Effects of Non-Ionic Micelles on the Rates of Intramolecular General Base-Assisted Nucleophilic Reactions of Piperidine with Ionized Phenyl Salicylate

Abstract

Pseudo-first-order rate constants (kobs) for piperidinolysis of ionized phenyl salicylate (PS-), obtained at a constant concentration of polyoxyethylene (23) dodecyl ether ([C12E23]T) and 0.02 M NaOH, follow the relationship: kobs=k0+knapp[zPip]T (where [Pip]T is the total concentration of piperidine). The nonlinear decrease in knapp with increase in [C12E23]T (from 0.001 to 0.080) is explained in terms of the pseudophase (PP) model of the micelle. The fraction of PS- (fPS-) decreases from 1.0 to 0.87, 1.0 to 0.69, and 1.0 to 0.03 with the respective increase in [C12E23]T from 0.06 to 0.08 M at 0.07 M Pip, 0.03 to 0.08 M at 0.04 M Pip and 0.02 to 0.08 M at 0.01 M Pip due to irreversible micellar entrapment of non-ionized phenyl salicylate (PSH) molecules. The values of kobs, obtained for piperidinolysis of PS- at 0.1 M Pip and 0.02 M NaOH, show an ∼5-fold monotonic decrease with increase in [C16E20]T from 0.0 to 0.16 M. These data follow the PP model of the micelle.