All boundaries is difficult to cross: political, legal, geographic boundaries, and also phase boundaries in chemical systems. Many desirable reactions cannot be brought about because the reactants are inaccessible to each other. One typical system is a system consists of water soluble nucleophilic reagent and an organic water insoluble electrophilic reagent. To solve the problem of this system, traditionally both reagents are solved in water-like and organic-like solvent, such as ethanol which has both hydrophilic nature from its hydroxyl group and lipophilic nature from its ethyl group. But this method has a limitation that the reaction rate decreased due to the solvation of the nucleophile. The other method, such as using of expensive dipolar aprotic solvents like DMSO has been applied but proven to have disadvantages such as difficulty of the separation during post reaction recovery.
A feasible and industrially successful method to solve such system is the use of phase transfer agents, which transfer reactive anions from the aqueous or solid phase into the organic phase, where the reaction occurs. And this 40 years since first mentioned in some early patents, Phase Transfer Catalysis (PTC) has proved to be a very important means of transcending phase barriers in heterogeneous systems. And Starks, with his first publication “Quaternary Ammonium Salts as Phase Transfer Catalysts” and his book published in 1978, “Phase Transfer Catalysis: I Heterogeneous Reactions Involving Anion Transfer by Quaternary Ammonium and Phosphonium Salts” is believed to have coined the phrase phase transfer catalysis.
It is estimated by Starks in 1994 that Phase Transfer Catalysis has been used in as many as 500 commercial processes, with wide ranging applications in the pharmaceuticals, agro-based chemicals, and polymer science. The reason is that PTC finds applications in primarily nucleophilic substitution reactions and in reactions in the presence of bases involving the deprotonation of weakly acidic organic compounds. Reactions which could be carried out by PTC include redox, polymerizations, synthesis of carbenes, addition reactions, condensations and so on, which are often part of a multistep synthesis process for fine chemicals manufacture.
Despites thousands of publications on the chemistry and the applications of PTC, comprehensive kinetic study and mathematical modeling of the PTC reactions is still lacking. That’s why, my research for my final project will be an attempt to review the kinetic studies and mathematical modeling of PTC system using a reaction model described below.
The PT catalyst (Q) used in above reaction is Polyethylene glycol, which is despite its rather low reactivity compared to common PT catalyst Ammonium Salts, Polyethylene glycol is proven to be low price and not poisonous, which is suitable to designing of continuous type of reactors.