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

Abstract

Conversion of biphasic reactions into triphasic reactions can lead to process intensification, waste minimization and selectivity enhancement. Unlike liquid–liquid (L–L) PTC, the Liquid–Liquid–Liquid phase transfer catalysis (L–L–L PTC) offers high order of intensification of rates of reaction and catalyst reuse. The rate of reaction is remarkably enhanced by the catalyst-rich middle phase, which is the main reaction phase. Separation of catalyst can be done easily and the separated catalyst can be reused several times by using L–L–L PTC. This leads to waste minimization and other benefits of Green Chemistry. Mandelic acid and its derivatives are used for their dual activities as antibacterial and anti-aging agents. In this work, mandelic acid was produced by L–L–L PTC reaction of dichlorocarbene with benzaldehyde. Dichlorocarbene was generated in situ by the reaction of chloroform and sodium hydroxide in the presence of poly ethylene glycol (PEG) 4000 as the catalyst. The selectivity to mandelic acid was 98%. The reaction mechanism and kinetics model were established to validate the experimental data.