Panache
International Hazard
Posts: 1290
Registered: 18-10-2007
Member Is Offline
Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
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Vacuum Filtering moisture sensitive crystals
Anyone have a good generalised technique for the vacuum filtration of crystals from cold dry solutions. My particular problems lies with the water
condensation from the air on the ~40 crystals as they solvate quickly.
Currently i manage it barely by insulating the buchner, filling it with the solution/crystal mixture, covering it with filter paper and a piece glass
then applying suction. It is winter here and the ambient floor is around ~15C so it not like there is huge amounts of moisture.
How is it done with moisture sensitive crystals that react with water, as i imagine i could not manage it with this technique. I don't have any
circumstance in mind but i can't think of how it may be done simply and this bothers me. Maybe there is no real way to do it simply.
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Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
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Mood: No Mood
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For such sensitive compounds, schlenk vac filtration technics are usually used. This consists of a double male-end tube, with a glass frit in the
middle, and inlets for vacuum and inert gas. One side is connected to the schlenk containing the slurry/suspension, and a empty flask on the other
side, evrytthing properly purged etc. The whole setup is then tilted quickly so that the slurry/suspension is tranfered to the filtration tube, and
then either inert gas over pressure or slight vacuum is applied, to push/pull the supernatant into the empty flask, leaving the product on the glass
frit. It can then be washed by introducing cold, dry, degassed solvent into the first flask, rincing the flask and tilting the setup again to wash the
crystals. Then they can be dried by applying vacuum for a while, and either kept in the sealed tube until further use, or transfered to a flask etc to
be sealed under inert gas...
Indeed, this isn't a easy/practical way to do at home. You could use a "dry box" made from a large sealeable box in plastic or a larger esistant
plastic bag with holes for your hands, throw in some dessicant for a few hours, then do your filtration and transfert your solids into adessicator
directly. This could only be suitable for somewhat water sensitive compounds, the most delicate one will need rigorous inert conditions.
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