- Effects of and on Intramolecular General Base-Catalyzed Methanolysis of Ionized Phenyl Salicylate in the Presence of Cationic Micelles
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Pseudo-first-order rate constants obtained for methanolysis of ionized phenyl salicylate (PS(1-)) at constant , , or , and and at 35 deg C show a decrease with the increase in (where CTABr represents cetyltrimethylammonium bromide) from 0.0-0.01 M.These observed data obey a pseudophase model of the micelle.The micellar binding constants (KS) of PS(1-), pseudo-first-order rate constants (kM) for methanolysis of PS(1-) in the micellar pseudophase and cmc are almost unchanged with the change in from 0.005-0.050 M.The increase in from 0.0 to 0.3 M at 0.01 M KOH decreases KS from 5140 to 653 M-1 and cmc from 1.9 x 10-4 to 0.2 x 10-4 M.Pseudo-first-order rate constants, kM, are almost independent of at 0.01 M KOH.
- Khan, M. Niyaz
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p. 3190 - 3193
(2007/10/03)
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- Kinetic probe to study the structural behaviour of mixed CH3OH-CH3CN-H2O solvents. Effects of inorganic salts on the kinetics and mechanism of intramolecular general base-catalyzed methanolysis of ionized phenyl salicylate in mixed CH3OH-CH3CN solvents with a constant content of H2O
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The effects of [MCI] (M+=Cs+, K+, Na+ and Li+) on the rates of methanolysis of ionized phenyl salicylate (PS-) have been studied at 30°C in CH3OH-CH3CN solvents with a constant content of H2O. The observed data are explained in terms of the assumption that methanol molecules exist in monomeric, dimeric and in general polymeric forms in CH3OH-CH3CN-H2O solvents. The observed pseudo first-order rate constants, kobs 1, obtained at a constant [H2O] and [MCI] [M+=Cs+, K+ and Na+) obey the relationship: Kobs1 = α[CH3OH]T/(1 + KA[CH3OH]T) where α is the apparent second-order rate constant, KA is the association constant for the dimerization of CH3OH and [CH3OH]T is the total concentration of methanol. Both α and KA reveal a decrease with the increase in H2O content from 4-30% (v/v) at a constant [K+] or [Na+]. The magnitudes of KA decrease with the increase in [K+] or [Na+] at a constant content of H2O. At considerably low content of H2O (≤20%, v/v), the decreasing effects of the cationic concentrations on KA vary in the order Na+ > K+. The presence of different [Cs+] does not reveal any detectable effect on α and KA obtained at various contents of H2O (4-30%, v/v) in mixed CH3OH-CH3CN-H2O solvents containing 0.01 M NaOH. The increase in [K+] or [Na+] decreases α at a constant content of H2O. The dependence of kobs1 upon the content of CH3OH (%, v/v) turns out to be different in the presence of Li+ ions than in the presence of Cs+, K+ and Na+ ions. The observed data show that Li+ ions cause almost complete depolymerization of polymeric methanol structure (i.e. KA?0) under the experimental conditions. The calculated values of α different contents of H2O are explained in terms of ion pair formation between PS- and M+ (M+ = Li+ , Na+ and K+) where ion pair complex (PS-. M+) is considered to be nonreactive towards CH3OH. The effects of [MCI] (M+ =K+, Na+ and Li+ ) on kobs 1 at 90% (v/v) CH3OH in mixed aqueous solvents are attributed to both ion pair complex, (PS- .M+) formation and the effects of [MCI] on α and KA.
- Khan, Mohammad Niyaz
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p. 1047 - 1055
(2007/10/03)
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