Reactions of 4-Nitrophenyl 2-Thiophenecarboxylates with R₂NH/R₂NH₂⁺ in 20 mol % DMSO (aq). Effects of 5-Thienyl Substituent and Base Strength

Reactions of 4-Nitrophenyl 2-Thiophenecarboxylates with R₂NH/R₂NH₂⁺ in 20 mol % DMSO (aq). Effects of 5-Thienyl Substituent and Base Strength

Reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a-e) with $R_2NH/R_2NH{_2}^+$ in 20 mol % DMSO (aq) have been studied kinetically. The $2^{nd}$ order kinetics, ${\beta}_{nuc}$ = 0.88-0.98, and linear Hammett and Yukawa-Tsuno plots observed for these reactions indicate an addition-elimination mechanism in which the $2^{nd}$ step is rate limiting. The ${\beta}_{nuc}$ value increased with a stronger electron-withdrawing 5-thienyl substituent, the Hammett plots are linear except for X = MeO, and Yukawa-Tsuno plots are linear with ${\rho}$ = 0.79-1.32 and r = 0.28-0.93, respectively. The ${\rho}$ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C=O bond and a decrease in the resonance demand. These results have been interpreted with enhanced N-C bond formation in the transition state with the reactivity increase.