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Author: Subject: Make Potassium (from versuchschemie.de)
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[*] posted on 2-12-2010 at 11:30


maybe naoh cant be reduced by magnesium and koh can
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[*] posted on 2-12-2010 at 11:31


I can't say I have a lot of understanding about this whole affair, but one thing does strike me immediately. The boiling point of t-butanol is 82 °C and the reflux is being carried out at 200 °C. The partition of the t-butanol is biased toward the vapor phase. The concentration of t-butanol is going be highest in the distillate before it hits the surface of the liquid in the boiling chamber. If it doesn't get appreciable mixing before it evaporates again, it's like having a whole lot less of the reagent. If this is at all relevant (I'm not sure it is), then there are three things I can think of that would help.

1. Ensure that there's adequate excess t-butanol to occupy the gas phase between the boiling liquid and the condenser and the steady-state liquid flow on the condenser. It's like the amount of holdup in an ordinary distillation. It seems possible that the same amount of reactants should they succeed in a small vessel might fail in one too large.

2. Introduce the distillate to the bottom of the boiling flask with a funnel. That will promote greater intimate contact of the t-butanol and the solid reactants before the t-butanol evaporates. This improves the contact geometry of the reactants.

3. Supercool the distillate (that is, below its dew point) before introducing it back into the boiling flask. The t-butanol will take longer to heat up, promoting greater contact time between the reactants.

The only other idea I've got is to try a higher-boiling alcohol, like 2-methyl-2-butanol (t-amyl alcohol). It's boiling point is 102 °C and may have a more favorable partition and better contact times.
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[*] posted on 2-12-2010 at 12:35


Quote: Originally posted by watson.fawkes  
1. Ensure that there's adequate excess t-butanol to occupy the gas phase between the boiling liquid and the condenser and the steady-state liquid flow on the condenser. It's like the amount of holdup in an ordinary distillation. It seems possible that the same amount of reactants should they succeed in a small vessel might fail in one too large.



Patent (Example 1: potassium) mentions a '1 litre four necked flask', production of 34 g of K (87 % of theor.), considerably larger than our German friend...

Example 3 (potassium from potassium alcoholate) mentions potassium tertiary amylate, here heated with Mg chips and decalin as solvent... indicating decalin (if easier available) may be a substitute for Shellsol...

In example 5 (cesium from CsOH), the solvent used is undecane (C11H24), BP 196 C, with some t-butanol, indicating the inert solvent isn't really critical appart from min. BP...



[Edited on 2-12-2010 by blogfast25]
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[*] posted on 2-12-2010 at 13:39


Thing is though I wouldn't trust their examples. Len1 already made a convincing argument that some of the things they wrote up as if they had measured them were clearly just numbers that they had calculated (and not calculated correctly at that). They could easily have found one reaction that worked and then (based on a poor understanding of what was going on) written up a bunch of related 'examples' that would have no chance of success.
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[*] posted on 2-12-2010 at 13:45


Two thoughts:

Preform the potassium tert-butoxide to avoid volatility issues. Either use a small amount of sacrificial potassium in tBuOH or 3A molecular sieves with KOH and tBuOH.

The author lists the source of his magnesium as "Ebay, junkyard - Chip filed down myself." This is (almost surely) not reagent grade...what if it had some aluminum alloyed into it? Perhaps this allows the KOH to etch the surface of the chips giving a much higher surface area. Does anyone have this sort of alloy available for testing?




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[*] posted on 2-12-2010 at 17:26


One thing that sounds like a possible idea to try is to add in a small amount of a phase transfer catalyst, or even something like a crown ether. Heck, trying something like glycerine (cheap, readily available, potential chelator for K+ in non-polar solvents) comes to mind too.

