FOOF

Other names: dioxygen difluoride, fluorooxygen hypofluorite, fluorine peroxide, oxygen perfluoride

O₂F₂

31/50 uncommon

"Being a high energy oxidizer, dioxygen difluoride reacted vigorously with organic compounds, even at temperatures close to its melting point. It reacted instantaneously with solid ethyl alcohol, producing a blue flame and an explosion. When a drop of liquid 0₂F₂ 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 0₂F₂ was added to 0.5 mL of liquid CH₄ at 90°K., a violent explosion occurred."

—Streng (1963)

FOOF (dioxygen difluoride) is widely regarded as one of the most dangerous chemicals ever synthesized. First prepared by Otto Ruff in 1933, this pale yellow volatile liquid or gas exists only at cryogenic temperatures, decomposing violently above -100°C. FOOF combines the oxidizing power of oxygen with the reactivity of fluorine, creating a compound so energetic that it can cause virtually any substance to combust on contact—including materials normally considered fireproof. As Derek Lowe memorably described, "FOOF is only stable at low temperatures; you'll never get close to room temperature with the stuff without it tearing itself to pieces." Even its synthesis involves passing fluorine gas through 2% ozone at -100°C, a procedure so hazardous that few laboratories would attempt it. FOOF represents the extreme edge of oxidative chemistry, fascinating theoreticians while terrifying practical chemists.