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ScienceSquirrel
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| Quote: | Originally posted by DNA
Just some questions on Argon, I'm planning on buying a argon cylinder to do reactions under inert atmosphere and I have couple of choices:
2L including reducing valve = 197.50 euro (NL)
5L including reducing valve = 185 euro (DE)
10L including reducing valve = 267.5 euro (NL)
I prefer to buy it in the netherlands since I also live there and then I can even pick them up insted doing it by post.
Germany offers a bigger cylinder for a nice price too.
How long would one last with 2L cylinder, or otherwise stated how much gas does one use for an organic reaction approx?
Thanks in advance.
[Edited on 29-8-2008 by DNA] |
That all depends on the scale that you are working on and how sensitive your materials are.
Some things can be done under a simple argon blanket using an inlet and a bubbler and just flushing the flask with gas.
Other things require the full treatment, degassing the solvents to remove air and a constant positive flow of gas.
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Klute
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I know the ones sold in my area, having a approx. volume of 5L indicate 500L gas. Might be different pressures though. Justa sk for the filling
pressure, and calcualte the volume at STP with PV=nRT.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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DNA
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They would be around 200 bars.
I'm planning on using them for BF3xEt2O/NaBH4 reductions and for LiAlH4 reductions.
Maybe some times for Pd/C reductions.
I think for LiAlH4 it is sufficient to gas the solvent with Ar and pulling it vacuum until it starts boiling but that doesn't need that much of Ar I
guess.
A constant flow probably will only be needed while adding the chemicals and for maybe half an hour until it is refluxing at that time the reaction is
pushing up solvent gasses up to halfway the condenser.
That way air is being excluded anyway, then also using a drying tube on top and also having put a Ar blanket over it in the beginning should do the
trick I suppose 
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Klute
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It can be safer to introduce a stream of argon when quenching excess LiALH4 to dilute the H2 to minimize explosion hazard. Same for diborane
reductions (as you don't want to breath any expeled gas).
I'd love to hear about your diborane reductions. I'm plannign on reducing some teriary amides soon, and plan on trying LiALH4 and diborane from
BF3.ET2O and NaBH4 in THF. Got to prepare and purify the amides first, which isn't easy :S
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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DNA
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I already have done quite some reductions with BF3xEt2O and it is really great exept from the toxicity of the gasses.
DO and absolutely DO mix the THF and BF3xEt2O in portions else it won't work.
So add NaBH4 in flask and chill to 0*C then add 2ml THF then 0,5ml BF3xEt2O then again 2ml THF then again 0,5ml BF3xEt2O and so on.
If you would pour in all the THF and then later all the BF3xEt2O I have had several failures.
Quite good yield around 70-80% with the method I described, small detail but very important.
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jarynth
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Welding argon from the DIY store here comes in thin walled bottles (of the torch gas kind, same nozzle as well) at an affordable price (about $20 for
about 1-2 liters compressed). Would this be suitable as an inert gas or would it still contain huge traces of water etc? Unfortunately I don't recall
seeing purity details on the bottle. I might inquire with the manufacturer.
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Klute
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I use thsi kind of argon in small disposable low pressur ebottles, and have had no problem with humidity. I used a CaCl2 in-line drier at first, btu
seeing that it hadn't cake dup even afetr several bottle's, I consider them as dry. Very sensitive reactions would surely require adequate
purification though, to remove traces of CO2 (which is the major contaminant in mine), possibly H2O and O2. But if you have invested into schlenk
lines, degassed and distilled solvents stillls, etc, you could just aswell throw in a little more money to get good argon from Air Liquide or
similar...
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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tapira1
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Use of Ar
We use Ar baloons for reactions (even for big ones); in this way you can control how much you use (unless you need to vent som gaseous reaction
product). Your argon is too expensive; you should check for other qualities, which also work well.
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MagicJigPipe
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| Quote: | | Another no-no is that the helium you can get cheaply in party stores is not pure helium. Due to people breathing in helium to make their voices higher
pitched, small amounts of O2 (Up to 5% I believe) are mixed in with the He so that suffocation doesn't occur. That oxygen will completely mess up any
reaction you plan on doing. Pure He with no oxygen added isn't nearly as cheap. |
I mentioned this elsewhere on the forum but I figured it can't hurt to say it again. The "party helium" sold at Wal-Mart in the US is 99.995% He. No
O2 or air (no more than 0.5 mL/L anyway). This information came from the company that makes (fills) and distributes the containers.
[Edited on 9-7-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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chemrox
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Don't screw around with those little oygen bottles! Get at least a 40 CF bottle or you'll be running down to the supplier for more gas before your
experiment is finished. It's not maintaining the head that uses up gas but the sweeping and flushing steps. I use a 40. I started with a 20 and
traded with my supplier for the larger tank. The smaller ones might be ok for H2 for a medium pressure machine.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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redox
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So I went to the welding store, and $210 later...
I own a 20 CF argon tank w/regulator!
My quite small but growing Youtube Channel: http://www.youtube.com/user/RealChemLabs
Newest video: Synthesis of Chloroform
The difference between chemists and chemical engineers: Chemists use test tubes, chemical engineers use buckets. |
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JJay
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I've been looking at picking up a small argon cylinder.
This one I think is a little too small, but it would function well in an inert gas setup, right?
https://www.grainger.com/product/GASCO-Argon-Calibration-Gas...
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MrHomeScientist
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It depends on what volume you are trying to inert. Someone here sent me a great paper, "The Manipulation of Air Sensitive Compounds" by D.F. Shriver
and M.A. Drezdzon, that goes into great detail on this sort of thing. In chapter 2.2 it talks about how to inert a chamber via the purging method,
which is likely what home experimenters will use. To summarize, inerting a chamber requires purging it with somewhere between 1 and 7 volumes of gas,
depending on how well the gases mix. Also, rapid purging is more effective than slow purging, according to the paper.
For my homemade glove box, I assumed the worst case and purged through 7 volumes before working in it. I could figure this out because I bought a flow
meter for my cylinder and so I know the rate of gas entering the box and the volume of the box.
I have a 40 CF cylinder that I bought from my local AirGas shop for this purpose. I haven't used it much, but it looks like 3-4 7-volume purges and
the cylinder is gone. So your small cylinder might only be "one time use" depending on the size of your chamber.
Also, "inert" gas depends on what you are working with, of course. CO<sub>2</sub> might be inert enough for some applications. But argon
is pretty cheap, once you get past the cost of the cylinder.
[Edited on 10-27-2017 by MrHomeScientist]
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JJay
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I will probably be using small volume glassware with inert gas, but my largest flask is 3L, and it would be nice to be able to use it with an inert
atmosphere.
I'd like to play with some organometallics, so I can't use carbon dioxide as inert gas (otherwise I'd just make it). I will definitely have a look at
that book if I can find it.
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