Unusual effects of pure nonionic and mixed nonionic-cationic micelles on the rate of alkaline hydrolysis of N-hydroxyphthalimide

摘要

Pseudo-first-order rate constants, k_(obs), for the alkaline hydrolysis of N-hydroxyphthalimide, 1, at 0.02 M NaOH and 30°C remain essentially independent of the total concentration of C_(12)E_(23), [C_(12)E_(23)]_T, at ≤0.005 M C_(12)E_(23). The increase in [C_(12) E_(23)]_T from 0.005 to 0.015 M causes a nonlinear decrease in k_(obs). The rate of hydrolysis becomes either too slow or the change in absorbance values becomes significantly small to allow a reliable observed data fit to a first-order kinetic equation at ≥0.020 M C_(12)E_(23) in the absence and presence of total concentration of cetyltrimethylammonium bromide, [CTABr]_T ranging from 0.003 to 0.020 M. The values of fraction of nonionized 1, F_(SH), obtained at reaction time t = 0 and 0.02 M NaOH, remain ~0 at ≤0.010 M C_(12)E_(23) while they increase from 0.39 to 0.89 with the increase of [C_(12)E_(23)]_T from 0.015 to 0.10 M. The values of k_(obs) show a nonlinear decrease of ~5-fold with the increase of [C_(12)E_(23)]T from 0.0 to 0.010 M in the presence of 0.02 M NaOH and [CTABr]_T range of 0.003 to 0.020 M. The values of F_(SH) remain ≤~0.10 at ≤0.015 M C_(12)E_(23) while they vary between 0.40 and 0.90 within a [C_(12)E_(23)]_T range 0.02 to 0.05 M in the presence of 0.02 M NaOH and [CTABr]_T ranging from 0.003 to 0.020 M. The values of F_(SH) represent the fraction of nonionized 1 trapped almost irreversibly by pure C_(12)E_(23), and mixed C_(12)E_(23)-CTABr micelles.