Thermodynamics of the interactions of catechol with transition metals. Part I. Free energy, enthalpy, and entropy changes for the ionisation of catechol at 25 °C. Comparison of the temperature-coefficient method with direct calorimetry

Abstract

A detailed potentiometric and calorimetric study of the first proton ionisation of catechol has been made. Dissociation constants for the ionisation were determined in the temperature range 15–45 °C, and the range of ionic strength 0·060–0·180M, with KNO₃ as ionic background. Thermodynamic quantities have been calculated and values of ΔH for the ionisation have been determined both by the temperature-coefficient method and also by direct calorimetry. The results were in good agreement. An approximate value of ΔH for the second proton ionisation has also been determined by potentiometry.