I don't have any MgO or cheap KOH (just a bottle of sigma reagent grade I'm saving) so I'm holding off for now. I'm also waiting to try to get my hands on a tank of nitrogen gas to create an inert atmosphere to do this experiment right.
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[*] posted on 2-12-2010 at 19:42


well I since gave up boiling my paint thinner , mg, naoh, isopropanol slurry. nothing was happening, when watered down, no reaction, but i'm not giving up on this, i'll try with other solvents i have around, I heard that lamp fuel has a boiling point in the range of 200 C. If this whole business has any chance of working , i'm pretty sure it would be due, as bbartlog said, to a catalyst that's already present in the solvent and not so much the tert-butanol.
But we need more folk to have a go at this!

[Edited on 3-12-2010 by condennnsa]
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[*] posted on 2-12-2010 at 19:55


No it has nothing to do with a catalyst in the solvent, this is expressed in the patent.




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[*] posted on 2-12-2010 at 23:11


I'll have a go later.
Watson.fawkes mentioned one concern of mine so I wont mention it again. Potassium melts at 63 deg C and both the t-butanol and isopropyl alc. boil at 82 degC. I'm not sure why the temperature has to be as close to the bp of the solvent apart from optimising the rate of reaction?
The initial stage if the reaction on that forum involves heating the reactants before the butanol is added. I'm assuming this is to rid the contents of any water so 200 degC or where the solvent starts boiling is good. After the evolution of H2 has completed I would let things cool to the bp of the alcohol (80 degC) and do everything to prevent air accessing the system. So what if things proceed slowly.

2 things that don't make sense to me though. According to the reaction equation he provides MgO is formed. I don't see any in his flask. What happens ot the MgO?
Also, I find it unnatural for the potassium to form beads like that. As the reaction proceeds the precipitated K would have to be ultra clean for it to merge like that even at those temperatures without some sort of 'fluxing' condition helping it along. I would expect a gunky mass to accumulate at the bottom of the flask.




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[*] posted on 3-12-2010 at 07:08


Quote:
So what if things proceed slowly.


If the reaction rate were to be halved for every 10C lowering of temperature, then you'd be looking at a reaction that took 4000x as long or so. The author on versuchschemie (pok?) suggests that 20-30 minutes is long enough to be able to see whether K globules are forming (though not to run to completion... that takes four hours). So potentially eight to twelve weeks at 80C to see whether you'd be getting anywhere, over a year to finish the reaction. Sometimes slowly really is ... too slow.

Quote:
MgO is formed. I don't see any in his flask.


There are bits of crumbly-looking white/gray stuff in his flask (up until he transfers the K to another container). In the first couple of pictures I assume the bits are KOH, but after that presumably MgO.
The beads, dunno. Surface tension should be high (I don't find the beading up strange), but I wouldn't be surprised if there's a ton of gunk trapped within the beads.

I'm interested in watson.fawkes observation about the boiling point of the tert-butanol. In order for it to not gas off, it would have to react fairly rapidly (turning into alkoxide, presumably) after being added. I suppose that the reason that it is added mixed in with some solvent is to provide a little bit of thermal buffering, giving some more contact time before it evaporates. Even so, it seems strange that it would be able to form a substantial amount of alkoxide in the short time it would be in the solution, especially given that it is just dripped in on top (no thistle tube or anything like that to try to bring it closer to the KOH on the bottom).

There's another thing about the post on versuchschemie that strikes me as odd: after excluding air via the balloon-with-pinhole (nice trick), he must have allowed quite a bit of air back in while slowly adding the catalyst solution with a dropper. Did he repeatedly unstopper the flask (he says the t-butanol was added over half an hour)? If so it certainly suggests that inert atmosphere is not required. But maybe he dripped the stuff in through the existing tube after removing the balloon, which sounds awkward but would I guess have made for a lot less air getting in the flask.
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[*] posted on 3-12-2010 at 08:09


Quote: Originally posted by froot  
2 things that don't make sense to me though. According to the reaction equation he provides MgO is formed. I don't see any in his flask. What happens ot the MgO?
Also, I find it unnatural for the potassium to form beads like that. As the reaction proceeds the precipitated K would have to be ultra clean for it to merge like that even at those temperatures without some sort of 'fluxing' condition helping it along. I would expect a gunky mass to accumulate at the bottom of the flask.


