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 decreases at still
higher SDS concentrations. The observed kinetic effects in the presence of the cationic surfactants
tetradecyltrimethylammonium salts of Cl-, Br-, NO3
-, and SCN- anions, in general TTAX (with X being
Cl-, Br-, NO3
-, or SCN-), depend on the nature of the micellar counterion; for example, the addition of
TTANO3 decreases the reaction rate for the entire concentration range investigated, while the presence
of TTASCN calatyzes the reaction. The varying micellar effects are quantitatively interpreted on the basis
of reaction mechanisms, with consideration given to the possible nitrosating agent in every case.