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Publication Type
Journal Article
Author, Analytic
Abdur-Rashid, Kamaluddin; Dasgupta, Tara, P.; Burgess, John
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Article Title
Kinetics of oxidation of ascorbate by tetranuclear cobalt (III) complexes ('hexols') in aqueous solution
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Journal Title
Journal of the Chemical Society. Dalton Transactions
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Reprint Status
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Date of Publication
1996
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Issue ID
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Page(s)
1393-1398
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Notes
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Abstract
The kinetics of oxidation of L-ascorbic acid (H2A) by cobalt (III) hexols, [Co{CoL4(m -OH)2}3]6+ [L4 = (NH3)4, (en)2, or tren ; en = ethane-1,2-diamine, tren = tris(2-amionethyl)amine], was studied as a function of pH, L-ascorbic acid concentration, temperature and ionic strength, using stopped-flow and conventional spectrophotometric techniques. The rate of the reaction is first order with respect to the concentration of each reactant and increases as [H+] decreases. The kinetic data indicate involvement of the monoprotonated and depronated ascorbate species (HA - and A2-) in the redox process. For L4 = (NH3)4 the rate constants, k2 amd k3 are 0.22 0.02 and (5.51 0.09) x 105 dm3 mol-1 s-1 respectively at 25 C, and the corresponding activation parameters are D H2 = 103 7 kJ mol-1, D S2 = 89 22 J K-1 mol-1 and D H3 = 46 3 kJ mol-1 and DS3 =19 11 J K-1 mol-1. Variations in rate constants and activation parameters for the series of complexes mentioned above are discussed. The Fuoss theory was applied to the redox process to estimate the ion-pair formation constant and the rate constant for the electron transfer....
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