11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

solubility in the organic phase, thus enhancing the overall reaction. The reaction scheme isshown in Fig. 6. For the same reaction system, but using quaternary ammonium saltinsteadPEGs,theactiveintermediatebecomesPhOQproducedfromsolidNaOPhreactedwith catalyst QBr. The solubility of PhOQ varies in different kinds of solvent and leads todifferent reaction rates. The variations in the catalytic intermediate PhOQ with respect totimeforchlorobenzene, dichlorobenzene, andheptaneare shown in Fig. 7,from whichtheconcentration PhOQ in heptane is the least. However, the overall reaction rate in heptaneis still at a high level; this shows that the interfacial reaction is dominant in this case [207].B. Adsorption Effect on the Solid Surface1. Formation of the Active ComplexIn contrast with the reaction mechanism of heterogeneous and homogeneous solubilization,Yufit et al. [208] proposed a new mechanism for SLPTC that included step-by-stepformation of a cyclic ternary complex [208]. This mechanism is based on the formation oftwo pairs of binary complexes (BCs) and ternary complexes (TCs) obtained from theorganic reactant RX, the solid reactant MY, and the PT catalyst QX adsorbed on asolid salt surface as follows [208]:RX þ MY þ QX Ð TC1 Ð TC2 Ð RY þ MX þ QXð97Þð98ÞThey also analyzed the energetics of the substitutions with solid salts of different strengthof M—Y bonds and concluded that the rate-determining step was the rearrangement ofFIG. 6 Reaction scheme for benzyl bromide reacted with sodium phenoxide using PEG as thecatalyst in SLPTC.Copyright © 2003 by Taylor & Francis Group, LLC