EXCITED-STATE DEPROTONATION OF 2-NAPHTHOL BY ANIONS

The excited-state deprotonation of 2-naphthol by hydrogen phosphate, acetate, formate, hydrogen carbonate, fluoride, and benzoate ions in aqueous solutions has been investigated over a temperature range of 20-50-degrees-C. In neutral solutions containing increasing concentrations of these proton acceptor anions, the fluorescence of the free acid form of 2-naphthol is quenched and that of its conjugate base is enhanced. Rate constants for these excited-state deprotonation reactions have been determined by applying a modified Stern-Volmer kinetic model to the 2-naphthol free acid fluorescence intensity measurements. The rate constants are found to show some correlation with the base strengths of the anions. Enthalpies and entropies of activation for these reactions have been determined. These along with solvent effects on the reaction will be presented and discussed.