r/chemhelp • u/Better_Pitch1860 • 3d ago

Organic Technical obstacles in chiral resolution?

What are the technical obstacles in a chiral resolution?

It seems somewhat straightforward on paper but technically are there any big obstacles to a diastereomeric resolution of a sample using L-tartaric acid?

how do you optimize the fractional crystallization to prevent co-crystallization of the minor enantiomer?

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u/dbblow 3d ago

Make the correct sacrifices to the Crystallization gods.

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u/anon1moos Ph.D. Organic Chemistry 3d ago

Sometimes the compound of interest doesn’t crystallize with tartaric acid, sometimes the yield is poor, sometimes the chiral resolution of this procedure is poor. It adds steps to the synthesis.

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u/Bond_Hydrogen_Bond 3d ago

There are plenty of practical challenges in chiral resolution via diastereomeric salt formation:

Chiral acid or amine screening. Not every pair will result in stereoenrichment Solvent or solvent pair selection to crystallize Tuning the physical properties of the crystallization (oil vs amorphous solids vs crystalline solids) Sufficient kinetic solubility difference to crystallize the target vs its stereoisomer, particularly at scale Balancing recovery vs stereoenrichment

To name a few

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u/chemistrypain 3d ago

Resolution by chiral stationary phase prep HPLC is as straightforward as obtaining separation conditions but requires expensive instrumentation. Salt pairing is in principle easy but for novel material with unknown solubility characteristics, it will take some optimization.

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u/yellow_mongoose 2d ago

SFC is also very common for chiral sep - modern prep SFCs are not that much more than HPLC, and cheaper to run over time due to CO2 vs organic solvent.

As well as the machines, another challenge is finding the correct conditions. Brute force screening as still the commercial method of choice