Quantitative Models of Rate Effects of Aqueous Micelles
Rate enhancements by cationic surfactants of the SN2 reaction of Cl- with methyl naphthalene-2-sulfonate (MeONs) follow a typical pseudophase model in which the interaction between Cl- and micel-lized surfactant is written as an equation of the Langmuir form with a binding constant, KC1. The binding of MeONs is written in a similar form with a binding constant, Ks. Values of Ks are insensitive to surfactant structure, but K C1 decreases with decreasing length of the alkyl tail and increasing bulk of the cationic head group. For most surfactants kinetic values of KC1 agree with those from variations of 35C1 NMR line widths. However, for reactions of Br-with MeONs in cationic micelles values of KBr. from 79Br- NMR line widths are much smaller than those estimated kinetically.
KeywordsHead Group Order Rate Constant Alkyl Tail Micellar Surface Cationic Micelle
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