Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: nielsgeode on October 11, 2008, 08:04:57 AM
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What I sometimes do is make a solution of my compound in a solvent where it is well soluble in (eg THF, toluene) and layer some pentane on top of it. The pentane will slowly diffuse into the other solvent layer where it will produce crystals :)
Problem: I always have some mixing when carefully putting the pentane on top. Anyone any suggestions for this to have less mixing of the layers when starting the crystallisation?
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What about a large pipette/burrette or something that could deliver the pentane straight to the surface of the THF so it doesn't have to fall far under gravity. Slowly increase the amount over the surface as it runs out (Rather than just pouring from a beaker). ? You could have the tip of the pippette just above the surface of the THF and let it run out slowly - lifting the pippette as the level goes up.
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There are other tips on layering miscible fluids of differing densities. You might try using using a spoon (or flat spatula) to avoid splashing, for instance:
http://www.chemicalforums.com/index.php?topic=25814.msg97650#msg97650
It helps if you can keep cats away, as well. ;D
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Use a vessle with straight sides (i.e. not a round bottomed flask). Tilt vessle diagonally then run pentane over THF layer by pipetting down side of vessle, then slowly tilt back up-right!