Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/xmlui/handle/10054/10236
Title: Kinetics and mechanism of oxidation of ascorbic acid by cobalt(III) amino polycarboxylato complexes in weakly basic media
Authors: MAKOTE, RD
CHATTERJEE, C
Keywords: Electron-Transfer Reactions
Aqueous-Solution
Ruthenium
Iron
Issue Date: 1999
Publisher: NATL INST SCIENCE COMMUNICATION
Citation: INDIAN JOURNAL OF CHEMISTRY SECTION A-INORGANIC BIO-INORGANIC PHYSICAL THEORETICAL & ANALYTICAL CHEMISTRY, 38(8), 783-791
Abstract: The kinetics of outer-sphere oxidation of L-ascorbic acid ((H(2)A) by Co (nta)(gly)(-), Co(nta)(ox)(2-) and Co(nta)(pic)(-) complexes have been investigated in weakly basic aqueous media (pH = 7.6 to 9.6) at 30-46 degrees C. The pseudo-first order rate constant, k(obs) shows first order dependence on ascorbic acid concentration, and increases rapidly with decrease in hydrogen ion concentration. The experimental data fits the rate law. -d[complex]/dt = 2{(k(1)K(1) [H+] + k(2)K(1)K(2))/(K-1[H+] + K1K2 + [H+]2)}[complex] [H(2)A](tot). The observed inverse acid dependence suggests a mechanism involving HA(-) and A(2-) pathways, for which the specific rate and activation parameters have been determined. Comparison of second order rate constants reveals that the A(2-) is at least 10(3) times more reactive than HA(-) in the case of all the complexes used for the study. The higher redox reactivity is accompanied by a lowering of enthalpy of activation. The reactivity of metal complexes is greatly influenced by the ligand field effect of the coordinated groups and the presence of pi-acceptor ligand provides a low energy pathway for electron transfer from a pi-donor ascorbate anion leading to rate enhancement. Reduction potentials for the metal complexes have been estimated with the help of Marcus equation.
URI: http://dspace.library.iitb.ac.in/xmlui/handle/10054/10236
http://hdl.handle.net/10054/10236
ISSN: 0376-4710
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