Effects of non‐ionic and mixed cationic–non‐ionic micelles on the rate of alkaline hydrolysis of phthalimide

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. Copyright © 2002 John Wiley & Sons, Ltd.