kilomentor | 03 June, 2009 19:47
Reently Amelia sent Kilomentor a question. She wrote:
Hi, I would like to know what is a good method to remove DMF from my compound. My compound is very polar (with acid and 2 phenol groups)and might not be very soluble in ether. As the compound is a sticky solid, I suspect a tiny amount of DMF is trapped in the solid as I tried freeze-dry vacuum and passing through silica gel column. Do you have a good idea? Thanks.
It is always more difficult to recommend a purification strategy without knowing the full structure. At the same time there is usually good reason for confidentiality.
You say, Amelia, that you think your compound might be insoluble in diethyl ether. If so then triturating with such antisolvent could be an excellent method to remove traces of DMF if present. DMF is miscible with diethyl ether so if your product is essentially insoluble the separation could be excellent and it would certainly be simple and rugged. If too much of your product is dissolved a mixture of ether and hexanewould further reduce the solubility of the diphenolic acid.
Another off the wall idea is from the Kilomentor article “Another Way to Separate Phenolics by Crystallizing of Co-crystals?” 21 March, 2008. Carboxylic acids that are also phenols might be expected for structural reasons to form quite insoluble co-crystals from dry dioxane. The article points out an exception that ortho hydroxy benzoic acids would not be expected to work.
Yet again, if the DMF is tightly complexed to your compound and this is suggested by the failure of freeze drying and passing it through a silica column you might need to make a hydrophobic derivative in order to remove the hydrogen bonds of that hypothetical complex. Complete silylation of your compound would attach at least three trimethylsilyl groups. The derivative would become more and could become soluble in hydrocarbon solvents. Hexane and acetonitrile are immiscible phases and DMF would I think prefer to be in the nitrille phase while your persilylated product may now prefer the hydrocarbon. Kilomentor has written an article about catalysts for quick persilylations and hydrolysis back to product would be facile.
Finally, if your compound is soluble in benzene, you might try adding some sodium iodide to a solution in benzene or other similar solvent. in J. Am. Chem. Soc. 82, 2895 (1960) it is reported in footnote a of Table III that DMF and sodium iodide form an insoluble complex from benzene in a molecule ratio of 1:3! I do not know whether this is actually true and I have never tried this so I would test it out with some DMF in benzene but none of your compound first.