[briteyellowness]

why would crystallization be a better way to separate diastereomeric salts?  can i use extraction with different solvents to separate it?

[movies]

Crystallization is used because in the solid phase the way the crystals pack requires a certain diastereomer in order to maintain the crystal polymorph.  In solution this doesn't happen because the molecules are too far apart.

You might, however, be able to separate enantiomers by extraction with a chiral solvent.  In theory it might be possible to separate diastereomers by extraction (although probably not diastereomerics salts) since in principle diastereomers can have very different physical properties.

[Borek]

Chromatography with chiral stationary phase (is it in English?).

[movies]

Yeah, that's another good point, Borek.  (And your English is right!)

[laotree]

Commericially available chiral AD or OD column. They are normal phase column, very powerful in separating chiral isomers.

[movies]

There are lots of different chiral stationary phase columns available.  Unfortunately, the cost is pretty astronomical!

[laotree]

There are lots of different chiral stationary phase columns available.  Unfortunately, the cost is pretty astronomical!

Sorry I am in Industry.

[movies]

Oh, so money is no object for you then.  

[The Good Doctor]

Hi!!

The most "known" methods to separate diastereomers is crystallization or...chromatography. Since they have like we know different physical properties, a normal colomn should be enough too separate them. Off course it's not allways the case! It can that by "coincidence" they can't be separate on silica. Another way then (sometime a hard way, cause you have too find a good solvent(s) for it) is crystallization. In this technique one kind of diastereomer will recognize his own mates and will form a crystal...

On the other hand enantiomers ("theoretically") can't be seperate cause they have the same physical properties. To seperate them a "chiral" medium should be need! example: convert them to diastereomers and then seperate them. Seperate them on chiral column (expansive as hell!!!), kinetic resolution (mostly enzymatic). Mind that some enantiomers also can be separate by crystallization..if u got luck..just like "the shaking hands recognition" right hand recognize right hands...no left.
 

[The Good Doctor]

...for diastereomeric salts separation in peptide synthesis...electrophoresis is also a possibility..
TGD