by John Walker

Space filling model of FOOF molecule

Space-filling model of FOOF molecule. (Public domain image by Wikimedia user Benjah-bmm27.)

Elsewhere we've discussed chlorine trifluoride, but now we'll take it to a whole new level of nasty and discuss dioxygen difluoride (O2F2) or, as onomatopoeically inclined chemists prefer to rewrite the formula, FOOF.

Foof! is what happens when this insanely reactive compound encounters almost anything. Even at −160 °C it decomposes slowly into OF2 and oxygen. At higher temperatures it explodes when coming into contact with almost any substance, including water ice.

So how do you make it? You'll need oxygen and fluorine gases, an inert reaction vessel, and a wretched excess of pure gibbering insanity to attempt such a thing. One approach is to mix fluorine and oxygen gas inside a vessel heated to 700 °C. The diatomic fluorine dissociates into fierce monatomic fluorine, which binds to the oxygen molecules to produce FOOF. You then must cool the resulting substance quickly to cryogenic temperatures lest it decompose in ways infelicitous to your health, laboratory, or prospects for tenure in the chemistry department. You can also prepare FOOF at low pressure with an electrical discharge, or by exposing oxygen and fluorine to MeV level electromagnetic radiation.

Once you've made it, about all it's good for is bragging among other chemists, many missing fingers and limbs, that you've done so, and causing havoc. One A. G. Streng wrote in 1962:

Being a high energy oxidizer, dioxygen difluoride reacted vigorously with organic compounds, even at temperatures close to its melting point [119°K]. It reacted instantaneously with solid ethyl alcohol, producing a blue flame and an explosion. When a drop of liquid O2F2 was added to liquid methane, cooled at 90°K., a white flame was produced instantaneously, which turned green upon further burning. When 0.2 (mL) of liquid O2F2 was added to 0.5 (mL) of liquid CH4 at 90°K., a violent explosion occurred.

and so on. Below its melting point, it is an orange solid, above a reddish liquid which is just looking for trouble. Its boiling point has been calculated to be around 216°K (−57 °C—winter in Antarctica), but nobody has measured this for the excellent reason that the compound blows up well before you reach the boiling point. As Derek Lowe wrote of another preternaturally nasty compound, “…I'd like to shake the hand of whoever determined that property, assuming he has one left.”

Derek Lowe, upon whose delightful series “Things I Won't Work With” I have based this essay, calls FOOF “Satan's Kimchi ”. I'm not sure Satan could take the heat.

I regret there are no videos of experiments with FOOF, but there is an insufficient number of people crazy enough to make them. Hey, think of it as a new niche!

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by John Walker
March, 2016

This document is in the public domain.