Effects of cetyltrimethylammonium bromide (CTABr) micelles on
second-order rate constants (k
n
obs)
for
the nucleophilic reactions of amines (n-butylamine,
piperidine, and pyrrolidine) with ionized phenyl
salicylate
(PS-) reveal a decrease of nearly 4-fold for
n-butylamine, 13-fold for piperidine, and 17-fold for
pyrrolidine
with an increase in [CTABr]T from 0.0 to 0.01 M at 35
°C. These results show that the binding constants
(K
N) of amines with CTABr micelles vary in the
order K
N for n-butylamine >
K
N for piperidine > K
N
for
pyrrolidine. The observed data are explained in terms of the
pseudophase model of the micelle. The values
of K
N for n-butylamine, piperidine,
and pyrrolidine turn out to be so small that they could not be
determined
kinetically. The significantly lower rate of aminolysis in the
micellar pseudophase compared to that in
the aqueous pseudophase is attributed to both micellar medium effect
and different locations of amine and
PS- in the micellar pseudophase.
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