Oxalic acid, photocatalytic oxidations

Photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated (Sun and Pignatello, 1995). In addition to the dominant hydroxyl radical mechanism, Sun and Pignatello found evidence that direct hole oxidation may be the mechanism for the photocatalytic degradation of some organic compounds. The assumed mechanism for this oxidation is H+ acting as an electron-transfer oxidant, while O behaves like a free OH and abstracts H or adds to C=C multiple bonds. Hole oxidation has been used to explain the oxidation of oxalate and trichloroacetate ions, which lack abstractable hydrogens or unsaturated C-C bonds. Whether the reaction... 

Mendive, C.B., D.W. Bahnemann and M.A. Blesa (2005). Microscopic characterization of the photocatalytic oxidation of oxalic acid adsorbed onto Ti02 by FTIR-ATR. Catalysis Today, 101(3 1), 237-244. 

Recently, Imamura et al. (2011) studied the photocatalytic reduction of nitrobenzenes and aminonitrobenzenes to aminobenzenes and diaminobenzenes, respectively. These reactions were conducted in aqueous suspensions of titanium (IV) oxide (Ti02) as catalyst and formic acid or oxalic acid as electron donors using de-aerated and aerated conditions under UV light. 

Formic acid and oxalic acid are green sacrificial reagents because they are easily oxidized and converted into CO2, which is separated from the solvent under acidic conditions. The photocatalytic effect in the presence of formic acid can be attributed to the photo-Kolbe reaction, originally evidenced by Kraeutler and Bard (1978) in the presence of various carboxylic acids ... 

Photocatalytic oxidation of oxalic acid enhanced by silver and copper deposition on a TIO2 surface... 

In the photocatalytic reduction of nitrobenzenes, positive holes in the valence band were effectively removed by formic acid and oxalic acid. These hole scavengers are greener sacrificial reagents because they are easily oxidized into CO2, and thus formed CO2 molecules are removed from the liquid phase in the presence of organic acids. The photocatalytic reduction of nitrobenzenes would be more attractive if positive holes are utilized for synthesis of valuable compounds, not for fruitless degradation or mineralization. Utilization of positive holes enables simultaneous production of two valuable reduced and oxidized compounds. In the case of reduction of nitrobenzene using oxalic acid (Eq. 9.15), atom efficiency (AE) [64], which is defined in Eq. 9.16, is calculated to be 23.7 % ... 

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