No, no, the MgO is there alright.

And this is exactly how I would expect liquid potassium to behave in an inert liquid: with purity that behaviour has little to do. The only thing that somewhat stops the globules from merging into larger ones is surface tension. Think mercury, really. A round bottomed flask instead of a conical flask would give a slight advantage because it would promote contact between the reagents but also slightly push the formed globules together. I think gentle stirring rather than vigorously is probably to be preferred to promote metal coalescence. Keep it moving but not flying...

The potassium is likely to be quite free of impurities as neither the solvent, the alcohol nor the MgO are soluble in it. That’s somewhat similar to the formation of a regulus of molten metal during various Goldschmidt style (thermite) reduction reactions: there too fine globules of molten metal merge into a pool, pushing out any insoluble impurities (slag).

The patent does recommend passing the molten metal over a suitable filtering media. Purity could be checked superficially by reacting the metal with water and slightly acidifying the obtained KOH solution: any remaining occlusions in the metal should show up as turbidity of the solution…

What I did find especially strange about the patent is where in Example 1 (Potassium from KOH) they use KOH with about 9 % water and then compensate the amount of Mg used exactly to stoichiometry (acc. Mg + H2O = MgO + H2O). Deliberate? In Example 2 (Sodium from NaOH) there’s no mention of water and the alcohol is added straight from the beginning…

I will be trying this relatively shortly with ‘deodorised kerosene’ and 2-methyl-2-butanol (t-pentanol). If it does work there are some areas where improvement could be envisaged to turn this into a slightly more productive method:

1. higher boiling solvent to cut down on reaction times
2. other, perhaps longer chain t-alcohols
3. lower ratio of reaction media to reagents: our German friend simply divided all quantities in Example 1 by 10. Had he used only 25 ml of ‘solvent’, would it have made much difference? An idea of the solubility of the K t-butanoate in Shellsol might be enlightening there…


[Edited on 3-12-2010 by blogfast25]
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[*] posted on 3-12-2010 at 08:22


Quote: Originally posted by bbartlog  
There's another thing about the post on versuchschemie that strikes me as odd: after excluding air via the balloon-with-pinhole (nice trick), he must have allowed quite a bit of air back in while slowly adding the catalyst solution with a dropper. Did he repeatedly unstopper the flask (he says the t-butanol was added over half an hour)? If so it certainly suggests that inert atmosphere is not required. But maybe he dripped the stuff in through the existing tube after removing the balloon, which sounds awkward but would I guess have made for a lot less air getting in the flask.


No, he states he used a syringe (‘Spritze’) although he doesn’t show it. Presumably the syringe goes straight through the rubber stopper or is inserted between the stopper and the flask neck. He does recommend drop funnel ('oder besser: einem Tropftrichter in 2-Hals-Kolben').

A two holed bung with refluxer and drop funnel in place would be the simplest solution…


[Edited on 3-12-2010 by blogfast25]
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[*] posted on 3-12-2010 at 08:47


In the mean time there have been failures to reproduce the method too, for instance:

Echelot on 28/11, 15.36, who got nothing:

http://www.versuchschemie.de/hartmut.php?t=14677&postdays=0&...

One guy also warns against using molten potassium in conjunction with Teflon coated stirrer bars;

(CF2)n + 2 n K == n C + 2 n KF is potentially nasty!
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[*] posted on 3-12-2010 at 09:14


OK, if I were to bet my money I'd go for "bogus".

The author simply had some potassium to fake the pics with, because it IS potassium. Time will show I was right and pretty much all the above discussions are a waste of time and Internet bills.

Len also said something about feeling "ashamed" for the wasted time, chems and credibility he credited this project with once the failure was so obvious. WiZ should hopefully jump in with some stories such as "gold from seawater".

