Kinetic Evidence for Near Irreversible Nonionic Micellar Entrapment ofN-(2′-Methoxyphenyl)phthalimide (1) under the Typical Alkaline Reaction Conditions

M Niyaz Khan,Azhar Ariffin,Yoke-Leng Sim

doi:10.1155/2014/592691

Abstract

The values of pseudo-first-order rate constants (k obs) for alkaline hydrolysis of 1, obtained at 1.0 mM NaOH and within [ CmEnT] (total concentration of CmEn) range of 3.0–5.0 mM for C12E23 and 10–20 mM for C18E20, fail to obey pseudophase micellar (PM) model. The values of the fraction of near irreversible CmEn micellar trapped 1 molecules (F IT1) vary in the range ~0–0.75 for C12E23 and ~0–0.83 for C18E20 under such conditions. The values of F IT1 become 1.0 at ≥10 mM C12E23 and 50 mM C18E20. Kinetic analysis of the observed data at ≥10 mM C12E23 shows near irreversible micellar entrapment of 1 molecules under such conditions.

Highlights

The 2-state Hartley model of micelle of 1936 is still under extensive use [1]
In order to gain a better and clear understanding of this unusual finding, we started studying such effects on the rate of alkaline hydrolysis of esters and imides under variety of reaction kinetic conditions. This includes the use of reaction kinetic probe molecules of different structural features in the presence of pure CmEn (m/n = 12/23, 16/20, 18/20, and 16/10) and mixed CmEn-CTABr micelles [8,9,10,11,12]
The for Hydrolysis of 1 at 1.0 mM NaOH rate of alkaline hydrolysis of 1 was studied within [C12E23]T range of 3–50 mM, but the absorbance of the reaction mixtures within [C12E23]T range of 10–50 mM remained unchanged in the reaction time (t) range of ∼15 s

Summary

Introduction

The 2-state Hartley model of micelle (i.e., hydrophilic headgroup/palisade/Stern layer, and hydrophobic core) of 1936 is still under extensive use [1]. In order to gain a better and clear understanding of this unusual finding, we started studying such effects on the rate of alkaline hydrolysis of esters and imides under variety of reaction kinetic conditions. This includes the use of reaction kinetic probe molecules of different structural features in the presence of pure CmEn (m/n = 12/23, 16/20, 18/20, and 16/10) and mixed CmEn-CTABr micelles [8,9,10,11,12]. The unusual and unexpected observations of these studies are as follows. (i) The decrease of hydroxide ions from the neighborhood of micellized reaction kinetic probe molecules with the increase of R (= [CmEn]T/[NaOH] at a constant value of [NaOH]) at a typical value of Rt which represents a typical value of [CmEn]T/[NaOH] above which kobs versus [CmEn]T data fails to obey PM model. (ii) The observed data (kobs versus [CmEn]T) obey PM model at R ≤ Rt. (iii) The rate of hydrolysis of reaction kinetic probe molecules almost ceased when R ≫ Rt. (iv) The unusual observation of (iii) could be detected with C12E23, C16E10, and C18E20 but not with C16E20 under approximately similar conditions

Methods

Results

Discussion

Conclusion