Temperature effect on the steric and polar Taft substituent parameter values

Abstract

The concept of linear free-energy relationships (LFER) is applied in different fields of chemistry, such as toxicology or kinetics. The knowledge of reactivity from the reactant structure can aid biomass valorization processes by decreasing the number of experiments to carry out in the kinetic modeling stage. The Taft equation, based on LFER, represents a link between the kinetics and the structure of the species involved in the reaction, by quantifying polar, steric and resonance effects, also known as Taft substituent parameters. This equation was used in different reaction systems in different studies, but none considered the influence of temperature on the steric and polar Taft substituent parameters. In this work, we investigated this aspect by re-evaluating the substituent parameters of the Taft equation applied to the esterification of levulinic acid by methanol and ethanol, and the saponification of methyl and ethyl levulinates. Levulinic acid was chosen because it is a promising platform molecule. We found that the Taft substituent parameters are relatively sensitive to temperature and vary linearly within the same temperature range, the steric effect decreases by almost half while the polar effect grows less significantly.