HELP!!! for THF drying
Moineau
Hi!
I need to use very dry THF(tetrahydrofuran)to do some polymerization.
I have choose to reflux it over sodium and to use benzophenone as a
drying indicator. The problem arises from the fact that I don't know the
proportion of benzopheneone to add. For 3 L of THF, people tell me
amounts varing from 2 to 30 g!!!
Does anybody knows the right amount to add and also the way benzophenone
changes its colour from yellow to deep blue (or even deep purple).
Thanks a lot!
Michael ALEXANDRE
University of LIEGE
--BELGIUM--
E-Mail : s90...@student.ulg.ac.be
Paul A. Deck
Moineau <s90...@student.ulg.ac.be> wrote:
>Hi!
>I need to use very dry THF(tetrahydrofuran)to do some polymerization.
>I have choose to reflux it over sodium and to use benzophenone as a
>drying indicator. The problem arises from the fact that I don't know the
>proportion of benzopheneone to add. For 3 L of THF, people tell me
>amounts varing from 2 to 30 g!!!
>Does anybody knows the right amount to add and also the way benzophenone
>changes its colour from yellow to deep blue (or even deep purple).
I suggest you get the book "The Manipulation of Air-Sensitive
Compounds" by Shriver and Drezdzon (Wiley). This book tells you how
to purify solvents.
Essentially you need enough sodium benzophenone to maintain the deep
blue or violet color. If you start with good solvent, and if you have
decent technique, you should NOT need 30 grams of benzophenone to
start with. Later on you might have to add some more.
The blue and violet colors arise from one-electron reduction of
benzophenone to the ketyl radical anion. I recall that two-electron
reduction gives the red color responsible for the violet appearance
(red plus blue), but I can't remember where I heard or read that.
Please be careful quenching the still after you no longer need it.
Sodium can be carefully oxidized by isopropanol, then ethanol, and
then by very carefully adding water to kill the last bits and
neutralize some of the strong bases that have formed. I recommend you
do this under a nitrogen purge.
Paul
Paul A. Deck
Assistant Professor of Chemistry
Virginia Polytechnic Institute and State University
Eric Lucas
Moineau wrote:
>
> Hi!
>
> I need to use very dry THF(tetrahydrofuran)to do some polymerization.
> I have choose to reflux it over sodium and to use benzophenone as a
> drying indicator. The problem arises from the fact that I don't know the
> proportion of benzopheneone to add. For 3 L of THF, people tell me
> amounts varing from 2 to 30 g!!!
> Does anybody knows the right amount to add and also the way benzophenone
> changes its colour from yellow to deep blue (or even deep purple).
>
>
> Michael ALEXANDRE
> University of LIEGE
> --BELGIUM--
> E-Mail : s90...@student.ulg.ac.be
Add a small scoopful (half a gram or so), see if it goes blue after
refluxing a while. Further refluxing should take it all the way to
purple. If not, add some more. It ain't rocket science, so just try it
and stop worrying. You'll need to replenish your benzophenone as it
gets used up, so don't add too much at any one time. Use a delicate
touch and you and your still will be happy campers.
The blue color comes from the mono-anion (radical) of benzophenone when
it accepts one electron from the sodium metal. The dianion
(benzophenone + 2 electrons) is deep blood red. The purple color comes
from a mixture of the two.
For purifying solvents, I've read that purple is the most effective, and
is the color you should aim for. It has something to do with the fact
that the radical anion reacts most rapidly with oxygen (a (di)radical
itself) and the dianion reacts most rapidly with water. A mixture of
the two apparently scavenges both most effectively. If the pot's blue,
you may just need to let it reflux longer, or perhaps add more sodium.
If it's red, add more benzophenone and collect the distallate while the
pot stays purple (before it reverts to red).
Good luck.
Eric Lucas
Uncle Al Schwartz
Moineau wrote:
>
> Hi!
>
> I need to use very dry THF(tetrahydrofuran)to do some polymerization.
> I have choose to reflux it over sodium and to use benzophenone as a
> drying indicator. The problem arises from the fact that I don't know the
> proportion of benzopheneone to add. For 3 L of THF, people tell me
> amounts varing from 2 to 30 g!!!
> Does anybody knows the right amount to add and also the way benzophenone
> changes its colour from yellow to deep blue (or even deep purple).
