Micellar Effects on the Reaction of (Arylsulfonyl)alkyl Arenesulfonates with Hydroxide Ion. Microenvironmental and Substituent Effects in the Stern Layer of Cationic Micelles

Article abstract of DOI:10.1021/jo00196a010

The reaction of the sulfonates p-XC6H4SO2CH(R)OSO2C6H4Y-p 1a-g with hydroxide ion (involving nucleophilic attack at sulfonate sulfur) is accelerated (7-25 times) in the presence of CTAB micelles (32.1 deg C).The kinetic data are analyzed in detail by using the pseudophase ion-exchange (PPIE) model, taking into account partitioning of the reactants between the micellar and aqueous pseudophases and competition between hydroxide ions and detergent counterions for binding to the micelles.Binding constants obtained from the kinetic analysis are compared with those from ultrafiltration experiments.Generally, the PPIE model reproduces the experimental rate constants quite well, except at low detergent concentration (around the cmc).The second-order rate constants for reaction in the micellar pseudophase are 4-12 times smaller than those for reaction in bulk water.Therefore the observed catalysis is purely the result of the high local concentration of both reactants in the micellar pseudophase.The substituent effects for the reaction in the micelles reveal an increased susceptibility for variation of Y.No evidence for orientational effects was found.It is shown that the binding of the sulfonates with the micelles is mainly determined by the presence of the aryl groups.Based on a comparison with kinetic solvent effects on the reaction in 1,4-dioxane-water, it is suggested that the rates in the micellar pseudophase reflect a decrease in micropolarity at the binding sites of the substrate molecules.