From: Mitsuhiko FUJIWHARA (pxk12345$##$nifty.ne.jp)
Date: Sat Jul 01 2000 - 22:00:53 EDT
In the mail "ORGLIST: Drying THF", Matthew J Dowd <mdowd$##$hsc.vcu.
edu> wrote;
Matthew> > from P2O5, then from KOH, then finally from Na/
benzophenone ketyl (as
Matthew> > outlined in Perrin, DD & Armarego, WLF Purification of
Laboratory
This should be the best way, I believe.
The long induction time may be due to the limited surface area. I
also have experienced similar cases. What I do in such cases, I cool
the system, then scratch the surface of the sodium in the flask
(not picked out, just inside THF) by using micro spatula.
THIS IS VERY DANGEROUS AND I NEVER RECOMMEND THIS TO YOU.
This is just for your information. I guess the same effect can be
attaind by some efforts to expand the surface area; like wash the
sodium with hexane, cut into many pieces, etc.
Matthew> > Also, how long should the indicator last in the Na flask?
Blue color of ketyl is NOT the indicator (even though we actually
utilize the color as the indicator), but it is the genuine active
spicies. Use of sodium metal alone have some shortcomings;
-NaOH generated is not soluble to THF and as a result the core
of sodium is not effective. This is also troublesome when we
wash the system.
-No indication if the system is OK.
-Usually we cannot expect the removal of peroxide present in THF.
The advantage of using ketyl is that ketyl is the active species and
we can consume all of Na, and the radical anion is not reactive
enough to effect Birch reduction of aromatic ring, so the method is
compatible for hexanes and even for toluenes.
For organometallics, especially for the d8-THF NMR study of
organometallics, Na-K alloy should be used.
For the usual organic chemistry, LiAlH4 should be OK, but the
distillate usually contain trace amount of Al, which sometimes act
as catalyst poison.
____________________________________________________________________
Mitsuhiko FUJIWHARA, Ph.D. Fine & Aroma Chemical Laboratory
Takasago International Corporation
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