Process intensification and waste minimization in liquid-liquid-liquid phase transfer catalyzed selective synthesis of mandelic acid

► Conversion of bi-liquid phase to tri-liquid phase reactions is beneficial. ► Process intensification and waste minimization in L-L-L phase transfer catalysis. ► Mandelic acid synthesis by L-L-L PTC reaction of dichlorocarbene with benzaldehyde. ► PEG 4000 is an efficient catalyst, with 98% selectivity at 45 °C. ► Establishment of mechanism and kinetics.