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blogfast25
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Today I performed an experiment using decalin as a solvent. Decalin, or decahydronaphtalene, has the advantage of a higher density compared to
straight or branched alkanes of similar C numbers: 0.896 which is higher than that of molten potassium: 0.828 (at MP, Wiki). It’s also inert and has
the right boiling point (trans: 187 C, cis: 196 C, mine is racemate I think).
Nurdrage had previously reported excellent results with tetralin which has an even higher density.
To demonstrate that K should float in decalin, a few small and fairly dirty K balls were suspended in decalin in a test tube, at 90 C. They float
alright albeit not very convincingly (the dirt dropped off on melting):
So the usual set up with the usual ingredients (2M2B as catalyst) was tested, 50 ml decalin scale:
Using a sand bath the temperature rise was less steep and the initial hydrogen evolution (dehydration step) gentler than last time. Everything else
also proceeded as normal:
• Checking for hydrogen (inverted test tube over refluxer top) tested positive each time
• Solvent clouded over as usual: formation of MgO
Except: no floating potassium!
I stopped the test slightly prematurely due to a technical problem and cooled down to below 70 C. After decanting off the supernatant liquid no
potassium balls were observed but the grey/blue sludge did prove full of extremely fine potassium. No coalescence whatsoever though. Quite
disappointing…
[Edited on 2-6-2013 by blogfast25]
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MyNameIsUnnecessarilyLong
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Had success with ~30g Mg chips freshly made on lathe, 60g KOH freshly crushed from flake, and 10.4mL t-butyl in approximately 300-350mL of Lamplight
Ultra-Pure Paraffin Oil in a 500mL RBF. Most of the potassium ended up as fine particles with the few largest balls being about .5 - 1mm. I
transferred it to another flask and plugged it into a rotary evaporator to see if spinning would help coalescence. It didn't, and actually looks like
a lot of the K particulate might've oxidized in the process.
I'm going to try centrifuging a small portion in the next few days.
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blogfast25
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Quote: Originally posted by MyNameIsUnnecessarilyLong  | Had success with ~30g Mg chips freshly made on lathe, 60g KOH freshly crushed from flake, and 10.4mL t-butyl in approximately 300-350mL of Lamplight
Ultra-Pure Paraffin Oil in a 500mL RBF. Most of the potassium ended up as fine particles with the few largest balls being about .5 - 1mm. I
transferred it to another flask and plugged it into a rotary evaporator to see if spinning would help coalescence. It didn't, and actually looks like
a lot of the K particulate might've oxidized in the process.
I'm going to try centrifuging a small portion in the next few days. |
Well, that's certainly an novel approach [centrifuging] in this here context.
How long was your run and what was the average temperature (estimate)?
Did you load all reactants at once or did you used the stepped procedure (patent)?
[Edited on 14-6-2013 by blogfast25]
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MyNameIsUnnecessarilyLong
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by MyNameIsUnnecessarilyLong | Had success with ~30g Mg chips freshly made on lathe, 60g KOH freshly crushed from flake, and 10.4mL t-butyl in approximately 300-350mL of Lamplight
Ultra-Pure Paraffin Oil in a 500mL RBF. Most of the potassium ended up as fine particles with the few largest balls being about .5 - 1mm. I
transferred it to another flask and plugged it into a rotary evaporator to see if spinning would help coalescence. It didn't, and actually looks like
a lot of the K particulate might've oxidized in the process.
I'm going to try centrifuging a small portion in the next few days. |
Well, that's certainly an novel approach [centrifuging] in this here context.
How long was your run and what was the average temperature (estimate)?
Did you load all reactants at once or did you used the stepped procedure (patent)?
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I ran it for about 1 & 1/2 - 2 hours one night but switched it off and restarted it the next day for an additional 2 & 1/2 hrs. After the
initial run, the medium was whitish-grey and very viscous-almost jelly consistency and when cooled, a 3-4mm thick whitish layer formed at the surface.
No potassium was seen at that point.
The 2nd run became a darkish grey color about 1hr in, and that's when little potassium balls started popping out.
I mixed everything together in one pot. I tried this synthesis at half-scale last year and dripped in the t-butyl once everything started refluxing,
and I got absolutely nothing from that except brownish-grey sludge. I was also using mineral oil for that one instead of thin parrafin oil, and the
magnesium was made by grinding a Mg firestarter into oil, and flaked KOH was added instead of crushed.
I broke all my high temp thermometers a few months ago, so I'm not certain how hot it was. It was at a very slow boil (roughly 5-10 bubbles per
second), and just by touching the flask it didn't feel to me much hotter than a flask of boiling water. I'd guess it was around 250F.
I noticed that some t-butyl was dripping out of the top of the condenser at the same time the hydrogen was evolving. I sucked air through the
condenser manually and that didn't seem to condense it fast enough. Next time I'm going to try coolant.
