Role of third phase in intensification of reaction rates and selectivity:  phase-transfer catalyzed synthesis of benzyl phenyl ether

Abstract

In the current work, the merits of the creation of a third phase in a typical biphasic reaction have been illustrated. The advantages of liquid−liquid−liquid phase-transfer catalysis (L−L−L PTC) have been brought out over liquid−liquid phase-transfer catalysis (L−L PTC) by considering the etherification of phenol by benzyl chloride to benzyl phenyl ether. L−L−L PTC is a novel strategy for waste reduction and improving profitability, in which a catalyst-rich middle phase is formed between the other two phases, wherein the main reaction takes place and intensifies the rates of reaction as well as offers better selectivity including catalyst reusability, unlike in the L−L PTC. The etherification of phenol with benzyl chloride under L−L PTC is accompanied by side reactions that lower the selectivity, and the catalyst cannot be recovered but wasted as an effluent, causing a load on the environment. However, the transformation of L−L PTC into L−L−L PTC leads to 100% conversion of the limiting reactant benzyl chloride with 100% selectivity to benzyl phenyl ether. The catalyst-rich phase is recovered and reused to some extent. This also helps in waste minimization, which is a major theme of green chemistry. The current work deals with the effects of different kinetic and processes parameters on enhancement in rates and selectivities in L−L−L PTC over L−L PTC. A mathematical model is also developed.