This case clearly belongs to my collection of such holly grails:
- phorone
- Hodge's easy WP (albeit he clearly made it as a joke)

The only reaction I've been impressed with all these past 10 years is the Calgon reduction for WP making.

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[*] posted on 3-12-2010 at 09:21


I've been asking myself, eversince I saw Pok's results, is if this really does work, how come the alkali metal producers did not implement it? It should certainly be way cheaper than any electrolytic process.

All the reagents are dirt cheap, and the alcohol non-consumable... something's fishy here.

a_bab, it is possible that he faked it , but what the heck would be his motive? Just making a mess with solvents, adding rubble and potassium to it, melting it , coming up with calculations and costs, just to post it on some forum??? that'd be crazy

[Edited on 3-12-2010 by condennnsa]
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[*] posted on 3-12-2010 at 09:29


Ok so I began my attempt this afternoon.
For the solvent I used technical oil which was a judgement call on my part and for the catalyst I used isopropyl alcohol.
I could not locate any magnesium today so I used a camping firestarter which is a block of Mg (supposedly) with a piece of flint. I used a drill press to produce the shavings.



I used the same setup as described.



I do not have the means to read temperatures above 110 degC but I heated the flask to well above 100 degC. As described I got the evolution of gas but did not test for hydrogen. This evolution of gas slowed up and I turned the heat off and let it cool to 80 degC.



I prepared a syringe with isopropyl alcohol and some of the technical oil as described. I expected the 2 to be miscible with each other but this was not the case.



As it was cooling I added a drop from the syringe and waited if the alcohol fizzed into vapour from the heat. When it was cool enough I added the lot, swirled it, and left it for a few minutes for it to get used to what I did to it. It turned a tea colour. I then turned up the heat again and continued swirling it and the tea colour darkened. No 'beads' appeared.



This is it so far and I'll post again later.





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[*] posted on 3-12-2010 at 09:42


I found another post by Pok detailing this procedure , before he started a dedicated thread, this post has more pictures and some additional information:

here is the translation:
http://translate.google.com/translate?hl=en&sl=de&u=http://w...

he says:

" (?) The dropwise addition of tert-butanol must be slow (! Exactly as directed), it evaporates much more abruptly when it hits the hot Shellsol mix, but again condenses and forms K-alkoxide can react with Mg (? ). "

the info and pics he provided makes it really credible...

[Edited on 3-12-2010 by condennnsa]

[Edited on 3-12-2010 by condennnsa]
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[*] posted on 3-12-2010 at 09:48


Quote: Originally posted by a_bab  


[big snip]because it IS potassium. Time will show I was right and pretty much all the above discussions are a waste of time and Internet bills.



So you want to rebutt the guy's post on the basis of the photos, photos which tell you 'it IS potassium'... And you don't see the contradiction there? How do you know from the photo 'it IS potassium'? For all you know they're aluminium balls: I have one just like it...

We all do well to be sceptical about this but I believe it's worth trying to repeat the experiment.

Two other experimenters on versuchschemie claim to have seen ample amounts of hydrogen, one saw a small amount of K. Where does the hydrogen come from? Water + Mg? There's not enough water there. Alkanes + Mg? Hardly likely...

No, this is definitely worth revisiting, IMHO...


[Edited on 3-12-2010 by blogfast25]
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[*] posted on 3-12-2010 at 09:59


Quote: Originally posted by froot  
Ok so I began my attempt this afternoon.
For the solvent I used technical oil which was a judgement call on my part and for the catalyst I used isopropyl alcohol.
I could not locate any magnesium today so I used a camping firestarter which is a block of Mg (supposedly) with a piece of flint. I used a drill press to produce the shavings.


Your experimental conditions are rather far removed from pok’s. No temperature reading is a disadvantage, if reduction does take place, the rate is very strongly dependent on temperature.

