TY - JOUR
T1 - Role of copper dimers and the participation of copper(III) in the copper-catalysed autoxidation of ascorbic acid. Part III. Kinetics and mechanism in 0.100 mol dm-3 potassium chloride
AU - Jameson, Reginald F.
AU - Blackburn, Ninian J.
PY - 1976
Y1 - 1976
N2 - 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.
AB - 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.
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U2 - 10.1039/DT9760001596
DO - 10.1039/DT9760001596
M3 - Article
AN - SCOPUS:37049108074
SN - 1472-7773
SP - 1596
EP - 1602
JO - Journal of the Chemical Society, Dalton Transactions
JF - Journal of the Chemical Society, Dalton Transactions
IS - 16
ER -