Pic of reactor during the first 10 minutes:
http://i.imgur.com/d1dxcK8.jpg
[Edited on 6-15-2013 by MyNameIsUnnecessarilyLong]
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blogfast25
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Interesting how you obtain a jelly like solvent too. I get that every time the reaction is successful. I think it's the K-alkoxide exuding from the
solvent.
250 F sounds really lo me.
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MyNameIsUnnecessarilyLong
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Has anyone tried re-using solvent from previous reactions?
Most of the particulates have settled out and it looks pretty clear now. This thin paraffin oil is relatively expensive and I'd like to not have to
buy more for each rxn.
Maybe. I just remembered I have an IR thermometer. Do you think taking a reading on the glass exterior above the mantle portion would give an accurate
representation? Or would it be better to pull the flask out of the mantle for a sec and read the bottom?
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blogfast25
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| Quote: Originally posted by MyNameIsUnnecessarilyLong | Has anyone tried re-using solvent from previous reactions?
Most of the particulates have settled out and it looks pretty clear now. This thin paraffin oil is relatively expensive and I'd like to not have to
buy more for each rxn.
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I don't think there should be a problem with that a all and have been meaning to try that. Remember that it may contain some dissolved K t-butoxide
but that's not a problem either...
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Sublimatus
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Do we have any good guesses as to the composition of the white smoke seen in MyNameIsUnnecessarilyLong's photo above? I'd always assumed it was the
t-butanol, but I'm running the reaction against just now, and the smoke appeared even though I hadn't added any alcohol yet.
It appeared when the reaction mixture reached ca. 90 C, slowly at first, and then became more dense along with violent bubbling of the solvent.
Around 130 C the smoke was pushed out of the apparatus (presumably by hydrogen), and no more was generated.
Is this smoke the result of some reaction between the magnesium and hydroxide? The magnesium and the solvent? Is it simply an aerosol kicked up by
the sudden escape of the hydrogen gas?
This run I'm using kerosene as the solvent. In the past I've used mineral oil and lamp oil (smelled of naptha). In all cases I've seen this smoke,
accompanied by violent bubbling, which then subsides about as quickly as it began.
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hyfalcon
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I would guess it's the water being driven off by those temperatures.
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Sublimatus
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There's something I hadn't considered.
I suppose I could try condensing it next time. Thanks for the hypothesis. 
Edit:
TLDR below.
Well, I've just finished my fourth shot at getting this reaction to work. All four runs have seemingly yielded no potassium.
All four runs were with 3.5 grams 99.96% very thin magnesium turnings broken up to very small pieces and roughed up in a mortar and pestle under oil,
7.0 grams ACS grade potassium hydroxide prills, and 1 mL of redistilled t-butanol.
During all four runs, beginning at ca. 90 C, a vigorous evolution of gas bubbles and dense white smoke was observed for a few minutes. Capturing some
of the gas after the smoke had dissipated confirmed that hydrogen was present.
In the first three runs, the catalyst was added before heating. In the fourth run the catalyst was added at ca. 140 C, after the evolution of smoke
had stopped.
The first and second attempts used mineral oil as the solvent, the kind you find at the pharmacy. Approximately 4 hours at 220 C gave no potassium.
The resulting reaction mixture was composed of very black remnants of the magnesium turnings and an insoluble white material, possibly MgO or Mg(OH)2.
The third attempt used lamp oil as the solvent. The exact composition is unknown, but it smelled precisely like the mineral spirits one can buy as
paint thinner, and had a maximum boiling point of ca. 160 C. 4 hours at that temperature gave the same result as the first two attempts.
The fourth attempt used kerosene as the solvent. The source was a blue quart bottle sold by Coleman as kerosene for their line of lamps. It smells
very similar to automotive diesel. The maximum temperature achieved during the reaction was ca. 185 C, which was maintained for 4 hours before
shutting down.
As before, the result was a few remaining black fragments of magnesium and an insoluble white material. No potassium spheres or fines were observed.
Water was carefully added to a small portion of the solvent and sludge to see if any reaction would occur. No heat, fizzing, or fire occurred.
TLDR: I've tried three solvents, (mineral oil, naptha?, and kerosene) with the best quality reactants I can obtain, but no potassium has been
isolated.
Is there anyone with insight or suggestions as to what might be wrong?
The temperature might be the culprit, but I can't see any way to exceed the temperatures I've reached. Cranking up the hot plate seems to have no
effect once vigorous boiling has begun.
[Edited on 6/16/2013 by Sublimatus]
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MyNameIsUnnecessarilyLong
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When I went to transfer the mixture to another flask after it partially cooled, more white smoke would suddenly appear. I closed it up and let it cool
down to about room temp, then opened it up and there was still a small amount of smoke coming out of the solution.
