Crystallization

1. Crystallization a.k.aApplied Voodoo…

2. Blog entry that says it all… • I have a difficult compound that I'm trying to purify these days. • The usual methods someone in my position would use aren't too helpful, unfortunately. • That would be some variation on column chromatography, either by hand or through an HPLC, but it doesn’t work here… • So I'm going back to a classic method, one thatgoes back to at least the 1800s: recrystallization.

3. Blog entry that says it all… • It's common among chemists to moan about crystallization being a lost art, and compared to a century ago, I'm sure it is. • Back then, it was the only game in town, so people got pretty skilled. But we still use it, and we can still get it to work when we need it. • For those outside the field, it's pretty easy to describe what's going on. • You take your compound up in somesolvent that will dissolve it when it's warm, and not dissolve it when it'scool. • Heat your stuff up, make a clear solution, and sit back and wait forthe crystals to start growing and snowing.

4. Blog entry that says it all… • Sometimes, anyway. If you're too aggressive with the solvent, or yourstarting material is too messy, then when things cool down your compoundwill "oil out," which is just what it sounds like. • You get this rain of goo piling up in the bottom of the flask; the only thing to do is start over.