Unusual Effects of Pure Nonionic and Mixed Nonionic–Cationic Micelles on the Rate of Alkaline Hydrolysis ofN-Hydroxyphthalimide

Effects of nonionic micelles on the rate of alkaline hydrolysis of N-(2′-methoxyphenyl)phthalimide (1): Kinetic and rheometric evidence for a transition from spherical to rodlike micelles under the typical reaction conditions

“…It has been observed that an increase in the total concentration of cetyltrimethylammonium bromide ([CTABr] T ) from 0.0 to 0.03 M has no effect on the apparent pK a of the conjugate acid of 4 in the presence of 0.02 M C 12 E 23 [15], which is considered to be unusual in view of our understanding (through pseudophase ion exchange model of micelle) of the occurrence of ion exchange of HO À /Br À at CTABr micellar surface [16][17][18]. The observed kinetic data (k obs vs. [C m E n ] T ), reported in earlier studies [9][10][11][12][13][14][15], failed to obey PM model at greater than the typical values of R t (=[C m E n ] T /[HO À ] T ). The plausible reason(s) for such observations remained unknown.…”

“…But the presence of C 12 E 23 micelles caused significant near irreversible trapping of 6 at R P 5.0 and 0.02 M NaOH [14]. The origin of near irreversible micellar trapping of one of the reactants under the typical reaction conditions was not explored in all these studies [9][10][11][12][13][14][15]. It has been observed that an increase in the total concentration of cetyltrimethylammonium bromide ([CTABr] T ) from 0.0 to 0.03 M has no effect on the apparent pK a of the conjugate acid of 4 in the presence of 0.02 M C 12 E 23 [15], which is considered to be unusual in view of our understanding (through pseudophase ion exchange model of micelle) of the occurrence of ion exchange of HO À /Br À at CTABr micellar surface [16][17][18].…”

“…The near irreversible micellar trapping of anionic N-hydroxyphthalimide (6) could not be observed in the alkaline hydrolysis of 6 in the presence of C 16 E 20 (with R 6 8.5) and C 18 E 20 (with R 6 5.0) at 0.02 M NaOH [13]. But the presence of C 12 E 23 micelles caused significant near irreversible trapping of 6 at R P 5.0 and 0.02 M NaOH [14]. The origin of near irreversible micellar trapping of one of the reactants under the typical reaction conditions was not explored in all these studies [9][10][11][12][13][14][15].…”

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

“…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 C m E n ( m / n = 12/23, 16/20, 18/20, and 16/10) and mixed C m E n -CTABr micelles [ 8 – 12 ]. The unusual and unexpected observations of these studies are as follows.…”