Pseudo-first-order rate constants (k obs ) for the alkaline hydrolysis of phthalimide (PTH) show a monotonic decrease with the increase in [C 16 E 20 ] T (total concentration of Brij 58) at constant [CH 3 CN] and [NaOH]. This micellar effect is explained in terms of the pseudophase model of micelles. The rate of hydrolysis of PTH in C 16 E 20 micellar pseudophase appears to be negligible compared with that in the aqueous pseudophase. The values of k obs for C 12 E 23 (Brij 35) show a sharp decrease at very low values of [C 12 E 23 ] T followed by a very slow decrease with increase in [C 12 E 23 ] T at relatively higher values of the latter. The rate of hydrolysis becomes too slow to monitor at [C 12 E 23 ] T !0.04 M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C 12 E 23 ] T !0.05 M in the presence of 0.006-0.02 M CTABr at 0.02 M NaOH whereas such characteristic behavior is kinetically absent with C 16 E 20 . The values of k obs , obtained at different [NIS] T (where NIS represents C 16 E 20 and C 12 E 23 ) in the presence of a constant amount of CTABr, follow the empirical relationship k obs = (k 0 kK[NIS] T )/(1 K[NIS] T ) where k and K are empirical parameters. The values of k are only slightly affected whereas the values of K decrease with increase in [CTABr] T for the mixed C 16 E 20 -CTABr micellar system. The rate of hydrolysis of PTH at !0.01 M C 12 E 23 and !0.01 M CTABr reveals the formation of phthalic anhydride whereas this was not observed in the mixed C 16 E 20 -CTABr micellar system under similar experimental conditions. a Conditions: [phthalimide] 0 = 2 Â 10 À4 M, [NaOH] = 0.02 M, 35°C, l = 300 nm and aqueous reaction mixture for each kinetic run contained 2% (v/v) CH 3 CN. b Y obs = k h w/k obs with 10 4 k h w = 24.6 s À1 . c Calculated from Eqn. (4) with (1 À c.m.c.K s ) = 0.99 and K s = 7.5 M À1 . d Error limits are standard deviations.

Pseudo‐first‐order rate constants (kobs) for the hydrolysis of phenyl salicylate (PSH) and phenyl benzoate (PB) in the alkaline medium show a monotonic decrease with the increase in [C16E20]T (total concentration of Brij 58) at constant [CH3CN] and [NaOH]. This micellar effect is explained in terms of the pseudophase model of micelles. These results show a characteristic difference between the effects of [C16E20]T and previously published effects of [C12E23]T (total concentration of Brij 35) on the rates of aqueous cleavage of PSH and PB at [CnEm]T/[NaOH]≥∼3. The values of kobs, obtained at different [C16E20]T in the presence of a constant amount of CTABr, follow the empirical relationship kobs=(k0+θK[C16E20]T)/(1+K[C16E20]T), where θ and K are empirical parameters. The values of θ are not affected whereas the values of K decrease with increase in [CTABr]T in a mixed C16E20–CTABr micellar system. The values of θ at different [CTABr]T show that θ>k0 for hydrolysis of PSH and θ<k0 for hydrolysis of PB in the presence of 0.01 M NaOH. The effects of [CTABr]T on K and θ are explained in terms of the pseudophase model of micelles coupled with the empirical relationship KS=KS0/(1+KC16E20/S[C16E20]T). Copyright © 2004 John Wiley & Sons, Ltd.

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A kinetic probe, which involves the determination of pseudo-first-order rate constants (k(obs)) for the nucleophilic reaction of piperidine (Pip) with ionized phenyl salicylate (S(-)) at constant [Pip](T) (= 0.1 M), [S(-)](T) (= 2 x 10(-4) M), [CTABr](T), < or = 0.10 M NaOH and varying concentration of MX (= 3-ClC(6)H(4)CO(2)Na and C(6)H(5)CH=CHCO(2)Na), gives the following information. The nonlinear plots of k(obs) versus [MX] reveal indirectly the occurrence of more than one independent ion-exchange processes at the CTABr micellar surface. These observed data fit to a kinetic relationship derived from an empirical equation coupled with pseudophase micellar (PM) model. This relationship gives an empirical constant (K(X/S)) that is used to determine the usual ion-exchange constant (K(X)(Y)). The values of K(X)(Br) (Y = Br) have been calculated for X = 3-ClC(6)H(4)CO(2)(-) and C(6)H(5)CH=CHCO(2)(-). More than 12-fold larger value of K(X)(Br) for X = 3-ClC(6)H(4)CO(2)(-) than that for X = 2-ClC(6)H(4)CO(2)(-) is attributed to the presence and absence of viscoelasticity in the respective presence of 3-ClC(6)H(4)CO(2)(-) and 2-ClC(6)H(4)CO(2)(-).