,l -dioxide into 4,4 -azopyridine Ijl -dioxide , and hydrazine in presence of copper reduces it to 4-aminopyridine 1-oxide . ... 

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