The Role of Carbonate in Catalytic Oxidations

Shanti Gopal Patra; Amir Mizrahi; Dan Meyerstein

doi:10.1021/acs.accounts.0c00344

The Role of Carbonate in Catalytic Oxidations

Acc Chem Res. 2020 Oct 20;53(10):2189-2200. doi: 10.1021/acs.accounts.0c00344. Epub 2020 Sep 25.

Authors

Shanti Gopal Patra¹, Amir Mizrahi², Dan Meyerstein^{1

3}

Affiliations

¹ Department of Chemical Sciences, The Center for Radical Reactions and the Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications, Ariel University, Ramat HaGolan Street, Ariel 40700, Israel.
² Department of Chemistry, Nuclear Research Centre Negev, Beer-Sheva 84190, Israel.
³ Department of Chemistry, Ben-Gurion University, Beer-Sheva 8410501, Israel.

Abstract

CO₂, HCO₃^-, and CO₃^2- are present in all aqueous media at pH > 4 if no major effort is made to remove them. Usually the presence of CO₂/HCO₃^-/CO₃^2- is either forgotten or considered only as a buffer or proton transfer catalyst. Results obtained in the last decades point out that carbonates are key participants in a variety of oxidation processes. This was first attributed to the formation of carbonate anion radicals via the reaction OH^• + CO₃^2- → CO₃^•- + OH^-. However, recent studies point out that the involvement of carbonates in oxidation processes is more fundamental. Thus, the presence of HCO₃^-/CO₃^2- changes the mechanisms of Fenton and Fenton-like reactions to yield CO₃^•- directly even at very low HCO₃^-/CO₃^2- concentrations. CO₃^•- is a considerably weaker oxidizing agent than the hydroxyl radical and therefore a considerably more selective oxidizing agent. This requires reconsideration of the sources of oxidative stress in biological systems and might explain the selective damage induced during oxidative stress. The lower oxidation potential of CO₃^•- probably also explains why not all pollutants are eliminated in many advanced oxidation technologies and requires rethinking of the optimal choice of the technologies applied. The role of percarbonate in Fenton-like processes and in advanced oxidation processes is discussed and has to be re-evaluated. Carbonate as a ligand stabilizes transition metal complexes in uncommon high oxidation states. These high-valent complexes are intermediates in electrochemical water oxidation processes that are of importance in the development of new water splitting technologies. HCO₃^- and CO₃^2- are also very good hole scavengers in photochemical processes of semiconductors and may thus become key participants in the development of new processes for solar energy conversion. In this Account, an attempt to correlate these observations with the properties of carbonates is made. Clearly, further studies are essential to fully uncover the potential of HCO₃^-/CO₃^2- in desired oxidation processes.

Publication types

Research Support, Non-U.S. Gov't