Kinetics and mechanism of intramolecular general base‐catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles

The alkanolysis of ionized phenyl salicylate, PS − , has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH 2 CH 2 OH and CH 3 OH) contents of 15–74 or 92%, v/v. The alkanolysis of PS − involves intramolecular general base catalysis. At a constant concentration of SDS, [SDS] T , the observed pseudo first‐order rate constants, k obs , for the reactions of ROH with PS − obtained at different concentration of ROH, [ROH] T , obey the relationship: k obs = k [ROH] T /(1 + K A [ROH] T ) where k is the apparent second‐order rate constant and K A is the association constant for dimerization of ROH molecules. Both k and K A decrease with increase in [SDS] T . At a constant [ROH] T , the rate constants, k obs , show a decrease of nearly 2‐fold with increase in [SDS] T from 0.0–0.3M. These results are explained in terms of pseudo‐phase model of micelle. The rate constants for alkanolysis of PS − in micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous‐alkanol pseudophase. This is attributed largely to considerably low value of [ROH] in the specific micellar environment where micellar bound PS − molecules exist. The increase in [ROH] T decrease the value of the binding constant of PS − with SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PS − are explained in terms of the porous cluster micellar structure.