Organic Reactions in Microemulsions

Abstract

The use of microemulsions as media for organic reactions is a way to overcome the reagent incompatibility problems that are frequently encountered in organic synthesis. In this sense, microemulsions can be regarded as an alternative to phase transfer catalysis. The microemulsion approach and the phase transfer approaches can also be combined, i.e. the reaction can be carried out in a microemulsion in the presence of a small amount of phase transfer agent. A very high reaction rate may then be obtained. The reaction rate in a microemulsion is often influenced by the charge at the interface and this charge depends on the type of surfactant used. For instance, reactions involving anionic reactants may be accelerated by cationic surfactants. The surfactant counterion also plays a major role for the reaction rate. The highest reactivity is obtained with small counterions, such as acetate, that are only weakly polarizable. Large polarizable anions, such as iodide, bind strongly to the interface and may prevent other anionic species to reach the reaction zone.