I'm recrystallizing perfluorophenyl azide NHS ester according to established protocols using IPA as the singular recrystallization solvent.
When I take a subsample of 30 mg crude, dissolve in hot IPA, slowly cool down for more than 20 minutes, then add a few crystals of the pure produce as a seed, I get very long crystals of pure product.
When I try this at the same crude to solvent ratio for larger batches of 300 mg, I get a white powder instead after adding a few crystals of pure product as seed. I can't seem to get large crystals. Are there some tips I can use to get this to work consistently for larger batches of crude?
Found a good solution that may help others. I took the hot solution and stuck it in an incubator set at 35C. I waited 30 minutes, then added some seed crystals. The slightly higher temperature slowed crystallization down just enough to form nice needle-like crystals. Then it's a simple ramp down to 25C, then 4C to continue growth.
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