Phase-transfer catalyst

Phase transfer catalysis (PTC) is a chemical process in which the reactants are present in at least two immiscible phases. In this case, one of the reactants is provided by a phase-transfer catalyst of the passage through the phase boundary in the phase in which the chemical process takes place.

General

Suitable phase transfer catalysts for anions are often quaternary ammonium salts, the transfer of cations into an organic phase happens for example with the help of crown ethers.

In the inverse phase transfer catalysis is the substrate, for example, carboxylic acid halides, by means of an inverse phase transfer catalyst, such as pyridine derivatives, towed to the aqueous phase and reacts there.

Examples

The phase transfer catalysis is applicable to many types of reactions. An example is the nucleophilic substitution. A reaction of the present in the aqueous phase of sodium cyanide and an alkyl halide such as 1- bromooctane does not take place under non- catalyzed conditions. By the addition of phase transfer catalysts such as phosphonium salts ( for example, hexadecyltributyl ) cyanide ions are easily transferred into the organic phase, where they react easily and quantitatively with the alkyl halide to give 1- Cyanooctan.

Subsequent work by Herriott and Picker showed the water / benzene, many such reactions are carried out at room temperature by the use of quaternary ammonium compounds in the system. By the use of chiral phase transfer catalysts, a stereoselective effect can be achieved if necessary in specific reactions.

Through the PTC certain reactions at higher conversion rates and yields can be carried out with fewer side products. Also, often the need for expensive solvents that would dissolve both reactants are reduced and allows the use of inexpensive water and common organic solvents.

The application of the PTC but is not limited to the system of water / organic solvent, it can also be applied to solid-liquid or liquid / gas reactions.