Purification of THF
Amadeu Sum
(tetrahydrofuran) to measure its Raman spectrum. The problem that I am
observing with the samples of THF is that there seems to be some
fluorescence contaminant present that is causing a really ugly sloping
background in the Raman spectrum between about 2000-500 cm-1. If anyone
could suggest ways to purify the THF or what is causing the fluorescence
background, I would greatly appreciate any help. For your information,
the THF that I being using is from Aldrich 99.5% spectrophometric grade,
and I used it as it come and I also tried distilling some of it, but the
distillation did not help. Any comments or suggestions can also be
directly forwarded to the me at as...@crystal.mines.colorado.edu
Thanks in advance for any help.
LARRES CYNTHIA Y
> I am having some problems in obtaining a good sample of THF
> (tetrahydrofuran) to measure its Raman spectrum.
In our organic synthesis lab we have a THF still under constant reflux. In the
pot we add benzophenone and sodium metal, which forms a sodium benzophenone
ketyl complex. The result is a royal blue solution due to some kind of electron
transfer(other shades of blue are ok but other colors are bad). You should keep
the still under inert atmosphere(Ar,He) to keep the THF clean. A good ref on
how to purify chemicals is "purification of laboratory chemicals" by Perrin and
?(it was perrin and perrin). We have found this method of purification to work
great. Good luck.
Louis (xlla...@ccvax.fullerton.edu)
William S Jenks
This is great for synthetic chemists and very effectively gets rid of
water and alchohols. The blue color derived from the radical anion of
benzophenone, which is stable in the absence of O2 or proton sources.
The problem with THF is that certain fluorescent things will codistill
almost no matter what you do. Benzene, for instance, is VERY difficult
to get out of THF. If anyone knows a good way, I'd like to know it. I
have also had a very difficult time getting benzene (or something
closely related) from methyl THF.
As to the Na/BP method, the reason I advise against it is that you will
probably distill up a tiny amount of benzophenone. Benzophenone would
be a disaster for your experiment.
If it was a problem for me, my first attempt would be to set up a still
under inert atmosphere and boil the THF with K for several hours. If
the mixture turns kind of brown, you're making progress. Then distill
off the THF. BE VERY CAREFUL WITH THE POTASSIUM. Obviously, you should
not distill all the THF off. You will need to quench the excess K with
something like t-butanol, which will take several hours. However, this
is far superior to a fire or explosion.
I used this method to remove MOST of the impurities from a lousy bottle
of MTHF recently. Hope it helps.
--
/---------------------------------------------------------------------------\
| William Jenks Photons from Heaven |
| wsj...@iastate.edu (515) 294-4711 |
\---------------------------------------------------------------------------/
Antoni S. Gozdz 21621
> I am having some problems in obtaining a good sample of THF
>observing with the samples of THF is that there seems to be some
>fluorescence contaminant present that is causing a really ugly sloping
>background in the Raman spectrum between about 2000-500 cm-1. If anyone
>could suggest ways to purify the THF or what is causing the fluorescence
>background, I would greatly appreciate any help.
THF readily forms nasty peroxides when exposed to air/oxygen, thus a
small amount (1-100 ppm) of an antioxidant (a substituted phenol etc)
is usually added to it. Now, these compounds, and especially their
oxidationn products, quinones, fluoresce like crazy. Distillation
might not help since they have some vapor pressure, or might get
transferred with the solvent mist.
A simple way to get rid of them is to pass the THF under dry argon
through a column of neutral or basic alumina (phenols are acids) and
use it right away, or, if you want to be fancy, distill it later under
argon (maybe from the yellow ketyl solution--the standard way to
prepare superpure solvents for anionic polymerization). This method
(chromatography on Al2O3) is also very efficient in getting rid of the
oxidation products from cyclopentanone and cyclohexanone which oxidize
readily.
A few years ago, I did a lot of alkenylsilane copolymerizations in
liquid SO2. Since traces of peroxides formed in these unsaturated
compounds on exposure to air would quickly react with SO2 in a redox
reaction to form radical anions etc. which rapidly initiated
copolymerization of SO2 with the alkene, I went through a number of
purification procedures to get rid of their traces. Al2O3 was
sufficient and the simplest.
