Kinetic Evidence for the Occurrence of Independent Ion-Exchange Processes in the Cationic Micellar-Mediated Reaction of Piperidine with Anionic Phenyl Salicylate

Abstract

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)(-).

Kinetic and rheological measurements of the effects of inert 2-, 3- and 4-bromobenzoate ions on the cationic micellar-mediated rate of piperidinolysis of ionized phenyl salicylate

“…These results may be attributed to the orientational effect of substituent Br in the benzene ring of Bz À . Almost similar results were obtained with X = 2-and 3-ClBz À [39,40]. The value of K Br X for X = 2-BrBz À is $2-fold larger than that for X = 2-ClBz À which could be ascribed to a few factors including electronegativity and polarizability effects of Cl and Br.…”

Determination of an Ion Exchange Constant by the Use of a Kinetic Probe: A New Semiempirical Kinetic Approach Involving the Effects of 3-F- and 4-F-Substituted Benzoates on the Rate of Piperidinolysis of Anionic Phenyl Salicylate in Aqueous Cationic Micelles

“…It has been concluded elsewhere , that the values of K X/S and K Br/S (for ion exchange Br − /S − ) are related to the usual thermodynamic ion exchange constant, K X Br (= K X / K Br ). The values of K X Br , obtained from this new approach/technique, for a few inorganic and organic anions (X) are listed elsewhere. , The value of K X Br with MX = 3-ClC 6 H 4 CO 2 Na (an inert salt with an anion acting as a viscoelastic counterion of a CTABr micelle) was found to be more than 12-fold larger than that with MX = 2-ClC 6 H 4 CO 2 Na (an inert salt with an anion acting as a nonviscoelastic counterion of CTACl) . Thus, the values of K X Br for X = viscoelastic as well as nonviscoelastic counterions would have predictive power for a counterion X to be either viscoelastic or nonviscoelastic.…”

Kinetics and Mechanism of Cationic Micelle/Flexible Nanoparticle Catalysis: A Review

“…These authors concluded that the viscoelasticity is associated with the specific orientation of the substituents of these counterions. However, recent studies show that the values of the ion exchange constants (K X Br ) for X = 2--OBz, 3--OBz and 3-ClBz are 44, 5 [30] and 50 [31] respectively. These results show that the values of K X Br may rationalise quantitatively the viscoelastic and nonviscoelastic nature of CTABr aqueous solutions containing these substituted benzoate counterions.…”

“…The values of K Br Cl (= 2.7 ± 0.1 and 2.6 ± 0.3 for M + = Na + and K + respectively) may be compared with the reported values of 2-3 [68], 2.7 [69] and 5 [70] obtained by the use of different physicochemical techniques. The values of K X/S or K X/S n can be determined using either semi-empirical kinetic (SEK) [5,14,31,67] or semi-empirical spectrophotometric (SESp) [71] methods. The SEK method involves kinetic measurements of an appropriate reaction probe molecule while the SESp method involves an appropriate spectrophotometric probe molecule.…”

“…Similarly, for another counterion Y -, K Y/S n = Ω S K Y /K S where K Y represents the cationic micellar binding constant of Y -. Thus, the ratio K X/S n /K Y/S n gives the usual thermodynamic ion exchange constant K X Y (= K X /K Y ) provided K X/S n and K Y/S n have been determined in the presence of micelles/ nanoparticles of identical structural features such as spherical or wormlike micelles or vesicles/ nanoparticles [14,31,66]. If the values of K Y/S n and K X/S n have been determined in the presence of micelles/nanoparticles of different structural features, say for example, in spherical (SM) and nonspherical (NSM) micellar/nanoparticle pseudophases, then the ratio (K X/S n ) NSM /(K Y/S n ) SM = R X Y = K X NSM /K Y SM where K X NSM and K Y SM represent the cationic micellar/FN binding constants of counterions Xand Yin the presence of NSM and SM respectively [66].…”