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Author: Subject: Make Potassium (from versuchschemie.de)
White Yeti
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[*] posted on 29-11-2012 at 19:19


I did consider steric hindrance as a potential drawback, but all things considered, it might work equally well as a catalyst because it has a higher boiling point and it is more soluble in nonpolar solvents, as opposed to tert-butOH which is rather soluble/miscible with water. The higher boiling point would allow it to persist in solution for longer before boiling off, making it more available and decreasing reaction time, possibly improving yield.

@tetrahedron: Terpineol could be worth a try, but the higher steric hinderance could bring some issues. Its lower price could make it a good catalyst to try out though.




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[*] posted on 30-11-2012 at 13:17


WY:

alpha-Terpineol was tried by me and didn't work at all. Very disappointing...

Linalool is definitely worth a shot.

There's another longer chain t-alcohol that was tested by 'garage chemist' but it didn't work either.

Another one worth considering is tetrahydro myrcenol. Not easy to get though. I have dihydro myrcenol but haven't had time to test it.




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[*] posted on 1-12-2012 at 12:37


I remember reading about alternate catalysts upthread, it's a shame most attempts did work. I think that experimenting with catalysts is more a matter of academic curiosity than preparatory improvement at this point.

That being said, I remember seeing a mechanism for this reaction, but for some reason I can't find it. If I could find it, the following question would perhaps be unnecessary.

I was wondering if tertiary thiols could catalyse this reaction, thioterpineol for example. Thioterpineol specifically might not work because of its structural similarity to terpineol, which yielded poor results. Other tertiary thiols could potentially be used, as long as the smell doesn't become overwhelming.




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[*] posted on 1-12-2012 at 13:26


Quote: Originally posted by White Yeti  
I remember reading about alternate catalysts upthread, it's a shame most attempts did work. I think that experimenting with catalysts is more a matter of academic curiosity than preparatory improvement at this point.

That being said, I remember seeing a mechanism for this reaction, but for some reason I can't find it. If I could find it, the following question would perhaps be unnecessary.

I was wondering if tertiary thiols could catalyse this reaction, thioterpineol for example. Thioterpineol specifically might not work because of its structural similarity to terpineol, which yielded poor results. Other tertiary thiols could potentially be used, as long as the smell doesn't become overwhelming.


Tertiary thiols? 'Availability!' springs to mind... Really hard to obtain/synthesise.




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[*] posted on 3-12-2012 at 05:42


Quote: Originally posted by White Yeti  
I was wondering if tertiary thiols could catalyse this reaction

why fix a synth that isn't broken? is t-BuOH really so hard to get?

From Mercaptans and Derivative Chemistry:
Quote:
The bond strength between the hydrogen and the larger sulfur atom is weaker in the case of mercaptans (RSH) than is the oxygen-hydrogen bond strength in alcohols (ROH). As a result, mercaptans are more reactive, more highly ionized (RSH H+RS-) and more acidic than alcohols.

Quote:
A characteristic reaction of mercaptans is mercaptide formation. When methyl mercaptan is bubbled into 25% aqueous sodium hydroxide, the hydrated sodium mercaptide, CH3SNa • 4.5H2O, precipitates out as crystalline needles.

the way it's described, this reaction is more favorable than the corresponding alcoholate formation. i wonder how this added acidity would affect the original mechanism:
Quote: Originally posted by Polesch  

if still interested: Sulfole® 120 t-dodecyl mercaptan (msds)
Quote:
Sulfole® 120 mercaptan is a mixture of tertiary mercaptans, predominantly tertiary dodecyl mercaptan (thus the source for its acronym TDM). This product contains highly branched C12H25 alkyl mercaptan isomers, produced by the addition of hydrogen sulfide to propylene tetramer. It is used as a chemical intermediate to introduce bulky C12H25 alkyl-thio substituents into chemical substances. Its major use is as a chain transfer agent to control molecular weight of polymeric systems undergoing free-radical polymerization.


[Edited on 3-12-2012 by tetrahedron]
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[*] posted on 3-12-2012 at 08:53


@tetrahedron:

No, t-butanol isn't really hard to get (and 2-methyl butan-2-ol (or M2B2) works fine too).

The main goal of looking for alternative catalysts is to speed up the reaction for sodium synthesis. One expected (but as yet totally unproven) route is to use longer chain t-alcohols because they can be reasonably expected to have more soluble Na alkoxides.




