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

Abstract

through "molecular lines of force", the simple re~ognition'~ of the alternate charge relay effect described by Pople and Gordon42 seems adequate to account for gross effects at both CY-and 0-carbon atoms. ConclusionsThe findings reported here are based on an extensive set of substituents that exceeds the requirements for a minimal set to test correlative ability.19,22 Although a set of substituent constants similar to u+ values can be devised to give the best correlations with SCS at the @-carbon atom, these constants fail completely when applied to SCS data at the a-carbon. The DSP approach is therefore mandated. A comparison of currently existing parameters for DSP treatments showed that both the Taft and Swain approaches gave very good results for the @-carbon data. In fact, for the substituents employed, Taft's uR* scale tuR+ for electron donors and uR-for electron withdrawers) (42) Pople, J. A.; Gordon, M. J. Am. Chem. SOC. 1967,89,4253-4261.correlates reasonably well with Swain's R values. The correlation between uI and F is unsatisfactory if the dimethylamino and phenyl groups are included, but excellent if they are excluded. Swain's parameters are definitely superior for the a-carbon data, where electronic effects are largely (80%) inductive. These results suggest that multiple resonance scales may be unnecessary and, possibly, that the Swain and Taft parameter sets would give nearly identical results if uI and F were more nearly parallel. The discrepancy seems to be in the aI value for either the dimethylamino or phenyl group, or both.Supplementary Material Available: Tables giving the chemical shifts for 0-carbon atoms (S-I) in all series and for a-carbon atoms (S-11) in the para-substituted series, and adjusted correlation coefficients, R2, for correlations of shifts for @-carbon atoms in each para-substituted series (S-111) and meta-substituted series (S-IV) with various DSP treatments (4 pages). Ordering information is given on any current masthead page.of of Second-order rate constants for nucleophilic attack of hydroxide ion a t the sulfonate sulfur atom of a series sulfonates R1S02CH20S02R2 (la-g) in the presence of CTAB micelles (at 50 "C) have been analyzed in terms 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 Rz (alkylaryl, alkyl) had only a minor influence on the rate constant for reaction in the micellar pseudophase (k,). The same conclusion holds if the rate constants k, 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 la-g bound to the cetyltrimethylammonium bromide micelles is significantly affected by the hydrophobicities of R1 and Rz. These findings are reconcilable with recent vi...

Diels-Alder Reactions in Micellar Media

“…For example, extensive structural changes in substrates were expected to influence the depth of penetration of the substrate into the micellar core with a concomitant change in the efficiency of the micellar catalysis. This expectation was not borne out in practice [99,100].…”