A Kinetic Study on Aminolysis of 2-Pyridyl X-Substituted Benzoates: Effect of Changing Leaving Group from 4-Nitrophenolate to 2-Pyridinolate on Reactivity and Mechanism

Abstract

Second-order rate constants (kN) have been measured spectrophotometrically for nucleophilic substitution reactions of 2-pyridyl X-substituted benzoates 8a-e with a series of alicyclic secondary amines in H2O at 25.0 ± 0.1 o C. The kN values for the reactions of 8a-e are slightly smaller than the corresponding reactions of 4-nitrophenyl X-substituted benzoates 1a-e (e.g., kN 8a-e T

Theoretical investigation of nucleophilic substitution reaction of phenyl carbonyl isothiocyanates with pyridines in gas and polar aprotic solvent

“…Note that the Marcus equation probably cannot be applied to the intermediate state, (I) because the reaction energy for the RC -Ix 2 is as large as the energy barrier (DE a -DE 0 ) in the gas phase (24.90 kcal mol À1 ). The intrinsic barrier hindering the reorganization of leaving group departure and phenoxy nonleaving group reorganization, can be obtained from eqn (8) with DE 0 (for only TS, (I-x 3 )) equals to À21.18 kcal mol À1 (Table 4). This gives an alternative intrinsic Marcus activation barrier of DE 0 a = 11.96 kcal mol À1 .…”

“…Experimental information on nucleophilic substitution in carbonyl, sulphonyl and phosphoryl systems is abundantly available in the current literature survey. For example, Lee et al [1][2][3][4] report a substantial contribution in the understanding of reactions of benzyl chlorides with phenoxides, while Tjuno, 5 Castro 6,7 and Um 8,9 are worth noting with respect to their investigations on nucleophilic substitution reactions involving diethyl 4-nitrophenyl phosphate triesters. By contrast, direct theoretical investigations of Hammett reaction parameters are rather scarce, often due to data inconsistencies.…”

“…These phenomena help to characterize the qualitative nature of the reaction and the activation energies. For insight into the nature of the TS, the DE ‡ can be rationalized in terms of the Marcus equation, 25 see eqn (8):…”