Mechanistic Study of the Reactions of l-ascorbic Acid and Oxalic Acid with an Octahedral Manganese(IV) Complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane |
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Authors: | Suprava Nayak Anadi C. Dash |
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Affiliation: | (1) Department of Chemistry, Utkal University, Bhubaneswar, 751 004, India |
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Abstract: | The MnIV complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane (MnIVL) with phenolate-amido-amine coordination is reduced by l-ascorbic acid and oxalic acid obeying overall 1:1 stoichiometry. The reactions are biphasic and MnIIIL− is the reactive intermediate. The product of oxidation of ascorbic acid (H2Asc) is dehydroascorbic acid and that of oxalic acid (H2OX) is CO2, while MnII is the end product from MnIV. Both MnIVL and MnIIIL− form outer sphere adducts with H2Asc and H2OX with high values of equilibrium constants of formation (Q>102 dm3 mol−1, I = 0.5 mol dm−3, 25.8 °C, 1.5% v/v MeOH+H2O). The adduct formation is diffusion controlled and is attributed to hydrogen bonding interactions between the reactants. The rate constants for the electron transfer in (MnIV/IIIL, H2A), (MnIV/IIIL, HA−) (H2A = H2Asc, H2OX) and for (MnIVL, H2Asc)+H2Asc, (MnIIIL−, HAsc−)+HAsc− are reported. There was no evidence of direct coordination of the reductants to the MnIV/III center indicating an outer sphere (ET) mechanism. |
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