Effects of Nonionic, Cationic, and Mixed Nonionic–Cationic Surfactants on the Acid–Base Behavior of Phenyl Salicylate

Effects of Nonionic and Mixed Cationic–Nonionic Micelles on the Rate of Alkaline Hydrolysis of 4-Nitrophthalimide

“…Thus, we presume the occurrence of the same reaction mechanism in both aqueous and micellar pseudophases for alkaline hydrolysis of 4-nitrophthalimide under the present reaction conditions. It should be noted that the pH-independent rate of hydrolysis of 4-nitrophthalimide is equal to Similar results were obtained in the study on the effect of mixed C 12 E 23 / CTABr micelles on pK a of phenyl salicylate (6). As has been mentioned earlier, k obs could be determined until [C 12 E 23 ] T became 0.07 M at 0.03 M NaOH (Table 1), so a few kinetic runs were carried out within the [C 12 E 23 ] T range 0.0 to 0.07 M at 0.03 M NaOH and 0.006 M CTABr.…”

“…The effects of mixed cationic/anionic surfactants on the rates of methanolysis of ionized phenyl salicylate (PS − ) and alkaline hydrolysis of phenyl benzoate have revealed that mixed micelles show a cationic nature when X ≤ 0.3 and an anionic nature when X ≥ 4, where X = [SDS] T /[CTABr] T (SDS = sodium dodecyl sulfate and CTABr = cetyltrimethylammonium bromide) (5). The pK a of phenyl salicylate remains unchanged with the change in [CTABr] T /[C 12 E 23 ] T from 0.5 to 1.5 at a constant [C 12 E 23 ] T (= 0.02 M), which seems to be an unexpected result (6). The present study was initiated with the aim of investigating the effects of C 12 E 23 (i.e., Brij 35) and mixed CTABr/C 12 E 23 micelles on the rate of alkaline hydrolysis of 4-nitrophthalimide.…”

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

“…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 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 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 ).…”

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

“…However, relatively recent studies involving kinetic and spectrometric probes strongly favor the multistate model of micelle [2–6]. The unusual effects of pure C 12 E 23 and mixed CTABr-C 12 E 23 micelles on the acid-base behavior of phenyl salicylate were observed in 1999 [7]. 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.…”