Electra
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Divided cell electrolysis for stable radical anion generation?
I have the compound Menadione. This compound can form redox cycles in the body and can also form stable radical anions that can exist in solution for
up to 22 hours (as per studies).
I was able to found some brief articles about the electro-reduction of it, but I didn't have full access to any of them.
If I were to reduce this in a divided cell, would the electrons stay with the Menadione? I know if it were to interact with the anode, the electrons
would leave, but I am unclear whether or not electrons can travel through the electrolytes and through the separating membrane. My understanding of
the mechanics of galvanic cell electrolysis are fuzzy with regards to radicals.
I want to isolate this compound in its radical anion state, either by electrolysis, or other means. Any suggestions?
edit:
I'm thinking of maybe trying to use zinc or iron metal to reduce the Menadione, but I'm not sure if that would work. The Menadione is a great
radical/electron redox agent, I'm just not sure if the metals would be strong enough to reduce it.
[Edited on 11-6-2014 by Electra]
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Metacelsus
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How did they form the anions in the studies (besides electro-reduction)?
You can probably get the full text of the papers if you request it in the references request thread.
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Electra
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There are a couple of ways. Menadione is one of the many organic redox catalysts, used in certain radical reactions so as to stabilize radical anion
intermediats and drive the reaction forward. This is particularly what I have been studying.
The problem I am met with is that most of the papers on Menadione have to do with its redox cycles in the human body, since, it is a nutritional
supplement. Though, it's cyclic electron withdrawing groups allow its methyl hydrogen to be very electro-positive and thus hold a charge easily and
stably, yet, be able to pass it on.
There is without a doubt that the radical anion is formed during electro-reduction, but I am just curious if it can be re-oxidized in a divided cell
if kept in the catholyte. Worse case, since it is more easily reduced than it is oxidized, over-reducing it for a time period should cause the radical
anion concentration to maximize, though I would like to find out some calculations if I can.
--
What I need to do is come up with an experiment to see if zinc metal can reduce this. Since the anion reacts with oxygen to form superoxide, I may be
able to work with that somehow to test whether it was reduced.
[Edited on 11-6-2014 by Electra]
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Electra
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In search of viable organic radical redox cycling catalyst
Wasn't sure whether to post this in reagents/acquisitions or Organic Chemistry. I picked the latter since the topic is a quite a well suited Org Chem
topic.
Benzyl Nitrile / Benzyl Cyanide has been reportedly used in the past before as a redox cycling catalyst. That is, it can stabilize and assist in the
transfer of radical anions in solution and undergo redox cycling. The only problem is Benzyl Nitrile is a list 1 chemical. All of the papers
documenting its use as a redox catalyst were done in universities and by people with a license to posses this chemical. I have no way of obtaining it,
nor do I wish to side step the law to obtain it even if I could.
So. I have been investigating the use of quinones as radical redox cycling catalysts. Quinones can redox cycle between Semiquinone forms. I currently
have my eye on Menadione http://en.wikipedia.org/wiki/Menadione . It's redoxing abilities are widely documented. I have actually found a very good source of it.
My reluctance with using a quinone/semiquinone cycle is because I recall reading somewhere that semiquinone radical anions can undergo addition to
other molecules, for some reason due to the oxygen carrying the negative charge. This, would effectively terminate any radical process. I am not sure
if this is an issue with benzyl nitrile as a redox agent. Now of course, whether or not an addition takes place, versus a simple electron-radical
transfer, entirely depends on the substrate and any present EWG/EDG's. While a quinone like Menadione may work well as a redox catalyst, I
also hope to find more [non-quinone's] to add to my list to experiment with.
The electron withdrawing groups are obviously key in stabilizing a radical anion intermediate, but molecules containing nitro groups such as
dinitrobenzene are known to be radical inhibitors, so a careful balance must be achieved, enough to stabilize the radical anion, yet, not restrict the
electron transfer.
Any suggestions?
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Nicodem
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Threads Merged
17-6-2014 at 06:14 |
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