Holder, Alvin A.,; Dasgupta, Tara P.,; Im, Sang-Choul
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Mechanism of the oxidation of L-ascorbic acid by the molybdatopentaaminecobalt(III) in aqueous solution
Transition Metal Chemistry
Date of Publication
A detailed investigation of the oxidation L-ascorbic acid by the title complex has been carried out using the stopped-flow technique over the ranges, 0.01 £ [ascorbate]T £ 0.10 mol dm-3, 6.96 £ pH £ 9.05 and 19.6 £ 0 £ 30.1 °C, 0.25 £ I £ 1.00 mol dm-3 and at ionic strength 1.0 mol dm-3 (NaNO3). The main products of the reaction are cobalt (II), molybdate (VI), and L-dehydroascrobic acid. The rate of the reaction is dependent on pH and the total ascorbate concentration in a complex manner, i.e. kobs = (k1K1K2+k2K1[H+]) [ascorbate]Tl K1K2+K1[H+]+[H+]2). The second order rate constants at 24.9°C are k1 = 16 ± 3 dm3 mol-1 s-1 and K2= (11.30 l 0.03) x 10-2 dm3 mol-1 s-1 DH1‡ =29 ± 7 kJ mol-1 DH2‡ = 99 ± 9 kJ mol-1, DS1‡ = -124 ± 30J mol-1 K-1, and DS2‡ = 67 ± 35J mol-1 K-1 An outer-sphere electron transfer mechanism has been proposed. The result are compared with the literature data for the oxidation by a series of other oxidants. ....