Re: ORGLIST:Methoxide vs Ethoxide

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From: Uno Mäeorg (uno$##$chem.ut.ee)
Date: Mon Apr 05 2004 - 12:34:09 EDT


Dear mister X,

You can evaluate the basiscity of these metal derivatives using the pKa
values of corresponding acids they are prepared from. So the ethanol is
slightly less acidic than methanol and therefore the ethoxide is more
basic. It is practically not possible compare the LDA and NaOEt, because
diisopropylamine is about 20 pKa units weaker than any alcohol. Of course
the solvent you are using is also important. You can use the Bordwell's
DMSO scale of pKa-s what is available in many sites in internet.
There are many details (type of metal, possible ligands, are you working in
kinetic or thermodynamic control, concentration, temperature etc.) using
this scheme of thinking, but roughly it works very well.

Regards

Uno

At 08:49 AM 4/2/2004 -0800, finechem wrote:

>Dear All,
>
>How effective as a base would Methoxide CH3O-Na+ be as
>compared to Ethoxide C2H5O-Na+ ?
>
>In terms of basic strength how would C2H5O-Na+ compare
>to LDA ( Lithium Diisopropyl Amide)?
>
>Thanks in advance
>
>
>
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