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[*] posted on 3-12-2012 at 23:37


Has anyone who's tried this synthesis experienced what I'd call localised gas eruptions that are fairly loud hissing like water refuxing back into hot oil,I used 250mesh magnesium powder,and a solvent called recosol D-60 b.p 195-205C and T-butanol,I let it go for a few hours and I never noticed any potassium form,I suspect my KOH or would the hot solvent drive off any water.

[Edited on 4-12-2012 by hames]
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[*] posted on 5-12-2012 at 08:50


Quote: Originally posted by hames  
Has anyone who's tried this synthesis experienced what I'd call localised gas eruptions that are fairly loud hissing like water refuxing back into hot oil,I used 250mesh magnesium powder,and a solvent called recosol D-60 b.p 195-205C and T-butanol,I let it go for a few hours and I never noticed any potassium form,I suspect my KOH or would the hot solvent drive off any water.

[Edited on 4-12-2012 by hames]


Any water in the solvent and in the KOH (all grades of KOH contain approx. 10 % water) is supposed to be reacted away by Mg + 2 H2O === > Mg(OH)2 + H2. This is the initial hydrogen evolution.




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[*] posted on 5-12-2012 at 09:20


One expected problem with the longer chain t-alcohols is their poor phase transfer. It seems obvious that the only way for potassium t-alkoxide to form is in that the t-alcohol first gets absorbed onto the KOH surface which is essentially a very polar hydrated surface. In this regard, t-butanol and t-pentanol appear optimal for potassium synthesis as was also demonstrated experimentally.

Meanwhile, sodium synthesis (if truly possible at all) represents the other problem, the problem of phase transfer of the sodium t-alkoxide from the hydroxide phase into the organic phase. Up to now the focus has been into using longer chain t-alcohols to solve this problem, but due to the above mentioned issue, perhaps the solution is best found in changing the solvent.




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[*] posted on 5-12-2012 at 10:37


@Nicodem:

To a somewhat more polar solvent? By blending solvents, a more polar solvent system could be envisaged. But higher polarity usually means introducing exoatoms which the alkali metals tend to be reactive towards...


[Edited on 5-12-2012 by blogfast25]




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[*] posted on 5-12-2012 at 11:10


The problem of solvent inertness is indeed an annoying one, but I remember someone managed to get the potassium process to work in tetraline which one could also intuitively expect to be unsuitable. Did anybody tried tetraline, cymene, diphenylmethane or other easily available high boiling alkylaromatic solvents for sodium production? This thread is too long and I don't have the motivation to look for such examples.

Also, other solvents that could be more polar and possibly inert to sodium are ethers. Though I'm not sure they would be inert above 180 °C needed for the reaction. Diphenyl ether is the most common solvent used for such temperatures, but I'm afraid it is also the most easy to cleave by a SET reduction (e.g., DOI: 10.1021/jo00143a014). Polyglymes tend to solvate alkali metals by dissociation into alkali cations and electrons, and are thus probably unsuitable (or not?), but simple high boiling dialkyl ethers might do.

Another option is to use a mixture of lower and higher t-alcohols, for example t-butanol and a long chain t-alcohol. One for the deprotonation process at the NaOH surface, the other for solubility.




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[*] posted on 5-12-2012 at 12:59


Quote: Originally posted by tetrahedron  

why fix a synth that isn't broken? is t-BuOH really so hard to get?


To this I answer:
Quote:
Experimenting with catalysts is more a matter of academic curiosity than preparatory improvement at this point.


The reason I said this is because it's obvious this method works if one doesn't try to pull it off with a cheapo solvent. It's more interesting to experiment with catalysts, which give insight into the reaction mechanism, and hold potential for marginal procedural improvement. There's more to talk about when it comes to catalysis.

As discussed above, one area that hasn't seen much improvement was the preparation of sodium via this method. But to be perfectly honest, I think the electrolysis of sodium hydroxide is a more viable route to preparing sodium in large quantities.




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[*] posted on 20-12-2012 at 22:14


I finally worked out a method to get good KOH from NaOH, KCl, and H2SO4. It also generates free hydrochloric acid, which I'm bubbling into distilled water. If that t-butanol arrives, I might be well on my way to trying this experiment myself!