>
> Thanks a lot!
>
> Michael ALEXANDRE
> University of LIEGE
> --BELGIUM--
> E-Mail : s90...@student.ulg.ac.be
You reflux THF under nitrogen or argon over an excess of
Na/benzophenone. Green is the benzophenone radical anion. Deep
purple is the dianion, and your THF is clean, dry, peroxide-free,
and ready to be distilled. The proportions are insensitive to
the results as long as you don't use too little. The Na is
consumed faster than the benzophenone, so see those excess little
silvery balls roiling in the soup.
A good THF still is so purple that you can see the colored wall
splashes washing back into the main pool.
WARNING! Glyme has a slight tendency to explode; higher glymes
>do< explode. Benzene won't go past green. Toluene slowly undergoes Birch reduction. Et2O is OK.
--
Alan "Uncle Al" Schwartz
Uncl...@ix.netcom.com ("zero" before @; 24 hour delay)
http://www.netprophet.co.nz/uncleal/ (best of + new)
http://www.ultra.net.au/~wisby/uncleal.htm (lots of + new)
(Toxic URLs! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Simon Friedman
In article <321A19...@student.ulg.ac.be> Moineau <s90...@student.ulg.ac.be> writes:
>Hi!
>
>I need to use very dry THF(tetrahydrofuran)to do some polymerization.
>I have choose to reflux it over sodium and to use benzophenone as a
>drying indicator. The problem arises from the fact that I don't know the
>proportion of benzopheneone to add. For 3 L of THF, people tell me
>amounts varing from 2 to 30 g!!!
>Does anybody knows the right amount to add and also the way benzophenone
>changes its colour from yellow to deep blue (or even deep purple).
>
>Thanks a lot!
>
>Michael ALEXANDRE
>University of LIEGE
>--BELGIUM--
>E-Mail : s90...@student.ulg.ac.be
Here's an alternative to distillation that I've found works
quite well, though some folks think its "cheating".
Get a fresh bottle of HPLC grade unstabilized THF (1l or what
you need) which starts off with something like < .01% water.
Dump in an inch and a half of recently activated 4A molecular
sieves, put a septum on and purge with Ar or N2. Use it
the next day.
I've used this to do LDA carbanion chemistry with good yields.
(better than with with distilled THF)
Hope this helps,
Simon
frie...@cgl.ucsf.edu
10057...@compuserve.com
Why distill it?
Why not just dry it with molecular sieves? It's a whole lot
safer...
Jon Stagg
webs...@sprynet.com
> Moineau <s90...@student.ulg.ac.be> writes:
> Hi!
>
> I need to use very dry THF(tetrahydrofuran)to do some polymerization.
> I have choose to reflux it over sodium and to use benzophenone as a
> drying indicator. The problem arises from the fact that I don't know the
> proportion of benzopheneone to add. For 3 L of THF, people tell me
> amounts varing from 2 to 30 g!!!
> Does anybody knows the right amount to add and also the way benzophenone
> changes its colour from yellow to deep blue (or even deep purple).
>
> Thanks a lot!
>
> Michael ALEXANDRE
> University of LIEGE
> --BELGIUM--
> E-Mail : s90...@student.ulg.ac.be
>
>>>>
Use a 2 / 1 ratio (weight) of potassium to sodium metal in your THF still. Be sure to keep it under nitrogen. Reflux and Stir. The sodium -
potassium will form a liquid metal alloy in the still which gives a very clean oxide free metal surface to dry the solvent. 2-3 grams total metal
should be enough to dry 2-3 liters of fresh reagent grade THF. The resulting solvent will be water, peroxide, alcohol and inhibitor free.
When the solvent is dry, you will see a blue color in the solution without the use of benzophenone. You can then distill the THF into your
flask for use. I have used this method to dry THF for use in high vacuum anionic polymerizations of PMMA where we were targeting highly
stereoregular, controlled molecular weight and narrow polydispersity polymers. We were able to produce polymers with number average
DP’s of 200 with PDI’s less than 1.10.
When you are done, be sure to handle the waste in the still safely. Although you can distill the THF in this type of still to dryness when there
is active metal (the metal kills the peroxides) you should have at least 100 to 200 ml of solvent over the metal before you try to kill the alloy.
