Article
Non-Heme Manganese Catalysts for On-Demand Production of Chlorine Dioxide in Water and Under Mild Conditions
† Brown Laboratory, Negishi Brown Institute, and Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
‡ Department of Bioinspired Science, Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea
§ School of Chemical Engineering, Purdue University, Forney Hall of Chemical Engineering, 480 Stadium Mall Drive, West Lafayette, Indiana 47907, United States
J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja5001642
Publication Date (Web): February 5, 2014
Copyright © 2014 American Chemical Society
Abstract
Two non-heme manganese complexes are used in the catalytic formation of chlorine dioxide from chlorite under ambient temperature at pH 5.00. The catalysts afford up to 1000 turnovers per hour and remain highly active in subsequent additions of chlorite. Kinetic and spectroscopic studies revealed a MnIII(OH) species as the dominant form under catalytic conditions. A MnIII(μ-O)MnIV dinuclear species was observed by EPR spectroscopy, supporting the involvement of a putative MnIV(O) species. First-order kinetic dependence on the manganese catalyst precludes the dinuclear species as the active form of the catalyst. Quantitative kinetic modeling enabled the deduction of a mechanism that accounts for all experimental observations. The chlorine dioxide producing cycle involves formation of a putative MnIV(O), which undergoes PCET (proton coupled electron-transfer) reaction with chlorite to afford chlorine dioxide. The ClO2 product can be efficiently removed from the aqueous reaction mixture via purging with an inert gas, allowing for the preparation of pure chlorine dioxide for on-site use and further production of chlorine dioxide.
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