Chemistry Forums for Students > Organic Chemistry Forum for Graduate Students and Professionals
Schlenk technique- argon inert atmosphere
Grasshopper:
Hi, gurus of the chemical forums (fora?). Sorry if this is a stupid question (!) just trying to improve my understanding...
For... reasons, I'm currently using a fume hood that's connected to argon but not nitrogen. I seem to recall, from some murky corner of my memory, that I was once told that it's a bad idea to pull argon across a cold trap (cooled by liquid nitrogen) however I don't remember why and I can't find any info about this (so I am wondering whether my memory is faulty).
I could do with degassing some solvent, preferably by freeze-thaw. If I repeatedly freeze the solvent then pull the argon out of the vessel across the cold trap, is that a safety hazard?
Thanks!!
wildfyr:
I've never thought of it before, but I think it's because you can condense your argon. BP of argon is - 185C, BP of nitrogen is - 196C. You'll have liquid or solid argon in the trap. When you take LN2 off the trap, the argon will boil, gain a lot of volume and explode your shlenk trap.
Grasshopper:
Ah, thanks Wildfyr. So... pulling air across the cold trap is normally OK because we take care not to do it for extended periods of time, and also because oxygen is only 20% of the air... pulling a small amount of argon for a short time may be OK, but will be 100% of the gas in there and has higher boiling point than N2...
Anyway, I think I will find some other way of de-gassing my solvent just in case. I am all in favour of no explosions in the lab ;D
OrganicDan96:
what about using dry ice/acetone instead of LN2
wildfyr:
I'd just like to note that pulling air containing oxygen is an even worse idea than pulling argon. You really shouldn't pull more than whatever the volume of your enclosed system is, plus very minor leaks that are unavoidable. If you hook your system up to a vacuum gauge and it can't get below 100-200 millitorr, you may be putting yourself in a dangerous situation.
Condensed oxygen will expand when warmed, just like argon, but there is another danger. Liquid oxygen can react with any organics inside the trap to make who-knows-what peroxy species, many of which are extremely sensitive explosives.
I did this once by being stupid and it scared the heck out of me seeing that blue liquid gently boiling in my trap. Luckily my hoodmate and I were clean workers. We just opened the vacuum lines to air and let it boil out slowly.
Navigation
[0] Message Index
[#] Next page
Go to full version