RE: ORGLIST:problem of reduction

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From: Moens, Luc (Luc_Moens$##$nrel.gov)
Date: Thu Jun 03 2004 - 12:14:46 EDT


Dear friends,

There is a specific method to work up LAH reactions that involves the use of saturated aqueous potassium sodium tartrate (Rochelle salt) for the work up. In all the cases that I have encountered, it has avoided the formation of the gel-like emulsions (Li/Al salts) that can make the work-up very challenging, and facilitated the phase separation with organic solvents such as ethers. In addition, it avoids the use of strong acids such as HCl which may be incompatible with the product that you are trying to isolate. In case you are struggling with the THF dissolution in the water phase (and the resulting emulsion), it may be wise to either remove most of the reaction solvent through rotary evaporation before work-up, or to use THF/pentane mixtures to carry out the extraction. The latter promotes better phase separation. In any case, try to avoid THF as a solvent whenever possible because it is miscible with water.

Wishing you success,

Luc
*******************************************************
Luc Moens, Ph.D.
Senior Scientist
National Renewable Energy Laboratory (NREL)
National Bioenergy Center (NBC)
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> ----------
> From: everybody-admin$##$orglist.net on behalf of S.BARTOLI$##$soton.ac.uk
> Sent: Thursday, June 3, 2004 9:10 AM
> To: stephanie
> Cc: everybody$##$orglist.net
> Subject: Re: ORGLIST:problem of reduction
>
> Why don't you treat it with a 1M HCl aqueous solution (pour your reaction
> mixture into the HCl solution under vigorous stirring after quenching it with
> EtOAc)and then filter the solid, which should be your alcohol? That's what I
> used to do.
> Hope it helps. If you have any questions let me know.
> Cheers,
>
> Sandra
>
>
>
> Scrive stephanie <roulle.stephanie$##$wanadoo.fr>:
>
> > Hello everybody,
> > I have a problem with a reduction. I want to reduce an ester to an
> > alcohol with LiAlH4 / THF. The reaction is perfect but my problem is the
> > treatment. The alcohol obtained is very cristalline and insoluble in all
> > solvant. It precipitate when I treat my reaction.
> > I tried to hydrolyse with HCl and extract with dichloromethane and there
> > is precipitation. I also tried to hydrolyse with Na2SO4 with water and
> > also precipitation and I cannot separate Na2SO4 and the obtained
> > alcohol. I tried at last to hydrolyse with THF/water, there is also
> > precipitation, I evaporate the THF and put isopropanol and filtrate. The
> > problem is that my yield is over 100% because I have also aluminium
> > hydroxyde and I cannot separate them of my product.
> > Can anybody help me please ???
> >
> >
> > stephanie
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