Outer-sphere electron-transfer reactions of ascorbate anions

Abstract

Rate constants for the one-electron oxidation of ascorbate dianion (A^2-) by bis(terpyridine)cobalt(III)ion (8.5 × 10⁶ dm³ mol^-1 s^-1) and pentaammine(pyridine)ruthenium(III) ion (6.0 × 10⁹ dm³ mol^-1 s^-1), and of the monoanion (HA^-) by tetraammine (bipyridine)ruthenium(III)ion (2.1 × 10⁵ dm³ mol^-1s^-1) have been determined in aqueous solution at 25ºC and ionic strength 0.1 (NaNO₃ or NaClO₄). It is shown that these rate constants, and other published rate constants for oxidation of HA^- and A^2-, are consistent with the Marcus cross relation, on the assumption that the self-exchange rate constants for both the HA^-/HA and A^2-/A^-couples are 10⁶ dm³ mol^-1 s^-1. One electron redox potentials for the ascorbate/dehydroascorbate system have been derived from scattered literature data.