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Author: Subject: Doable synthesis of F2 in amateur setting?
woelen
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[*] posted on 3-2-2018 at 13:15
Doable synthesis of F2 in amateur setting?


An interesting read I found is the following:

https://sites.google.com/site/ecpreparation/extreme-oxidizer...

It states formation of K2MnF6, precipitating from an aqueous solution with 50% HF in it.

The reaction equation is this:
2 KMnO4 + 2 KF + 10 HF + 3 H2O2 --> 2 K2MnF6 + 8 H2O + 3 O2

I have some 48% HF and I have KHF2 (of course I also have KMnO4 and can make quite concentrated H2O2, 30% should be achievable from 12% H2O2). The KHF2 brings in additional HF. So, with the chemicals I have it should be possible to do this.

I am still somewhat reluctant to do this experiment. Although I have 48% HF, the number of experiments I did with this stuff is almost zero. It is so badly toxic and scary. This experiment, however, looks really interesting. I have read papers about making K2MnF6, but they used SbF5 as one of the reactants, totally beyond reach of an amateur-setting, but the chemicals, mentioned in the link above, can be handled in an amateur-setting, albeit that with HF one must be extremely careful.

I have PE-testtubes and beakers. I think I'll give it a try with freezing-cold solutions. If there is anyone here who has done something similar, then I would like to know of that experience. Practical info and theory on paper may make a big difference.




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[*] posted on 3-2-2018 at 13:21


Doubtless this does not need saying : be VERY careful !

Our favourite Amateur Chemist needs to preserve himself (while doing the amazing chemistry).




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woelen
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[*] posted on 3-2-2018 at 13:28


Yes,thanks for your concerns. I will be careful. I know of the dangers of HF. But I think it is doable. I only will do this at ml scale (I only have a little under 100 ml of 48% HF), but I am aware that even ml quantities of HF are dangerous. I especially take utmost care not to get any of this on my skin and I will have a solution of CaCl2 around, ready to grab, next to the experiment to convert the fluoride to insoluble and non-toxic CaF2.



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clearly_not_atara
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[*] posted on 3-2-2018 at 13:33


Doesn't the synthesis of F2 from fluoromanganates also depend on SbF5?

2 K2MnF6 + 4 SbF5 >> 4 KSbF6 + 2 MnF3 + F2

But maybe you can get away with using PF5 instead of SbF5? PF5 can be made from arsenic trifluoride and phosphorus pentachloride, eliding the need for anhydrous HF:

3 PCl5 + 5 AsF3 >> 3 PF5 + 5 AsCl3

But AsF3 is also generally made with anhydrous HF. But since it is not a Lewis acid you can probably use silver fluoride instead:

3 AgF + AsCl3 >> 3 AgCl + AsF3

AsCl3 can in turn be made by chlorinating arsenic with excellent selectivity. Of course the chemicals here are also toxic. But you knew that.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 3-2-2018 at 13:39


What would you like written on your headstone? Best to let us know now, otherwise we'll just put "Played with F2"

Don't know enough to really be able to weigh in on this, but looks good. Hope it works out, 'cause i'm sure not going to try it!




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[*] posted on 3-2-2018 at 14:30


Interesting. Is this reaction is being driven by the acid helping to peel the oxygen atoms off the manganate, with F+ ions then able to associate with it, and the resulting manganate fluoride crashing out of solution (thus driving the reaction forward by removing product from solution....)

Or am I underestimating the oxidizing power of the acid/peroxide mix and it progresses through fluorine (F2 or F• radicals) after all?
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[*] posted on 3-2-2018 at 15:05


I hope you will consider looking into buying some calcium gluconate.

It seems to be the best emergency treatment to prevent damage during transit to the hospital.

Kays medical has 40 gram tubes for around $20, don't know if they sell to ordinary citizens, but somebody must.





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[*] posted on 3-2-2018 at 15:59


I suggest performing the reaction in a xenon atmosphere with UV light. XeF2 is a solid which is much more easily handled and can be stored indefinitely, giving you some record of the experience. It sounds easier than trying to ampoule F2...



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 3-2-2018 at 18:46


Form the OP,
extreme oxidiser + PE test tubes and/or beakers does not sound like a good combination.




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[*] posted on 3-2-2018 at 19:18


He probably meant PTFE. woelen is about to do something I wouldn't do in my life (maybe if someone is paying a million bucks, but unlikely).



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[*] posted on 4-2-2018 at 01:49


Quote: Originally posted by woelen  


I have PE-testtubes and beakers. .

