A Cyclic Voltammetric Study of the Proton Abstraction from Selected Aromatic Ketones by Superoxide
The proton-abstraction by O2√− from weakly acidic compounds, like aliphatic ketones (with pKas≈21), is endothermic and consequently slow. In this work, by employing selected aromatic ketones as proton donors (with pKas≈19), it has been possible to accelerate the rate of the α-proton abstraction by O2√− to the point that it is observable within the time scale of cyclic voltammetry. Digital simulations of the cyclic voltammograms of O2 in the presence of those ketones allow determination of the rate constants of the proton abstraction. Those rate constants were found to increase as the degree of conjugation in ketones increased, consistent with a slow endothermic rate determining step. Furthermore, because ketones as proton donors are very weak acids, it was possible to avoid any subsequent acid-base type of reaction between HO2− and the ketones, and to observe a new, kinetically reversible redox wave at E1/2=0.34 V versus O2/O2√− in DMSO, assigned to the HO2√/HO2− redox couple.
C. M. Collins et al., "A Cyclic Voltammetric Study of the Proton Abstraction from Selected Aromatic Ketones by Superoxide," Electrochimica Acta, Elsevier, Mar 2000.
The definitive version is available at http://dx.doi.org/10.1016/S0013-4686(99)00425-9
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