Catalysis in Two-Phase Systems: Phase Transfer and Related Phenomena

This chapter focuses on catalysis in two-phase systems, and discusses the nature of this type of catalysis. A catalyst is a substance (chemical entity) which accelerates a chemical reaction (without being consumed) via a decrease of its activation energy. There are many types of catalysis for which this definition can be applied; some difficulties are encountered, however, in the case of the phase-transfer catalysis (PTC) and catalytic two-phase (CTP) systems. The main function of the catalyst is introduction of the reacting species into the site where the reaction partner is located and where the reaction proceeds. So using formal terms of activation energy one can perhaps consider that the main function of the PTC and CTP catalysts is to decrease the activation energy of the transfer of the reacting species to the reaction site. The PTC and CTP reactions usually do not require any organic solvents (when one of the reactants is a liquid), or require them only in small amounts, just sufficient to dissolve organic reactants. The PTC and CTP methodologies mimic to some extent the high-dilution technique, because in the organic phase the concentration of the reacting species can be only a fraction of that of the catalyst. The two-phase procedures are not only simpler and more convenient than traditional methods, but they usually give better yields of desired products of higher purity, whereas side reactions are