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Author: Subject: Make Potassium (from versuchschemie.de)
UnintentionalChaos
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[*] posted on 5-12-2010 at 08:21


Quote: Originally posted by Pok  
Quote: Originally posted by condennnsa  

Pok, what is your opinion on Len1's attempt at this?
Couple of things that come in my mind, is that he used much coarser magnesium, and that he stirred the mix continuously. It seems that mg powder might be more suitable for this procedure.


I only read a little bit of his attempt:

1. He powdered the KOH. This is not necessary as I used commercially available KOH chips with success (although the chips will clump together at a certain temperature). Maybe, during powdering the KOH absorbs water from the air due to its extremely high hygroscopicity. This could lead to so much water in the reaction that all the Mg is used up to decompose the absorbed water and nothing is left to react with the KOH.
I personally opened the new KOH-bag very fast and weighted the KOH as fast as possible trying to avoid large water absorption from the air.

2. The Mg really looks very coarse. The best way to obtain a suitable size of Mg particles is (as I experienced) to file them off with a normal medium file (not fine, not extremely coarse) by hand - not with a (drill) machine or so. I used Mg of about 99% purity (old printing plates). As the authors of the patent don't give more details, I think Mg of 98-100% purity is OK. I think TOO fine Mg powder also wouldn't be the best way, because it could react TOO fast (especially at the beginning where only water from the KOH is decomposed by the Mg and yields large amounts of hydrogen in a very short time!)

3. I don't think that stirring continiously is really bad here (the patent really sais "continiously stirring"!). But it wasn't necessary in my case. It might yield finely divided K-globules but they definitely should be visible. If you use a teflon coated stirrer, the teflon might react with the potassium as someone on versuchschemie.de seems to have experienced.

4. Exclusion of air (which possibly wasn't ensured at his attempt) AND evolution of hydrogen must be ensured. The cheapest and easiest way for me was a valve-like method (balloon with tiny hole). If you don't exclude the air really tightly potassium (which is swirled around in the mix by turbulences) at the solvents surface will react with the tiniest amounts of oxygen and will be lost.

5. ensuring reflux is very important as the tiny neccessary amount of tert.butanol will otherwise be lost very fast.

6. len1 himself also took into consideration the possibility of impure agents. This could be a problem, of course.

Maybe my modifications just prevented some possible sources of trouble. Just compare my description with his one (also on the original page versuchsschemie.de where you can read it in detail).

As I said, I've done the experíment several times with success. And even when there was "no success" I gained at least many tiny K-globules. So I don't think that you can make many mistakes if you just do it the way i did it.

Quote: Originally posted by blogfast25  


One very obvious question is where did you by the Shellsol solvent?


As condennnsa said, "Kremer Pigmente" offers Shellsol D70. This is my source.


Pok- How sure are you that the printing plates are high purity magnesium? Have you successfully tried this procedure utilizing reagent magnesium?

Additional thoughts for others-

If this turns out to be an issue of reagent contact, perhaps we should try using the NaOH/KOH eutectic mixture. If that works, we can go back to the drawing board with plain KOH.




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[*] posted on 5-12-2010 at 08:22


Something that comes to mind is that the magnesium is passivated to a degree. Grignards usually need a little kick to get started (crushing with a glass rod, some iodine crystals, sonication). Perhaps either creating the magnesium chips under oil (ie: drill press on a Mg block under mineral oil) or transferring Mg chips in and adding a pinch of iodine prior to addition of KOH might activate the surface more. Since the solvent is non-polar I'd expect any chemistry to really only happen right at the contact point between a piece of Mg and a pellet of KOH.

Another thought is that while probably few people have access to the equipment (or have never used it), mechanical stirring might provide better results due to the above reasoning due slight grinding action, and also just because the paddle can help push potassium globules together.

Once I can find any sand for a sand bath, I'll have to give this a go on small scale with many varying conditions before scaleup.

