Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: baum0372 on June 04, 2014, 07:57:11 PM
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I'm sure most of us here have used molecular sieves to dry solvents, but have you guys come across some powder or residue that makes the solvent turbid? It seems that the sieves sometimes shed into solvents making them cloudy.
I recently added some to 2,2,2-trifluroethanol in the glovebox to dry them, and I am wondering if there is any way to remove the turbidity while still keeping them in the glovebox? Thanks!
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If you want to be sure your molecular sieves wont shed fines (that powdered stuff they accumulate by rubbing against each other when dry,) then you should use the molecular sieves that are sealed in a porous PTFE pouch. At this point, you only solution may be to distill your solvent. I know you won't be able to filter these fines away. I outta know, I did try to once.
edit: fix istill to distill
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YES, this happens to me with THF and DMSO all the time. It actually makes my distilled DMSO turn yellow - it makes me so paranoid. I have yet to find a solution to it, but many reactions can be done with mol sieves in them anyway. If filtration is as difficult as Arkcon says (not sure what he used when he tried), then try giving a little celite a go. Let us know what you find!!!
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A lab mate of mine actually used sieves to dry chloroform the other day, and it corroded the aluminum seal underneath the plastic cap of the vial, dropping a nasty black mess into the solvent in addition to turning it yellow as well.
As far as removing the residue I ended up transferring a plastic syringe and 0.22μm PTFE filter into the glovebox and filtering the solution to get rid of the sieve powder. The other thing I noticed that worked it just to let it sit for 3-5 days, then carefully pipette the liquid from the top of the flask or vial.
Would washing the sieves with the desired solvent for some time get rid of any acidic impurities in the sieves? Can these just be recycled again to avoid the issue with solvents turning yellow?