Column Chromatography does not match the TLC w/same solvent

[rahin_59]

Hi Everyone,

In the process of synthesis of a new lipid, I have faced this problem with purifing the compund.
In TLC samples (with e.g. 6:1 TCM:Methanol) fractions are seperated perfectly fine, the Rf of my product is 0.15 while impurites have Rf ~0.4-0.5.
Problem is when I run the Column Chromatography using the same solvent as TLC. In the first or second fraction, all the compound comes out impure.
It is very unusuall in two aspect.
1- it comes out this early while with Rf=0.15 it is more expected to come out after the 25th fraction.
2- it does get seperate with TLC but not with the column.
I have repeated this enough that I know it is not the technic.
The compound has -COOH, -CONH-, benzen ring with unsaturated tail. I wonder if anyone had the same experience with column and if you have any suggestion.
Any comments will be greatly appreciated.
TNX :?: [/b]

[kx5]

Mainly this type of problem arises when TLC system is not properly developed. For your kind information why are you doing a column if you have COOH group in your molecule, extract your compound into sat NaHCO3 sol. to make sodium salt of acid which will be pure. I you really want to do a column try to develop new TLC system may be using MeOH/DCM, Acetone/DCM,CHCl3,PetEther.

bye.bye