11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

transfer of catalyst from the reaction phase to the normal phase. The reaction mechanismcan be separated in three ways based on the reaction path, and can be described asfollows.(a) Normal Liquid–Liquid Phase Transfer Catalysis (N-LLPTC). Traditionally, moreapplications of PTC have been reported in N-LLPTC. The reaction mechanism (8) ismostly applied to alkylation, esterification etherification, and simple displacement reactionsin which a nucleophilic agent is transferred to the organic phase through the solublecatalyst therein:ð8ÞMechanism (8) was first presented by Starks [33] for the reaction of 1-chloro-octane andaqueous sodium cyanide.(b) Inverse Liquid–Liquid Phase Transfer Catalysis (I-LLPTC). The organic reactantis converted, by means of a reagent (e.g., pyridine 1-oxide, PNO) partially soluble inthe organic phase, into a reactive ionic intermediate and transferred into the aqueousphase where reaction takes place to produce the desired product. The processes havebeen termed inverse phase-transfer catalysis [34–36]. The reaction mechanism can beexpressed as follows:ð9ÞThere are several examples where I-LLPTC has been used to synthesize acid anhydrides,by means of a substitution reaction, and ketones from oxidation of alcohols [37–40]. The reaction of an acid chloride (RX) with the carboylate ions (M þ R 0 ) catalyzed byPNO is to proceed through an intermediate 1-(acyloxy)pyridinium chloride formed in theorganic phase. PNO and N,N-dimethylaminopyridine (DMAP) are widely used as inversePT catalysts. The formation of hippuric acid was conducted in the presence of 4-dimethylaminopyridineas inverse PT catalyst [41].(c) Reverse Liquid–Liquid Phase Transfer Catalysis (R-LLPTC). This reactionmechanism was expressed as follows:Copyright © 2003 by Taylor & Francis Group, LLC