Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: tomek on December 06, 2019, 06:12:46 AM
-
I am trying to purify a piperidinecarboxylic acid derivative after its ethyl ester hydrolysis. I refluxed the reaction in 10% aq. HCl for 15 hours and there was still some of the ethyl ester present (I even found m/z corresponding to the methyl ester when I did LCMS ???). I will go with higher HCl concentration or longer reaction time next time, but assuming this reaction cannot be driven to completetion then I would like to be able to purify the product.
I searched the forum looking for clues and I found some of you suggesting to use ion-exchange resins. My understanding of the process is that I can dissolve my crude in MeOH, stir with an anion exchanger to trap the acid (cation xchng would trap the noth the acid and unreacted ester because of amino group) and then elute with acid (eg. 1M HCl). Finally adding SCX will mop up the excess of Na+ and also trap the product so flushing with 2M ammonia in MeOH should release the pure compound. Please correct me if I am wrong.
I would be also grateful for other suggestion regarding this issue. Particularly any advice on ion exchange chromatography. If you have good references to recommend that would be awesome.
Thanks!
-
You can just do acid/base extractions? I.e.dissolve in DCM, extract with 1% NaOH, then titrate it to just protonate the carboxylate and not the pipiridine. Hopefully the product will crash out, or just extract again with DCM.
-
I have used Dowex-50 ion-exchange resins to desalt amino acids. One of the typical protocols is to use a 20-fold excess of exchange capacity versus all cations. After binding and washing with water (to rinse away anything that won't bind), I add 2 M ammonia to elute the amino acids, which lose their positive charge.
If I use Dowex-1, I usually put it into the acetate form because acetate binds more weakly than chloride does, but I still have a large excess of the exchanger present. First I apply the amino acid, and then I rinse with water. I usually elute with HCl, but I think that I may have eluted once or twice with acetic acid. I have not used resins in alcohol. If an amino acid has an aromatic ring, that can be a problem with polystyrene-based resins.