The phenomenon of rate enhancement of a reaction between @CT01038@ located in different phases (immiscible liquids or solid and liquid) by addition of a small quantity of an agent (called the 'phase-transfer @C00876@') that extracts one of the reactants, most commonly an @A00358@, across the @I03082@ into the other phase so that reaction can proceed. These catalysts are salts of '@O04291@' (e.g. tetraalkylammonium salts) or agents that complex inorganic cations (e.g. @C01421@ @E02221@). The @C00876@ @C00907@ is not consumed in the reaction although an @A00359@ does occur.