From: Christopher Paul Borella (cborella$##$ic.sunysb.edu)
Date: Fri Mar 24 2000 - 21:11:48 EST
Well I'm not sure about the titration, I normally just titrate with di
phenyl acetic acid. However, when we must prepare n-BuLi
(normally we buy from aldrich except for very large scale) we
sonicate for 3hr rather than heating. We found this normally gives
quantitative conversion of the BuCl. The solution is then transfered via
canula to remove the LiCl. Heating of the solution may be causing
decomposition, or dimerization.
Hope this helps
-chris
On Fri, 24 Mar 2000, [ISO-8859-15] Olga Tšubrik wrote:
> Dear Colleagues,
>
> I hope somebody can give me a good advice for my problem.
> I synthesized butyllithium by reacting BuCl with excess Li (seven hours
> boiling in dry hexane). Then I let the solid phase to settle and
> then I siphoned the solution with the argon pressure to the
> dry flask. The solution is clear.
> All the procedure was done in oven-dried apparatus with dry inert gas
> flow (Ar). But now I have a problem with the determination of the BuLi
> concentration. I did it twicely.
> 1. Firstly I hydrolyzed the aliquot of BuLi
> by some water and then I titrated it with HCl. I got 1.76M for the
> concentration.
> 2. Secondly I did the so named "double-titration". I react BuLi with
> benzylchloride in ether (five minutes for reaction). BuLi must react
> with PhCH2Cl and the impurities will remain (BuOLi, LiOH).
> Then I decomposed the mixture with water and titrated it with HCl. Now I
> got 0.60M for the impurities concentration and so only 1.16M for the BuLi
> concentration. Is it possible I have so many impurities in my reagent?
> (It means that air humidity and oxygen reacted with the product!)
> What do you think about such "double-titration method"?????
> Can I trust this method? Or can somebody advice me something better?
> All the reagents were pure and dry.
>
> Can someone give me some ideas and suggestions? Help!
>
> Thank in advance.
>
> Olga Tshubrik
>
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