THE OXIDATION OF L-ASCORBIC-ACID BY TRISOXALATOFERRATE(III) IN WEAKLY ACIDIC AQUEOUS-SOLUTION REVISITED - EVIDENCE FOR PARALLEL INNER-SPHERE AND OUTER-SPHERE ELECTRON-TRANSFER REACTION PATHS

The oxidation of L-ascorbic acid by trisoxalatoferrate(III) was reinvestigated as a function of pH, ascorbic acid and oxalate concentration, in terms of a multistep process that involves the formation of an intermediate ascorbate-oxalate complex. The kinetic data indicated rapid formation of the intermediate complex, followed by a slower electron-transfer process between the redox partners that occurs in two parallel reaction paths involving an inner-sphere and outer-sphere process. A direct comparison of the electron-transfer rate constants for these processes was possible following a calculation of the outer-sphere precursor formation constant. The self-exchange rate constant for the Fe(C2O4)33-/4- system was estimated to be 2.1 X 10(4) M-1 s-1 at 25-degrees-C and is discussed in reference to similar data for related systems.