N. Pirinccioglu et al., Reactions within association complexes: The reaction of imidazole with substituted phenyl acetates in the presence of detergents in aqueous solution, J ORG CHEM, 65(8), 2000, pp. 2537-2543
The bimolecular rate constants for reaction of imidazole with phenyl acetat
es complexed with sodium dodecyl sulfate (SDS) or cetyltrimethylammonium br
omide (CTAB) micelles obey Bronsted equations with beta(1g) similar to that
of the reaction in aqueous solution. The dissociation constants of ester (
Ks) and the hypothetical dissociation constant (K-TS) Of the transition sta
te of the micelle complexes obey Hansch equations with similar sensitivitie
s (p) to pi(-0.66 and -0.589 for K-S and -0.735 and -0.495 for K-TS, respec
tively). The slopes also indicate that the microsolvation environments asso
ciated with the transition state and the complexed ester have aqueous chara
cter. The relative values of K-TS and K-S indicate that the transition stat
e of the reaction of imidazole with ester is more weakly complexed to both
micelles than is the reactant ester. Log K-TS values are linear functions o
f log K-S for reactions with both CTAB and SDS; the slopes are, respectivel
y, -0.893 and -1.19 consistent with a slightly more "water-like" medium for
the transition state than for the site of binding of ester with CTAB-micel
le and slightly less for the SDS-micelle. The results for ester and transit
ion state are consistent with the location of the phenyl residue in a hydro
phobic region that possesses water molecules. It is concluded that the acet
yl group in the complexed transition state is located in an aqueous part of
the Stern region, whereas the phenyl residue is in a part of the Stern reg
ion that possesses alkane components. The derived kinetic and complexation
parameters in these experiments refer to micelles with Stern regions that h
ave been maintained at constant ionic compositions.