In the field of organic synthesis the final product may be in the form of wax/oil during the work up to overcome this and to obtain the solid products what methods should be done?
Hi Elsayed,
look at my notes in : https://www.researchgate.net/post/How_can_amorphous_solid_be_made_crystalline
In short: use dry solvents, dried substance, substance is better in salt form, check for absence of stereoisomers.
Sometimes new substance need staying for some monthes before it begun to crystallize. But after this first nucleation, remelting and cooling often lead to fast crystallization.
Some compounds can be forced to crystallize or solidify by dissolution in chloroform or methylene chloride followed by addition of hexanes until cloudy or milky and rotary evaporation. You may need to repeat several times.
Regarding hygroscopic polar organic compounds, the most important thing is the use of freshly dried solvents (as already mentioned) in order to avoid the formation of sticky/waxy products and facilitate their isolation. Often reprecipitation (repeatedly if needed) from a (dried) polar solvent induced by addition of ether (or other non-polar solvents) can help in many cases. Additionally if you manage to isolate your compound as a precipitate and you intend to filtrate, while washing with volatile solvents (such as ether) never leave the solid exposed to air; cooling, upon evaporation of your washing solvent, can cause condensation of water on the surface of your solid leading back to a waxy product. And finally, (solid) impurities can hamper the solidification of a product. Removing these impurities (eg chromatography) can often lead to solid products.
Any method which can increase molecular weight will get you to more solid products. Also a nucleating agent can be added, this would induce cristallization.
Most of organic molecules (except liquid with low molecular weight) have ability to form crystals.
For each molecule, the initiation of crystallization process is specific, depending of solvant, concentration, temperature. I would recommand a screen of conditions (the equipment Crystals 16 from Aventium is usefull for that purpose - 16 places with ramp of temperature and turbidimetry but tubes are enough). Select lot of solvants with range of properties (from dipolr aprotic to very hydrophobic..) and try pure solvants (different concentration, heat and cool) then try mixture... It is always surprise to found the right solvant but I am sure there is one for your compound.
You can use a mixture of two solvents. Dissolve your oil/waxy material into one of the solvents and use the other one to crystalize your product. Once you see formation of turbid in the solution, then quickly put it in the freezer and leave it overnight, it might need more time than that. Or you can use chromatography to clean it. Good luck!
For any waxy or liquid organic compound to exist in solid state which is not the standard state of that Compound. It is better to use the best combination of solvents that will support the crystallization.
Depending on the nature of the product, the physical appearance may vary. You can try one thing.
First dissolve your compound in a minimum amount of highly volatile solvent (DCM, Ether, Chloroform). Then add non polar solvents (Hexane, Pentane) slowly on the sides of the vessel. Please note, is there any formation of small dust like things. If it is so, add little more of solvent. Then remove the solvent under vacuum. You will get solid product from viscous one.
you can also try a quick column if above mentioned techniques doesn't help you, it helped me as well in such cases
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