I am often asked why reversed-phase TLC data does not translate well to reversed-phase flash column chromatography. There are several reasons for this and in this post I will attempt to explain the challenges associated with reverse-phase TLC as a method development tool for reversed-phase flash chromatography.
For most organic reaction mixture purifications the process is fairly straightforward. Use hexane/ethyl acetate or, for polar compounds, DCM/MeOH. But what do you do if this doesn't work and your compounds are basic organic amines?
In this post, I re-examine the options available to achieve an acceptable organic amine purification when typical separation methods are insufficient.
You have performed your synthesis and now it is time to purify the reaction mix. You have used thin-layer chromatography (TLC) and see a separation but when you try to purify with flash column chromatography, you can’t get the target compound separated from an impurity. So, what is happening (or isn’t happening)?
In this post I will give some input on why some separations are not transferable from TLC.
Organic and medicinal chemists frequently utilize flash chromatography to purify their reaction mixtures. Normal-phase flash chromatography is most often used but may not the best methodology, especially when the compounds are quite polar and/or ionizable.
For these molecules, reversed-phase flash chromatography is preferred but often is not used due to an uncertainty regarding the best solvent choices and the reversed-phase mechanism. In this post, I will discuss how organic solvent choice in reversed-phase chromatography can influence the chromatographic separation.
TLC is the tool most used for normal-phase flash chromatography method development. For many chemists, a solvent system of hexane (or heptane) + ethyl acetate is the first, and sometimes only, solvent system evaluated. Though often useful, ethyl acetate may not always provide the optimal purification conditions.