I made Imines by oxidation of Amines I want to isolate them by using column chromatography. I used Activated neutral alumina oxide as given in reference papers but after after column when I check TLC it shows a a clear spot but when I check with GC and NMR there is no Imine. I also used silica gel as well but I have same issue with it. I used hexane as an eluent. Need help asap
The imine is probably decomposing on the column due to the slightly acidic nature and moisture content of the Alumina and Silica. Try deactivating the acidic groups on the stationary phase by including a few percent of a tertiary amine like triethylamine in the mobile phase. For mostly aliphatic imines I used 25% diethylether in hexane plus 1% trethylamine as the TLC and silica gel column chromatography solvent.
Also consider other column types such as cyano, which can also be run as normal-phase with normal phase solvents.
http://www.isco.com/WebProductFiles/Applications/101/Application_Notes/AN100_Purification%20of%20Delicate%20Compounds%20with%20RediSep%20Rf%20Gold(r)%20Diol%20and%20Cyano%20Columns.pdf
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