Those are fine for HF, but I suspect that, from the point of the perfluuromanganates, they look like "fuel".
I'd go with PTFE or at least FEP (actually I'd just not go there but...)
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[*] posted on 4-2-2018 at 01:55


I have two probably obvious questions.
At mL scale how will you be certail you have achieved your objective?
Once you have made it... Then what? Surely not storage. But reacting with something (non human)... What will you choose?

This sounds fascinating from a distance. Be sure to set up a camera.




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[*] posted on 4-2-2018 at 02:19
unresearched speculation


If there is such a substance as K2MnCl6 then the synthesis and properties may be similar so maybe you could try that first,
substituting Cl for F avoids the HF fear factor ?

A speculative answer to j_sum1 ... probably something like http://woelen.homescience.net/science/chem/exps/mn2o7/index.... hopefully :D




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woelen
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[*] posted on 4-2-2018 at 07:43


I tried, but without success, but I will post what I did and what results I obtained.

I prepared two solutions, both at appr. 5 degrees C:
1) Appr. 1 gram of KHF2 in 3 ml of 48% HF, added appr. 0.5 ml of H2O2 to it (exact concentration unknown, but will certainly be well above 20%, made this by freezing out of a little of 12% H2O2 and removing ice). This solution is colorless and stable. No production of oxygen, no decomposition. Freezing out was not that easy, our fridge is set to -20 C but freezing the H2O2 was very slow. It is remarkable how well KHF2 dissolves in the HF.

2) Appr. 0.5 gram of very finely powdered KMnO4 (crunched to a very fine dark grey powder), added appr. 2.5 ml of 48% HF. The solid quickly dissolves, but almost immediately the liquid started foaming, faster and faster, until it foamed over the rim of the test tube. Also, white fumes and a purple gas were repelled from the test tube. After the reaction, a precipitate settled in the test tube, dark brown. Most likely this is just hydrous MnO2. So, concentrated solutions of KMnO4 in concentrated HF decompose. The gas most likely is oxygen, MnO2 is formed, and KF (or KHF2) goes in solution.

So, making solution (2) failed. I tried again, but now with only appr. 100 mg of KMnO4 in appr. 2.5 ml of cold 48% HF. This time, the solution was stable. It did not foam, there was only very slight bubbling, but the solution could be set aside, and its color was very intense purple, just like an aqueous solution of KMnO4.

At this point I dripped solution (1) very slowly into solution (2). With each drop there was effervescence of a colorless gas (oxygen), but after a few drops the solution was colorless and clear :(
All permanganate simply is reduced to manganese(II) by the H2O2. This is a well-known reaction at low pH. I am quite sure that the solution does not contain any MnF6(2-) ions. According to literature ( http://pubs.rsc.org/en/content/articlelanding/2017/tc/c7tc02... ) the ion is light brown in solution and the solid is bright yellow. It can be washed with HF+acetone. They only used 40% HF, I used 48% HF, but they used 35% H2O2, mine most likely is less concentrated. I did not have very good stirring, just swirling of a test tube.

I am wondering why I did not see any formation of the MnF6(2-) complex. Maybe my solutions were too warm, or I added too much H2O2. I need to read more about this. The paper mentions that K2MnF6 is not available commercially due to instability at higher temperatures.




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[*] posted on 4-2-2018 at 08:12


Bravo !

Brave of you to even try !




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[*] posted on 4-2-2018 at 09:42


@woelen: That's an interesting idea. I had my doubts that would work, too. But if you are already trying, I had the idea to make a video section on Fluorine preparations on my Youtube Channel for perhaps 2019 or so and already collected a few ideas in summer. I don't have that list at the moment but if I find it I give you a copy. Turns out there are quite some chemical (not electrochemical) ways to make F2, at least in trace, as proof of principle method. It would at least be worth trying them out for once but I don't have that much time at the moment.




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[*] posted on 4-2-2018 at 09:57


The reason why I picked this synthesis is that it requires only common chemicals besides the HF, available to many home chemists. The more well known synthesis of K2MnF6 (and from that F2) requires the use of SbF5 and anhydrous HF, both definitely not suitable for home chemistry. Working with 40% HF as is done in the paper, mentioned above, is doable in a home setting, albeit that great care is required.



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[*] posted on 4-2-2018 at 11:06


Cool! Woelen is getting more and more a real mad scientist. I have full trust Woelen is one of the guys around here who could pull this off in a successful way.

About the peroxide, I have at least half a liter what was once bought as 30%. I don't know what percentage it is now, but titration could tell. I would be happy to send you some.

