Abstract
Pseudo-first-order rate constants (k obs ) for pH-independent hydrolysis of phthalimide (1), obtained at constant total concentration of cetyltrimethylammonium bromide (CTABr]T), 2.0 × 10−4 M 1, 0.02 M KOH and varying concentration of inert salt MX (=(CH3)4NCl and (CH3)4NBr), follow a kinetic equation derived in terms of pseudophase micellar (PM) model coupled with an empirical equation. This derived equation gives empirical constants. F X/S and K X/S where S represents anionic 1. The magnitude of F X/S is the measure of the fraction of micellized anionic 1 transferred to the aqueous phase by the limiting concentration of X − and the magnitude of K X/S is the measure of the ability of the ion X −, to expel another counterion ion S − from the cationic micellar surface to the aqueous phase through ion exchange process X −/S −. The values of the empirical constants, F X/S and K X/S , are used to determine the usual ion exchange constant . The values of F X/S are ∼1 for MBr and in the range 0.97–0.78 for MCl within [CTABr]T range 0.006 −≤0.016 M. The mean value of is 2.4 ± 0.1 and it is comparable with those obtained by other kinetic probes (with M+ = Na+) as well as physicochemical techniques.
Acknowledgments
The authors thank the University of Malaya for financial assistance (Grant no. RG022/09AFR).
Notes
a [1 0] = 2.0 × 10−4 M, λ = 300 nm, represents mean value of δ ap values obtained within [(CH3)4NCl] range as shown in the Table 1 and aqueous reaction mixture for each kinetic run contained 2% v/v CH3CN.
b Total concentration of CTABr surfactant.
c Error limits are standard deviations.
d Calculated from Equation (Equation2) and kinetic parameters listed in Table 4.
a [1 0] = 2.0 × 10−4 M, λ = 300 nm, represents mean value of δ ap values obtained within [(CH3)4NBr] range as shown in the Table 2 and aqueous reaction mixture for each kinetic run contained 2% v/v CH3CN.
b Total concentration of CTABr surfactant.
c Error limits are standard deviations.
d Calculated from Equation (Equation2) and kinetic parameters listed in Table 4.
a [1 0] = 2.0 × 10−4 M, λ = 300 nm, aqueous reaction mixture for each kinetic run contained 2% v/v CH3CN, and A∞ values remained zero within the limits of their standard deviations.
b Error limits are standard deviations.
a k 0 = k obs at [MX] = 0 as well as the values of k 0 at 0.006, 0.010 and 0.016 M CTABr represent the mean values, obtained by carrying out ≥3 different kinetic runs, with the respective standard deviations of ±0.10, ±0.02 and ±0.08.
c Error limits are standard deviations.
d K X/S = K X/S × .[ Citation 6 ]
e
f These parenthesized mean values of K X/S calculated from Equation (Equation3) with F X/S = 1.0 as described in the text.