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Author: Subject: Storing over drying agents - degradation?
monolithic
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[*] posted on 16-3-2019 at 05:23
Storing over drying agents - degradation?


If I'm doing something that requires a dry solvent I will dry and re-distill on an as-needed basis. I do this because threads on media bottles slowly leak and there's always a head of air above the solvent, so I can't trust the solvent to be pure weeks or months from when I prepare it.

Needless to say, I'm getting tired of doing this. Can I store, for example, anhydrous DMF over MgSO4 and not expect some sort of interaction or degradation of the solvent by the drying salt?

[Edited on 16-3-2019 by monolithic]
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DavidJR
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[*] posted on 16-3-2019 at 05:34


Molecular sieves 3A are a good near-universal choice for this use. Only common solvent they're not compatible with is acetone.
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XeonTheMGPony
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[*] posted on 16-3-2019 at 05:55


So long as you carefully select the drying agent I wouldn't say so, I store my Chloroform over CaCl and have noticed no issues over the course of time
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monolithic
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[*] posted on 16-3-2019 at 06:12


Quote: Originally posted by DavidJR  
Molecular sieves 3A are a good near-universal choice for this use. Only common solvent they're not compatible with is acetone.


Yes, I've thought about buying some molecular sieves. :) But I was wondering if I could store with what I have on hand (MgSO4)?
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RogueRose
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[*] posted on 16-3-2019 at 06:30


I forget is it was this site or another chemistry forum but I recently read something similar about people storing solvents with a drying agent and it turned out bad. IIRC, it might have been DCM over molecular sieves and some others. I don't recall what happened exactly but it messed up both the solvent and the drying agents.

IDK how long this stuff was stored or if it was done in excessive heat, but I'd look into this before making it a standard.
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monolithic
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[*] posted on 16-3-2019 at 07:50


Quote: Originally posted by RogueRose  
I forget is it was this site or another chemistry forum but I recently read something similar about people storing solvents with a drying agent and it turned out bad. IIRC, it might have been DCM over molecular sieves and some others. I don't recall what happened exactly but it messed up both the solvent and the drying agents.

IDK how long this stuff was stored or if it was done in excessive heat, but I'd look into this before making it a standard.


If it was acetone, I know molecular sieves and acetone are a no-go.

Since it seems molecular sieves are much more commonly used for storage, do they have a shelf life? I see there are some molecular sieves on eBay that were manufactured in the early 2000s. Obviously they can be regenerated, but does their effectiveness degrade over an almost 20 year period?
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TheMasterOfTheInternet
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[*] posted on 16-3-2019 at 18:55


Once I was storing elderly THF over sodium shavings. After some months some clear yellowish gel was formed on the sodium and the THF turned yellow. I asked several professors, teachers and other chemists and noone had an idea what it could be.


[Edited on 17-3-2019 by TheMasterOfTheInternet]
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[*] posted on 16-3-2019 at 19:02


Quote:

Since it seems molecular sieves are much more commonly used for storage, do they have a shelf life? I see there are some molecular sieves on eBay that were manufactured in the early 2000s. Obviously they can be regenerated, but does their effectiveness degrade over an almost 20 year period?

I they were stored well (sealed, dry, clean) and never used they should work almost like new I think.
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