Could you tell/pm the city you live Woelen? I'm traveling quite a bit nowadays, if it is on route I could maybe drop it off if you are interested.

An ampoule of XeF2 would be far beyond cool...

Edit, I have a freezer that goes below -30, I could try to see if I can freeze some water out of my peroxide.

[Edited on 4-2-2018 by Tsjerk]
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[*] posted on 4-2-2018 at 11:17


Any other chemist would be mad to try it. Woelen, on the other hand....I just hope he's very careful.

[Edited on 4-2-2018 by DraconicAcid]




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[*] posted on 4-2-2018 at 11:30


@DraconicAcid: I understand your concern, I will be very careful.

Just to give an impression of what I do:
- I do not pour the HF.
- I put the bottle of HF in a plastic sink.
- I first put the solids and the H2O2 in the PE-test tubes
- Next, I put the PE-test tubes in a special PE-beaker, with a little water at the bottom
- From the bottle, I transfer 48% HF to both of the test tubes, using a long PE-pipette. I do not have to move around the bottle, nor the test tubes for transferring the HF. If I accidentally spill some HF, then it will be contained in the plastic sink.
- Using a PE-bar, I dissolve the solids and mix the H2O2 with the HF.
- Using another PE-pipette, I carefully drip the H2O2/KHF2 solution in 48% HF into the solution of KMnO4.
The entire procedure is done without a single transfer of test tubes, beakers or bottles out of the plastic sink.
When the experiment is done, I simply run a lot of water in the sink. With a PE-stick I carefully tip over the PE-tubes and beaker and allow a lot of water to dilute all of the stuff and then I let it run away under a running tap, using a chain to open the sink. This is not a really environmental issue, all those people brushing their teeth with fluorinated tooth paste produce MUCH more fluoride waste than I do with my 5 ml of 48% HF.

After flushing all the stuff with water I keep running water around the sink and its walls, and over the beaker, test tubes and pipettes, just to be sure that no drops of HF remain unnoticed and not rinsed away.

Finally, inhalation risk is minute. HF at concentration of 48% does not fume when it is cold (appr. 5 C).

[Edited on 4-2-18 by woelen]




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[*] posted on 4-2-2018 at 11:35


I found a paper in which a solution containing HF, KHF2 and KMnO4 forms K2MnF6 in the presence of Si, this being intercalated in the fluorosilicate precipitate:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.921...




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 4-2-2018 at 22:25


What is the reaction of hydrofluoric acid and potassium permanganate forms permanganic acid and potassium fluoride

Also manganese pentafluoride decomposes with heat therefore it is a solid storage medium for flourine gas

Now we only need a compound that can store ozone and release it when it is heated to decomposition point

[Edited on 5-2-2018 by symboom]




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[*] posted on 5-2-2018 at 00:01


I have read more about the reaction. Apparently the stirring and the VERY careful addition of H2O2 is most important. You have to add JUST enough H2O2, it is very easy to overshoot and add too much and then the compound is destroyed.

This makes doing this experiment on a test tube scale more difficult. I first will try doing this experiment with dilute solutions (in KMnO4 and H2O2, not dilute in HF), adding single drops with H2O2 and each time swirling. I do not want to handle the test tubes with my hands holding them, I will use some clamps. If this mechanism does not work, then it probably is beyond what I can do. Then I need to work on a bigger scale, in beakers, using a stir-bar and a magnetic stirrer. I, however, do not feel comfortable to use 100 ml or so of a 48% HF solution and stirring that with a magnetic stirrer. It also will use up my entire stock of HF.

It is, however, already quite interesting to see what kind of reactions there are in concentrated HF-solutions with common salts. It is weird to see that KMnO4 decomposes in conc. HF and that this gives a faint purple vapor. This most likely is MnO3F.




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[*] posted on 5-2-2018 at 01:34


I would like to advice anyone to keep their eyes open forthese kind of pipettes.

New they are very expensive, but second hand you can probably easily find them for a hobbyist friendly price. They are great for precise pipetting of small volumes. The plastic one-time use tips are available in all kinds of material, usually they are made of PP.

I would advice Gilson pipettes, as they are easier to clean/repair compared to Eppendorf pipettes.

https://www.ebay.com/b/Gilson-Lab-Pipettes/26417/bn_57065143...
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[*] posted on 5-2-2018 at 02:20


Or economise and get 100 disposable PE pipettes for £1 ?
At £0.01 per piece they really are disposable :D
Plus, you can crimp or melt them shut to act as a short term storage vial.
I do not rely on the graduations/callibration however.




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