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21.
The kinetics of hydrolytic cleavage of saccharin has been studied at 60°C within the [ōH] range of 0.1 to 3.0 M. The observed pseudo first-order rate constants, kobs, follow an empirical relationship: kobs = B[ōH] + [C[ōH]]2. The B and C terms are attributed to the formation of dianionic and trianionic tetrahedral intermediates on the reaction path. It is concluded that the ionized form of saccharin is the major reacting species under the present experimental conditions. The positive ionic strength effect and the negative effect of 1,4-dioxan on the rate of hydrolysis favor the proposed reaction mechanism. The analysis of the observed activation parameters indicates that the increase in the contribution of C term to kobs causes the slight increase in both ΔH* and ΔS*. A significantly large negative value of ΔS* favors the proposed mechanism. 相似文献
22.
General base-catalyzed and uncatalyzed nucleophilic cleavage of both unionized (SH) and ionized (S–) phthalimide have been observed in ethane-1,2-diamine buffer solutions of pH 7.46–8.60. General base catalysis appears to be insignificant in the pH range of 9.17–10.10. 相似文献
23.
Pseudo-first order rate constants (kobs) for alkaline hydrolysis of phthalimide (PTH), obtained at constant concentration of cetyltrimethylammonium bromide (CTABr) and 35°C, vary with the concentration of organic salts ([MX]) according to the relationship: kobs = (k0 + K [MX])/(1 + K [MX]) where and K are empirical parameters. The values of K at 0.01 M CTABr are nearly 2 times larger than the corresponding K values at 0.02 M CTABr for sodium benzoate, disodium phthalate and disodium isophthalate. 相似文献
24.
M. Niyaz Khan 《国际化学动力学杂志》2002,34(2):95-103
The kinetics of the aqueous cleavage of N‐ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC A B , where ENMBC, A , and B represent ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]carbamate, N‐hydroxyl group cyclized product of ENMBC, and o ‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002 相似文献
25.
The values of pKams (Kams represents ionization constant of conjugate acid of amine base in mixed water–acetonitrile solvent) for all amines, except for charged amine bases, show a mild decrease (ca. 0.1–0.4 pK units) with the increase in CH3CN content from 2 to ∼60% v/v. However, the pKams values at 70% v/v CH3CN become nearly equal or slightly larger (by ≤0.7 pK units) than the corresponding pKams at 2% v/v CH3CN for all neutral and charged amines. The values of pKams for phenol increase from 10.17 to 13.38 with the increase in the content of CH3CN from 2 to 70% v/v in mixed aqueous solvent. Taft reaction constants, ρ*, obtained from the plots of pKams against ∑σ* for primary and secondary amines decrease by ca. 0.8 ρ* units with the increase in the CH3CN content from 2 to 70% v/v. The values of pKams show an empirical linear relationship with the corresponding values of pKaw (where pKaw represents the pKa obtained in aqueous solvent containing 2% v/v CH3CN), which allows the estimation of a pKa in mixed H2O CH3CN solvents from that in water. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 146–152, 2000 相似文献
26.
M. Niyaz Khan 《国际化学动力学杂志》1998,30(4):301-307
The effects of mixed CH3CN(SINGLEBOND)H2O solvents on rates of aminolysis of ionized phenyl salicylate, PS−, reveal a nonlinear decrease in the nucleophilic second-order rate constants, knms, (for aminolysis) with increase in the content of CH3CN until it becomes ∼50%, v/v. The values of knms remain almost unchanged with change in the CH3CN content within 50 to 70 or 80%, v/v. The effects of mixed CH3CN(SINGLEBOND)H2O solvents on pKa of leaving group, phenol, and protonated amine nucleophile have been concluded to be the major source for the observed mixed solvent effects on knms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 301–307, 1998. 相似文献
27.
