paulr1234
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A slightly different need for dry THF
Forgive the lengthy pre-amble to my question, I just wanted to set some context.
I'm conducting some private research into carbon-nanotube based electro-active polymers. These novel new materials can exert actuation forces when
subjected to electrical current, due to the electroconstriction of the carbon-carbon bond.
Typically the carbon nanotubes (abbreviated to CNTs hereafter) are suspended in a polymer/solvent which is passed through a filtering substrate, to
create a sheet of mechanically active material.
One such preparation (the one I started my experimentation with) can be found here: http://ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap/Nanotube-PrepP...
I response to that posting I am indeed trying to improve upon the formulation/procedure. One area of inquiry I am pursuing is suspending additional
conductive materials (nanoscale conducting powdered metals) alongside the CNTs to change the electrical properties of the polymer carrier.
I started by replacing the H2O in the PVA/PAA formulation in that link with a water based solution of laser prepared colloidal gold. This is proving
to be an interesting direction and I'd like to experiment with some other metallic powders with different conductive qualities.
I'll spare you all the superfluous details but basically the premise here is that one might improve the conductive passage through the polymer,
creating a greater availability of electrons to the CNTs (and consequently increasing the actuation levels).
The problem, I suspect, with using gold and maybe platinum is that whilst they are great, chemically stable conductors, they might actually work too
well (causing conductive bypasses in the polymer base) and also, being heavier metals, are subject to saturation and distribution issues (they
'settle' unreliably forming stratified layers) plus they do not sonicate well in water and are expensive.
I'd therefore like to experiment with some other conductors, perhaps starting with silver, copper and maybe even iron. Unfortunately these more
reactive metals can oxidize very quickly at the nano-scale. A deterioration hastened by the presence of the barest traces of moisture.
So... I'm rethinking my thinking, moving on to other potential carrier polymers such as polyvinyl chloride, vinylidene chloride and
polyvinylpyrrolidone. This brings me to THF as a potential solvent.
Fortunately, I have a liter of anhydrous THF from Sigma Aldrich:
http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en...
This has been sitting unopened in my solvent cabinet (cool, dark and dry) for about 9 months and has the Sigma 'Sureseal' cap intact.
My first question is, whether I might still expect this product to be considered anhydrous. It feels like a slightly foolish question but I lack the
knowledge that some of the more experienced organic chemists who read this forum, might have.
Basically what I am actually asking is whether this anhydrous product preparation might be used (on first opening) in a highly moisture sensitive
procedure, or whether one should always redistill this solvent as a matter of course? (let's say, for arguments sake, that these preparations are just
as sensitive as a delicate organic technique that would typically require a very dry sample of THF).
Sigma actually doesn't say that much on it's website, just this:
"Sigma-Aldrich offers a full range of high-purity solvents with extremely low water levels specifically manufactured for moisture sensitive Organic
and Biotech applications. Sigma-Aldrich also carries various drying agents such as molecular sieves, which are typically compatible with organic
solvents"
Also, as a category B peroxide forming solvent that is approaching the 12 month shelf life, I obviously want to handle this carefully but as it has
never been opened and (I think) it is packed under a dry nitrogen blanket (Sigma doesn't say but I've read elsewhere that they do this).
This is a stabilized product to begin with and, as it has never been exposed to the atmosphere, I am curious whether one could safely assume it to be
peroxide free at first opening. Reading BASF's website seems to suggest that even un-stablilized THF actually reaches a point of equilibrium after
long storage:
"In a closed system with a limited supply of oxygen, peroxides cannot be formed after the oxygen has been consumed. The peroxide that is formed during
this period decomposes with time. Consequently, unstabilized THF may be almost peroxide-free after long storage periods despite peroxide formation in
the initial stages."
From: http://www2.basf.us/diols/pdfs/thf_brochure.pdf
I'd really like to avoid having to redistill this THF or buy a fresh batch (at $77 per liter + hazmat packing and shipping) but I could if I had to.
I've carefully examined the amber bottle with a flashlight and see no evidence of peroxide crystal formation whatsoever. My next step was going to be
taking a 5ml or 10ml sample and boiling it to dryness in a test tube over a small alcohol burner (I have a safe area to do this). All being well I
would then proceed directly to my experiments, any doubts and I'd run the entire batch through an alumina column and then redistill from sodium and
Benzophenone (both of which I have on hand).
