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Topic: nonane contamination  (Read 6927 times)

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Offline phth

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Re: nonane contamination
« Reply #15 on: November 29, 2017, 08:58:24 PM »
pgk, isnt it standard to allow glassware to cool down under N2 flow or vacuum? phth is an experienced enough chemist not to make that mistake! (I hope).

Yeah, I understand.  I noticed that the ground glass connection between the RBF and tube connectors were ruining my vacuum, so I went on the side of not heating them up to long to prevent the glassware from warping.  Teflon tape is the way to go though, so I guess it doesn't matter...

Offline pgk

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Re: nonane contamination
« Reply #16 on: November 30, 2017, 10:14:16 AM »
Vacuum is not a good choice because air (humidity content included) will violently penetrate into the flask, when vacuum being broken. Besides, N2 is not visible and it is lighter than air and consequently, it will escape first from the hot flask and leave space to moisturized air to penetrate thereinto.
Another option is cooling glassware in a desiccator with P2O5. But I doubt if there are available desiccators that are large enough, to contain a 500ml three-neck flask plus the appropriate condenser plus the dropping funnel, etc. 
« Last Edit: November 30, 2017, 11:40:03 AM by pgk »

Offline wildfyr

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Re: nonane contamination
« Reply #17 on: November 30, 2017, 01:19:42 PM »
You don't break the vacuum with air after pulling vac on heat dried glassware, you gently backfill with dry nitrogen from a tank, typically via a valve system on a shlenk line, then add reagents and solvents. The system never sees ambient air.

This is basic air/water free procedure in most labs...right? I pray?

Offline pgk

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Re: nonane contamination
« Reply #18 on: November 30, 2017, 02:17:10 PM »
Yes, right!
Gradual break of vacuum with simultaneous and slight nitrogen flow, is the way to avoid the violent penetration of air. However, this is a convenient technique in industrial or pilot scale, using steel equipment but it is rather delicate in the lab and needs special attention, especially when working with tiny glassware.

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