1
$\begingroup$

I have a problem while synthesize the schiff base. I synthesized using absolute ethanol as solvent and use reflux method for 4 hours generally. The problem occur on TLC where there is still two spot on the product which one of them are very clear (top one) (which I guess the ligand formed) and another one were very light, while on NMR spectra, whereby there is a singlet peak at approximately 10.0 ppm which I assumed that it is from the aldehyde itself which probably not completely reacted. I also tried several derivatives based on benzaldehyde and aniline but some of them have to be recrystallize which I havent found the suitable solvent system yet.

So with all due respect, I really need help especially those who have an experience on synthesizing schiff base and also share to me some ideas to recrystallize my ligands.

$\endgroup$
  • 1
    $\begingroup$ So basically, you need a method to separate reactant from product, right? Have you tried column chromatography? $\endgroup$ – Jan Dec 25 '17 at 13:38
  • $\begingroup$ No, I havent tried column chromatography, will it work? because based on my understanding, column chromatography usually used for compound which may consist of more than 3 different material. $\endgroup$ – Ashraf Kahar Dec 25 '17 at 14:12
  • $\begingroup$ The std conditions for Schiff base formation is Dean-Stark reflux in Toluene with acid catalysis. You may find this superior to ethanol reflux. I second the suggestion of column chromatography for purification $\endgroup$ – Waylander Dec 25 '17 at 15:36
1
$\begingroup$

The reaction needs acid catalysis but ethanol is fine as solvent. There will always be some starting materials left, but since the product is a solid and the reagents are liquid, the best (and cheapest) is to purify it through recrystallization.

For this, dissolve the product in the smallest quantity of hot ethanol and then add water until precipitation occurs.

$\endgroup$
  • $\begingroup$ Schiff's bases are susceptible to hydrolysis. Avoid water in recrystallization and ethanol for that matter. Go with the Dean-Stark trap, acid catalyst and rerecrystallization with non-hydroxylic solvents. $\endgroup$ – user55119 Dec 30 '17 at 16:08
  • $\begingroup$ True. It is an equilibrium, but it is favored to the Schiff base. And you have no acid in the recrystallization, so water is not a problem. $\endgroup$ – Raoul Kessels Dec 30 '17 at 16:14
  • $\begingroup$ Actually I have tried to dissolve my compound in water but it really doesnt dissolve either in cold or hot condition, so I keep on trying to use other solvent combination such as DMF, THF, DCM and etc. Some of my friends did get crystal compound but it need a lot of patience and as it involve try and error step. However regarding recrystallize using ethanol and water, is it okay if we have tried that our compound does not dissolve at all with water because referring to the concept of recrystallization, "Soluble in hot, insoluble in cold", or its actually gonna work out if I keep on going. $\endgroup$ – Ashraf Kahar Jan 2 '18 at 15:04
  • $\begingroup$ The idea is to dissolve it in hot ethanol and then precipitate it with water. The product is soluble in hot ethanol and insoluble in water. $\endgroup$ – Raoul Kessels Jan 5 '18 at 17:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.