The research of the azo–hydrazone equilibrium by means of AM1 method based on the example of an azo dye – the Schäffer salt derivative

An AM1 and ZINDO/S method, azo–hydrazone equilibrium of an azo dye (Schäffer acid derivative) and a model dye (2-naphthol derivative) were examined by means of quantum-chemical methods of calculations. Calculations performed for an isolated molecule (in vacuum) evidenced a higher stability of an azo form [A]. Hydration of dye molecule shows that a hydrazone form [H] is more stable in water solution. These researches confirm practical conclusions about the superiority or the exclusive occurrence of dyes in hydrazone form in real structures of o-hydroxyazo dyes.