title: Dramatic enhancement of enone epoxidation rates in nonionic microemulsions.
abstract: The ability of microemulsions to dissolve polar and non-polar components with a huge internal interface can overcome the reagent incompatibilities frequently encountered in organic reactions. We investigated model epoxidation reactions of alpha,beta-unsaturated enones and alkaline hydrogen peroxide in different nonionic microemulsions, both in the presence and absence of a phase-transfer agent (PTA). The obtained reaction profiles were compared with those for the corresponding surfactant-free two-phase systems. In addition, we defined a time constant tau as a measure for the rate of turnover. The epoxidation of trans-chalcone using an n-alkyl-polyoxyethylene surfactant based microemulsion was fastest in the system with the PTA (tau=66 min) and slightly slower without the PTA (tau=77 min). It was still slower in the two-phase system with a PTA (tau=114 min) and extremely sluggish without a phase-transfer agent. With n-alkyl beta-D-glucopyranoside as the surfactant the conversion was twice as fast than in the former microemulsion systems, but the PTA did not accelerate the reaction further (tau=35 and 33 min). The epoxidation of vitamin K(3), the second model system, was extremely accelerated. It proceeded a factor of approximately 35 faster in the microemulsion (tau=1.44 min) than in the corresponding two-phase system (tau=57 min).
authors.affiliation: Department of Physical Chemistry, University of Cologne Luxemburger Strasse 116, 50939 Köln, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wielpütz
authors.forename: Thomas
authors.initials: T
authors.lastname: Sottmann
authors.forename: Reinhard
authors.initials: R
authors.lastname: Strey
authors.forename: Friederike
authors.initials: F
authors.lastname: Schmidt
authors.forename: Albrecht
authors.initials: A
authors.lastname: Berkessel