[selinezgi]

We have synthesized an unknown solid in our laboratory and we want to purify it to proceed with analysis, but in TLC check we have seen that this product has two spots and one of them is the starting material, so we think that it decomposes on silica. That is why we cannot use column chromatography for purification. Is there another purification technique that you know where this decomposition will not be a problem?
Thank you..

[Dan]

in TLC check we have seen that this product has two spots and one of them is the starting material, so we think that it decomposes on silica. That is why we cannot use column chromatography for purification.

The other possibility is that the reaction did not go to completion. Have you attempted silica chromatography?

You can verify whether or not the compound is unstable on silica by running a 2D TLC (link)

Is there another purification technique that you know where this decomposition will not be a problem?
Thank you..

Can you give the structure? You say that it is an unknown solid, but that you synthesised it yourself - what was the starting material and what conditions did you use?

[selinezgi]

The reason why we cannot perform column is that we are affraid that the starting material will come along with the product with the solvent that we used in TLC and we cannot use solvents having high polarity, since the product will give reaction with them.
The product is a derivative of quinoline and it has a Bromine.

[kriggy]

You can just try and if it co-elutes just put the fractions together and try again with different mobile phase. What mobile phase did you use for the TLC? You can just use different ratio of those solvents to get bettter separation (ie. if they are close together, then using less polar mobile phase will get you better separation)

[selinezgi]

We used 5% methanol-Ethyl Acetate mixture as solvent system.
The product and the starting material spots are too close, very polar solvents react with the product and when we decrease the solvent polarity the chromatography may take too much time and I am still not sure whether the starting material would come or not.
Maybe using a stationary phase different than silica might work?

[rolnor]

Yes, you can try aluminium oxide instead of silica. Also you can use a few percent triethylamine i the mobilephase if the compound is acid sensitive.