Could this be a reaction between the potassium and humidity?
Have you tried using powdered/crushed KOH?
[Edited on 6-16-2013 by MyNameIsUnnecessarilyLong]
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Sublimatus
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I did grind the KOH in the second run, but not the rest. I should've been more consistent. 
I'll grind it up and give it another go in a day or so. I'll report back with success or to beg for more suggestions.
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blogfast25
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| Quote: Originally posted by Sublimatus | I did grind the KOH in the second run, but not the rest. I should've been more consistent.
I'll grind it up and give it another go in a day or so. I'll report back with success or to beg for more suggestions. |
In your case I would suggest to:
* try a reagent grade Mg powder or a clean pyro grade
* try to measure temperature at least once, just to be certain. Too low temperature slows down everything. You could even measure it in a 'dummy run',
if you have no means of inserting a thermocouple during reaction.
My psychic octopus tells me you're close to success!
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Sublimatus
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It's 99.96% magnesium. I'd be surprised if that wasn't clean enough, but I'll look around to see if I can find better. Perhaps the 0.04%
contamination is a serious poison for the reaction.
I've had a high-temperature thermometer (-10 to 260 C) right in the reaction solvent on every run. The temperatures I report are the approximate
average I observed over the four hours, as there's a small amount of fluctuation.
If your psychic octopus is confident, I'll press on.
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blogfast25
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Sublimatus:
My email notification is on the blink, so I had to 'quickread' your comment. Grrr...
220 C and 99.96 % Mg seem more than adequate. But for the latter a truly powdered form may be worth trying. Octopussy is nodding vigorously so it's
all good...
Once the greatest experimenter on this board ('len1') didn't get any K either, so there are are some exceptional conditions that can cause failure.
Truly bizarre.
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hyfalcon
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I just got my heat source set up in the shop. I've got 200-325 mesh mixed with some 2X4 mm chips of Mg and also some thin machine turnings. I'm
going to try a run with a mix of all three. I'm going to pick up some white sand for a sand bath latter today. I'll probably make the run tomorrow.
[Edited on 17-6-2013 by hyfalcon]
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blogfast25
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Fingers painfully crossed! 
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Pyrocystis Lunula
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Greetings everyone! Longtime reader here who has decided to join in the quest for Potassium.
I have been trying this synthesis for the past few days and have been met with failure on the 5 runs I have attempted so far. Here is a quick rundown
of what I have tried
Note: All trials use the same Mg, KOH, and t-butanol. Mg is a coarse powder that appears dark but still has plenty of shiny pieces in it. KOH is tech
grade flakes from EBay. T-butanol is 99% from Ebay with freeze/melting point matching literature. All trials have used 125ml erlenmeyer flasks and an
electric coil kitchen hotplate that I have previously recorded reaching approximately 220 C when dehydrating some baking soda as a test. I dropped my
high temperature thermometer and haven't bought a replacement yet.
Trial 1: 3.1g Mg, 6.1g KOH, 1ml t-butanol all placed into flask with 50ml melted paraffin wax (only solvent I had available the first day). Hotplate
was set to high and refluxer attached with PTFE tap being used to make an airtight seal. After approximately 5 minutes bubbling began and continued
for the next hour. The solution gradually became cloudier and more opaque. After 4 hours, I turned off the heating and checked for any signs of
potassium. No globules were identified and there was no reaction when water was poured over the mix after the wax was liquified with mineral spirits.
Trial 2: Same amounts as trial one but t-butanol was added after the bubbling had died down, mixed with 10ml of mineral spirits. A small amount of
vapor escaped the refluxer but the majority of the liquid dripped back into the solution. Solution once again became opaque but no signs of potassium
at the end of the 4 hours, failing water test once again.
Trial 3: 3.5g Mg, 6g KOH and 1.25ml t-butanol in 50ml of hypoallergenic baby oil. All added in beginning. Bubbling began as normal, solution once
again became opaque, but after 4 hours of heating on high there were no balls of potassium. The contents had enlarged and turned a brownish color,
very much resembling the sand mentioned before. Upon cooling, I noticed a gel-like layer coated the sediment underneath the baby oil. The oil was the
same viscosity, but the gel was thick and opaque. Mixing with water produced no bubbling.
Trial 4: Suspecting that my magnesium was simply too oxidized to react and form the potassium, I tried activating it by mixing the powder in a weak
hydrochloric acid solution. The powder was then filtered off and immediately pressed dry with filter paper until no moisture came off. 3.1g of this
powder was then mixed with 6.1g KOH and 1ml of t-butanol in another 50ml of fresh baby oil. Bubbling appeared to be more viscous, but this could have
simply been water I did not properly remove from the powder. In the end, the flask looked almost the same as the last trial with another layer of gel
covering the sediment under the baby oil. Once again, no bubbling with water.
