Journal of Molecular Catalysis A-Chemical, Vol.179, No.1-2, 143-153, 2002
Effects of salts and mixed aqueous-acetonitrile solvent on the rate of alkaline hydrolysis of 4-nitrophthalimide in the presence of cationic micelles
Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of 4-nitrophthalimide decrease with the increase in [CTA-Br](T) (total concentration of cetyltrimethylammonium bromide) at constant [CH3CN] and [NaOH]. This micellar effect is explained in terms of pseudophase model of micelle. The increase in the content of CH3CN from 5 to 15% v/v decreases CTABr micellar binding constant (K-S) of ionized 4-nitrophthalimide (NPT-) from 3650 to 370 M-1, increases the critical micelle concentration (cmc) from 2.8 x 10(-4) to 7.0 x 10(-4) M and decreases the pseudo-first-order rate constants (k(M)(h)) for hydrolysis of NPT- in the micellar pseudophase from 3.57 x 10(-4) to 2.24 x 10(-4) s(-1). The rate constants k(obs) obtained at constant [NaOH], [CH3CN], [CTABr](T) and varying concentrations of NaX (X- = Br-and Cl-), follow the relationship: k(obs) = (k'(0) + thetaK[NaX])/(l + K[NaX]), where theta and K are empirical parameters. The values of theta and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: K-S = K-S(0)(l + K-X/S [NaX]), where K-S is the CTABr micellar binding constant of NPT- in the presence of NaX. The value of K-Br/S(=K-Br(Cl)) is 3.5. (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords:4-nitrophthalimide;base;hydrolysis;kinetics;salts;mixed solvents;micelles;cationic surfactants