tensor9 - 19-3-2012 at 14:51
I don't really want to bother with a still because the demand for THF in my lab is not enough to warrant the hassel. I'm going to share some ideas I
have and would like to get some feedback from you all.
For small amounts (<250 mL), I have been storing THF over a sodium benzophenone ketyl (purple dianion) in a storage flask (http://www.chemglass.com/product_view.asp?pnr=AF-0522), then either vacuum transferring it or distilling it out of the flask for collection. BTW,
the seal on these flasks is quite impressive. The purple ketyl persisted for a year of storage in this flask (and would've continued to do so if I
hadn't broken it.)
But now I need more solvent but would prefer to forgo any vacuum transfers or distillations. This presents a couple of difficulties. For one, storage
over the sodium benzophenone of course inhibited peroxide formation. The necessary distillation also naturally removed unwanted contaminants from the
THF.
Storage over activated molecular sieves dries THF as well (or better) than distilling from sodium/benzophenone, but of course without the benefit of
deoxygenation. My chemistry is not THAT oxygen sensitive, so I'm ok with this. (Freeze pump thaw could take care of that should the need present
itself.) The problem is the storage of THF in between uses. If I sequentially dry it (at least two consecutive dryings over 20% w/v sieves) and store
it w/o distillation but always under N2, the BHT stabilizer will be present and inhibit peroxide formation, but could possibly affect my chemistry. If
I remove the BHT by some pre-distillation I would be paranoid about peroxide formation. Apparently activated alumina removes typical phenolic peroxide
inhibitors (and any peroxides that may be present).
So is the solution just to store it over sieves and pass it over a small column of activated alumina immediately before use? How practical would this
be?
Thanks.
[Edited on 19-3-2012 by tensor9]
niertap - 26-3-2012 at 19:21
Why are you so worried about peroxide formation? I believe the major concern for them is if you find a jar of ether during a lab clean out that
hasn't been used since the 60's. If kept from light and oxygen peroxides won't form. If you are that worried about them or that they will mess up
your work I'm sure you could purchase BHT and add it back in. sigma sells it for kg/$50 and acros has a smaller size 50g/$15.