Heterogeneous organic reactions are often encountered in organic synthesis. These reactions are generally slow, have low yields, and have incomplete reactivity. However, if a water-soluble inorganic salt is used, the organic substance is dissolved in an organic solvent having a small polarity, and a small amount (0.05 mol or less) of a quaternary ammonium salt or a quaternary phosphonium salt is added, and the reaction proceeds easily. Such a substance which promotes the reaction rate and transfers negative ions between two phases is called a phase transfer catalyst. In other words, phase transfer catalysts (PTCs) are a class of catalysts that can assist in the transfer of reactants from one phase to another that is capable of reacting, thereby accelerating the reaction rate of the heterogeneous system.
Figure 1. Phase transfer catalytic reaction
The phase transfer catalyst has the advantages of accelerating the reaction rate, lowering the reaction temperature, high product yield, and simple synthesis operation. It can usually be divided into the following categories:
Figure 2. Phase transfer quaternary ammonium catalyst