Effect of Cationic Micellar Reaction Field on Reaction Kinetics of Meisenheimer σ-Complex Formation between 1,3,5-Trinitrobenzene and Hydroxide Ion

Kinetic studies were done by using stopped-flow method for the Meisenheimer σ-complex formation reaction between 1,3,5-trinitrobenzene (TNB) and hydroxide ion in cationic micellar solutions of dodecyl-trimethylammonium bromide (DTAB), myristyltrimethylammonium bromide (MyTAB) and cetyltrimethylammonium bromide (CTAB) dissolved in aqueous solution, for the purpose of elucidating the influence of the microscopic heterogeneity of reaction field. The reaction rate analysis based on a pseudo-phase ion exchange model led us to a conclusion that the partition of reactant molecules between the micelle and water phase, and ion exchange between hydroxide ion and bromide ion existing as counter ions of cationic micellar surface were important. On the activation process, the enthalpy-entropy compensation relationships worked over the wide range of surfactant concentration. The derived isokinetic temperature, T_ revealed that in CTAB the reaction might be of enthalpy-control, and that in MyTAB be of entropy-control