Micellar Effects on the Reaction of (Arylsulfonyl)alkyl Arenesulfonates with Hydroxide Ion. 2. The Absence of Substrate Orientational Effects in a Series of Sulfonates of Different Hydrophobicities

Article abstract of DOI:10.1021/jo00221a032

Second-order rate constants for nucleophilic attack of hydroxide ion at the sulfonate sulfur atom of a series of sulfonates R₁SO2CH2OSO2R₂ (1a-g) in the presence of CTAB micelles (at 50 deg C) have been analyzed in terms of the pseudophase ion-exchange (PPIE) model.It is shown that the catalysis by the micelles is caused by the increased reactant concentrations in the micellar reaction volume.Large variations in the hydrophobicities of the substituents R₁ and R₂ (alkylaryl, alkyl) had only a minor influence on the rate constant for reaction in the micellar pseudophase (k_m).The same conclusion holds if the rate constants k_m are corrected for the different propensities of the sulfonates to respond to changes in the polarity of the reaction medium as expressed in the dielectric constant.Therefore there is no evidence that the depth of penetration and/or the orientation of the sulfonates 1a-g bound to the cetyltrimethylammonium bromide micelles is significantly affected by the hydrophobicities of R₁ and R₂.These findings are reconcilable with recent views cincerning the morphology of micelles.