Saturday, June 13, 2009

resolution step 2

I recrystallized the material from the resolution, and the ee went up to 98.9%. Perhaps I didn't use a sufficient volume of solvent or enough wash. In any case it will be easy to recrystallize again to get the ee up enough.

I took the mother liquor from the bulk resolution, which was heavily enriched in the diasteromer salt, and free based it. The opsque, dark brown, mixture was treated with D-tartaric acid, and crashed out to give the much more enriched salt. Interestingly, when the boiling solution of base was added to the boiling solution of acid, in similar concentration to the racemic case, the salt started to come out of solution even before I was done mixing the two. The already highly enriched enantiomer gave almost optically pure material (96.8% ee) that had only a hint of color. In a typical resolution of this compound from racemic I expect to get >75% ee, so this was a pleasant surprise.

I didn't add a pic of the mother liquor because it was on the rotovap when I took this, and I expect everyone is familiar with what a flask full of tar being stripped looks like.

I recrystallized the D-tartrate salt to get the ee up, and it took nearly twice the volume of solvent it would have if it were 75% ee, presumably due to the significantly higher optical purity.

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