At least for myself I want to try the following conditions

Reagents: Mg prepared under oil, Mg with iodine surface activation, Mg with mechanical crushing next to KOH
'catalyst': (calling the tBuOH this since we can't seem to confirm its mechanism yet) use KOtBu charged directly in during the reaction, ethylene glycol, glycerine
Solvents: hexanes, distilled mineral oil
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UnintentionalChaos
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[*] posted on 5-12-2010 at 08:25


Quote: Originally posted by aonomus  

At least for myself I want to try the following conditions

Reagents: Mg prepared under oil, Mg with iodine surface activation, Mg with mechanical crushing next to KOH
'catalyst': (calling the tBuOH this since we can't seem to confirm its mechanism yet) use KOtBu charged directly in during the reaction, ethylene glycol, glycerine
Solvents: hexanes, distilled mineral oil


Didn't it get posted upthread that alkoxides with alpha hydrogens are unstable? That would certainly be the case for glycerin and ethylene glycol.




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[*] posted on 5-12-2010 at 08:35


@UnintentionalChaos: Hm, good point, I must have missed it.
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[*] posted on 5-12-2010 at 08:56


The question of good reagents contact (between Mg and KOH) would become less pressing with the mechanism I proposed above: a K t-alkoxide might be reasonably soluble in the solvent (Shellsol or equivalent) and easier to reduce than KOH itself. The t-alcohol would then play the classic role of an activation energy reducer, i.e. a catalyst...

[Edited on 5-12-2010 by blogfast25]
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[*] posted on 5-12-2010 at 09:41


The third photo posted by pok here (true size):

http://www.sciencemadness.org/talk/files.php?pid=194182&...

… does show, no matter how the metal was obtained, that it includes small pockets of impurities. Not a problem that re-melting, or better filtering, couldn’t solve though…
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[*] posted on 5-12-2010 at 12:08


Would this work with NaOH?

NaOH would presumably be easier to work with - fewer problems relating to absorbed water

On the other hand the higher melting point of the Na might be an issue?
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[*] posted on 5-12-2010 at 12:24


Quote: Originally posted by Mossydie  
Would this work with NaOH?

NaOH would presumably be easier to work with - fewer problems relating to absorbed water

On the other hand the higher melting point of the Na might be an issue?


Please read the patent (first page of this thread)...
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[*] posted on 5-12-2010 at 12:26


@ blogfast25:

I also think that the tert.butanol works like a catalyst (see also description on versuchschemie.de).

About my 3rd picture: this aren't impurities. This are just some oxide coated smaller K globules wich got flattened by pressure of my pincette and attached to the clean cut surface of the massive K block. The K really is very pure. Just believe me :P .
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[*] posted on 5-12-2010 at 12:40


Quote: Originally posted by UnintentionalChaos  

Pok- How sure are you that the printing plates are high purity magnesium? Have you successfully tried this procedure utilizing reagent magnesium?


The seller (once upon a time on ebay) told me about the Mg printing plates: "99% pure Mg" if I remember correctly. They were mainly used to print signs for wine bottles.

No, I didn't try it with reagent magnesium. But as the authors of the patent didn't specify the purity (I think), I just think it should be quite pure Mg. 99,9% Mg should work equally good or better.
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[*] posted on 5-12-2010 at 13:13


Quote: Originally posted by aonomus  
Something that comes to mind is that the magnesium is passivated to a degree. Grignards usually need a little kick to get started (crushing with a glass rod, some iodine crystals, sonication). Perhaps either creating the magnesium chips under oil (ie: drill press on a Mg block under mineral oil) or transferring Mg chips in and adding a pinch of iodine prior to addition of KOH might activate the surface more. Since the solvent is non-polar I'd expect any chemistry to really only happen right at the contact point between a piece of Mg and a pellet of KOH.
This hypothesis about a contact-point reaction is interesting. If true, there are a number of things to draw from it and ways to improve the reaction:
  • It would account for there being a very slow reaction in a well-agitated mixture, since the particles would be suspended and only occasionally in contact with each other.
  • Doing the reaction in a vessel that increases particle contact area should improve the rate, such as a pear-shaped flask. A column might work if it helps to compact the reactants.
  • Instead of stirring, kneading the reactants with a masher of some form. A glass rod with a high-tech rubber boot might be feasible. Something like a pair of muller wheels might work, in a configuration as is used to reprocess foundry sand or grind black powder. It's certainly not an off-the-shelf item, but it's easier than making a ball mill that operates at 200 °C under reflux.
  • Create a more intimate contact by preprocessing the reactants. Fuse KOH and make shavings of Mg right into the molten KOH. Pour out in a layer to cool and then break up into pieces.
All this is contingent upon point-contact being significant, but it's also a way of testing the hypothesis.
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[*] posted on 5-12-2010 at 13:17


