Synthesis, structural elucidation, solvatochromism and spectroscopic properties of some azo dyes derived from 6-chloro-4-hydroxyquinoline-2(1H)-one

• 6-Chloro-4-hydroxyquinoline-2(1H)-one was used as a coupling component.
• Solvatochromism of the azo dyes was studied.
• Acidic dissociation constants were measured and correlated with Hammet substitution constants.

Malondianilide (I) derived from p-chloroaniline was cyclized to 6-chloro-4-hydroxyquinoline-2(1H)-one (II) in moderately good yield using polyphosphoric acid as catalyst. This compound was then coupled with some diazotized aromatic amines to give the corresponding azo disperse dyes 1–12. A systematic study of the effect of solvent, acid, base and pH upon the electronic absorption spectra of the dyes 1–12 was carried out. In DMSO, DMF, CH3CN, CHCl3, EtOH and acidic media (CH3COOH, acidified EtOH) these dyes that theoretically may be involved in azo-hydrazone tautomerism have been detected only as hydrazone tautomers T1 and T2. The acidic dissociation constants of the dyes were measured in 80 vol% ethanol-water solution at room temperature and ionic strength of 0.1. The results were correlated by the Hammett-type equation using the substituent constants σx.

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