A Kinetic Study on Nucleophilic Displacement Reactions of Aryl Benzenesulfonates with Potassium Ethoxide: Role of K+ Ion and Reaction Mechanism Deduced from Analyses of LFERs and Activation Parameters

摘要: Pseudofirst-order rate constants (kobsd) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a–f and Y-substituted phenyl 5a–k with EtOK in anhydrous ethanol. Dissection kobsd into kEtO– kEtOK (i.e., second-order dissociated EtO– ion-paired EtOK, respectively) shows that is more reactive than EtO–, indicating K+ ion catalyzes reaction. The catalytic effect exerted by (e.g., kEtOK/kEtO– ratio) decreases linearly as substituent X benzenesulfonyl moiety changes from an electron-donating group (EDG) to electron-withdrawing (EWG), but it independent electronic nature Y leaving group. concluded proceed through a concerted mechanism analyses kinetic data linear free energy relationships th...