Sciencemadness Discussion Board

Fluorine Generation

Sauron - 27-5-2007 at 05:51

As a matter of curiosity, is there any laboratory method of generation of F2 other than electrolysis.

Brauer has pretty good details on a couple of different electrolytic methods but I was rather more interested in any alternative - other than buying a lecture bottle or a cylinder, something that can't be done here without special government dispensation.

I ran across a reaction involving BrF3 and this is prepared from the elements. So far I have not found a commercial source for BrF3 either. It is a liquid, so this is a bit surprising.

[Edited on 27-5-2007 by Sauron]

Oxydro - 27-5-2007 at 07:23

I quote from the great Wiki:
Quote:

In 1986, preparing for a conference to celebrate the 100th anniversary of the discovery of fluorine, Karl Christe discovered a purely-chemical preparation by reacting together at 150 °C solutions in anhydrous HF of K2MnF6 and of SbF5. The reaction is:

K2MnF6 + 2SbF5 → 2KSbF6 + MnF2 + F2

This is not a practical synthesis, but demonstrates that electrolysis is not essential.


But I'm fairly sure thats not going to work for you :P. I don't think you're going to find anything "easier" than the Moissan process

Sauron - 27-5-2007 at 07:45

Interesting but 21 years old. Hasn't anyone surpassed this in two decades?

Anyway I will simply look a bit harder for the commercial source for this interhalogen (like maybe Fluorochem). Negatory with Aldrich, and Alfa. Not a good omen.

Anyway the "great wilki" may be in error. This from the chemieonline.de webforum:

auch möglich:
K2MnF6 + 2 SbF5 --> 2 KSbF6 + MnF3 + 1/2 F2 (bei 150°C)
wobei K2MnF6 und SbF5 so hergestellt werden:
2 KMnO4 + 2 KF + 10 HF + 3 H2O2 --> 2 K2MnF6 + 8 H2O + 3 O2
SbCl5 + 5 HF --> SbF5 + 5 HCl

Quelle: RIEDEL, Anorganische Chemie, deGryter, 4. Aufl.

--------------------------------------------------------------------------------

So is it MnF2 or MnF3 and is the yield of F2 really this wretched?

[Edited on 27-5-2007 by Sauron]

roamingnome - 27-5-2007 at 08:35

MicroGen Fluorine Generators Eliminate any Supply Problems
http://www.future-fab.com/documents.asp?d_ID=1103


i think a i saw something about degrading CFC's to HF in-situ generation

not_important - 27-5-2007 at 09:35

Quote:
Originally posted by Sauron
Interesting but 21 years old. Hasn't anyone surpassed this in two decades?

Anyway the "great wilki" may be in error. This from the chemieonline.de webforum:


Wiki has a typo, or someone 'corrected' the 'obviously wrong' MnF3

Go here
http://classes.uleth.ca/200303/chem3810a/ps7.pdf
for a study sheet which includes a scan of Inorganic Chemistry's report of the process, along with some other interesting items.

[Edited on 27-5-2007 by not_important]

JohnWW - 27-5-2007 at 13:55

In that non-electrolytic preparation above, the F2 generated would, surely, quickly re-oxidize the MnF3 byproduct to MnF4 or higher oxidation states, unless immediately removed. Incidentally, F2 gas is supposed to be deadly poisonous - has anyone here breathed it, and lived to tell the tale?

BTW The discovery of F2 by electrolysis of a fused salt in 1886 quickly led to the discovery that year of the electrolytic method for the smelting of aluminium from fused purified Al2O3 and Na3AlF6 (cryolite, originally a rare mineral from Greenland), which is still used commercially today (in places having access to relatively cheap and abundant electricity generated by hydro-power, mainly in parts of Norway, Canada, New Zealand, and Australia).

Sauron - 27-5-2007 at 18:21

As that reaction is conducted in anhydrous HF and at 150 C it is perfectly clear that it is done in a F2 and HF capable pressure reactor and that once complete the whole thing must be cooled back down to liquify the HF and only then can the F2 be isolated.

Anyway it is very clearly NOT a practical preperative method. It is a laboratory curiosity only.

Nerro - 28-5-2007 at 03:20

The preparation of F2 is done by electrolysis of liquid anhydrous HF with some KHF2 added for conductance (like putting salt in water to make it conduct).

But what is used to make the reactor? Teflon coating? Nickel?

Sauron - 28-5-2007 at 05:24

See Brauer's Handbook of Preparative Inorganic Chemistry for details of construction of lab scale electrolysis cell for F2 generation, also for distillation of anhydrous HF from KHF2 (which is done in 5mm thick copper retort,)

So if you can get KHF2 you can produce anhydrous HF and with that you can obtain F2 by hydrolysis. If you dare.

1200 g KHF2 yields 250 g anhydrous HF. And HF is 95% fluorine by mass. That's about 6 mols F2.

Eclectic - 28-5-2007 at 05:24

As I recall (from 30 years ago) copper works. I believe there is an apparatus design in "Inorganic Synthesis".

UnintentionalChaos - 28-5-2007 at 06:15

There is a product floating around called armour etch glass etching cream, which I know contains at least some NaHF2 or NH4HF2. Its a shame that it's quite expensive, although available in some craft stores, probably due to in part to hazardous materials shipping costs. An old generic MSDS I found for Armour Products suggests a minimum of 30% fluoride compounds (up to 60%) with titanium dioxide and citric acid as the other ingredients (as well as water, I assume)

unionised - 28-5-2007 at 06:51

There is a trick for getting fluorine but it' not as much use as you might think. Plasma etching gives rise to all sorts of odd reactive species, F2 and F. are among them. Only really useful for trashing things.

Sauron - 28-5-2007 at 07:27

At the end of the day, unless I am willing to make a serious investment in an electrolytic cell and associated equipment, and ensure I can obtain KHF2, and built an HF still, then the proper thing for me to do is forget this whole idea and simply spend me time and money on something else.

But at least I got my question answered.

BromicAcid - 28-5-2007 at 08:02

I've got a scan of the cell from inorganic chemistry here:

http://www.sciencemadness.org/talk/viewthread.php?tid=2358

vulture - 28-5-2007 at 13:49

US5068127 apparently uses CrF3 as a "fluorinated vapor donor" whatever that might be...

Doesn't AgF3 decompose into AgF2 and fluorine when heated?

Pyrovus - 29-5-2007 at 05:01

CuF2 decomposes to CuF and F2 at around 1000°C or so, though this probably isn't all that practical - not to mention that I imagine fluorine would likely be even nastier at those temperatures. I know there's a few more high oxidation metal fluorides which decompose upon heating to give fluorine, but I can't remember them off the top of my head.

JohnWW - 29-5-2007 at 14:15

High oxidation state metal fluorides which readily thermally decompose, at various temperatures, are CrF6, AgF3, AuF5, PtF6, CuF3. There may also be ones of Ni, Pd, Co, Rh. But they are made by methods involving, at least indirectly, the use of electrolytically produced F2, anyway.