The E1cb route for ester hydrolysis; volumes of activation as an additional criterion of mechanism
作者:Neil S. Isaacs、Tariq S. Najem
DOI:10.1039/p29880000557
日期:——
of esters which possess an acidic proton at the α or vinylogous position can, in principle, hydrolyse by the E1cb route via a ketenoid intermediate. To the kinetic evidence for such a mechanism in the hydrolyses of 4-hydroxybenzoates, malonates, acetoacetates and fluorenecarboxylates is now added the further criterion of volumes of activation. Values of ΔV‡ for reactions proceeding by the E1cb route
Aminolysis of 2,4-Dinitrophenyl X-Substituted Benzoates and Y-Substituted Phenyl Benzoates in MeCN: Effect of the Reaction Medium on Rate and Mechanism
作者:Ik-Hwan Um、Sang-Eun Jeon、Jin-Ah Seok
DOI:10.1002/chem.200500647
日期:2006.1.23
indicating that the electronic nature of the substituent X in the nonleaving group does not affect the rate-determining step (RDS) or reactionmechanism. The Hammett correlation with sigma- constants also exhibits good linearity with a large slope (rho(Y) = 3.54) for the reactions of 2 a-h with piperidine, implying that the leaving-group departure occurs at the rate-determining step. Aminolysis of 2,4-dinitrophenyl
Nonlinear Hammett plots in pyridinolysis of 2,4-dinitrophenyl X-substituted benzoates: change in RDS versus resonance contribution
作者:Ik-Hwan Um、Li-Ra Im、Eun-Hee Kim、Ji Hye Shin
DOI:10.1039/c0ob00031k
日期:——
Second-order rate constants (kOH–) have been measured for nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzoates (1a–j) with Z-substituted pyridines in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The Hammett plots for the reactions of 1a–j with pyridines consist of two intersecting straight lines, i.e., a large ρ value for the reactions of substrates (1a–c) possessing an electron-donating
Hydrolysis of 1-(X-substituted-benzoyl)-4-aminopyridinium ions: effect of substituent X on reactivity and reaction mechanism
作者:Ik-Hwan Um、Eun-Hee Kim、Ji-Sun Kang
DOI:10.1039/c1ob06137b
日期:——
A kinetic study is reported for hydrolysis of 1-(X-substituted-benzoyl)-4-aminopyridinium ions 2a–i, which were generated in situ from the nucleophilic substitution reaction of 2,4-dinitrophenyl X-substituted-benzoates 1a–i with 4-aminopyridine in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The plots of pseudo-first-order rate constants kobsdvs.pyridine concentration are linear with a large positive
Activation volumes for ester hydrolysis via elimination–addition
作者:Neil S. Isaacs、Tariq S. Najem
DOI:10.1139/v86-190
日期:1986.6.1
leaving group may undergo hydrolysis by elimination to an intermediate ketene, which rapidly hydrates. Examples are found in p-hydroxybenzoate, malonate, and acetoacetate esters of nitrophenols. The evidence for this mechanism (E1cb type) includes the independence of rate with pH in the region of dissociation of the acidic proton and, in particular, positive volumes of activation that contrast sharply