Theoretical Studies of Oxidation of Organic Compounds by Ferrate(VI) and Ferrate(V)

This project is focused on theoretical studies of the oxidation of various organic substrates by ferrate(VI), FeO42- and ferrate(V), FeO43-. These species are very strong oxidants that can oxidize a variety of organic substrates and the mechanisms of these oxidation reactions are of fundamental interest. Ferrate(VI) has been used as an environmentally friendly oxidant for water treatment because it can be readily prepared and it gives nontoxic Fe(III) product. Nature also makes use of a number of heme and non-heme enzymes such as cytochrome P-450 and methane monooxygenase to perform various oxidation reactions via high-valent iron oxo intermediates. The kinetics and mechanisms of the oxidation of various organic substrates by ferrate(VI) have been extensively studied but in some cases contradicting mechanisms were proposed. The theoretical aspects on the oxidations of organic compounds by ferrate species are largely unexplored. In this project, we plan to study the oxidation of alkanes, aliphatic amines, anilines, phenols and organosulfur compounds by ferrate(VI) and ferrate(V) using density functional theory and polarization continuum model methods. We explore the potential energy surfaces of these reactions and evaluate the activation barrier of rate-determining step. In general, there are several possible pathways for the oxidation of an organic compound by a metal oxo species: (a) 1etransfer, (b) H-atom transfer/proton-coupled 1e- transfer, (c) hydride transfer/protoncoupled 2e- transfer (d) O-atom transfer. Depending on the pH, the ferrate(VI) species can exist in various protonated forms: H3FeO4+, H2FeO4, HFeO4- and FeO42-. Thus, we investigate the reaction mechanisms for each possible pathway by ferrate(VI) species and its protonated forms. In particular, we examine the spin/electron density from reactants to transition state structure to products in order to elucidate the detailed mechanisms. The 1e- reduction of FeO42- by various substrates would generate FeO43-, which is known to be a stronger oxidant and would react faster than FeO42-. However, very few kinetic information on oxidation by ferrate(V) species is known. Hence, we also perform theoretical calculations on oxidation by FeO43- and its protonated forms. The predicted mechanisms and activation barriers will be correlated with the experimental results from the literature. Additional experimental studies, including deuterium isotope effects and 18O-labeling experiments, will be performed by Co-I’s team in order to clarify the mechanisms. Our proposed work should provide valuable insights into the detailed mechanisms of oxidation of organic functional groups by ferrate(V) and ferrate(VI). It makes an important contribution to the reactivity of iron oxo species in general.