Phenylhydrazono-phenylazo tautomerism. : Part III. Reactions of phenylformazans and certain bis(phenylhydrazones) with strong acids☆☆☆

Add time:08/21/2019    Source:sciencedirect.com

The behavior of diphenylformazans, 2-oxo-1,3-bis(phenylhydrazones), 1,2-bis-(phenylazo)ethylene, and the phenylhydrazone of 4-oxo-1-phenyl-5-phenylazo-3-pyridazinecarboxaldehyde on protonation has been examined spectrophotometrically. These compounds form purple, blue, or green protonated cations. The nature of the spectral changes suggests that the highly colored cations have resonance-stabilized structures. Phenylosazones and bis(phenylhydrazono) compounds that cannot form resonance-stabilized cations on protonation do not usually give the blue-color reaction. Structures are proposed for the cations derived from diphenylformazans and certain 2-oxo-1,3-bis(phenylhydrazones).Treatment of the red, enolic tautomer of 2-oxo-1,3-bis(phenylhydrazono)-cyclohexane with perchloric acid in acetic acid yields a new, stable, dark-blue, crystalline salt. Dissolution of this salt-in acetic acid, followed by addition of ice-water, yields a previously described yellow hydrate of the keto tautomer. Dissolution of the hdyrate in ethanol and warming regenerates the red, enolic tautomer.E.s.r. measurements of colored solutions of 2-oxo-1,3-bis(phenylhydrazones) or diphenylformazans did not show the presence of radical species, thus indicating the ionic character of the products formed on protonation.

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