aab18011 - 27-4-2021 at 12:58
Recently was running a small scale grignard with Iodobenzene and Acetophenone, and have run into a slight issue. I currently have a solution of
1,1-diphenyl ethanol in n-hexane. I have tried to crystallize it out, but it wont seem to budge. After cooling it to -5C, a slight amount has crashed
out, but I cannot seem to force more out. Was wondering if I anyone knows any tricks?
I will be trying acetone in the mix to try and force it out. Acetone should be miscible with hexane.
njl - 27-4-2021 at 13:09
You can try removing more of the hexane then cool as low as possible and wait. To improve yield and speed up crystallization, scratch the bottom of
the container with a glass rod and/or add a seed crystal. Alternatively, you can strip away all of the hexane and work up the solid that remains. I
try to avoid using solvent systems to crash products out of solution since it leaves a relatively large volume of solvent that can't be reused without
processing.
DraconicAcid - 27-4-2021 at 13:21
Are you sure your product will even be soluble in hexane? I'd expect it to be more soluble in acetone.
I'm not that familiar with diphenylethanol, but triphenylmethanol isn't soluble at all in petroleum ether, and is precipitated from DCM by the
addition of pet ether. n-Hexane isn't that different from pet ether, and your product has a higher ratio of hydroxyls to carbons.
[Edited on 27-4-2021 by DraconicAcid]
aab18011 - 27-4-2021 at 13:28
thanks for the advice njl
and as for your question draconic, I am following my universities synthesis which says to use ligroin or n-hexanes to extract from a solution of
diethyl ether and to slowly boil off ether until it is entirely dissolved into hexanes. The only other products in this are side reaction products
that have colored it blackish-red. But unfortunately, they did not qwrite much else. I did find another paper the other day from MIT's organic lab
class saying the same thing, and they said that cooling to 0C should be enough for the whole thing to crystallize, but their method was on a scale of
1 mole rather than 0.1 moles like mine. I still have a stock solution of my reaction products, and so I will try and dissolve in acetone, but I did
not think to try acetone as I couldnt find much solubility information. I will try that and let you know how it goes. Thanks!
DraconicAcid - 27-4-2021 at 13:32
I suspect that the intent was to dissolve the product in ether, add hexane, let the ether evaporate to make the product precipitate. So it should be
soluble in ether, not in hexanes.
aab18011 - 27-4-2021 at 14:33
On a smale scale, it seems like the light boiling to dryness worked. I didnt quite get it dry,but I left it at like 1/10th of its original amount and
it seems to me that it has crashed out. Not entirely, but it did. I am now working on a larger scale to see if it behaves similarly.
njl - 27-4-2021 at 16:58
If what I suggested works I don't see why you shouldn't go for it, however I think Drac is right in that the point of the ether/hexane solvent system
is to precipitate the product from the hexane. Then again, you have the procedure and we don't.