Tony
---------------------
Antoni S. Gozdz
to...@nyquist.bellcore.com
ja...@tiac.net
as...@slate.mines.colorado.edu (Amadeu Sum) wrote:
Amadeu -
I used to work in an organometallic lab where I used
trifluromethanesulfonic acid to protonate a Schrock-type alkylidene in
THF. The reaction was very sensitive to the purity of the THF, as you
might well imagine.
The best purification technique I found was to pour the THF into a
round bottom and sparge with Argon for 10 mins., then QUICKLY add some
sodium sand and sparge for an additional 10 mins., then add some
benzophenone. If you started with pretty good THF, it should turn deep
purple almost immediately. Then, I would quickly distill under Argon into
another flask with a high vacuum stopcock and bring it into an inert
atmosphere box.
Just before I would use it, I would (inside the box) place the THF in
yet another flask with a high vacuum stopcock and some more
Na/benzophenone ... if it isn't immediately purple then your box
atmosphere is crap! Anyway, I would then remove it from the box, place it
on a high vac line, and perform AT LEAST TWO freeze-pump-thaw cycles to
remove gases. Then I would vacuum transfer the THF into another flask for
immediate use, leaving the Na/benzophenone behind.
I know this may be tedious ... but it worked... One precaution ...
don't let the THF sit over Na/benzophenone for too long ..... a side
reaction can occur whereby sodium ethoxide and ethylene is formed. I can
only imagine how horribly ethylene would screw up your measurement!
Good Luck.
Wheatley N
>(tetrahydrofuran) to measure its Raman spectrum. The problem that I am
>observing with the samples of THF is that there seems to be some
>fluorescence contaminant present that is causing a really ugly sloping
>background in the Raman spectrum between about 2000-500 cm-1. If anyone
>could suggest ways to purify the THF or what is causing the fluorescence
>background, I would greatly appreciate any help.
>
The flourescent compound could be 2,6-di-tert-butyl-p-cresol, which is
added as a `stabilizer' to commercial THF. Have you tried distilling off
sodium wire, or off sodium benzophenone ketyl?
Nigel
BILL CONSIDINE
AS>could suggest ways to purify the THF or what is causing the fluorescence
AS>background, I would greatly appreciate any help. For your information,
AS>the THF that I being using is from Aldrich 99.5% spectrophometric grade,
Column chromotography on Al2O
3?
bi...@execnet.com
---
ş DeLuxeı 1.1 #9385 ş Gimme that old-time Religion. The hymns are better
Yevdokimov Artiom
: I am having some problems in obtaining a good sample of THF
Interesting problem : on your place I would have tried various oxydations and a final distillation from K or Na. The problem with the oxydations is that they may form peroxides (by the way, as K, Na treatment either) but you, as is mentioned in the other responce, cannot use benzophenone.
Oh, BTW, the compound that you have may not be co-distilled with THF but simply travelling in the microscopic layer of liquid THF ON THE GLASS uniting the distiller and the condensor. To get rid of this layer (which is being formed by almost all polar substances) one may use careful overheating the piece of connection somwhere not very far from the heating flask. This will destroy the layer and (hopefully) prevent the contamination. I do not if it'll help in this case, but it DEFINITELY helps with a fine d
istillation of water.
Hope it helps.
Artem
O----------------:) the lost electrone.
Joe Ragosta
nf9...@sgdna1.weizmann.ac.il (Yevdokimov Artiom) wrote:
> Amadeu Sum (as...@slate.mines.colorado.edu) wrote:
> : I am having some problems in obtaining a good sample of THF
> : (tetrahydrofuran) to measure its Raman spectrum. The problem that I am
> : observing with the samples of THF is that there seems to be some
> : fluorescence contaminant present that is causing a really ugly sloping
> : background in the Raman spectrum between about 2000-500 cm-1. If anyone
> : could suggest ways to purify the THF or what is causing the fluorescence
> : background, I would greatly appreciate any help. For your information,
> : the THF that I being using is from Aldrich 99.5% spectrophometric grade,
> : and I used it as it come and I also tried distilling some of it, but the
> : distillation did not help. Any comments or suggestions can also be
> : directly forwarded to the me at as...@crystal.mines.colorado.edu
>
> : Thanks in advance for any help.