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[*] posted on 3-1-2013 at 06:57


Quote: Originally posted by Nicodem  
One expected problem with the longer chain t-alcohols is their poor phase transfer. It seems obvious that the only way for potassium t-alkoxide to form is in that the t-alcohol first gets absorbed onto the KOH surface which is essentially a very polar hydrated surface. In this regard, t-butanol and t-pentanol appear optimal for potassium synthesis as was also demonstrated experimentally.

Meanwhile, sodium synthesis (if truly possible at all) represents the other problem, the problem of phase transfer of the sodium t-alkoxide from the hydroxide phase into the organic phase. Up to now the focus has been into using longer chain t-alcohols to solve this problem, but due to the above mentioned issue, perhaps the solution is best found in changing the solvent.

Quote: Originally posted by White Yeti  

As discussed above, one area that hasn't seen much improvement was the preparation of sodium via this method. But to be perfectly honest, I think the electrolysis of sodium hydroxide is a more viable route to preparing sodium in large quantities.


So, have 2-methyl pentane-2-ol and 2-methyl hexane-2-ol been tested for potassium and sodium synthesis?
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[*] posted on 17-1-2013 at 15:09


For anyone looking for some tertiary butyl alcohol, I was looking through eBay recently for a couple of chemicals and noticed someone is selling about 250ml of the alcohol for about $30. Not that terrible of a price, especially since some people are having such a difficult time obtaining it...

Heres a link... http://www.ebay.com/itm/Tertiary-Butyl-Alcohol-250ml-/170974...
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[*] posted on 17-1-2013 at 15:26


Quote: Originally posted by Beldensb5  
For anyone looking for some tertiary butyl alcohol, I was looking through eBay recently for a couple of chemicals and noticed someone is selling about 250ml of the alcohol for about $30. Not that terrible of a price, especially since some people are having such a difficult time obtaining it...

Heres a link... http://www.ebay.com/itm/Tertiary-Butyl-Alcohol-250ml-/170974...


As long as you are making K it isn't that bad for the small quantities required. If you need it as a reagent that is somewhat expensive. I got twice that much for 5$ less from a chemical supplier!

[Edited on 17-1-2013 by Mailinmypocket]
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[*] posted on 25-1-2013 at 15:04


I love to fix syntheses that aren't broken, so what about replacing the KOH with preformed KOR? When R is tAmyl it can be made anhydrously from KOH and tAmyl alcohol with azeotropic distillation and a Dean-Stark trap. I've no confidence in the reported melting points of KOtBu and KOtAm though, but I'd ideally go to a solventless system....
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[*] posted on 26-1-2013 at 06:23


Quote: Originally posted by EdMeese  
I love to fix syntheses that aren't broken, so what about replacing the KOH with preformed KOR? When R is tAmyl it can be made anhydrously from KOH and tAmyl alcohol with azeotropic distillation and a Dean-Stark trap. I've no confidence in the reported melting points of KOtBu and KOtAm though, but I'd ideally go to a solventless system....


Production of alkali metals by reduction of the t-butoxides with Mg is covered by the patent [see page 1] on which this thread is based. But for hobbyists it's a little heavy on the t-butanol!

With KOH we use only 0.1 mol of t-BuOH per mol of KOH, with K t-BuO the ratio of K/t-ButOH becomes 1.

Reacting KOH with t-ButOH produces water of course, the enemy of this reduction reaction. So you'd need to obtain water free K t-ButO.




[Edited on 26-1-2013 by blogfast25]




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[*] posted on 26-1-2013 at 13:02


making the dry KOtBu is quite a pain, that (and presumably a lower mp) was the main reason for thinking t-amyl alcohol was the way to go. But I don't have a bucket of that yet either.

And thanks, I didn't do the homework it seems :-)
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[*] posted on 26-1-2013 at 13:19


Quote: Originally posted by EdMeese  
making the dry KOtBu is quite a pain, that (and presumably a lower mp) was the main reason for thinking t-amyl alcohol was the way to go. But I don't have a bucket of that yet either.

And thanks, I didn't do the homework it seems :-)


What makes you think the K alkoxide of t-amyl alcohol (don't let me try and 'go IUPAC' on this!) is easier to obtain water free, compared to K t-butoxide?


