[mira]

Hello,
I am seeking some advice regarding a chromatography problem. I have recently been preparing a set of compounds (specifically cyclic alcohols). Upon purifying them on regular silica which I normally use (which is slightly acidic,) I start to observe elimination by-product (which is induced by the silica I am assuming). In our lab we don’t normally use “neutral” silica so I tried to neutralize some silica on my own. I stirred a slurry of silica in small amount of triethylamine. After collecting the silica solid, I used it for separation but this time I started to see some decomposed compound streaking on the column. So I assumed that the Et3N has reacted with my compound.
I was wondering if anyone can suggest a better separation technique/medium that is neutral and mild? Or even any suggestions how to properly neutralize silica in the lab?
Any tips are greatly appreciated,
Many thanks…

[fledarmus]

I have rarely seen neutralized silica in the manner you described used with success. Typically if the acidity of the silica gel is an issue due to peak broadening because it is interacting with basic groups on the molecule, you can use a low percentage of triethylamine in the eluant to improve the separation, but in your case, where the issue is decomposition on the column, that may not be helpful. It is easy enough to check - run a 2-D TLC. Cut a small square TLC plate, spot your sample in one corner, and elute it in one direction using an eluant with a small amount of triethylamine. Do the same with the eluant you used previously. Let the plates stand for a few minutes to dry, then put the plates in sideways and let them elute the other direction. Spots off of the diagonal indicate decomposition of material on the plates.

Usually when people find that silica gel is acidic enough to decompose their compounds and adding TEA to the eluant doesn't work, the switch is to neutral or basic alumina columns.