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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: TrevorGage on March 18, 2020, 01:28:32 AM

Title: Recrystallization Solvent ?
Post by: TrevorGage on March 18, 2020, 01:28:32 AM
What to recrystallize methyl 3,5-dibromobenzoate from?

Literature says ethanol but it doesn't work. Compound precipitates and does not crystallize.

Melting point is 63 C.omegle (https://omegle.onl/) discord (https://discord.software/) xender (https://xender.vip/)


I have also tried DCM, or DCM/hexane and the same thing happens.
Title: Re: Recrystallization Solvent ?
Post by: hollytara on March 18, 2020, 08:56:34 AM
You get a powder (microcrystals) instead of discernible crystals? 

I always like to recrystallize methyl esters from methanol if using an alcohol - no chance of transesterification.

If you are getting a powder, that means the temperature/solubility curve is very steep - so you can suddenly become greatly oversaturated and have rapid crystallization. 

You can - dissoive to saturation at room temperature.  Then add a known amount of extra material - don't saturate at hgh T. 

Or - lower the temperature more slowly. 
Title: Re: Recrystallization Solvent ?
Post by: pgk on March 18, 2020, 01:46:48 PM
Try recrystallization with ethanol containing a little THF. It may work.
Title: Re: Recrystallization Solvent ?
Post by: barbarahansen on January 12, 2021, 09:59:31 AM
The precipitate was collected by filtration and recrystallized from a mixture of ethanol and water.

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Title: Re: Recrystallization Solvent ?
Post by: jeffmoonchop on January 12, 2021, 12:04:11 PM
Are you doing it by antisolvent method? may be too rapid. Dissolve in minimum amount of solvent at an elevated temp. Cool the solution slowly. You may need to hold the solution at a temp for a long time if its not crystallizing by primary nucleation. If you know the solubility cool to just below the solubility and hold, try scratching the solution with a sharp object to encourage heterogeneous nucleation. Or leave the sharp object suspended so it has something to grab onto when it decides to go. When it does go the nucleation rate will be low because the supersaturation is low, then you're more likely to grow onto existing nuclei, rather than forming many nuclei (powder).
Title: Re: Recrystallization Solvent ?
Post by: jeffmoonchop on January 12, 2021, 12:06:11 PM
Also, once it is growing, you can start to decrease the temp again (slowly) to get more material out of solution to maximize yield