Effects of mixed H2O ? CH3CN solvents on the Brønsted coefficient for the intramolecular general base‐catalyzed cleavage of ionized phenyl salicylate in the presence of primary and secondary amines

摘要: Nucleophilic second-order rate constants, knms, for the reactions of several primary and secondary amines with ionized phenyl salicylate (PS−) show a nonlinear decrease increase in content CH3CN from 2 to ≤50% v/v mixed aqueous solvent. The values knms remain almost unchanged change at >50% v/v. nucleophilic reactivity toward PS− reveal Bronsted plots different coefficients, βnuc, constant solvents. βnuc 0.4 nearly 0 0.22 0.12 70% knms/kMeOHms (where kMeOHms represents reaction MeOH H2OCH3CN solvents), obtained within 2–50%v/v CH3CN, fit an empirical equation: log (knms/kMeOHms) = θ + λX where X is % λ are constants. It has been shown empirically that both function coefficient βlg. used calculate βlg these all except Tris lie −0.32 −0.46. effects water–acetonitrile solvents on pKa leaving group, phenol, conjugate acid amine nucleophile have concluded be major source observed solvent knms. unusually very close zero. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 153–164,