Quote: Originally posted by Pok  
- the glaspipe (25 cm long!) was surrounded by wet toilet paper (which cooled the pipe so that pipe acted like a reflux condenser)
Did you notice, perchance, if there were two condensation limit heights in the tube?—one for D70 and the other for tert-butanol. In the configuration you're using, you might have had both. Any observation you've got here would inform how the tert-butanol is behaving in its vapor phase.
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[*] posted on 5-12-2010 at 13:23


I wish I had time to try this. Although I don't think I have a source for Shellsol. Has anyone located it?
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[*] posted on 5-12-2010 at 13:31


@ Watson:

Something like a Banbury internal mixer, huh?

http://composite.about.com/library/glossary/b/bldef-b532.htm

Feed a paste of the ingredients, mix for required time and out comes a paste of potassium and by-products, ready for filtering!

It don't hurt to dream! :D
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[*] posted on 5-12-2010 at 13:41


Quote: Originally posted by Pok  
About my 3rd picture: this aren't impurities. This are just some oxide coated smaller K globules wich got flattened by pressure of my pincette and attached to the clean cut surface of the massive K block. The K really is very pure. Just believe me :P .


I contended much higher up that a clever hoaxer could achieve quite easily these very convincing photos by starting from a highly agitated emulsion of molten K (or Na) in kerosene (or similar) with some convincing looking grit thrown in. I'm not calling you a liar though, because I can't prove anything either way and because I'd like to believe you.

Not long now before a small army or SM experimenters gets to work! :cool:

I will follow the progress at versuchschemie.de too...
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[*] posted on 5-12-2010 at 13:42


Quote: Originally posted by Mister Junk Pile  
I wish I had time to try this. Although I don't think I have a source for Shellsol. Has anyone located it?


Look a bit higher up. These people will possibly not know what hit them!
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[*] posted on 5-12-2010 at 15:59


It's the t-butanol, t-amyl alcohol, or other tert alcohol that would be the hangup for me. Can't find anything OTC aside from a few % mixed with other alcohols as entropy51 pointed out (and t-butanol seems to azeotrope with water and methanol so purification would be difficult).



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[*] posted on 5-12-2010 at 16:26
U.S. sources of Shellsol D70


In the U.S., we don't have the same chain of German-based art supply stores. I've been looking for alternate sources. The CAS number is 64742-47-8. As I learned, it doesn't describe a single product, but a set of them parametrically by distillation parameters IBP (initial boiling point) and DP (dry point).

Not exactly a match, but easily the most common, this CAS is about half of what's in WD-40.

There's a product called "Protocol SafeClear Xylene Substitute" with the same CAS number. It's available here, and if you want to spend more money, at Fischer.

Citgo has five different product on this page, with the same CAS number. All of these have a much greater proportion of cycloalkanes than Shellsol D70 does. The one that most closely matches the distillation parameters is the highest-boiling of them; it's called "170 Solvent 66/3".

Equivalent products: Exxsol D80 (from ExxonMobil), Mosspar H (from Petro S.A.), Tarksol SC Plus (from Tarksol, and boils a bit hotter).

In my area, the yellow pages category that holds all the petroleum product distributors is "Oils - Lubricating". These products are all made by oil companies, and finding their distributors is the likely way of getting them at reasonable price.

I also suspect that certain products labeled "odorless mineral spirits" at art stores might be adequate.
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[*] posted on 5-12-2010 at 16:44


Quote: Originally posted by BromicAcid  
It's the t-butanol, t-amyl alcohol, or other tert alcohol that would be the hangup for me.
BLD Science carries 99% grade for about $25 / 250 ml. They sell to small folk. They've got other quantities and grades. This was the only vendor on Google Shopping.

Edit: I thought most would want 99% 250 ml and not the bigger and purer one I posted first. But for whatever reason, there's a $25 hazmat fee in the computer on the small package and not on the larger 99.5% 1 L for $60. Perhaps they'll drop the hazmat if you point it out. Perhaps you'll have extra to share with friend.

