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

Abstract

The Mn IV complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane (Mn IV L) with phenolate-amido-amine coordination is reduced by L-ascorbic acid and oxalic acid obeying overall 1:1 stoichiometry. The reactions are biphasic and Mn III L ) is the reactive intermediate. The product of oxidation of ascorbic acid (H 2 Asc) is dehydroascorbic acid and that of oxalic acid (H 2 OX) is CO 2 , while Mn II is the end product from Mn IV . Both Mn IV L and Mn III L ) form outer sphere adducts with H 2 Asc and H 2 OX with high values of equilibrium constants of formation (Q>10 2 dm 3 mol )1 , I=0.5 mol dm )3 , 25.8°C, 1.5% v/v MeOH+H 2 O). The adduct formation is diffusion controlled and is attributed to hydrogen bonding interactions between the reactants.

Ligand substitution and electron transfer reactions of trans-(diaqua)(salen)manganese(iii) with oxalate: an experimental and computational study

“…The oxidation of oxalate by Mn III and its complexes including Mn III OX + is known to generate the oxalate radical, C 2 O 4 À c which decomposes in a fast step to yield the radical CO 2 À c and CO 2 . 18,23 Recently the computer simulation of the complex oxalic acid permanganate reaction which involve the oxalate complexes of Mn III unearthed the less known crucial role of the radical CO 2 À c. 24 The dimerisation of CO 2 À c is also fast and regenerates oxalate. If this is a major step of the loss of C 2 O 4 À c then the overall stoichiometry of the reaction of Mn III complex with OX 2À /HOX À /H 2 OX will be 1 : 1.…”

Oxalate production via oxidation of ascorbate rather than reduction of carbon dioxide

“…Interestingly, oxidation of ascorbic acid by transition metal compounds, especially those of copper, has been well-known for more than a century 17 , 18 . Since then, the reaction mechanisms for such oxidations have been intensely studied 18 – 22 . More specifically, oxidative degradation of ascorbic acid by (a) inorganic oxidants (sodium periodate 23 , sodium hypoiodite 24 ); (b) oxygen 25 , 26 ; and (c) O 2 in the presence of Gd 27 , 28 , Co 27 , Pd 29 , Pt 29 , Cd 30 , Fe 31 , or Cu 32 compounds is reported to yield oxalate as a degradation product (see Supplementary Fig.…”