Studies of azo and azoxy dyestuffs. Part 17. Synthesis and structure determination of isomeric α and β phenylazoxypyridines, N-oxides, and methiodides. A reexamination of the oxidation of phenylazopyridines and X-ray structure analyses of 4-(phenyl-α-azoxy)pyridinium methiodide and 4-(phenyl-β-azoxy)pyridine-N-oxide

Abstract

In an extension of Wallach rearrangement studies into the phenylazoxypyridine series, an investigation of 4-, 3-, and 2-phenylazoxypyridines, the N-oxides, and methiodides is reported. Oxidation of 4-and 3-phenylazopyridine with peracetic acid gives rise to the a and p phenylazoxypyridine-N-oxides, contrary to previous literature reports on the obtention solely of the a isomers. 2-Phenylazopyridine, however, yields only the 2-(phenyl-a-azoxy)pyridine-N-oxide. These results are rationalized on the basis of field, resonance, and steric effects. An unprecedented reactivity difference has been observed in the reactions of the a , p isomers of phenylazoxypyridines under conditions of the Wallach rearrangement. This reactivity difference permits the isolation of the a-azoxy isomers from the a,p mixtures. Unequivocal confirmation of the structures has been obtained from X-ray crystal structure determinations of two representative compounds in this series, viz. 4-(phenyl-P-azoxy)-pyridine-N-oxide (11) and 4-(phenyl-a-azoxy)pyridinium methiodide (12), which itself was formed by deoxygenation of 4-(phenyl-a-azoxy)pyridine-N-oxide, followed by methylation with methyl iodide. The crystal structure of 11 was solved by direct methods and refined by block-diagonal least squares to R = 0.041 for 2479 observed reflections. The asymmetric unit contains two independent molecules, both of which are planar. The structure of 1 2 was determined by the heavy-atom method and refined by full-matrix least squares to R = 0.043 for 1718 observed reflections. The molecules are not planar, the pyridine ring being rotated by 36.5" from the phenylazoxy plane. Evidence is presented for the existence of intramolecular C-H -. . O and C-H N bonds in crystal structures of trans-azoxyarenes. The carbon atoms involved in these hydrogen bonds are ortho to the azoxy group and can act as proton donors as a result of the inductive effect of the adjacent nitrogen.

Supramolecular networks via pyridine N-oxide CH···O hydrogen bonding in the crystal structures of 2,2′-dithiobis(pyridine N-oxide) and its complexes with 1,2,4,5-tetracyanobenzene and pyromellitic dianhydride

“…Precedence for PO self association via hydrogen bonding can be found in the Cambridge Structure Database (CSD). 5 The open network character of the homochiral fragments of 1 suggested that guest inclusion in a DTPO lattice might be possible. To test this possibility, DTPO was crystallized in the presence of electron-deficient additives TCNB and PMDA.…”

Structure of a Fluorinated Azoxy Compound: Fluoro(trifluoromethyl)-diazene-2-oxide, CF3N(O)NF

“…No structural parameters are known for other halogen or CF 3 substituted azoxy compounds. X-ray diffraction studies of some azoxyarenes, however, have been reported in the literature . The mean NN bond length in these compounds (1.268 ± 0.013 Å) is within uncertainties equal to that in CF 3 N(O)NF (1.287(15) Å), and the mean NO bond length (1.265 ± 0.010 Å) is slightly longer than that in CF 3 N(O)NF (1.231(6) Å).…”

Photoisomerization and Thermal Isomerization of Shuttlecock- and Bowl-Equipped (Phenylazo)pyridines

“…These lengths are similar to those in azobenzene (1.247(2) Å), 4,4′-azobispyridine (1.2513(15) Å), and some 4-(phenylazo)pyridine derivatives (1.260−1.261 Å) . The lengths of the NN and N→O bonds of BmtNN(O)Py are 1.28 (average) and 1.26 (average) Å, respectively, which are similar to those of 4-(phenylazoxy)pyridine N -oxide (1.274(2) (average) and 1.265(2) (average) Å, respectively), indicating that the lengths of the NN and N→O bonds in these compounds are not influenced by the presence of these bulky substituents.…”