Furch
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Peroxide removal bmo. metabisulphite
Hello.
Since I don't currently have no access to the standard chemicals for removal of peroxides in ether(s), an idea occured... Would it be possible to
reduce any peroxides by action of aqueous sodium metabisulphite (i.e. sodium bisulphite) on the contaminated ether in question (in this case THF and
Et2O)? Seing how bisulphite is quite the reductant and all...
I was thinking maybe shaking the peroxide contaminated ether with an excess of 10% metabisulphite/water solution and then just distill the ether.
Also, since I usually use my ethers for water-sensitive reactions such as Grignards etc., I most often sodium dry it before use. You might think that
the sodium metal is indeed a powerful enough reductant to eliminate any traces of peroxides in there. If so, then conventional peroxide removal prior
to sodium drying ether could be considered heavily redundant.
Do you agree or disagree with this last statement?
I would mostly appreciate any thoughts on the first question in this post, however.
Sincerely,
Furch
\"Those who say do not know, those who know do not say.\" -Lao Tzu
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Eclectic
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Use FeSO4 solution. If you don't have it, make it. Sodium peroxide in ether is probably not a happy combination. 
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Furch
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Thanks for the quick reply, Eclectic!
The reason I prefer not to make-and-use FeSO4 was because I like using chems from a supplier with guaranteed purity, as extensively as possible...
Indeed, it's a bit of a paradox considering the forum we're in, but it's just the kind of guy I am. We all have our preferences, I guess.
So using metabisulphite is not preferable in your opinion?
Point well taken concerning sodium peroxides, however 
Furch
[Edited on 16-9-2007 by Furch]
\"Those who say do not know, those who know do not say.\" -Lao Tzu
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S.C. Wack
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Well if you don't want water in the ether then it's best to not add solutions to it...regardless of whether or not you're drying it later. I have
already posted in the relevant thread a great method for removing peroxides, as a bonus this does not involve water. Soft copper turnings.
Unbelievers should add bright Cu to ether that gives a positive test for peroxides before calling bullshit. Oxygen evolution is vigorous and
instantaneous. The Cu will not be so bright afterwards.
I almost feel like Sauron and his ubiquitous TCT now...but not quite.
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leu
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Sodium bisulfite solutions have been used to remove peroxides from ethers in various published papers, but soft copper works more easily so unless one
was working with something like diisopropyl ether it's really not necessary 
Chemistry is our Covalent Bond
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Furch
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Thanks all, you've been most helpful!
I've got an opened bottle of about 100 ml Et2O, a couple of years old, and it has a very slight precipitate in it (probably peroxides)... Would you
treat this with one of the above mentioned methods, or would you take it to the shooting range and go apeshit on it with some primary explosive?
I.e., is it worth the risk to treat the ether when a peroxide precipitate has appeared?
\"Those who say do not know, those who know do not say.\" -Lao Tzu
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garage chemist
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Ether does not precipitate peroxides. The peroxides are all highly soluble in it and only during distillation or evaporation will they become
dangerous. You can open the bottle without risk, and check for peroxides.
Ether is also almost always delivered stabilized which lasts very long. My 2 years old ether bottle, opened frequently, is still entirely free of
peroxides.
The "peroxides crystallizing in the screw threads" thing is reserved to diisopropyl ether, one of the few ethers that actually can pose a peroxide
hazard even without concentration of the peroxides by evaporation.
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Furch
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Thanks for that, GC. Since I haven't had any problems with peroxides earlier in my ether related experiments, I would have to agree that the peroxide
hazard is somewhat exaggarated.
I'll edit the above statement when the bottle blows up in my face  Seriously
though... I've always though of Et2O as hazardous due to its volatility combined with flamability. It's just that it's been so much fuzz concerning
peroxides lately, so I just wanted to make sure.
I consider this thread closed for my part. Thanks a lot for participating, all!
Furch
\"Those who say do not know, those who know do not say.\" -Lao Tzu
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