I have been trying to purify a small molecule containing N-hydroxy and ketone group. The synthesis involved use of weak inorganic base e.g., sodium carbonate. Typically the purification used extraction or recrystallization using a polar organic solvent like ethanol or acetone to extract the polar molecule.
However the phenomenon is like this:
1. Once ethanol was added to the mixture in excess, white precipitate forms with water as "oil" stuck to the bottom of a flask. In this case, I could only purify some of the salt but not the target compound.
2. I also tried rotary evaporation, but the final form is a very sticky and gummy.
3. I then tried to dry the water at 120 C, leaving the salt and compound in the solid and tried to use polar organic solvent to extract it. Nothing or very little was dissolved, leaving colored solid at the bottom.
4. Recrystallization was also attempted, but since water is much less volatile and favors solute dissolution, the result is basically a precipitation of salt.
5. I have tried to add acid to change the pH condition, but the result is similar.
So the question is, is there any other good way to purify this hydrophilic, highly polar compound from salt?
You need to specify the chemical compound. They have different properties and solubility.
Best regards.
Ion-exchange resins are often used for this kind of separation. You may want to try a mixed-bed resin, which contains both cation- and anion-exchangers in the hydronium and hydroxide form, respectively. See, for example, http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0032/0901b803800326ca.pdf?filepath=liquidseps/pdfs/noreg/177-01837.pdf&fromPage=GetDoc
Thanks for the answers first, and sorry that I didn't put up the chemical structure as the name is somehow complicated: it's two N-hydroxyphthalimide groups joined by a ketone group at 3,3' position of the aromatic rings. This is my expected compound, but what actually came out may not be exactly the same.
For John, salt separation was what I wanted to do but for separating all of them...the real target is compound purification. The precipitation only removes a small part of the salt, most of them remained dissolved in the ethanol/water mixture. The compound info is provided above. As you've pointed out, no transition metal was involved in the synthesis.
Try to get solid nitrophenylhydrazone to identify ketone by melting temperature. Then outline the method of separation.
Best regards.
You can try to use polar non soluble in water diluent. such nitromethane, nitrobenzene, C2H4Cl2, CHCl3 etc.
To separate highly water soluble polar organic molecule from inorganic salt dissolved in water.You have to concentrate reaction mixture under vacuum to a 10% volume and then cool when organic compd. will crystallize leaving water soluble eletrovalent compd. in aque. solution. It works just like separation of sugar from concentrated sugar juice.
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