Micellar effects on SN2 reactions of alkyl naphthalene-2-sulfonates:: The role of hydrophobic substituents

Reactivities of methyl naphthalene-2-sulfonate, MeONs, and its 6-alkyl derivatives, alkyl = Me, n-C6H13 and n-C12H25, 6-Me-MeONs, 6-Hex-MeONs, and 6-Do-MeONs, respectively, are compared for reactions in cetyl trialkylammonium bromide micelles, n-C16H33NR3Br, R = Me, Et, n-Pr, n-Bu, CTABr, CTEABr, CTPABr, CTBABr, respectively. Similar experiments were made on reactions of Br- with n-butyl and n-decyl naphthalene-2-sulfonates, BuONs, and DeONs, respectively. Reactions with OH- were followed in cetyl trialkylammonium hydroxide, alkyI = Me, Et, n-Pr, CTAOH, CTEAOH, and CTPAOH, solubility permitting. Some reactions with OH- or Br- were also followed in mixed-ion systems of CTAOMs or CTPAOMs (OMs = MeSO3). Micellar rate effects were analyzed by using pseudophase treatments including interionic competition in mixed-ion systems. Second-order rate constants in the micellar pseudophase increase systematically with increases in substrate hydrophobicity and for reactions with Br-, but not OH-, they also increase with bulk of the cationic head group. (C) 2001 Academic Press.