Spectrophotometric investigations of the role of the organic solvent on the acid dissociation constants of some azo dyes derived from 2-aminobenzothiazole

Proton dissociation constants (pKa) of a set of hydroxyl azo dyes in various organic solvent + water mixtures have been determined. The results obtained were discussed in terms of the solvent characteristic. Effects of hydrogen-bonding interactions and solvent basicity on the ionization process have been also discussed. In a nutshell, the pKa values of the investigated compounds were found to be largely depending on both the ratio and the nature of organic cosolvent. In addition, it was very important to know with which structures we are dealing in liquid solutions and how these structures influence physicochemical properties of individual tautomers and their acidity constants. Thus, theoretical calculations have been done in order to obtain an insight into structure features and physicochemical properties of the compounds under study.