M. Niyaz Khan 《Advances in colloid and interface science》2010,159(2):160-128
A new method, based upon semi-empirical kinetic approach, for the determination of ion exchange constant for ion exchange processes occurring between counterions at the cationic micellar surface is described in this review article. Basically, the method involves a reaction kinetic probe which gives observed pseudo-first-order rate constants (kobs) for a nucleophilic substitution reaction between the nonionic and anionic reactants (R and S) in the presence of a constant concentration of both reactants as well as cationic micelles and varying concentrations of an inert inorganic or organic salt (MX). The observed data (kobs, versus [MX]) fit satisfactorily (in terms of residual errors) to an empirical equation which could be derived from an equation explaining the mechanism of the reaction of the kinetic probe in terms of pseudophase micellar (PM) model coupled with another empirical equation. This (another) empirical equation explains the effect of [MX] on cationic micellar binding constant (KS) of the anionic reactant (say S) and gives an empirical constant, KX/S. The magnitude of KX/S is the measure of the ability of X− to expel S− from a cationic micellar pseudophase to the bulk aqueous phase through ion exchange X−/S−. The values of KX/S and KY/S (where Y− is another inert counterion) give the ion exchange constant, KXY (= KX/KY where KX and KY represent cationic micellar binding constants of X− and Y−, respectively). The suitability of this method is demonstrated by the use of three different reaction kinetic probes and various MX. 相似文献
28.
Pseudo‐first‐order rate constants (kobs)—obtained for the cleavage of ionized phenyl salicylate (PS?) at constant [NaOH], [MeCN], [CTAZ]T (total concentration of cetyltrimethylammonium chloride and bromide), [Pip]T (total concentration of piperidine), and varying concentrations of sodium cinnamate, acetate, and butanoate ([NaX])—follow the relationship: kobs = (k0 + θ K[NaX])/(1 + K[NaX]), where θ and K are empirical parameters. The values of θ are almost independent of [CTAZ]T, while K values decrease with the increase in [CTAZ]T within its range 0.006–0.020 M. The values of θ and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: KS = KS0/(1 + ΨX/S [NaX]), where KS is the CTAZ micellar binding constant of PS? in the presence of NaX. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 288–294, 2001 相似文献
29.
Khan MN 《The Journal of organic chemistry》1996,61(23):8063-8068
A slight modification of the Gabriel synthesis of primary amines is suggested on the basis of the observed and reported values of rate constants for the alkaline and acid hydrolyses of phthalimide, phthalamic acid, benzamide, and their N-substituted derivatives. The suggested procedure requires shorter reactions time and milder acid-base reaction conditions compared with the conventional acid-base hydrolysis in the Gabriel synthesis. A slight modification in the Ing-Manske procedure is also suggested. Pseudo-first-order rate constants, k(obs), for hydrolysis of N-phthaloylglycine, NPG, decrease from 24.1 x 10(-3) to 7.72 x 10(-3) and 6.12 x 10(-3) s(-1) with increasing acetonitrile and 1,4-dioxan contents, respectively, from 2 to 50% v/v (all the percentages given in the paper are vol %), while increasing the organic cosolvents content from 50 to 80% increases k(obs) from 7.72 x 10(-3) to 19.7 x 10(-3) s(-1) for acetonitrile and from 6.12 x 10(-3) to 52.8 x 10(-3) s(-1) for 1,4-dioxan, in aqueous organic solvents containing 0.004 M NaOH at 35 degrees C. The rate constants for NPG hydrolysis decrease from 2.11 x 10(-2) to 1.19 x 10(-4) s(-1) with increasing MeOH content from 2 to 84%, in aqueous organic solvents containing 2% MeCN and 0.004 M NaOH at 35 degrees C. 相似文献
30.
The rate of formation and disappearance of phthalic anhydride (PAn) intermediate in the aqueous cleavage of N-methoxyphthalamic acid (NMPA) under acidic pH was studied spectrophotometrically in mixed CH3CN-H2O solvents. The rate of formation of PAn from NMPA is almost independent of the change in acetonitrile content from 20 to 70% v/v in mixed aqueous solvents. The rate constants for the formation of PAn from NMPA are approximately 10-fold smaller than the corresponding rate constants for the formation of PAn from o-carboxybenzohydroxamic acid (OCBA). These observations are ascribed to the consequence of the occurrence of slightly different mechanisms in these reactions. 相似文献