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.