Trial 5: Currently in progress. 3g Mg were placed under 50ml of fresh baby oil which a tiny amount of iodine had been dissolved in. This was rapidly
stirred and gently heated. The powder appeared to become brighter with small shiny flecks floating after stirring was stopped. When most of the purple
iodine color cleared, 6g KOH and 0.75ml t-butanol were added, the refluxer once again attached, and heating started. Bubbling proceeded normally and
as of 2 hours of heating the oil is still clear. The powders have gained volume and a slight crust is apparent on the top. Will report results later
this evening. UPDATE: Now at 6 hours of heating, oil has become a cloudy pale yellow color. I've decided to just let it run for the rest of the night,
hoping the extra time might give the reaction a better chance.
I believe my magnesium is the culprit here. I ordered a fresh ingot from galliumsource to file or drill turnings from that will not be heavily
oxidized. Examining portions of the previous wax runs that did not have water, I noticed a thin layer of the gel-like coating on the reactants. Is
this the K-butoxide?
[Edited on 18-6-2013 by Pyrocystis Lunula]
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MyNameIsUnnecessarilyLong
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Have you tried breaking up the slag and stirring things occasionally?
My mix was cloudy after the first couple hours and couldn't see any K. I saw a small pile of shiny Mg and KOH in the bottom that was encased in a hard
Mg-oxide aggregate, so I reached in with a metal skewer and carefully broke everything up and swirled the flask periodically every 15 minutes or so.
The mix eventually became grey after about an hour of that
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blogfast25
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Pyrocystis Lunula:
Thanks for joining our potassium 'fun/misery' and thanks also for that very concise first post (please keep reporting like that).
When no potassium is obtained at all, I'm inclined to blame the reducing agent, even though quite mysteriously we don't really know WTF might be wrong
with it!
So by all means try a different and hopefully better grade of Mg.
Good luck.
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MrHomeScientist
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I don't believe that's correct. If you look back a few pages at one of my other posts, I put up a few pictures of the smoke from one of my runs. It
seems to condense into a white solid as the smoke dissipates. This has me pretty convinced that it is t-butanol boiling off. My runs still produced K,
so I apparently don't lose it all in the smoke plume.
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Sublimatus
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| Quote: Originally posted by MrHomeScientist | | I don't believe that's correct. If you look back a few pages at one of my other posts, I put up a few pictures of the smoke from one of my runs. It
seems to condense into a white solid as the smoke dissipates. This has me pretty convinced that it is t-butanol boiling off. My runs still produced K,
so I apparently don't lose it all in the smoke plume. |
I don't think that's right. In my last run I didn't add the t-butanol until after the white smoke had been generated and escaped from the
apparatus between 90 and 130 C.
Next time I try this I'm going to include a cold trap to try to condense the smoke and see what it is.
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MyNameIsUnnecessarilyLong
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| Quote: Originally posted by MrHomeScientist |
I don't believe that's correct. If you look back a few pages at one of my other posts, I put up a few pictures of the smoke from one of my runs. It
seems to condense into a white solid as the smoke dissipates. This has me pretty convinced that it is t-butanol boiling off. My runs still produced K,
so I apparently don't lose it all in the smoke plume. |
My white smoke definitely smelt like t-butyl. Could be an azeotrope with whatever water gets liberated
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hyfalcon
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I've got less then an hour of reflux left. It isn't looking too good at the present. Air is definitely not enough cooling. I stacked two condensers
and a fractionating column together to keep things under reflux. I don't know if we are starting out dry enough for this to work right or not. How
hard is it to dry your KOH out somewhat before starting? I used 500ml of a water thin paraffin based lamp oil. MSDS says that it boils at 220 C. I
added 61.9 g of KOH to a 1000ml 2-necked flask along with 10.5g of 200-325 mesh pyro grade Mg along with 10.5g of Mg chips and then 10.5g of Mg
turnings. I had the normal H2 emission at the expected temperatures. If I did anything wrong in retrospect, I think I used too much t-butanol. I
tried something different to to t-butanol. I added 3ml at the start and mixed another 7ml in some extra lamp fuel and added to a sep funnel that I
had on the second neck. After I started hard reflux and start dripping the extra t-butanol in on a timed release. I'll report back when the reflux
is done and things have cooled and I can check for fines.
---------
Well, on clean up, I had a couple flashes of light in the flask when I doused it in the 5 gallon bucket of water. I noticed a lot of unreacted Mg in
the bottom of the flask. Somehow I don't think my swirling was enough to keep the reactants mixed properly.
[Edited on 19-6-2013 by hyfalcon]
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elementcollector1
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Too little Mg, I think... I always thought the ratio was 6.1g KOH:3.1g Mg, or 61g and 31g in your case.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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