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Author: Subject: ether peroxides
Jor
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[*] posted on 26-5-2009 at 15:22
ether peroxides


I have a pretty old bottle of ether (maybe 2-3 years old), wich i bought second hand from my supplier, when it was half full (400mL in a 1L bottle)

In the end of 2008 I did a peroxide test on my ether and it was negative. No peroxides.

Today I did another test. There was still 250mL in the bottle. A large KI crystal (i think 250mg) was dissolved in 2mL 1M HCl, and about 3mL of ether was added. After coming back a minute later, both layers had turned light yellow --> peroxides!
So this means the BHT is used up?

I was wondering what I should do? I am not sure what to think about these peroxides, some people say they are extremely dangerous, and some say they are only dangerous when you evaporate off the solvent. I will certainly never distill it. I use ether relatively common, as I make many inorganic chemicals (coordination compounds) and many times I wash them with ethanol followed by about 1-2 washes with ether, wich helps me drying the material very quickly.
I do not think such low levels create a danger for opening the bottle, but to be certain, I keep the bottle upside down, so that any peroxides are dissolved, wich are possibly crystallised on the cap (formed by ether vapour oxidation, after all there is oxygen mixed with ether in the air above the liquid ether).

So what would you do? I have some difenylamine, wich is said to be a great stabiliser. Would it help to add this to my 200-250mL of ether, and if yes how much should I add?

I have also been thinking about destroying the ether, by alkaline hydrolysis, and flushing it away (ethanol). Although ether is expensive (25-30 EUR per liter), i rather buy a new bottle than a big accident. Or not... I have been considering not using Et2O anymore for washing salts. But it really helps (instead of ethanol alone), as evaporation is very quick, wich is essential for hygroscopic or unstable compounds. I have been considering using DCM as an alternative.

Or is there no danger? Ofcourse I'd rather not hydrololyse it to ethanol... Any advice would be greatly appreciated.
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[*] posted on 26-5-2009 at 16:18


Add some of your diphenylamine to it. A few milligrams will do, and stop further peroxide formation.
Keeping the bottle upside down is not necessary at all.

Peroxides crystallizing in the screw threads are a speciality of diisopropyl ether, which is one of the only ethers that pose an explosion hazard due to peroxides even without distillation.
With diethyl ether, there is no crystallization of peroxides in the screw threads.

It is possible to remove peroxides from ether, but for your applications, this operation is most likely unnecessary. It is also lossy. You can use the ether as it is.

Finally, you can't hydrolyse diethyl ether. Nothing will happen with NaOH or HCl solutions. Cleavage of primary alkyl ethers requires drastic conditions (heating with hydriodic acid under pressure, producing 2 moleculs of ethyl iodide).




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Arrhenius
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[*] posted on 26-5-2009 at 18:59


You can shake it up with aqueous ferrous sulfate, but personally, safety is pretty important. I'd dispose of it.

As far as DCM as a substitute, ether dissolves considerably more water.
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[*] posted on 26-5-2009 at 19:55


5% sodium metabisulfite is another method of removing peroxides. It is said to rapidly and efficiently destroy peroxides.



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[*] posted on 27-5-2009 at 07:09



DESTROYING PEROXIDES OF ISOPROPYL ETHER
A. C. Hamstead
I & EC Vol 56 No. 6
pp 37 - 42; DOI: 10.1021/ie50654a005

BTW there are several threads on this very topic. Just try to use the search option with "peroxide" in the subject and you will get several hits.
It appears from the list that before opening a bottle of "old ether" members first open a thread about peroxide in this forum :)

gsd

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[*] posted on 27-5-2009 at 11:28


Quote: Originally posted by gsd  

It appears from the list that before opening a bottle of "old ether" members first open a thread about peroxide in this forum :)

gsd

True, and annoying, but still better than opening a hole where their hands / faces should be.
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