Fe(III) and dioxygen: any reactions?

[Fab1976]

My question is:

 

Can an Fe(III) cluster type [Fe(III)3(mu3-O)(O2CR)6]+, where O2CR are monocarboxylic acids groups, react with dioxygen to produce a radical species able to initiate radical reactions, such as polymerization or else?

 

I have been browsing the literature but besides the reaction of Fe(III) ions with peroxides yet no answer to my question.

 

I thank in advance for any suggestions

 

Regards,

 

Fabrizio

[C1ay]

Welcome to Hypography but please don't double post.

[Fab1976]

Thanks!!

 

Sorry for double posting, but I am new of this forum and did not really know how it worked.

However, considering your quick reaction to my post I am definetely sure that it works very well!!

 

Cheers,

 

Fabrizio

[UncleAl]

The Fenton reaction is redox with Fe(II->III) generating radicals from hydrogen peroxide. Oxygen should also participate. All Fe(III) has no reason to do anything. One imagines highly oxophilic Fe(III) mu-oxygen bridges or periphral ligands could be displaced by alkaline peroxide, especially given the Alpha Effect. Cleavage would not be redox facilitated at nominal pH values. Fe(IV) needs strong alkali.

 

Superoxide is a mild reducing agent.

[Fab1976]

I am well aware of the fenton reaction and the involvment of hydrogen peroxide in generating high reactive hydroxyl radicals. About the generation of Fe(IV), well it interesting even though, as you say, high pHs are required.

 

Well, thanks for your suggestion anyway,

 

Regards,

 

Fabrizio

[UncleAl]

It doesn't mean a dead end, only a detour. Why use innocent ligands? First, get the peroxide in there. We know that small radius multiply charged centers stabilize peroxide - perborate, percarbonate. Second, have a substituted aromatic acid ligand that has photochemistry. Now you can introduce a redox channel at will either by pumping photostimulated electron density into an Fe(III) center or using the ligand itself as the redox center.

[Fab1976]

That's a very interesting proposal!

But let me explain the "why" of my post/question.

The cluster [Fe(III)3(mu3-O)(O2CR)6]+ (many examples are known in literature), has been synthetized throughout my Ph.D. and its catalytic activity towards the oxidation of lipids has been tested. It turned out that the cluster was active in that reaction, but there is a luck in understaning how that happened.

Fe(II) complexes are well known catalysts of the oxidation of lipids and other biomolecules. On the other hand, Fe(III) is supposed to be unactive unless combined with e.g. reducing agents. This makes a lot of sence if the Fe(II)/Fe(III) redox cylce is taken into account.

Returning back to my point, the system is made of:

 

neat lipid + solution of the complex (dosed in catalytical amonuts, <0.2%)

 

Results:

 

lipid oxidation after about 100 h!!!

 

What's has happen to the catalyst to become suddenly activeduring that 100 h ?

 

This remains still a bit a mistery!

 

Fabrizio

[UncleAl]

What's has happen to the catalyst to become suddenly active during that 100 h ?

 

The organic itself or its reaction with advantitous radicals eventually makes a species that reduces Fe(III). You then get positive feedback and autocatalysis, with exponential growth. Do it in an EPR tube and watch the magic happen by taking periodic spectra. Or put it in a Gouy balance and graph magnetic susceptibility over time.

 

Or the intense magnetic field, either way, quenches the autocatalysis by enforcing spin alignment.

 

If you repeat the reaction in a small tube instead of containment with lots of head space, you must wonder about the effect of limiting molecular oxygen availability. If you diddle with magnetic fields you must consider field strength and field divergence. You can do a pretty by putting cube NdFeB N40-45 magnets in a u-channel to make a Halbach array. Remember that magnetic field strength varies as the cube of separation. Snug in close.

 

http://www.matchrockets.com/ether/halbach.html

http://www.magnetricity.com/Articles/Halbach_Array.php

http://encyclopedia.thefreedictionary.com/Halbach+array

 

http://www.unitednuclear.com/giantmag.jpg

http://www.unitednuclear.com/magnets.htm

Last picture on page. woo hoo!

http://www.rare-earth-magnets.com/

http://www.rare-earth-magnets.com/SearchResult.aspx?CategoryID=21&KeyWords=Cube&All=True

[Fab1976]

Hello there!!

 

This a pretty interesting experiment you are proposing. I just have a couple of small questions: Fe(II) in not EPR active, so what should we see in the EPR spectra? On the other hand, don't you think that radicals produced during the oxidation reaction, such as peroxy, alkoxy, etc, may interfire with the measurements by overlapping with each other?

 

However, you have given me more ideas in a couple of days than many other people around me in weeks. Thanks!

 

Fabrizio

[UncleAl]

1) Fe(II) is not EPR-active. Total integrated signal should decrease if you get Fe(II). Since you are starting with only trace amounts of catalyst, a substantial fraction should be altered when things get going. You don't have to pop full spectra. You can sit on a partially saturated line and watch its intensity vs. time. And run controls! Signals can drift. (Periodically calibrate with a known stable free radical. You must know if a strong magnetic field affects kinetics or mechanism before you do EPR.)

 

2) Alkyl and alkoxy radicals will have different g values and multiplicities vs. the metal centers.

 

3) [Fe(III)3(mu3-O)(O2CR)6]+ has no intervalence transfer. If one or two of the Fe(III) centers is reduced to Fe(II) you may get a massive increase in optical absorption (re Creutz-Taube ion; Prussian blue; ferrites) and a vast change in EPR spectrum. You want to know if you do.

 

4) Have you done variable frequency cyclic voltammetry on your cluster? Do you know its redox potentials, whether they are reversible, and their kinetics?

 

5) Partially reduce your cluster, one and two electrons, chemically or electrolytically, and add it as catalyst. Is there still an induction period? Do spectroscopic changes obtain in the synthetic partially reduced clusters?

 

6) What happens to your reaction, Fenton or cluster, if you add suitable TEMPO or PROXYL derivatives, or free radical traps (Even N2O)? Do the former quench or initiate? Do the later quench?

 

7) Theory of Experimentation. If you have coupled variables you cannot make sense of things by examining them individually.

 

However, you have given me more ideas in a couple of days than many other people around me in weeks. Thanks!

“Discovery consists of seeing what everybody else has seen and thinking what nobody else has thought,” Albert von Szent-Gyorgyi. Step outside the frame and look in upon yourself. What should you be doing? Take a long hot shower. Let your mind drift.

 

It is not enough to know. You must know what you know.