Ooops: I see, azeoptropic distillation of the excess t-amyl alcohol/water mixture. All this compilcates the procedure no end of course. But it makes for interesting thoughts ;-)



[Edited on 26-1-2013 by blogfast25]




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[*] posted on 25-2-2013 at 08:22


About to try this at my school. Any advice?
Setup so far:
-Hotplate w/ stirrer, stir bar
-Mineral oil, 70 mL as solvent
-~1mL t-BuOH
-reflux condenser w/ rubber joint
-100mL Erlenmeyer flask

The mix will be lightly stirred to promote K production, but can I get away with heavier stirring?
Also, due to the length of the club, it would be wonderful to get this done in an hour, instead of the usual 3-4. Stirring greatly speeds up reaction time, according to the Raging Nurd, but by how much?
If speeding up time really isn't an option, I could always set up the mix in the morning, and come back later as it's finishing. Possibly.

Any thoughts?




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[*] posted on 25-2-2013 at 09:30


Quote: Originally posted by elementcollector1  
About to try this at my school. Any advice?
Setup so far:
-Hotplate w/ stirrer, stir bar
-Mineral oil, 70 mL as solvent
-~1mL t-BuOH
-reflux condenser w/ rubber joint
-100mL Erlenmeyer flask

The mix will be lightly stirred to promote K production, but can I get away with heavier stirring?
Also, due to the length of the club, it would be wonderful to get this done in an hour, instead of the usual 3-4. Stirring greatly speeds up reaction time, according to the Raging Nurd, but by how much?
If speeding up time really isn't an option, I could always set up the mix in the morning, and come back later as it's finishing. Possibly.

Any thoughts?


The stirring bit is controversial and I'm not convinced faster stirring works, as Nurdrage claims.

You can split the experiment into two parts, though: 2 hours for actual reaction, then cool to RT and stopper properly.

Then, next session, dilute flask contents slightly with fresh solvent, add a few drops of isopropanol (99 %) or ethanol (99%), transfer to a clean conical flask and heat to about 100 C (e.g. on steam bath). Swirling the flask regularly will make the droplets of K (assuming some formed in the first session, of course!) coalesce into larger and larger ones. This too will take 1 - 2 hours...



[Edited on 25-2-2013 by blogfast25]




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[*] posted on 25-2-2013 at 09:43


Might be able to do that... Maybe. The 2-hr reaction will be the tricky part, because the time window is only an hour and 20 minutes long. Could set up at lunch...
Or I could try to extend Science Club for the day to fit the time window. Unlikely, but possible.
Could make the lab into 2 days, but we do have other stuff to do.
I think that I'll give this a try at home this week, and then show it to the club next week. That way I might get 'familiar' with the experiment, and might be able to do it faster.
Can you tell I'm nervous? ;D




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[*] posted on 25-2-2013 at 09:59


Definitely a good idea to familiarize yourself with an experiment before showing it off, especially if it involves explosive metals! I rarely record my first attempt at an experiment for posting to YouTube - I almost always run into problems that would make a video presentation of it pretty boring :P I can't wait to try this one out myself - now that I have all the materials I just need to work out the logistics and set aside some time one of these weekends.

That's great that you have a Science Club; I feel like most schools nowadays don't have anything like that. Do you focus on chemistry or is it more broad?
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[*] posted on 25-2-2013 at 10:04


It's much more broad than chemistry, and more often focuses on physics (our coach was a physicist or something, he's retired now). We just went to the Science Bowl, which we've been training for all year. It focuses on everything from Math to Energy to Earth and Space, with Chemistry, Physics and others thrown in there as well. (We took fifth and fourth place with our two teams, too. :))

Anyway, enough OT bragging about our awesome club.

Unfortunately, can't actually try out stirring - so I guess it's the 4-hour long haul for me. If it works, I'll bring in a sample of K metal to the meeting and compare results. If it doesn't... Ah well.

EDIT: I have 40 mesh Mg 'powder' as well as turnings, and the powder should speed up the rate of reaction significantly. Only problem is, I might not recognize the potassium for the magnesium! :D
Also, I'm attempting to make my 125 mL Erlenmeyer as dry as possible for the synth, because any water, no matter how small an amount, is going to impact yield. Any suggestions for getting the glass super-dry?

[Edited on 25-2-2013 by elementcollector1]




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