sakshaug007
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Anodic oxidation of polyatomic anions
Hello Everyone,
I decided to start a topic regarding the mechanisms and products associated with anodic oxidation of polyatomic anions (e.g., ClO4-, NO3-, SO42- etc.)
in various solvents.
This may seem simple to many of you but for some reason or another I've never thought about the products formed from electrolytic oxidation of
polyatomic anions since there can be a host of reactions that can occur depending on the reactivity of the solvent and temperature, pH etc.
Therefore, my first question pertains to what products would form from the oxidation of NO3- either from electrolysis of a molten nitrate salt or from
a hypothetically inert solvent. My best guess is that NO2 (or NOx) and O2 gases form and simply leave the solution (see attachment) is this true? If
so, would a similar decomposition occur with ClO4- in which O2 and Cl2 gases are evolved?
Any information would be great.
Thanks!
[Edited on 23-4-2009 by sakshaug007]
Attachment: anodic NO3- decomposition.ppt (135kB)
This file has been downloaded 571 times
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sakshaug007
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So I know that sulfate can oxidize to peroxodisulfate at the proper voltage, but what would peroxodisulfate oxidize to under a higher voltage?
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woelen
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This would oxidize to SO3 and O2. Possibly also some SO4 and O3. For persulfate the question, however, only is hypothetical, because all known
persulfates decompose to pyrosulfate and oxygen, well before they could be melted. I know of no solvent, which could dissolve persulfate and would be
sufficiently inert to withstand the extreme oxidizing conditions.
Your topic nevertheless is quite an interesting one. I also have wondered what happens with many anionic species when electrolysis is performed. I
have tried with many in aqueous solution with graphite or platinum anode, but unfortunately, water is severely limiting, because with most anionic
species, simply oxygen is produced at the anode.
Some examples which I tried in particular:
- potassium dichromate in somewhat acidic solution: Formation of oxygen at anode, no formation of peroxo species (these can very easily be detected
due to their intense blue color at medium to low pH).
- sodium bicarbonate: Formation of a mix of oxygen and carbon dioxide
- sodium acetate: Formation of a mix of ethane and carbon dioxide
- sodium monochloroacetate: Formation of a complicated mix of CO2, CO and in later stages Cl2 as well.
- tetrachloromanganate(II) (solution of MnCl2 in conc. HCl): Formation of a very dark green/brown manganese(III) or manganese(IV) species. Only small
quantities of chlorine gas are formed in such a solution.
I also have DMSO and tried a little with this solvent, but this solvent is oxidized easily, even more so than water. I really would like to have a
solvent, which is not easily oxidized.
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Hydragyrum
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This is a coincidence - I was wondering to myself about a week ago whether carbon could be deposited by reducing bicarbonate (or carbonate) - I
suspected not as else wouldn't I have heard of it? Carbon may not be so exotic, but plating it out would be really useful I think.
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Hydragyrum
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Quote: Originally posted by woelen  | | I also have DMSO and tried a little with this solvent, but this solvent is oxidized easily, even more so than water. I really would like to have a
solvent, which is not easily oxidized. |
Have you tried HMPA? (that is hexamethylphosphoric triamide, (Me2N)3P=O). It is a true wonder-solvent, you can even make blue solutions of alkali
metals in it, like ammonia.
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sakshaug007
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| Quote: Originally posted by Hydragyrum |
Have you tried HMPA? (that is hexamethylphosphoric triamide, (Me2N)3P=O). It is a true wonder-solvent, you can even make blue solutions of alkali
metals in it, like ammonia. |
This definitely sounds like an interesting solvent that I would like to attempt the electroplating of lithium in. Do you happen to know where to
obtain any?
[Edited on 20-5-2009 by sakshaug007]
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sakshaug007
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| Quote: Originally posted by woelen | I also have DMSO and tried a little with this solvent, but this solvent is oxidized easily, even more so than water. I really would like to have a
solvent, which is not easily oxidized.
|
I didn't realize DMSO oxidized easily. What are the products formed from oxidation?
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UnintentionalChaos
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| Quote: Originally posted by sakshaug007 | | Quote: Originally posted by woelen | I also have DMSO and tried a little with this solvent, but this solvent is oxidized easily, even more so than water. I really would like to have a
solvent, which is not easily oxidized.
|
I didn't realize DMSO oxidized easily. What are the products formed from oxidation? |
Dimethyl sulfone. Also known as MSM (methylsulfonylmethane), which is also available in bulk from health food stores.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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The_Davster
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DMSO is also easily reduced electrolytically to dimethylsulfide. Learning this firsthand was not pleasant.
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sakshaug007
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I found an article that addresses the electrochemical oxidation and reduction of DMSO. It specifies that it is "particularly" stable in cathodic
reduction and "fairly" stable in anodic oxidation with, yes, the primary product being dimethyl sulfone. Could anyone write the electrode potential
equations for this reaction? Is it dependant on the electrolyte present? As the article also states DMSO is reactive to the alkali metals (aside from
lithium). Will DMSO still undergo electrochemical redox in the presence of an unreactive electrolyte (e.g. triethylbenzylammonium perchlorate)?
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woelen
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Today I also tried electrolysis of CuCl2 in conc. HCl with platinum electrodes. This does not give any interesting results. Hydrogen is produced on
the cathode, chlorine is produced on the anode. The solution remains green/yellow and clear.
I also tried electrolysis of excess WO3 (until no more dissolves), dissolved in a solution of NaOH. This solution has composition Na2O.nWO3 (I don't
know the value of n, I just kept adding WO3 until no more dissolved). When such a solution is electrolysed, then nothing interesting happens, hydrogen
at the cathode, oxygen at the anode. No molybdenum blue is produced at the cathode and this surprises me. But on the other hand, when I add Na2S2O3 to
this solution, then nothing happens beside dissolving of the solid, but as soon as a drop of acid is added, the solution turns deep blue. Probably a
similar thing is true for electrolysis.
That HMPA solvent sounds very interesting. I'll see whether I can obtain some of that, I never heard of it before.
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Hydragyrum
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HMPA was 'discouraged' a few years back - apparently, it is a carcinogen... but someone should still produce/sell it I imagine (sorry, I know all this
stuff from years ago, but at present my chemistry collection is not very advanced - memories of a golden age, as it were...).
If one was courageous, it probably can be made from POCl3 and Me2NH, but be warned that HMPA needs a vacuum if you want to distil it.
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