title: Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.
abstract: The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology , 800 West Peachtree Street, Suite 400 F-H, Atlanta, Georgia 30332-0595, United States. Daisuke.Minakata@gatech.edu
authors.forename: Daisuke
authors.initials: D
authors.lastname: Minakata
authors.forename: John
authors.initials: J
authors.lastname: Crittenden
mesh_terms: D017665:Hydroxyl Radical / Q000737:chemistry*; D007700:Kinetics; D008697:Methane / Q000737:chemistry; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; D008697:Methane