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Reactions of 4‐nitrophenyl 2‐furoates (1a–e) with R2NH/R2NH2+ in 20 mol% DMSO(aq) have been studied. The reactions produced aminolysis products and exhibited second‐order kinetics. The Brönsted plots were linear with βnuc values of 0.75–0.89, which remained nearly the same for all 5‐furyl substituents. The rate data showed excellent correlations on the Yukawa‐Tsuno plots with ρ(x) = 0.72–1.1, and r = 0.55–0.95, respectively. The ρ 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 contribution. The results have been interpreted with the addition–elimination mechanism in which the second step is the rds. By comparing with the data for ArC(O)OC6H4‐4‐NO2 (Ar = Ph, thienyl), the effect of the aryl group on the acyl transfer reaction was assessed. [ABSTRACT FROM AUTHOR]

Reactions of 2,4‐dinitrophenyl 2‐thiophenecarboxylate (2a–d) with R2NH/R2NH2+ in 20 mol % DMSO(aq) have been studied. The reactions are overall second order, first order to the substrates, and first order to the nucleophiles. The Brönsted plots showed downward curves with pKa0 = 9.5, β1 = 0.22–0.34, and β2 = 0.85–0.92. The k1 values increased with a stronger electron‐withdrawing 5‐thienyl substituent and a stronger nucleophile, whereas the k2/k−1 values remained nearly the same for all 5‐thienyl substituents. The influence of 5‐thienyl substituent on the reaction rates showed excellent correlations on the Yukawa‐Tsuno plots with ρ = 1.28–2.16 and r = 0.20–0.60. The ρ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the carbonyl carbon and a decrease in the resonance demand. From these results, a stepwise mechanism with a change in the rate‐determining step has been proposed. [ABSTRACT FROM AUTHOR]