Non-Heme
Manganese Catalysts for On-Demand Production
of Chlorine Dioxide in Water and Under Mild Conditions
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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 Mn<sup>III</sup>(OH) species as the dominant form
under catalytic conditions. A Mn<sup>III</sup>(μ-O)Mn<sup>IV</sup> dinuclear species was observed by EPR spectroscopy, supporting the
involvement of a putative Mn<sup>IV</sup>(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 Mn<sup>IV</sup>(O), which undergoes PCET (proton coupled
electron-transfer) reaction with chlorite to afford chlorine dioxide.
The ClO<sub>2</sub> 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