How hazardous are peroxide-able ethers if stored properly?

This question is directed towards laboratory scientists and technicians who actually deal with ethers that can develop peroxides upon concentration (e.g. diethyl ether, THF, dioxane). I am already very familiar with the literature, the normal precautions (dispose of after 1 year, test for peroxides, etc.), how to remove peroxides (shake with ferrous salt or metabisulfate).

My question is how hazardous are peroxides in reality if stored properly. If a peroxide-able ether upon concentration is stored in a cool dark cabinet, is rarely opened, has an inhibitor (BHT or ethanol), and argon is used above the headspace, it is likely that the ether can be used for longer than a year?

Again, I need the input of an actual practitioner. Simply quoting written material will not help me, as I have consulted LOTS of written material and I believe I understand the theoretical issues. I am looking for practical experience. I have heard informally that some ethers are available in European countries as OTC solvents, and so it leads me to think that the standard warnings may be too severe. Thanks!

• I believe, that when I was still a student in university, we kept and used DEE and THF for more than a year, especially when dried and kept in inert atmosphere. I think most safety concerns apply to quantity. There are probably other reasons why you should not use solvents after a year or so... – Martin - マーチン Aug 18 '14 at 17:48
• One of may previous labs used some diethyl ester and THF, and no accidents occurred. As long, as they are properly stored (no direct sunlight, tightly sealed bottle, a tiny bit of $\ce{KOH}$ on the bottom of the bottle) they are reasonably safe. Of course, I would be a bit ... concerned in case of work with diisopropyl ester, but not so much. – permeakra Aug 19 '14 at 0:18
• @permeakra: Thanks! Can you answer these two questions I have: 1) do I need to pre-dry (I would assume yes with something not so water reactive), and 2) how much to use (I would assume you don't need much)? You seem to agree with my answer to 2). And I have no diisopropyl ether and agree that it is a higher order of storage danger! – user467 Aug 19 '14 at 0:26
• 1) DEE and THF dissolve quite a bit of water, so boiling and then distillation of marketed solvent over excess of sodium or potassium hydroxide is common. In case of extra large quantities, another pre-drying stage may be economically justified, but in common labs it is usually dried with alkali hydroxide directly. The amount of hydroxide required for drying is very dependent on quality of the raw solvent, so no suggestion here. I would use roughly 1-2 table spoons per liter unless it is extremely wet. – permeakra Aug 19 '14 at 0:35
• 2) As far as I remember, it was a small amount. Again, 1 table spoon per liter should do. – permeakra Aug 19 '14 at 0:36

2 Answers

Peroxides are no fun. There have been explosions when ether solutions were concentrated to dryness. What you really want to do is store your ether over potassium hydroxide - hydroperoxides are slightly acidic, and the base forms hydroperoxide salts and pulls them out of solution.

Also, if you keep solvents for more than a year you clearly aren't turning them over fast enough. Keeping flammable material that you don't need just increases the danger in case of fire.

• Thanks for this. I've tried looking into this but could not find hard procedures. Two questions I have: 1) do I need to pre-dry (I would assume yes with something not so water reactive), and 2) how much to use (I would assume you don't need much)? – user467 Aug 19 '14 at 0:27

Having accepted Abel Friedman's very sound answer, I wanted to append a coda of sorts. After posting this question, I tested all my opened peroxide-able ethers (diethyl, THF), and there were no measurable peroxides despite being well past the 1 year mark. I double-checked that the test was valid with hydrogen peroxide, which produced a strong positive for peroxides.

I conclude that the standard recommendations for peroxides are similar to the warnings on MSDS sheets, in that they err on the side of extreme caution. As Abel Friedman says, peroxides are no fun! So testing and careful storage (full airtight containers, argon in the headspace, dark cool location, inhibitors) are essential. But if you do these things, the "store-by" dates do seem to be excessive.

As to the valid point that I might not be turning over my solvents fast enough, I realized that the converse could be true in a working lab. That is, solvents are used frequently, and thus are left out in the light and opened frequently. If these are not used quickly enough, there is a real risk of peroxides. But it would seem that dark airtight storage (and inhibitors!) does retard peroxide formation well beyond the recommended limits.