[Edited on 6-12-2010 by watson.fawkes]
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[*] posted on 5-12-2010 at 16:51


@watson.fawkes One thought I had about the contact-reaction hypothesis of mine was that there was some video of 'unconventional sodium' (or potassium?) made by lighting an alkali metal hydroxide and magnesium mixture a while back. I only vaugely recall something about this, mainly because of the magnesium fire and its poor product of low purity.

The process development side of me wants to make a way to make this reproducible in good yield, with readily available reagents... once I get a damned sand bath I can start experimenting...

Another thought is to take an aliquot of the reaction mixture (hot) and evaporate to dryness under inert atmosphere to take a look at what is in the reaction mixture. If KOtBu is being constantly turned over by reflux, then the levels of KOtBu should be fairly constant (bar loss of tBuOH upon sampling).

[Edited on 6-12-2010 by aonomus]
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[*] posted on 5-12-2010 at 16:52


T- butanol is easily made by the grignard synthesis from MeMgBr and acetone.
PainKilla has outlined how he successfully made MeBr from NaBr, H2SO4 and MeOH and used it to generate a substantial amount of 1,4-dimethoxybenzene from a solution of hydroquinone in aqueous NaOH.
For turning the MeBr into the grignard, it would have to be purified and dried by a H2SO4 washing bottle and CaCl2 drying tube and condensed in a receiver cooled by ice and salt, or simply dissolved into chilled absolute ether and this solution slowly added to Mg and a little iodine crystal.
For this grignard synthesis, the reflux condenser would have to be colder than 0°C (chilled water/glycol or alcohol as the coolant) to condense the evaporating MeBr, as the formation of the grignard reagent is very exothermic.

I have prepared tert-pentanol from EtMgBr and acetone, and find that this synthesis is excellent to practice the generation and use of a grignard reagent at home.
I mix all of the EtBr with the amount of abs. ether that gives a 2,5 mol EtBr/L solution and add some of it to the stochiometric amount of reagent grade Mg to which a small I2 crystal has been added, so that the Mg is completely covered by the solution.
It is carefully heated by a heatgun or small flame until the solution gets turbid and it starts to reflux on its own (reflux condenser with ice water and drying tube). The rest of the EtBr solution is added at a rate that maintains a gentle reflux of the ether. After all is added, the solution is refluxed for 30-60 minutes so that nearly all of the Mg has reacted (I like to use an excess, but it's not really necessary).
The addition of acetone to this solution is highly exothermic, with fizzing and sputtering. It is done drop by drop under magnetic stirring.
Then work up as usual, with cold dilute aqueous HCl (the tertiary alcohol doesn't dehydrate under these conditions, but be sure to give the ether solution a final thorough wash with aqueous Na2CO3 before distillation, as HCl traces would otherwise cause elimination to 2-methyl-2-butene).

This synthesis of potassium is most remarkable. Regrettably I can't try it at this time, due to lack of Shellsol solvent (what is this solvent made up of anyway?). I do have the t-butanol and 99,8% Mg powder, and the KOH which generally is of 85% purity with the remainder being water.
The t-butanol may not be replaceable in this synthesis, but I hope that the Shellsol is.




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[*] posted on 5-12-2010 at 16:58


Quote: Originally posted by aonomus  
once I get a damned sand bath I can start experimenting...
As a good Canadian, make a Rona run and pick up a bag of backyard playground sand.
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[*] posted on 5-12-2010 at 17:04


Or, go to your neigborhood pet shop. They should have a fine selection of clean sand.



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[*] posted on 5-12-2010 at 17:05


OK this is getting tiresome in that I have lost 3 post recently that managed to vanish from the board all together. The last being a post I JUST made here asking if it was possible that the molten K was acting as a catalyst of sorts dissolving trace amounts of Mg and allowing the reaction to proceed quicker. This would mean that until even trace amounts of K where made nothing at all would happen. Yet when the ball got rolling we would be able to generate large amounts of Molten K threw the process.

I would desire to amalgamate the Mg as a last resort to see if the higher reactivity gives faster better results. I had alot more written on the subject but I don't feel like typing it again. Moderators would you please help me in finding out why my post keep vanishing off the forum...... Is someone deleting them?





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[*] posted on 5-12-2010 at 17:15


Such a cheap, low temperature route to potassium metal needs to be confirmed. I think that diesel could potentially be substituted for Shellsol since they have similar boiling points and low aromaticity.

This is a supremely interesting thread!




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