>
> Interesting problem : on your place I would have tried various
oxydations and a final distillation from K or Na. The problem with t
> Oh, BTW, the compound that you have may not be co-distilled with THF but
simply travelling in the microscopic layer of liquid THF O
>
>
> istillation of water.
>
> Hope it helps.
>
> Artem
>
> O----------------:) the lost electrone.
We used extra-pure THF in graduate school. Everything was run under inert
atmosphere to keep oxygen and water out. The THF was distilled from K and
benzophenone. When the solvent was sufficiently pure, it had a bright blue
color (great indicator to let you know when your still is OK to use).
--
Regards,
Joe Ragosta
doc...@interramp.com
Andy Mobley
>
> I am having some problems in obtaining a good sample of THF
> (tetrahydrofuran) to measure its Raman spectrum.
Co-distillation of benzophenone can be a problem with high-boiling solvents
like THF. You might try doing preparative GC. It can be a real pain,
but it is really useful for obtaining small amounts of very pure
material. I imagine you don't need tons of THF for your raman spectrum.
Unless, of course, it is just a solvent for the real molecule.
Andy Mobley
Grad. Student
UC-Berkeley
Liz+Allan MacDonald
original post snipped...
>We used extra-pure THF in graduate school. Everything was run under inert
>atmosphere to keep oxygen and water out. The THF was distilled from K and
>benzophenone. When the solvent was sufficiently pure, it had a bright blue
>color (great indicator to let you know when your still is OK to use).
Anyone else have fond memories of disassembling that THF still and disposing
of the sludge? It lived in my hood and our group was moving to new labs. The
primary THF user (my boss) insisted that it could not be moved as is, since I
refused custody again. Everyone had a suggestion. I think we added methanol
dropwise over a few days, and then water.
Liz
Joe Roth
solvent for electrochemical experiments. For these experiments THF is purified
by distilling it from Na or K using benzophenone as an indicator. This
distillation is always performed under an inert gas such as N2 or Ar.
Benzophenone is electroactive. It is easily reduced. If co-distillation was
occuring it would interfer in electrochemical experiments.
Joe Roth
is NOT a high boiling solvent. It boils at 65.4 C. THF is a solvent commonly
used in electrochemical experiments. Before use the THF is purified by
distilling it from Na or K using benzophenone as an indicator. If the
benzophenone was co-distilling it would interfer with electrochemcal
experiments. Benzophenone is an electroactive substance which is easily reduced.
Greg Milligan
its way into the still, consuming either the metal or the benzophenone.
Often the blue can be regenerated by adding metal, benzophenone, or both.
Eventually, the still needs to be quenched and cleaned out.
--
Regards, Greg.
Susan Stoen
: I have used both. They both have worked well. The indicator has also been
: messed up when using either metal. The most common problem was that the
: solution in the distilling flask turned yellow. I changed from Na to K in an
: attempt to solve this problem. Since the problem appeared at one time or
: another with both metals I attributed it to impurities in the original THF.
: Pre-drying the THF over calcium hydride helped considerably. Since I have no
: proof either way the problem could have been with the metals. : )
Pre-drying is recommended when distillation of THF is desired. It will
eliminate some of the water in the THF but not all of it. Even pre-dried
THF will turn a still pot pea soup green or yellow! When this occurs,
carefully add sodium wire, finely divided sodium dispersion (available
from Aldrich, etc), or well-flattened sodium. Thestill pot usually comes
back pretty quickly; oh, it might usully helps to add a bit of benzophenone
too in case it has been used up.
It is also customary to have the still under an inert atmosphere of N2 or
Ar. This will help keep your still dry and purple/blue.
Best of luck with this still.
--Sue Stoen
sas...@lamar.colostate.edu
Captain Entropy
sas...@lamar.ColoState.EDU (Susan Stoen) wrote:
> Joe Roth (Joe....@DaytonOH.NCR.COM) wrote:
> : I have used both. They both have worked well. The indicator has also been
> : messed up when using either metal. The most common problem was that the
> : solution in the distilling flask turned yellow. I changed from Na to
K in an
> : attempt to solve this problem. Since the problem appeared at one time or
> : another with both metals I attributed it to impurities in the original
THF.
