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

摘要

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 σ~0 constants. Low magnitude of ρ_(LG) values indicate that the leaving group departure occurs after the rate-determining step. The Bronsted 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 (AΔG~≠), 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.