Thermodynamics and kinetics of proton-transfer reactions between bromophenol blue and aliphatic amines in chlorobenzene solution

Abstract

Values of K₂₉₈, ΔH°₂₉₈, ΔS°₂₉₈, k_f, and k_b have been determined for the proton-transfer reaction between bromophenol blue and mono-, di-, and tri-n-butylamine, trimethylamine, triethylamine, tri-n-propylamine, and tri-n-octylamine. Kinetic data were obtained by a microwave temperature-jump apparatus. Both kinetic and thermodynamic data show that three effects determine the magnitude of K₂₉₈: (i) the inductive effect; (ii) the steric effect on the approach of the reagents; (iii) the steric strain on the complex. The third effect is strong enough to cause values of K₂₉₈ for the mono-, di- and tri-n-butylamine series to be in the reverse order to that predicted by the inductive effect.