Even so, running a still is a hassle that I'd rather not have, which leads me to my final question.
If I do need to do this, I only have a cylinder of food grade (wet) nitrogen. Would it be safe, advisable and effective to bubble the nitrogen, first
through about 250ml of concentrated H2SO4 and then immediately through a 2" wide 12"column of freshly recharged drierite to be sure of its dryness?
This was just my first take on this. very happy to hear alternatives from the more experienced folks who inhabit this forum.
Anyone reading this going to SPIE in San Diego on March 6th?
http://spie.org/app/program/index.cfm?fuseaction=COURSE&...
I was just going for the day, would love to have a beer with anyone on the forum who has similar interests.
Everything contained in this public forum post at 8.11pm EST, February 19, 2011 should be considered the copyrighted property of the author.
[Edited on 20-2-2011 by paulr1234]
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vulture
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I'm not really sure what you're hoping to achieve by bubbling nitrogen through your THF? Are you familiar with cannula transfer and the like?
Dry THF is extremely hygroscopic and distilling it is only going to be useful if it's over Na or Na/K in completely inert atmosphere. Then you still
have the trouble how to transfer it to your reaction vessel (assuming you don't have a schlenk line).
A reasonable test for the dryness of THF is to add some LiAlH4. Even only slightly wet THF will display immediate bubbling.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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paulr1234
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Quote: Originally posted by vulture  | I'm not really sure what you're hoping to achieve by bubbling nitrogen through your THF? Are you familiar with cannula transfer and the like?
Dry THF is extremely hygroscopic and distilling it is only going to be useful if it's over Na or Na/K in completely inert atmosphere.
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Yes, the dried nitrogen is intended as the inert blanket commonly used in the Na/Benzophone distillation technique.
I actually didn't say I was planning on bubbling it through the THF but rather I said I would be bubbling it through some concentrated H2SO4 and then
through drierite (prior to its introduction to the THF distillation vessel to make sure it was completely dry).
[Edited on 20-2-2011 by paulr1234]
[Edited on 20-2-2011 by paulr1234]
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vulture
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Okay, so I assume you have access to Na/Benzophenone? In that case you could check the dryness by making a small amount and see if it turns blue.
The drying of the nitrogen seems a good idea. But I'm wondering if, when you have access to food grade nitrogen, you couldn't get drier lab grade?
It's dirt cheap.
Should you go the H2SO4, drierite route, make sure no H2SO4 is entrailed, this will cause polymerization of the THF over time.
As for the bottle you have, usually sigma indicates a "use before" date on it. That's the date until they guarantee the spec. Their sureseal septa are
quite crappy however, once they are punctured you cannot rely on them to properly reseal. Acros septa are much better in this regard.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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paulr1234
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Many thanks Vulture
>>Okay, so I assume you have access to Na/Benzophenone?
Yes.
>>In that case you could check the dryness by making a small amount and see if it turns blue.
Yes, was really gathering some info before cracking open my sealed bottle to do that test. That said I have also just read that the blue benzophone
color will vanish, e.g turn transparent as soon as you expose the dried THF to atmosphere. This would indicate that this 'indicator' is marking both
the presence/absence of oxygen as well as moisture.
>>The drying of the nitrogen seems a good idea. But I'm wondering if, when you have access to food grade nitrogen, you couldn't get drier lab
grade? It's dirt cheap.
Yes, just been a lazy and cheap. Should really call and get a cylinder of Dry N delivered.
>>Should you go the H2SO4, drierite route, make sure no H2SO4 is entrailed, this will cause polymerization of the THF over time.
yes, the plan was to run it through the H2SO4, then the Drierite before hitting the THF. Might add in a column of dry activated carbon between the
H2SO4 and the Drierite as well.
>>As for the bottle you have, usually sigma indicates a "use before" date on it. That's the date until they guarantee the spec.
Interestingly it does not.
>>Their sureseal septa are quite crappy however, once they are punctured you cannot rely on them to properly reseal. Acros septa are much better
in this regard.
Yes, I heard that - thanks again.
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