Abstract

Phase-transfer catalysis (PTC) is a method that allows reactions to occur in two-phase systems in an easy and efficient way. Typically salts, dissolved in water or as solids, react with organic substances in organic nonpolar solvents. Catalysts are mostly quaternary ammonium or phosphonium salts, or polyethylene glycols. Alternatively, much more expensive crown ethers or cryptands are applied, predominantly for laboratory purposes. Mechanistically, most of the common PTC applications involve the extraction of anions into nonpolar organic media wherein they have much higher reactivities than under normal conditions as a result of lesser solvent interactions.

Scope, mechanism, and examples of PTC are discussed, and the potential industrial importance of the method is stressed. Reactions that are mentioned in some detail include displacements, ester formation, ether formation, alkylation of carbanions, nucleophilic aromatic substitution, alkylation of N-heterocycles, polymerization of acrylates, oxidations, and carbene generation.