IONIZATION AND TAUTOMERISM OF FLUORESCEIN, RHODAMINE-B, N,N-DIETHYLRHODOL AND RELATED DYES IN MIXED AND NONAQUEOUS SOLVENTS

The protolytic equilibria of fluorescein, Rhodamine B and of asymmetri cal amino-oxyanthene dye, N,N-diethylrhodol (a 'hybrid' of Rhodamine B and Fluorescein) were studied in aqueous DMSO and EtOH (91 wt% of org anic cosolvent). The pK(a) values of these dyes, as well as of related substances were determined On the basis of the visible absorption spe ctra in various solvents conclusions are made about the tautomerism in the dye molecule. The values of the tautomeric equilibrium constants and of the microscopic ionization constants were obtained Some new dat a on the tautomerism of oxyxanthene monoanions in methanol are present ed.