Ghosh, Debjani ; Shukla, Atindra D. ; Banerjee, Rupendranath ; Das, Amitava (2002) Kinetics of oxidation of ascorbic acid and 1,4-dihydroxybenzene by semiquinone radical bound to ruthenium(II) Journal of the Chemical Society Dalton Transactions, 2002 (6). pp. 1220-1225. ISSN 1472-7773
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Official URL: http://pubs.rsc.org/en/content/articlelanding/2002...
Related URL: http://dx.doi.org/10.1039/B104585G
Abstract
In 40% (v/v) MeOH-H2O media, containing [H+] (0.001-0.038 mol dm-3), the semiquinone (sq) radical, bound to Ru(II) in [Ru(bpy)2(sq)]+1, oxidises ascorbic acid (H2A) to dehydroascorbic acid (A), and 1,4-dihydroxybenzene (H2Q) to p-benzoquinone (Q); 1 is itself reduced to [Ru(bpy)2(Hcat)]+2H. The reactions are centred at sq not Ru(II). The sq/cat couple in 1 is reversible and its E1/2 increases with increasing [H+]; rate of chemical reduction of 1 to 2H increases in parallel. Rate increases also with increasing mole percent of D2O in the solvent suggesting a preliminary protonation equilibrium producing 1H, in which a H+ binds to the π-electron cloud of Ru(II)-bound sq. Under the experimental conditions, the kinetically significant species are 1H, H2Q, H2A and HA-. The kinetic activity of HA- ion is only ≈200 times more than that of H2A. This testifies against a purely outer-sphere mechanism and suggests significant electronic interaction between the redox partners. Increased percentage of MeOH in the solvent decreases λmax for the LMCT band; reaction rate for ascorbic acid decreases in parallel.
Item Type: | Article |
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Source: | Copyright of this article belongs to Royal Society of Chemistry. |
ID Code: | 59961 |
Deposited On: | 08 Sep 2011 10:19 |
Last Modified: | 06 Jan 2012 08:48 |
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