Dr.Arz - 24-10-2014 at 08:52
How can one distill a compound that has high mp and high bp at ntp in a vacuum so that the substance doesn't solidify upon condensation? This is
because I understand that lowering pressure only lowers bp, not mp. Therefore if we have compound that melts at 90C and boils at 300C and we distill
it at 10mbar at 172C, doesn't it solidify almost instantly when touching the cold condenser? Should one circulate almost boiling water and immerse the
receiving flask to a hot bath in order to keep it liquid until it is done?
Nicodem - 24-10-2014 at 09:19
Depends on the scale, but if you just distilling a few dozens of grams, then you just use an air cooled condenser and initially help your self with a
heat gun.
Metacelsus - 24-10-2014 at 10:02
You could set it up as a sublimation, perhaps. The compound won't be subliming, but it will be depositing.
Oxirane - 25-10-2014 at 02:56
One could maybe make a vacuum reflux setup as a sublimator for smaller amounts? The crystals would deposit on the water cooled reflux condenser and
when it is done, use pure solvent to dissolve it and evaporate to get pure product. Actually one could deposit quite a large amounts if large reflux
column is used. I believe this could be quite a way to make food grade ammonium chloride. 
[Edited on 25-10-2014 by Oxirane]