zig
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Xylene failed to separate from methanol..Detergent contamination from KOH??
Ran into a ridiculous roadblock today..
After running an amalgam on a ketone (with the same old tried-and-true procedural details that have served me well) the methanolithic solution was
basified using 35% KOH in preparation of extraction / salting. Once basic an extraction *attempt was performed with 500ml xylene..which surprisingly
misc'ed into the soln, never bothering to separate as polar/nonpolars are expected to do. Attempts to force separation first with colorful language
and subsequently adding excess base soln were unsuccessful.
NaOH has always been used to basify instead of KOH, identifying it as the main variation in a previously successful procedure. The lightbulb finally
went on after some google fu asserted that KOH is commonly contaminated with...
Detergents.
...
DETERGENTS!
Youre telling me that my extraction was neutered by goddamn DETERGENTS?
So thats the cause of the *very subtle* soapy looking bubbles that are always present in my freshly made KOH solutions?
That mild pleasantly-soapy olefactory hallucination I always enjoyed while dissolving- that was real?
Well no shit, OF COURSE a detergent could fuck up the separation of polar/nonpolars! How could you possibly be unaware of it being a polar molecule
with a long non polar chain and all! Stupid rookie mistake, everyone knows that the first lesson Chem 101 is to MAKE SURE YOUR KOH DOESNT CONTAIN ANY
GOD DAMN SOAP!
So why? I know KOH is used in saponification and soapcraftery, but why is soap already there? And regardless of how it got there could it be removed
by say, distillation of all 1500ml MeOH/H2O/xylene followed by vacuum distillation of the freebase?
*Edit: Corrected Capitalization
[Edited on 7-2-2014 by zig]
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapor, soot and flame,
poisons and poverty; yet among all these evils I seem to live so sweetly that I may die if I were to change places with the Persian king."
-Johann Joachim Becher
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bfesser
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Quote: Originally posted by zig  | After running an amalgam on a ketone (with the same old tried-and-true procedural details that have served me well) the methanolithic solution was
basified using 35% KOH in preparation of extraction / salting.
. . .
And regardless of how it got there could it be removed by say, distillation of all 1500ml meoh/h20/xylene followed by vacuum distillation of the
freebase? |
Hard to tell, if you're going to remain vague as to what your substrate is. Depending on what the
<a href="http://en.wikipedia.org/wiki/Detergent" target="_blank">detergent</a> <img src="../scipics/_wiki.png" /> or <a
href="http://en.wikipedia.org/wiki/Soap" target="_blank">soap</a> <img src="../scipics/_wiki.png" /> is—yes, they're
different things—your solution could be as simple as adding an <a href="viewthread.php?tid=10110">appropriate transition
metal</a> cation to precipitate it out. I've never heard of such contamination in KOH; what was your source? Is it possible that you didn't
rinse your glassware well enough after previous washing?
<em>Also, please use appropriate capitalization in MeOH and H<sub>2</sub>O, at the very least.</em>
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zig
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| Quote: Originally posted by bfesser | . . .
your solution could be as simple as adding an <a href="viewthread.php?tid=10110">appropriate transition metal</a> cation to precipitate it
out. |
Thats way cool, thanks for the link. I suppose that percipitating an unknown in this fashion would require some old fashioned guess n check until the
correct anion is identified? | Quote: Originally posted by bfesser | | I've never heard of such contamination in OH; what was your source? Is it possible that you didn't rinse your glassware well enough after previous
washing? |
Sourced from several different forum discussions on KOH and non/polars becoming miscible. Not
super academic, I realize. I can post links later today. It is possible that I failed to wash all the soap out. Unlikely, but possible.
I suppose a better question would be, "what could cause non/poplars to become miscible?". Edited title to reflect.
[Edited on 7-2-2014 by zig]
<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: fixed
mismatched BBCode tags]
[Edited on 7.2.14 by bfesser]
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapor, soot and flame,
poisons and poverty; yet among all these evils I seem to live so sweetly that I may die if I were to change places with the Persian king."
-Johann Joachim Becher
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Ascaridole
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Titrate your KOH before attempting any purification. You may find your KOH is more pure than expected. As for it messing up your experiment,
errrr…..
