Theoretical analysis of naproxen reaction with sulfate and hydroxyl radicals in the aqueous phase: Investigating reactive sites and reaction kinetics

Abstract

In this study, we have utilized theoretical calculations to predict the reaction active sites of naproxen when reacting with radicals and to further study the thermodynamics and kinetics of the reactions with ·OH and SO4−·. The evidence, derived from the average local ionization energy and electrostatic potential, points to the naphthalene ring as the preferred site of attack, especially for the C2, C6, C9, and C10 sites. The changes in Gibbs free energy and enthalpy of the reactions initiated by ·OH and SO4−· ranged between −19.6 kcal/mol - 26.3 kcal/mol and −22.3 kcal/mol −18.5 kcal/mol, respectively. More in-depth investigation revealed that RA2 pathway for ·OH exhibited the lowest free energy of activation, suggesting this reaction is more inclined to proceed. The second-order rate constant results indicate the ·OH attacking reaction is faster than reactions initiated by SO4·-, yet controlled by diffusion. The consistency between theoretical findings and experimental data underscores the validity of this computational method for our study.