I have a simple biaryl I'm trying to purify by a flash column. I'm following a procedure from a paper (same exact product) on a 5 mmol scale, where they also purify this by silica gel column, using the same solvent system (just hexane). The product showed an Rf of about 0.3 on the TLC. I dry-loaded my sample and ran the column in hexane, but several column volumes later, NOTHING eluted.
I flushed with a polar solvent and got my crude sample.
More info about my columning technique to help get an answer:
I have a set procedure for running columns following https://labs.chem.ucsb.edu/zakarian/armen/how-to-do-flash-column-3.pdf
, but I use a slurry pack, and dry loading of the crude. After adding my dry load, I run through about half an inch of my solvent system to 'load' the sample into the silica. I then add sand, then the solvent system, then start the run. I collect a set amount of dead volume at the very beginning before collecting into fractions tubes, roughly 1 column volume worth, but don't throw it away until I am certain I have my product.
I have run several columns using this procedure with good separations in short times so I'm very concerned about this problem.
In this particular case
- The fractions were not too dilute since I combined all of them, including the dead volume at the beginning, and evaporated the solvent to leave behind an empty flask. The flush at the end gave me back the same mixture I started with.
- I checked the recovered crude by NMR and the product did not decompose
- I double checked the solvent system by running another TLC of the crude in hexane
If anyone could tell me what they think went wrong I would be very grateful.