I have carried out a recrystallization process for my isolated compound from a plant material. I have used ethanol and have allowed it to evaporate under a fumehood with the hope of forming crystals, however, oil-like droplets start to from instead, as the solvent level decreases. Why does this form and how may I avoid that and obtain crystals?
Dear Mohammad
There might be 2 reasons for this matter. First, you might have not done the recrystallization carefully and some impurities are still left in the solution and maybe the recrystallization solvent was not chosen correctly. Second, some compounds take some time to form crystals. This has happened to me. You can put those oil-like droplets in vacuum for a couple of times. This might also help.
Break,
"Another potential problem in recrystallization is that the solute sometimes comes out of solution in the form of an impure oil instead of forming purified crystals. This usually happens when the boiling point of the solvent is higher than the melting point of the compound, but this is not the only scenario in which this problem presents itself. If this begins to happen, cooling the solution will not stimulate crystallization, it will make the problem worse. If an oil begins to form, heat the solution until the oil portion dissolves and let the whole solution cool. As the oil begins to form again, stir the solution vigorously to break up the oil. The tiny beads of oil that result from this shaking may act as the nuclei for new crystal formation." See
---http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/recrystallization
Well, I prefer column chromatography for purification. You may try that too.
Good luck
Thank you Mina and Adel for your answers. I have actually managed to crystallize it by changing the solvent to methanol. Column chromatography is indeed the best and I have already used it, but I am recrystallizing in order to make it easier for me to use the compound in further reactions, otherwise the compound is already pure as per TLC analysis.
Do evaporation as slow as you can this allows the development of crystals.
Try different solvent or combination of solvents or dissolve and keep at lower temp.
first give information how did you isolate solid i mean first crystal , did you try water immissible solvents to recrystallization ? did you try bi phase solvents ? why am i asking you water soluble solvent may catch the moisture may be your compound is water soluble . if your compound is soluble in water soluble solvent at hot condition then add water immiscible solvent maintaining the ratio up to kill the miscible solvent it may works
all the best
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