A ring-opening reaction performed in microemulsions

Different types of microemulsion formulations have been explored as reaction medium for the rin opening nf a lipophilic epoxide. 1,2-epoxyoctane, with sodium hydrogen sulfite. In two-phase systems without surfactant or phase-transfer reagent the reaction is very sluggish. Microemulsions based on alcohol ethoxylate proved to be efficient reaction media, giving almost complete conversion of epoxide to hydroxysulfonate in 2 h at 75 degrees C. A microemulsion based on the anionic surfactant sodium dodecylsulfate gave a slower rate of epoxide consumption. In addition, the dodecylsulfate anion took an active part in the reaction. competing with the hydrogen sulfite ion as ring-opening reagent. Reactions were also carried out in Winsor III systems based on alcohol ethoxylate. Compared with the one-phase system, reaction in the Winsor III system was slow, probably due to unfavourable partitioning of the reagents between the middle-phase microemulsion, where the reaction occurs, and the excess oil and water phases. An attempt was made to increase the reaction rate in the Winsor III system by addition of a phase-transfer agent, tetrabutylammonium hydrogen sulfate. The phase transfer agent gave only a marginal accelerating effect, however. (C) 1998 Elsevier Science B.V. All rights reserved.