The key to PTC is the use of a catalyst, commonly a quaternary ammonium salt or a crown ether, which can solubilize the reactants into the organic or aqueous phase. For example, in a reaction involving an ionic compound and an organic substrate, the quaternary ammonium salt forms a complex with the ionic compound, allowing it to dissolve in the organic phase where it can react with the organic substrate. This process is often referred to as "phase transfer" because it effectively transfers the reactive ion from the aqueous phase to the organic phase.
