From: Jon Kremsky (jkremsky$##$primeorg.com)
Date: Thu Sep 07 2006 - 09:27:00 EDT
Chris:
KH is an exceedingly difficult reagent to handle. If you do not have any
experience with it, you should be aware that it is far more reactive than
sodium hydride. You cannot rinse off the oil as you can with sodium hydride
because it will spontaneously burst into flame.
The 35% refers to the amount of KH in a uniformly dispersed suspension. The
most convenient way to work with it that I have found is to agitate the
suspension by swirling, remove some amount into a tared, DRY flask under
inert gas, septum seal it and weigh. Use 35% of that weight as the amount
of KH. Rinse out the oil via syringe with hexane. Be certain to collect
the original pipette and all of the washings in a beaker which you will need
to quench separately and carefully.
This is not for the faint of heart.
Jon Kremsky
-----Original Message-----
From: everybody-bounces$##$orglist.net
[mailto:everybody-bounces$##$orglist.net]On Behalf Of Christopher Luus
Sent: Thursday, September 07, 2006 12:20 AM
To: everybody$##$orglist.net
Subject: ORGLIST: Use of Potassium Hydride
Can anybody advise me as to the correct use of potassium hydride (KH) in
the conversion of a ketone to the corresponding enolate salt? The KH is
supplied as an ~35% dispersion in mineral oil and appears as a while
sediment at the bottom of the bottle with a thick layer of mineral oil
above it. I am not sure if the 35% refers to the sediment or whether I
should homogenize the dispersion before use? I also wish to avoid having
to wash the dispersion due to obvious reasons of stability.
Any advice would be appreciated.
Regards,
Christopher Luus.
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