THE CATALYTIC EFFECT OF CATIONIC AMINO MICELLES ON THE HYDROLYSIS OF SUBSTITUTED PHENYL ESTERS

Article abstract of DOI:10.1016/S0040-4020(01)81445-9

The catalytic effects of two aminocationic micelles on the hydrolysis of substituted phenyldecanoate esters and a positively charced benzoate ester (CPNBA) were determined.The micellaric catalysts were of the general structure Br where n=2 (micelle 1); n=3 (micelle 2).The kinetics followed the expression: k_obs=k₀+k_cat x K_a/(K_a+H⁺)+k^c_OH->.From the comparison of the k^c_OH rates with specific base catalysis rates deduced from reactions in non catalytic micelles, it was concluded that the k^c_OH term, is compatible mainly with an aminolysis reaction catalysed by hydroxide ion.The Hammett and Bronsted correlations (ρ=2.8; β=1.0), in addition to the very small deuterium isotope effect, suggested that k_cat corresponded with a nukleophilic mechanism.The Bronsted plot of log k_cat vs pKa of the phenolate leaving groups in micelles 1 and 2 showed a biphasic behaviour.The break in the curve occured at pK₀=5.89 and pK₀=6.78 respectively.The partition ratio k^+/-/k_-a of the zwiterionic tetrahedral intermediate was derived from the experimental data and produced the following correlation: log k^+/-/k_-a=-0.92pK₀+0.43pK_N+2.466.The ester CPNBA exhibited a deuterium isotope effect of 2.1.From product analysis it was concluded that the reaction proceeds via a general base catalysis of aminolysis.