Insight into green phase transfer catalysis

There is a need to develop green, clean and smart chemical technologies. Waste reduction through clever strategies and catalysis are at the heart of green chemistry. In the case of over 600 industrial phase transfer catalyzed (PTC) processes in several industries, mostly practised as liquid-liquid PTC, the catalyst is not recovered and disposed as a waste. Liquid-liquid PTC can be replaced by solid-liquid (S-L), liquid-liquid-liquid (L-L-L), solid (catalyst)-liquid-liquid, solid-liquid-omega liquid, gas-liquid-solid (G-L-S) and capsule membrane PTC to recover and reuse the catalyst and also to enhance selectivity, thereby advocating the realm of green PTC. Use of microwaves and ultrasound will also help in increasing rates. MILL-PTC and MISL-PTC are attractive techniques to enhance rate and selectivities under mild input of microwave irradiation (MI). In cascade-engineered PTC, several steps are combined in a reactor using the same catalyst and solvent, if used at all, without separation, or with partial replenishment of the reactants for all the steps to get substantial waste minimization. This paper provides a new insight into PTC for some reactions of industrial importance.