A phase transfer catalyst facilitates the reaction in a heterogeneous system between general organic compounds that are soluble in organic solvents and compounds such as inorganic salt that are soluble in water. Quaternary ammonium salts, phosphonium compounds and crown ethers are examples of phase transfer catalysts.
Reactions that use phase transfer catalysts do not require the high polar solvents DMSO or DMF. Instead, they are carried out using nonpolar aprotic solvents and water. Phase transfer catalysts, sometimes referred to as PTCs, are used in green chemistry because they reduce the need for organic solvents and produce higher yields with fewer byproducts and waste materials.