Indirect Electrooxidation of Organic Substrates by Hydrogen Peroxide Generated in an Oxygen Gas-Diffusion Electrode

Russian Academy of Sciences
Russian Journal of Electrochemistry (Impact Factor: 0.5). 01/2004; 40(2):148-152. DOI: 10.1023/B:RUEL.0000016327.07214.69

ABSTRACT Indirect electrooxidation of phenol, formaldehyde, and maleic acid in cells with and without a cation-exchange membrane, with a platinum anode and a gas-diffusion carbon black cathode, which generates hydrogen peroxide from molecular oxygen, proceeds with high efficiency and various oxidation depths, which depend on the intermediate nature: the process involving HO
occurs selectively and yields target products, while the formation of HO2
and HO leads to the destruction of organic compounds to CO2 and H2O.

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    ABSTRACT: The generation and transformation of radicals on the cathode of indirect electrochemical oxidation were studied by chemiluminescence (CL) and UV-Visible spectra in the reactor with a salt bridge that connected the separated chambers. The CL intensity of 4 x 10(-9) mol/L luminol on the cathode with bubbling oxygen was about seven times that of the intensity without it, which was because of the generation of reactive oxygen species (ROS). The existence of ROS, especially the generation of the superoxide radical, could be affirmed by the fact that the CL intensity of 4 x 10(-9) mol/L 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one with bubbling oxygen was about four times that of the intensity without it. However, there was no chemiluminescence on the anode under the same condition. The change in the UV-Visible spectra of nitro blue tetrazolium and N,N-dimethyl-4-nitrosoaniline at the cathode chamber affirmed the transformation from oxygen to superoxide and hydroxyl radicals. The mechanism of the superoxide and hydroxyl radical generation and transformation on the cathode was discussed with the help of the experimental results and relative references.
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