But you did get ‘gas’, assumed hydrogen. How long did that last for?
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[*] posted on 3-12-2010 at 09:59


I did not read all about this topic, but just wanted to comment that the use of isopropanol is most likely futile. Metal alkoxides containing alpha-hydrogens are generally not stable up to 200 °C. They tend to decompose via beta-hydride elimination reactions, the rate at which they do so highly depends on the what metal alkoxide they are. I would expect potassium isopropoxide is not stable at the required conditions. The acetone formed in the decomposition is most likely to blame for the brown-red coloured crap formed via self condensation. On the other hand, t-BuOK is commonly used as a stable alkoxide at fairly high temperatures, so it might actually be long living at 200 °C as well. Also, tert-butoxides should be much more soluble in paraffins, which is another reason to stick to tert-butanol or higher homologues. The formation of t-BuOK should be fairly rapid at the given conditions, especially if Mg is finely divided and/or activated, so I don't think most of t-BuOH escapes, particularly if stirring is used or heating up is slow.

As to how this redox works, I have no good idea. I don't see how a "2 t-BuOK + Mg <=> (t-BuO)2Mg + 2 K" reaction could ever be favoured on the right side. Though at least the other part of the cycle, "(t-BuO)2Mg + KOH <=> 2 t-BuOK + Mg(OH)2" makes sense direction-wise. Quite weird. Anyhow, I would guess the most important factor is the activation of the Mg metalic surface and the quality&mesh of the metal.




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[*] posted on 3-12-2010 at 10:08


"blogfast25: So you want to rebutt the guy's post on the basis of the photos, photos which tell you 'it IS potassium'... And you don't see the contradiction there? How do you know from the photo 'it IS potassium'? For all you know they're aluminium balls: I have one just like it..."

This clearly shows you never had the opportunity to play with potassium or at least clean potassium balls, and notice their unique bluish hue as they start to oxidize. Few of us did, but those who did will understand what I mean. Their clean aspect in the pic is obvious because they melted and lost their cover, explaining the greyish color in the flask.
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[*] posted on 3-12-2010 at 10:15


Blogfast the bubbling lasted for about half an hour.
Thanks for the input Nicodem, that explains my tea then, the solvent cleared up after a while and a brown coagulate started appearing which confirms what you said.




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[*] posted on 3-12-2010 at 10:33


Quote: Originally posted by a_bab  
"blogfast25: So you want to rebutt the guy's post on the basis of the photos, photos which tell you 'it IS potassium'... And you don't see the contradiction there? How do you know from the photo 'it IS potassium'? For all you know they're aluminium balls: I have one just like it..."

This clearly shows you never had the opportunity to play with potassium or at least clean potassium balls, and notice their unique bluish hue as they start to oxidize. Few of us did, but those who did will understand what I mean. Their clean aspect in the pic is obvious because they melted and lost their cover, explaining the greyish color in the flask.


Camera's lie: a lot. Had I posted a photo of my Al ball covered in a light paraffin oil and claimed it was potassium you'd have gladly believed me.

And I have played with potassium, thanks very much. You assume too much...
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[*] posted on 3-12-2010 at 10:37


Quote: Originally posted by froot  
Blogfast the bubbling lasted for about half an hour.
Thanks for the input Nicodem, that explains my tea then, the solvent cleared up after a while and a brown coagulate started appearing which confirms what you said.


You see, purely intuitively, that seems a long time for just any water (from the oil and the KOH) reacting off...
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[*] posted on 3-12-2010 at 11:53


Blogfast, I am not assuming too much. Show me your stash of potassium and I believe you. BTW, dropping a piece or two of potassium in water while at high shool doesn't count here. I can, though, show you several pics with K, Na and Al in the same bottle under paraffin oil so you can see the difference. I'm aware about the camera faults, but K does have a bluish tinge

I would have not believed you with an aluminium ball. Don't forget the balls are slightly irregular, just like the real stuff. You obviously don't know what you're babbling about period.

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