Abstract
Ascorbic acid was utilized as a source of reducing equivalents in a multicomponent system that promotes the photoreduction of water. A summary of information on the redox characteristics of the various species generated in the oxidation of ascorbate in water is presented. Structures are given for ascorbic acid, ascorbate ion (HA/sup -/), dehydroascorbic acid, protonated ascorbate radical, and ascorbate radical. Data relevant to protonation equilibria, thermodynamic aspects, and reduction potentials are given as well as studies on the kinetics and stoichiometry of ascorbate oxidation reactions. The results of these studies illustrate some of the complexities of ascorbate as a reductant. Depending upon the pH and the propertes of the oxidant, H/sub 2/A, HA/sup -/, and/or A/sup 2 -/ may be the kinetically significant reducing agent(s). There is a discussion of the reactivities of the ascorbate radical/ascorbate couples toward outer-sphere redox reactions in terms of the driving force for the electron-transfer reaction and the intrinsic electron-transfer barrier associated with each of the reactants; and there is a brief discussion of the kinetics of the reduction of dehydroascorbic acid. (MWF)
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