Transesterification Kinetics Investigation of R‐Substituted Phenyl Benzoates with 4‐Methoxyphenol in the Presence of K₂CO₃ in DMF

Abstract

Transesterification of R‐substituted phenyl benzoates 1–5 with 4‐methoxyphenol 6 was kinetically investigated in the presence of K2CO3 in dimethylformamide (DMF) at various temperatures. The Hammett plots for the reactions of the 1–5 demonstrate good linear correlations with σ0 constants. Low magnitude of ρLG values indicate that the leaving group departure occurs after the rate‐determining step. The Brønsted coefficient values for the reactions (−0.2, −0.16, −0.13 at 15, 24, 36°C, respectively) demonstrate the weak effect of leaving group substituent on the reactivity of R‐substituted phenyl benzoates 1–5 for the reactions with 4‐methoxyphenol 6 in the presence of K2CO3 in DMF. The leaving group substituent effect on free energy (ΔG≠), enthalpy (ΔH≠), and entropy (ΔS≠) of activation was examined. It was shown that the activation parameters obtained depend weakly on the leaving group substituent effect. The reaction is entropy controlled in case the leaving group substituent becomes electron withdrawing.

Reactions of Aryl Benzoates with Potassium Aryloxides: Solvent Effects on Reaction Pathway and Kinetics

“…The reactions of carboxylic esters with anionic nucleophiles in solution still remain the subject of extensive studies although it has already been obtained a considerable body of data on the kinetics and mechanisms of those processes . Two distinct mechanisms are mainly discussed for these reactions in water, alcohol, and aqueous mixtures of organic solvents: concerted A N D N (the nucleophilic attack at a carbonyl center occurs concertedly with the leaving group departure) and stepwise A N +D N (the reaction occurs through a tetrahedral intermediate) .…”