Add solvent if needed. Then add isopropanol (100 ml) slowly and allow it to stir for an hour or so under nitrogen. Then slowly add fresh
reagent grade ethanol (50-100 ml) and allow it to stir for another hour or so under nitrogen. Carefully and slowly add 5-10 ml of water to the
solution and allow it to stir under nitrogen. Add another 50 - 100 ml of water and allow it to stir for several hours under nitrogen. If you do not
see any metal, and no bubbles are forming you probably have killed the alloy. I would then add another 100 ml of ethanol and allow it to
stir overnight before disposal of the solvent.
Geoff Webster
Paul A. Deck
webs...@sprynet.com wrote:
>Use a 2 / 1 ratio (weight) of potassium to sodium metal in your THF still.
Geoff has made some good suggestions and provided a useful procedure
for quenching the still pots with NaK in them.
We use NaK for drying small quantities of several solvents (C6D6,
THF-d8, etc.), so we like to keep a flask of the premixed alloy in the
lab. To make the alloy, we melt the potassium together with the
sodium in the glove box. A heat gun is used, and the process is
reminiscent of melting chunks of baker's chocolate into butter when
making one-bowl brownies. The alloy is then decanted from the slag,
which is cautiously quenched. We store our alloy in a glass Schlenk
flask in a bucket of vermiculite in a special vented cabinet with
other alkali metals. The hazards of storing the NaK are balanced
against the hazards of weighing out small quantities of potassium
every time we needed a half a gram of NaK for a Schlenk tube.
Here are a few facts and figures about NaK (taken from the Callery
Chemical Company product brochure), along with my editorial comments
on their practical significance.
Eutectic composition (lowest melting alloy): 77.8 % potassium by
weight.
The room temperature liquid range is about 40-85 % potassium by
weight. This means you don't need to worry too much about the
precision of weight when making up the alloy. Bear in mind the
potassium content will probably decrease with time.
Density is 0.855 g/cc at 100 degrees C. So you'll probably see a ball
of the alloy bobbing around in the hot still pot.
Viscosity is 0.505 centipoise at 100 degrees C, and with the low
density this means the alloy can be drawn into a syringe or Pasteur
pipette without difficulty, providing adequate precautions have been
taken to protect the alloy from ignition.
Melting point is -12.6 degrees (eutectic). Boiling point is 785
degrees C.
The Callery brochure has nice pictures of their 200-pound and
750-pound NaK shipping cylinders.
Scott Riley
I have used the activated 4A moleculare sieve to dry THF without the
septum and sparge. But think those are great additional steps.
--
"Science is built up with facts, as a house is with stones.
But a collection of facts is no more a science than a heap
of stones is a house." --- Jules Henri Poincare
Scott Riley
frie...@cgl.ucsf.edu (Simon Friedman) wrote:
>In article <321A19...@student.ulg.ac.be> Moineau <s90...@student.ulg.ac.be> writes:
>>Hi!
>>
>>I need to use very dry THF(tetrahydrofuran)to do some polymerization.
>>I have choose to reflux it over sodium and to use benzophenone as a
>>drying indicator. The problem arises from the fact that I don't know the
>>proportion of benzopheneone to add. For 3 L of THF, people tell me
>>amounts varing from 2 to 30 g!!!
>>Does anybody knows the right amount to add and also the way benzophenone
>>changes its colour from yellow to deep blue (or even deep purple).
>>
>>Thanks a lot!
>>
>>Michael ALEXANDRE
>>University of LIEGE
>>--BELGIUM--
>>E-Mail : s90...@student.ulg.ac.be
>
>
>
>
>Here's an alternative to distillation that I've found works
>quite well, though some folks think its "cheating".
>Get a fresh bottle of HPLC grade unstabilized THF (1l or what
>you need) which starts off with something like < .01% water.
>Dump in an inch and a half of recently activated 4A molecular
>sieves, put a septum on and purge with Ar or N2. Use it
>the next day.
>I've used this to do LDA carbanion chemistry with good yields.
>(better than with with distilled THF)
>Hope this helps,
>
>Simon
>frie...@cgl.ucsf.edu
Please remember that THF is peroxidizable! Use uninhibited THF for your
experiment and dispose of the left overs before it has a chance to
peroxidize. And don't make the mistake of leaving it for so long you
forget about it then someone else inherits the bomb.