chemrox - 21-11-2014 at 12:29
Every chemist who approaches using a gas for crystallization has to consider the method for introducing the gas into the mixture. It is tempting to
apply a glass frit but he quickly finds this to be fraught with problems. Mainly, the frit becomes quickly clogged with the crystals produced. This
also happens with tapered gas inlet tubes. After trying both I've settled on straight glass tubing. On the other hand when conducting an
esterification using an HCl catalyst, the frit may provide better saturation provided the resulting ester is a liquid or at least one that doesn't
solidify in the mixture. My gas drying tubes have fritted inlets. This seems to minimize the amount of H2SO4 needed for drying the gas.
Dr.Bob - 21-11-2014 at 12:34
If you keep some positive pressure on the frit, it should not absorb too much liquid and stay clear, but that means putting the gas on before putting
it in the liquid. I used to use gaseous reagents more, but now I use 4N HCl/dioxane more, it is the lazy man's source of HCl, but expensive. But it
gives fast creation of HCl salts and also great for removing tBoc groups.
chemrox - 21-11-2014 at 13:35
This would have worked in the last one I did as the amine was in ether/acetone. Expensive? Do you buy it or make it? I have an article somewhere on
making HCl/ether. The maintenance of positive pressure would almost require three hands. You need a Marie in the gas line to control the output flow
from the generator and prevent suck back. You also need a hand on the acid stop-cock to control gas generation..I do it but it's always a lot of fun
;^)
[Edited on 21-11-2014 by chemrox]
Metacelsus - 21-11-2014 at 17:02
I have such a frit, and I use it almost always. The only time I don't is when the inverted funnel technique is necessary, due to very high gas
solubility. I've never had problems with it getting clogged.