Bedlasky
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Photochemical oxidation of oxalate
Hi.
I read these two papers some time ago.
https://www.nrcresearchpress.com/doi/pdf/10.1139/v78-401
http://www.dwc.knaw.nl/DL/publications/PU00014693.pdf
Second paper is about fotochemical oxidations, first paper is about application of photochemical reaction in determining of oxalate.
I was impressed by the reaction of oxalate with ferric salt in acidic conditions and oxalate with iodine. I tested it under UV light and it work well.
But reaction with iodine takes place only in neutral pH (maybe slightly acidic or basic). For reaction of oxalate with iodine I use ammonium oxalate
and it works well without buffer (I once use CO2/HCO3- buffer with some oxalic acid and reaction works too).
I also tested reaction of permanganate with oxalate in acidic media under UV light - reaction is faster than in normal conditions.
Another good photoreaction is oxidation of another organic acids with Fe3+ salt in acidic conditions. I tested this reaction with citric and tartaric
acid under UV. Any of these acids release amount of CO2 that's the same as amount of COOH groups. Oxalic acid release 2 moles of CO2, tartaric 2
moles, citric 3 moles. Interesting is that reaction between tartaric or citric acid and iodine doesn't occur. Maybe is reaction of oxalic acid with
iodine specific? But I am not sure about this.
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Bedlasky
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About photochemical reactions are articles on my website in english and in czech.
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AJKOER
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Quote: Originally posted by Bedlasky  |
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Another good photoreaction is oxidation of another organic acids with Fe3+ salt in acidic conditions. I tested this reaction with citric and tartaric
acid under UV. Any of these acids release amount of CO2 that's the same as amount of COOH groups.
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During the photolysis, consider pumping in air/O2 (like from an air pump employed in your normal fish tank) if you wish to increase radical production
and breakdown organics (discussed below).
Here is a reference 'Mechanism of Ferric Oxalate Photolysis' (available at https://www.osti.gov/pages/servlets/purl/1398998) on the mechanics of the photolysis of the oxalate ion. To quote:
"Photon absorption and electron transfer generate an unstable oxalate radical anion, C2O4•−, that dissociates rapidly....Oxalate radical
dissociation generates thermally excited CO2 and CO2•− "
Or, I would describe the reaction mechanics as follows:
C2O4(2-) + hv --> C2O4•− + e-
C2O4•− --> CO2 + CO2•−
The introduction of a solvated electron (with a photocatalyst) can recycle, say Fe3+, to Fe2+ to keep recycling the redox reaction:
Fe3+ + e-(aq) --> Fe(2+)
Also, the action of the powerful reducing carbon dioxide radical anion, CO2•− (source: see Table I at https://www.bnl.gov/isd/documents/92710.pdf ), on ferric and even oxygen:
Fe3+ + CO2•− --> Fe(2+) + CO2
And, in the presence of air/oxygen, the superoxide radical anion:
O2 + CO2•− --> O2•− + CO2
At pH < 4.8, the perhydroxyl radical (see https://www.ncbi.nlm.nih.gov/pubmed/12042065):
H+ + O2•− = HO2• (Also, Table 3 at https://www.bnl.gov/isd/documents/92710.pdf )
As:
HO2• + HO2• --> H2O2 + O2
Or faster:
Fe2+ + HO2• --> Fe3+ + HO2- (see https://www.sciencedirect.com/topics/chemistry/fenton-reacti...)
And, even with H2O as a source for H+:
H+ + HO2- = H2O2
where the presence of ferrous and H2O2 in acidic conditions imply some possible Fenton chemistry as well:
Fe2+ + H2O2 --> Fe3+ + OH• + OH-
where the powerful hydroxyl radical is formed in this system with oxygen and can further attack organics (see, for example, https://www.sciencedirect.com/science/article/pii/S004565350... ). A more general but dated reference of interactions with OH• , see https://nvlpubs.nist.gov/nistpubs/Legacy/NSRDS/nbsnsrds46.pd... (albeit a large file).
Note, the creation of solvated electrons in a suitable medium, may also be able to directly act on O2 or CO2 creating respectively O2•− and
CO2•−.
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In place of pumping in air/oxygen, just performing the photolysis on a solution in a shallow vessel with much increase air contact together with some
surface agitation (like from mechanically induced vibrations) may also significantly improve degradation of the solution.
[Edited on 7-2-2020 by AJKOER]
[Edited on 7-2-2020 by AJKOER]
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Bedlasky
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Thank you very much Ajkoer for explanation. Would you mind adding it to the article? Of course I will mention you as the source of information.
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AJKOER
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| Quote: Originally posted by Bedlasky | | Thank you very much Ajkoer for explanation. Would you mind adding it to the article? Of course I will mention you as the source of information.
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No issue, just include my source links.
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