The kinetics of the copper(II)-catalysed oxidation of ascorbic acid by molecular oxygen have been investigated in the range pH 1.80-5.00 using 0.100 mol dm-3 KCl as background electrolyte. The reaction was followed both by continuous measurement of oxygen consumption (using a Clark-type oxygen-sensitive electrode) and by direct spectrophotometric measurement (on samples) of the unchanged ascorbic acid. At constant [H+] the rate law conforms to (i) where [L]T is the total concentration of ascorbic acid and [Cu]T is the total concentration -d[L]T/dt = -d[O2]/dt = k[Cu]T[L]T1/2[O2]1/2 (i) of CuII. On the basis of this, and on thermodynamic evidence, a chain mechanism is proposed in which a copper-copper binuclear species (containing both ascorbate and chloride ligands) is the reactive species. The dependence on [H+] is too complex, however, to be fully explained. Both one- and two-electron transfer mechanisms are discussed and preference is shown for that involving an initial two-electron transfer to the dioxygen and consequently to the participation of what is formally CuIII.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|State||Published - 1976|
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