Synthesis, characterization and solvatochromic behaviour of new water-soluble 8-hydroxy-3,6-disulphonaphthyl azohydroxynaphthalenes

Abstract

A series of five tetracyclic mono azo dyes based on the diazotization of 1-amino-8-hydroxynaphthalene-3,6-disulphonic acid and subsequent coupling with substituted (un)sulphonated naphthalene derivatives have been synthesized. The chemical structures of the dyes were established using UV–visible, IR, NMR as well as mass spectrometry. Based on the number of sulphonic acid and other hydrophilic groups they contain, the compounds showed varying extent of water solubility. Spectroscopic characterization revealed the existence of azo-hydrazone tautomerism and the influence of the structures of solvating solvents on the equilibrium. Statistical analysis of single, dual and multiparametric equations of Kamlet Abboud and Taft parameters showed that solvent polarity was the most significant contributor to the observed spectral patterns of the dyes in pure solvents. The compounds could find useful applications as solvatochromic probes, food and drug colour additives.

KEYWORDS:

• 1-amino-8-hydroxynaphthalene-3,6-disulphonic acid
• azo compounds
• synthesis
• spectroscopic characterization
• azo-hydrazone tautomerism
• solvatochromic properties

Acknowledgement

The authors gratefully acknowledge Dr Tapas Sarkar of the Indian Institute of Chemical Biology and Professor Ghatum Basu of Bose Institute, Kolkata, for their assistance with the NMR and mass spectral analyses.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Consortium for Advanced Research Training in Africa (CARTA) and the University of Ibadan TETFund Academic Staff Training and Development grant. CARTA is funded by the Carnegie Corporation of New York (Grant No--B 8606.R02), Sida (Grant No:54100113), the DELTAS Africa Initiative (Grant No: 107768/Z/15/Z) and Deutscher Akademischer Austauschdienst (DAAD).