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Topic: Chrial resolution through crystalization  (Read 2608 times)

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Offline TheUnassuming

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Chrial resolution through crystalization
« on: August 22, 2014, 01:06:35 PM »
I have a racemic, tertiary, benzyl alchohol gamma to a carboxylic.  I wish to try using a chiral amine to crystallize one of the enantiomers and thereby get enantio-pure substrate.  Does anyone have any experience doing this and if so what amines did you find to work the best (also what sort of substrate were you separating)? 
I have done this before in the opposite manner, using various sugar-acids to selectively crystallize one enantiomer of a racemic amine substrate and so am familiar with the process but am having some trouble finding very much relevant literature to this approach. 
When in doubt, avoid the Stille coupling.

Offline discodermolide

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Re: Chrial resolution through crystalization
« Reply #1 on: August 22, 2014, 01:09:01 PM »
This is usually trial and error. I have had success with the alpha-methylbenzylamines. which usually form nicly crystalline diastereoisomeric salts.
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Offline Arkcon

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Re: Chrial resolution through crystalization
« Reply #2 on: August 22, 2014, 01:49:07 PM »
And do the crystals grow as mirror images of each other, like Pasteur observed for tartrate crystals?
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Offline discodermolide

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Re: Chrial resolution through crystalization
« Reply #3 on: August 22, 2014, 02:42:24 PM »
Not that I noticed, but they were quite small. And allI was looking at was the MPt and rotation.
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Offline Enthalpy

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Re: Chrial resolution through crystalization
« Reply #4 on: August 22, 2014, 04:36:19 PM »
And do the crystals grow as mirror images of each other, like Pasteur observed for tartrate crystals?

I believe to understand that most compounds racemates would make a precise 1:1 stacking of right and left upon crystallization. The compounds that separate spontaneously  are very uncommon and useful, because these serve to separate the others. That is, if you have a right amine, its salts crystallize more or less easily with the desired right or left acid (boths salts aren't enantiomers) - and if you have the right acid, differing salt crystals lets you obtain the right or left amine.

So from the exceptional tartrate, keep the pure right or left tartric acid, use it to purify the desired amine that wouldn't separate otherwise.

I could be horribly wrong, so please take with caution.

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Probably a too big effort for a single compound... I hope the Czochralski process will improve crystallization of chemical compounds as well, especially for difficult operations like chiral separation:
http://www.chemicalforums.com/index.php?topic=65386.0

Offline TheUnassuming

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Re: Chrial resolution through crystalization
« Reply #5 on: August 23, 2014, 01:37:29 PM »
Thank for the help @disco, definitely will be giving that a go!  Getting good crystals period is an art, let alone using it to make diasteriomeric salts.   Its just nice to have an already validated starting point to branch out from.
I'll post here again with any results.  Cheers!
When in doubt, avoid the Stille coupling.

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