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turd
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| Quote: | | LiAlH4 usage brings with it the problem that the solvent (Diethyl ether or THF) in which the reduction will be carried out must be ABSOLUTELY dry. It
has to stand over sodium wire for several weeks (or use better drying agents like NaH and CaH2) and must be distilled in a distillation setup which is
flushed with dried inert gas and protected with a drying tube against atmospherical moisture. |
What are you talking about? I've done successful LiAlH4 reductions with normal Na/Benzophenone dried ether that was refluxed for a few hours. By the
way: CaH2 is not an exceptional drying agent. I use that one for pre drying ether.
Maybe your inert gas technique is lacking?
But of course, if NaBH4 works for your application, definitely use that! LiAlH4 has a tendency of giving side products you wouldn't think of.
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Drunkguy
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You dont have to use special drying agents, just the best that you have at your disposal.
Sure it fizzes violently but if you use an excess it should leave you with any less product. But the fizzing is very violent and scary. I would be
more concerned about detriment to your health than your yield if you select this reagent.
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matei
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You may use LiAlH4 to dry the ether (though it is quite dangerous; the ether must be absolutely free of peroxides and predried over CaCl2 and than
Na).
People in my lab use mostly ether dryed over Na and it is sufficiently dry for LiAlH4 reductions.
Anyway you should't mess with LiAlH4 outside a research laboratory.
[Edited on 13-11-2006 by matei]
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YT2095
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Why a "Research" Lab in particular?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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matei
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I don't mean strictly research, but academic etc. In any case not in your garage.
[Edited on 13-11-2006 by matei]
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YT2095
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LOL, If I was working in a Garage/shed/kitchen etc... I wouldn`t have asked the question in the 1`st place.
my Lab is building in its own right annexed to the house with it`s own store room, heating, lighting, electric, gas taps etc....
the only thing it has in common with a garage is that you can access it from the house.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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DeAdFX
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Telling him a that the chemical should only be used in a research lab isn't really going to convince him of using a different reagent or not doing it
all. However having a professor or someone of expertise watching over you while you conduct an experiment is always a good thing. See if one of your
professors or instructors(or whoever) can give an example of how to properly handle these strong reducing agents.
Since you seem determined to learn about these reagents seeking an authority would be the best route to go. Chances are you will probably encounter
the same saftey discouragement "talk".
However if you wish to do some self teaching thats ok. Prehaps it would be best to start with the tamer stuff(BH4-) and move on the more "dangerous"
stuff (AlH4-).
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Sandmeyer
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Even with Red-Al the yields suffer if toluene used hasn't been pre-dried.
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