A facile synthesis and tautomeric structure of novel 4-arylhydrazono-3-(2-hydroxyphenyl)-2-pyrazolin-5-ones and their application as disperse dyes

The main target of this paper was the synthesis of novel azo disperse dyes with better dyeing properties, together with a systematic investigation to determine their dominant tautomer(s) from 12 possible tautomeric structures. In this regard, novel azopyrazolin-5-one dyes were synthesised via the reaction of hydrazine hydrate with 2,3,4-chromantrione-3-arylhydrazones. The acid dissociation constants both in the ground and in the excited state for the series prepared were determined and correlated by the Hammett equation. The results of this correlation, together with spectral data, indicated that the compounds under scrutiny exist predominantly in the keto-hydrazo structure as a Z-configuration, both in the ground and in the excited state. Finally, the synthesised dyes were applied as disperse dyes for dyeing polyester fabrics, and their fastness properties were evaluated. Also, the position of colour in CIELAB coordinates was estimated and discussed.