ENOLIZATION OF BENZOYLACETONE IN AQUEOUS SURFACTANT SOLUTIONS - A NOVEL METHOD FOR DETERMINING ENOLIZATION CONSTANTS

The keto-enol tautomerism of benzoylacetone (1-phenyl-1,3-butadione) i n aqueous acidic solution at 25 degrees C was investigated by studying the influence of anionic, cationic, and nonionic surfactants in the U V-vis spectra of benzoylacetone. The percentage of the enol tautomer w as found to increase abruptly at surfactant concentration above the cr itical micelle concentration (cmc). A model is proposed to quantitativ ely interpret the experimental results, which allows for the determina tion of the enolization constant in water, K-E, and in micellar, K-E(m ), pseudophases; the binding constant of the enol tautomer to micelles , K-s; and the extinction coefficients of the ketonic and enolic forms , epsilon, of benzoylacetone. The formation of the enolate in the abse nce and presence of micelles in basic media was also studied. The acid ity constants of the enolic, K-a(E), and ketonic, K-a(K), forms of ben zoylacetone have been determined.