“…Due to their importance in biological processes as well as in synthetic applications, numerous studies have been performed to investigate the mechanism of acyl transfer processes. − One aspect of interest is whether nucleophilic attack at the carbonyl center occurs concertedly with leaving group departure (eq 1), or whether reaction occurs via a discrete tetrahedral intermediate (eq 2). …”
Section: Introductionmentioning
confidence: 99%
“…In ester aminolysis, it is now firmly established that the two-step mechanism obtains, in which the rate-determining step (RDS) is dependent on the relative basicity of the amine and the leaving group. − Thus the RDS changes from breakdown of the intermediate to its formation as the attacking amine becomes more basic than the leaving group by 4−5 p K a units. − …”
A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.
“…Due to their importance in biological processes as well as in synthetic applications, numerous studies have been performed to investigate the mechanism of acyl transfer processes. − One aspect of interest is whether nucleophilic attack at the carbonyl center occurs concertedly with leaving group departure (eq 1), or whether reaction occurs via a discrete tetrahedral intermediate (eq 2). …”
Section: Introductionmentioning
confidence: 99%
“…In ester aminolysis, it is now firmly established that the two-step mechanism obtains, in which the rate-determining step (RDS) is dependent on the relative basicity of the amine and the leaving group. − Thus the RDS changes from breakdown of the intermediate to its formation as the attacking amine becomes more basic than the leaving group by 4−5 p K a units. − …”
A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.
“…The aminolysis reactions of aryl esters in solution have been studied by several groups, and there is now considerable data on the kinetics and mechanisms of these processes 1–31. Aryl esters are compounds that depending on the nature of the nucleophile, the leaving group, and other factors can react by two possible mechanisms: (i) A concerted pathway 7–14, where the nucleophile attack at the electrophilic carbon in the carbonyl group occurs simultaneously with the leaving group departure within a single step.…”
Section: Introductionmentioning
confidence: 99%
“…Aryl esters are compounds that depending on the nature of the nucleophile, the leaving group, and other factors can react by two possible mechanisms: (i) A concerted pathway 7–14, where the nucleophile attack at the electrophilic carbon in the carbonyl group occurs simultaneously with the leaving group departure within a single step. (ii) A stepwise mechanism where the interaction of the nucleophile with the electrophilic carbon may lead to the formation of a tetrahedral intermediate, T ± , from which the leaving group detaches 1–11,15–31. In these reactions, as well as in other related ones, several factors have been described as affecting the kinetics and mechanisms, such as nucleophile nature 12,13,15,16,32–34, leaving‐group ability (nucleofugality) 14–31,35–38, nonleaving‐group effect 22–24,39,40, nucleophile–electrophile interaction 41, and solvent effects 14,42–47.…”
Section: Introductionmentioning
confidence: 99%
“…Our group has systematically studied the aminolysis of aryl esters in both aqueous solution 17–21,34 and 44 wt% ethanol/water 22–24. On the contrary, other groups have been studying acylation reactions in pure organic solvents, such as acetonitrile, dimethylsulfoxide, and also in their aqueous mixtures 25,26,28–31,42–47. Based on these results, it is possible to argue that the interactions between solvent and intermediate T ± , reactants, and transition state (TS) change the reaction mechanism 25,26,28–31,34.…”
We report a kinetic study on the reactions of secondary alicyclic amines toward 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6-trinitrophenyl acetates (1, 2, and 3) in ethanol/water mixtures of different compositions. It is found that (i) the intermediate in the reaction of 1 is stabilized in a mixture of 90 vol% ethanol; (ii) for the reaction of 2, the mechanism is stepwise in water but concerted in the mixtures; (iii) For the reaction of 3, the mechanism is concerted along the whole range of composition; (iv) the effect of NO 2 outweighs the solvent effect; (v) preferential solvation in the core of reaction can be ruled out. C 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: [687][688][689][690][691][692][693] 2011
Second-order rate constants have been measured for alkaline hydrolysis of O-aryl thionobenzoates (X-C(6)H(4)-CS-OC(6)H(4)-Y) in 80 mol % H(2)O-20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Hammett plot for the reaction of O-4-nitrophenyl X-substituted thionobenzoates (X-C(6)H(4)-CS-OC(6)H(4)-NO(2), 1a-e) exhibits a downward curvature. However, a possible traditional explanation in terms of a change in the rate-determining step (RDS) has been considered but rejected. The proposed explanation involves stabilization of the ground-state (GS) through-resonance interaction between the electron-donating substituent X and the thionocarbonyl functionality on the basis of the linear Yukawa-Tsuno plot obtained for the same reaction. The Brønsted-type plot for the reaction of O-aryl thionobenzoates (C(6)H(5)-CS-OC(6)H(4)-Y, 2a-i) is linear but exhibits many scattered points with a small beta(lg) (-0.35). The Hammett plot for the same reaction shows rather poor correlation with sigma(-) constants but much better correlation with sigma(o) constants. The alkaline hydrolysis of O-aryl thionobenzoates (1a-e and 2a-i) has been proposed to proceed through an addition intermediate in which bond formation is the RDS.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
