Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: baum0372 on June 25, 2013, 07:57:17 PM
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I am trying to separate a compound that I protected as the acetal using 2,2-dimethoxypropane. TLC shows that almost all of my original starting material converts to the protected compound, however, when I separate on a column (silica) I can only isolate around 60% of my compound. I have heard from others that acetals can degrade on silica since it is acidic.
So my question is (assuming the silica actually can degrade my compound) how I can neutralize the silica so that this doesn't happen, or do I switch to alumina to separate? Thanks!
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Surely if your compound were decomposing on silica you would see the same effect on TLC?
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Generally if a substance is degraded on silica your separation is terrible as it happens gradually as the sample passes through the column.
Acetals are not that unstable and as discodermolide points out this effect would be most likely observed on a TLC plate.
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Check the TLC after extraction to make sure nothing funny happens during workup. Check for possible degradation on silica using 2D TLC.
If the acetal were degrading I would expect you would be getting your diol back out. Do you recover your starting diol?
To answer your question though, you can deactivate the silica by putting a small amount of triethylamine in your mobile phase. I forget the amount I used to use, but something like a few drops per liter. You will have to experiment what works best for you.