> : Pre-drying the THF over calcium hydride helped considerably. Since I
have no
> : proof either way the problem could have been with the metals. : )
>
> Pre-drying is recommended when distillation of THF is desired. It will
KOH pellets work pretty well, but allow at least 30 minutes of stirring
under Ar. The solution will turn clear yellow due to the inhibitor
(usually BHT or a dihydroquinone) forming an anion. Let the mixture
settle and filter through glass wool to remove KOH dust. I have found
this method to work very well if enough time is allowed.
Pre-drying not only decreases the consumption of sodium, it greatly
decreases the amount of benzhydrol alkoxide formed in solution, which
significantly increases the useful lifetime of the still.
Always remember that the function of Na/benzophenone is to remove THE LAST
TRACES of moisture and oxygen; the bulk of the purification should be done
prior to this treatment (with reagent quality THF and pre-drying this is
already the case).
> eliminate some of the water in the THF but not all of it. Even pre-dried
> THF will turn a still pot pea soup green or yellow! When this occurs,
> carefully add sodium wire, finely divided sodium dispersion (available
> from Aldrich, etc), or well-flattened sodium. The still pot usually comes
> back pretty quickly; oh, it might usually helps to add a bit of benzophenone
> too in case it has been used up.
But FIRST, let the still reflux for an hour or two; the color will often
return to normal without any addition, or at most, a small amount of
benzophenone. When water and oxygen are introduced with the fresh THF,
the sodium tends to become coated with oxides etc.; letting it reflux for
awhile (stirring is almost essential) cleans some of the surface enough to
regenerate the radical anion again. Cutting the surface of the sodium can
speed things up. It's not a bad idea to do the refills at the end of the
day and leave it refluxing overnight; if the color hasn't returned in the
morning, it's definitely time to add a little benzophenone.
It is a good idea to set up the still with all the sodium you're ever
going to use and to add only small amounts (1-2 g) of benzophenone when
necessary to regenerate the radical anion. When the addition of
benzophenone no longer regenerates the desired color IT IS TIME TO CLEAN
OUT THE STILL, not add more sodium. My experience is that 3-4 mo. is
about the longest time that should pass between still cleanings anyway;
longer than this, and too much crud accumulates in the still pot. Also,
some people have reported that traces of a UV-active impurity accumulate
in the distillate; this is most likely diphenylmethane, from reduction of
benzhydrol alkoxide by sodium, but I've never been able to check this
because I've never let a still go that long between cleanings.
> It is also customary to have the still under an inert atmosphere of N2 or
> Ar. This will help keep your still dry and purple/blue.
Absolutely ESSENTIAL!!
> Best of luck with this still.
>
> --Sue Stoen
> sas...@lamar.colostate.edu
--
.delta. S
Captain Entropy
> Could anyone give me an explanation of the function of Benophenone used for
> the purification of THF? Thank you in advance for your support!
>
> Send to: r.k...@magnet.at
Benzophenone reacts with sodium (or other alkali metals) to form a radical
anion, which is intensely blue in color. This radical anion reacts very
rapidly with both H2O and O2 in solution, making it much more effective
for drying and deoxygenation than the heterogeneous (two-phase) reaction
at the surface of solid sodium. Ideally, the benzophenone should be
needed in only catalytic amounts to scavenge O2, as only the sodium should
be consumed, but if enough H2O is added benzophenone is reduced to the
alkoxide of benzhydrol, and more benzophenone must be added periodically
to maintain the radical anion in solution.
If a large excess of sodium is present, further reaction will lead to the
reduction of the radical anion to a dianion, which is intensely purple.
When benzophenone is used in small amounts (0.5-2 g for 2-3 liters of THF)
together with a large amount (5-20 g) of sodium, the resulting solution
has the appearance of Welch's grape juice, only more intense. (If your
still has some other appearance, a little more care is in order.)
--
.delta. S
Julie Shreve Keyer
Careful, THF can fool you sometimes. A blue still does not
always mean it is sufficiently dry. It is best to not collect
the THF until the still has remained blue/purple for at least
24 hours. Also, we used to predry ours over activated sieves,
which was usually good enough to not "kill" the still upon
addition of the new THF.
-Julie