Kinetic probe to study the structure of micelles: effects of inert inorganic and organic salts on the rate of alkaline hydrolysis of phthalimide in the presence of cationic micelles

Pseudo-first-order rate constants (k(obs)) for the alkaline hydrolysis of p hthalimide (PTH), obtained at a constant concentration of cetyltrimethylamm onium bromide (CTABr) and 35 degreesC, vary with the increase in the concen tration of sodium phenylacetate and sodium sulfate (MX) according to the re lationship: k(obs) = (k(0) + thetaK[MX])/(1 + K[MX]) where theta and K are empirical parameters. The value of theta /k(W)(h) (where k(W)(h) = k(obs) a t [CTABr](T) = [MX] = 0) is the measure of the extent of expulsion of ioniz ed PTH (S-) from CTABr micellar pseudophase to aqueous pseudophase by an in ert anion (X-) provided S- is fully micellized in the absence of X-. Thus, the values of theta /k(W)(h) for sodium phenylacetate (approximate to1) and sodium sulfate (approximate to0.12-0.19) are attributed to deeper micellar penetration of S- and phenylacetate ions compared to that of sulfate ions. (C) 2001 Elsevier Science B.V. All rights reserved.