I'm going to assume you did a clemensen reduction in acidic conditions hence your need to neutralize it with KOH/NaOH…
Perhaps some brine would help… I just can't see a small percentage of detergent screwing up a phase separation that badly, especially on a 500mL
portion of xylene… and besides if it did truly screw things up I'd expect a horrible emulsion that would just look ugly forever. The more believable
explanation for your problem is that KOH has a higher m.w. than NaOH therefore assuming a 35% w/v solution your KOH solution has a lower ionic
strength. Thats why I like to use Molar… Keeping that in mind methanol is soluble in water and xylenes to some extent and water is soluble in
methanol and xylenes to some extent, etc. We begin to see the problem, at least in my mind i do… hrmm..
So with a lower ionic strength from your base wash and a large enough volume of methanol and xylenes your polar phase is just taken along for a ride.
Adding the brine would probably increase the density and ionic strength of the water enough to pull it out into its own phase carrying most of the
methanol with it… Try it on a small scale se what happens and let us know!
Ascaridole, the masked bandit of chemistry!
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zig
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| Quote: Originally posted by Ascaridole |
Perhaps some brine would help… I just can't see a small percentage of detergent screwing up a phase separation that badly, especially on a 500mL
portion of xylene… and besides if it did truly screw things up I'd expect a horrible emulsion that would just look ugly forever. The more believable
explanation for your problem is that KOH has a higher m.w. than NaOH therefore assuming a 35% w/v solution your KOH solution has a lower ionic
strength. Thats why I like to use Molar… Keeping that in mind methanol is soluble in water and xylenes to some extent and water is soluble in
methanol and xylenes to some extent, etc. We begin to see the problem, at least in my mind i do… hrmm..
So with a lower ionic strength from your base wash and a large enough volume of methanol and xylenes your polar phase is just taken along for a ride.
Adding the brine would probably increase the density and ionic strength of the water enough to pull it out into its own phase carrying most of the
methanol with it… Try it on a small scale se what happens and let us know! |
Haven't gotten to titrate the KOH yet, it's on my to-do list I promise.
Sat. NaCl was a great idea. Morning after the KOH incident 400mL of the fucked up rxn mixture was poured into it's volume of sat. NaCl and solid NaCl
was added to the mixture until saturated. Sol'n was stirred thoroughly and left to separate (you'd better separate you sonofabitch!!)
...It worked! Sort of, anyway- separation was observed (between xylene / H2O and MeOH) but the layers still glommed together, making separation next
to impossible. In the end the entire ~2L rxn mixture was distilled off, yielding a grand total of 26mL product. Life could be worse!
Very interesting stuff that ionic strength bit! Seems that may have been the hangup. I still intend on titrating my KOH due to a sneaking suspicion
but on this day, a tedious distillation reigns king. Your advice is much appreciated Ascaridole, much obliged. 
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapor, soot and flame,
poisons and poverty; yet among all these evils I seem to live so sweetly that I may die if I were to change places with the Persian king."
-Johann Joachim Becher
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Ascaridole
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Nice to know it sort of worked. Ahhh the wonderful emulsion… An organic chemists arch enemy, next to random polymerization… A trick to break up
the emulsion next time is to gently heat it. Helps to reduce surface tension and allow the blobs of solvent to glob together into decent phases.
Another trick you could try would be to add a drop or in the case of a 2L volume a splash of diethyl ether. Kinda the same concept, ether somewhat
soluble in both phases reduces surface tension, lets the blobs phase separate nicely. Both methods don't work all the time but trial and error never
hurt unless your substrate is $100+/g
As for KOH purification there is a way to purify it but its so labor intensive its probably not practical for reaction workup. Sounds like your past
experience has had success with NaOH so might be worth it to just stick with that. Time is precious and NaOH is cheap enough.
Ascaridole, the masked bandit of chemistry!
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zig
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Seriously man, I loathe that shit. Awful. Boy I sure am glad that I'll never have suffer another emulsion, thanks to your pro tips! Its on YOUR head
now Ascaridole, when I employ these techniques using my treasured $10000/oz gold and ruby substrate.  I trust ya mayng.
Yup indeed, smooth sailing since I restocked on NaOH! I wasn't sure I wanted to spend all day cleaning $5/kg caustic shit. Time is precious, as you
said 
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapor, soot and flame,
poisons and poverty; yet among all these evils I seem to live so sweetly that I may die if I were to change places with the Persian king."
-Johann Joachim Becher
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gravityzero
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I have not heard of using xylene for extraction after amination, but I guess it would work. I've always read toluene being used.
The MeOH would stay with the water, as would mercuric salts. Brine could be used to facilitate separation.
Sometimes you might have to add more aqueous and solvent portions.
Once there is room for everything to migrate to its appropriate position, the emulsion should cease. This is all hypothetical and rarely plays out in
real life.
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