Micellar Catalysis in the Nitrosation of Benzoylacetone in an Acid Medium

Abstract

The nitrosation reaction of benzoylacetone (1-phenyl-1,3-butadione) by nitrous acid in an aqueous acid medium is studied in the presence of anionic and cationic micelles. The reaction involves enolization of the ketone, followed by electrophilic nitrosation of the enol. The presence of micelles strongly modifies the keto−enol equilibrium of β-dicarbonyl compounds, like benzoylacetone, in such a way that the enol percentage increases with the surfactant concentration. The increasing enol amount with surfactant concentration is quantitatively evaluated by studying the effect of surfactant addition on the UV−vis spectra of benzoylacetone; the results are used to explain the kinetic data. The addition of hydrogen dodecyl sulfate (HDS) to the reaction mixture increases the nitrosation reaction rate continuously until levels off at high HDS concentrations. In the presence of sodium dodecyl sulfate (SDS), the observed rate constant increases at low surfactant concentrations, passes through a maximum, and decreas...