Protolytic equilibria of fluorescein halo derivatives in aqueous-organic systems

The dissociation constants of fluorescein halo derivatives containing substituents in the xanthene ring and/or in the phthalic acid moiety were determined in 91.4 wt % aqueous ethanol. The tautomerism of the dyes was inferred from the electronic absorption spectra of ions and molecules in this solvent and of the dichloromethane and chloroform extracts of associates of the anions with tetra- n -butylammonium cations. The equilibria in two-phase systems were considered.