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January 13, 2006
How Not to Do It: Ether Peroxides
We've had a few incidents recently at the Wonder Drug Factory where people have been using some common solvents like ether or tetrahydrofuran (THF) and ended up with odd results. When they check their reactions, there's something else in there that hasn't turned up before. The same impurity turns up in completely different reactions, too, which narrows the possibilities down a lot. In a couple of these cases, the chemists involved went to the trouble of isolating this pesky impurity and getting NMR spectra of it.
The experienced chemists in my audience are already cringing; I can feel it. No, we didn't blow anything up. But the people involved are now the proud owners of clean NMRs of ether peroxides. These explosive little beasts are an unavoidable byproduct of storing ethereal solvents where ambient oxygen can get to them. Oxygen is just too reactive - which is fine for us, biochemically, since that keeps us alive, but it can be a real nuisance in other situations.
These solvents are usually sold with some inhibitor added, a free-radical sponge like BHT, for example. But over time - or if someone in the supply chain stored things improperly - this will get used up, and then peroxidation moves right along. In extreme cases, such as with the unstoppable di-isopropyl ether, you can even get crystals of the peroxide coming out of solution. I have never seen this in person, and I will be very glad if I never do
Biologists and physicians have, among chemists anyway, a reputation for treating bottles of ether much more cavalierly than we do. A colleague of mine witnessed this at first hand at a former company of hers. A note had gone out to all the departments to check for old ether bottles, went into the possibility of crystal formation, and told everyone to notify the haz-mat team if any bottles were uncovered. In the molecular biology department where my source was working, one of the lab heads promptly marched out and rooted through the cabinets, emerging a few minutes later with a can of ether of uncertain age. This person then held the can up to his ear while shaking it, listening to see if any solid material was sloshing around in there. Which is one way to find out.
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