Phase Transfer Catalysts

　A phase-transfer catalyst enables the reaction in a heterogeneous system between general organic compounds soluble in organic solvents and compounds soluble in water such as inorganic salts. The reaction can be accomplished in a biphasic system of an inexpensive nonpolar aprotic solvent and water without using DMSO or DMF which are high-polar solvents. A phase-transfer catalyst is soluble in both solvents, and it carries anions of inorganic salts into organic solvents and returns them into the water phase. Reactions usually progress under mild conditions with easy work-up procedures. For this reason, they are also used industrially. Typical phase-transfer catalysts are quaternary ammonium salts, crown ethers, and phosphonium compounds etc. Reaction examples are shown as follows.^1-4)