Sciencemadness Discussion Board

Does washing ether with a hydroxide solution make it safe enough to distill to dryness?

alking - 3-6-2018 at 12:46

Wouldn't any peroxides be washed away? What if you were to just add some water and distill it from that, would the peroxides safely dissolve into the water? These seem like the most simple methods of recovery to me, however I don't see people recommending either so I wonder if I'm missing something.

DavidJR - 3-6-2018 at 15:28

I'm not sure, but you could always just test it for peroxides?

alking - 3-6-2018 at 15:40

I don't have any KI on hand to do so. I have some Alumina that I could use but I'd rather not waste it if I don't have to and especially for the long run this would be good information to know if I plan to continue using Et2O.

arkoma - 3-6-2018 at 17:07

KI is cheap and multi useful

zed - 9-6-2018 at 12:10

Not distilling to dryness, is kind of a standard.

Peroxide formation doesn't start and end, with ethers.

Plenty of other materials, are prone to this problem.

Then, there might be things, other than peroxides, left in your dregs, that shouldn't be totally dried out or overheated.

I'm not the resident expert, perhaps someone present, has better insight?

aga - 9-6-2018 at 13:10

Why, exactly, do you need to distill to dryness ?

Makes no sense.

fusso - 9-6-2018 at 15:47

Adding OH-(aq) hoping to remove peroxides is just adding extra labour work. Youll have to add another unnecessary step of removing aq layer with sep funnel to ur experiment. Id rather simply leave a little bit of ether in flask just like every1 else. Thats simpler. Also u shouldn't boil anything to dryness anyways no matter what experiment ur doing (unless the aim is rly finding out whats left after boiling to dryness)

Metacelsus - 9-6-2018 at 18:28

The classic treatment to remove peroxides is a wash with FeSO4 solution. However, I would still avoid distilling all the way to dryness.

unionised - 10-6-2018 at 00:19

If you are redistilling ether then it makes sense to distil off as much as you can. That means distilling it down to nothing.

It's obviously best to remove any peroxides before doing this.
If you are unable to remove all the peroxides there's still a way round it.
Add something involatile to the ether- perhaps engine oil and then distil.
Any peroxides left behind will be diluted in the oil so, if they decompose, it won't matter much.

alking - 16-6-2018 at 13:24

I didn't realize this thread had more replies. I never intended to distill to dryness, I was just hoping to safely recover all or most of the ether without worry of peroxides. If I recovered all of it I'd add some water to prevent boiling it dry for instance. I did consider adding something I know the peroxides would be soluble in such as isopropanol, but then I'd have to deal with any azeotropes and wash it out post distillation. Adding a higher boiling oil is a good idea though that I hadn't considered. I wish I could find some solubility data for the peroxides, that would answer a lot of questions.

I did find an actual answer to my hydroxide wash question though and the short answer is that it works but only to a degree, it's not effective enough to remove all of the peroxides. I will update with the reference for that when I get home, it has all sorts of data about the effectiveness of various methods. The most effective/easy seemed to be washing it with sodium bisulphate.

alking - 17-6-2018 at 08:21

Here's the reference I mentioned yesterday, it actually was posted here, I didn't realize that.

http://www.sciencemadness.org/talk/files.php?pid=153704&...

I can't copy and paste from the pdf but on page 5 (or 41 by the page nums) it lists a chart showing various concentrations of NaOH sol that were shook with ether for 15 minutes and the amount of peroxides measured before and after. It does mention and imply that "steam distilling over a hydroxide solution" as being safe, but it doesn't go into any details than the brief mention so I question it. I don't think that even qualifies as an actual steam distillation seeing as there wouldn't be any steam or vapor phase interaction with the water.

I just realized that I did actually ask if it would be safe to distill to dryness, but I did not intend to actually do so, I just wanted to know if it was safe because if it is then I wouldn't have anything to worry about when approaching it. I do not really see a problem doing so with such low boiling solvents however (contaminants aside), if you do it on a water bath or an otherwise low/controlled temperature nothing significant would be distilled with it or cause any damage to the glassware.

[Edited on 17-6-2018 by alking]

Tsjerk - 17-6-2018 at 08:30

Quote: Originally posted by alking  
I do not really see a problem doing so with such low boiling solvents however (contaminants aside), if you do it on a water bath or an otherwise low/controlled temperature nothing significant would be distilled with it or cause any damage to the glassware.


I do not understand what you are trying to say. Peroxides explode on low temperatures just fine.

alking - 17-6-2018 at 10:11

No, that's what I meant by "contaminants aside." I was just speaking of dry distilling in general as people were saying you should never do so. It's a good rule of thumb but there are exceptions. If you have a low boiling solvent without harmful contaminants and good temperature control there shouldn't be any reason you could not safely and effectively distill it dry.

Chemi Pharma - 20-6-2018 at 10:51

Trying to remove organic peroxides from diethyl ether or THF with alkaline hydroxides is a bad idea. Many accidents have occurred following this procedure. Orgsyn.com have a few procedures alerting to it.

You'd better use FeSO4 (5 grs in 20 ml of water for each liter of ether or THF). This will destroy all of your peroxides, although it was an exothermic reaction and must be conducted with caution if your ether or THF are very, very old.

Then, separate the layers, dry with anhydrous magnesium or sodium sulfate and distill all the organic layer until dried with no fear at all.