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I have heard of liquid breathing, where an organism, usually a person, would be breathing in perfluorocarbon. Now I looked up perfluorocarbon on Wikipedia and I noticed, no oxygen at all, but fluorine that would rather bind to the molecules inside you and kill you. I mean, fluorine is electronegative enough to oxidize oxygen. So why doesn't perfluorocarbon fluoridate every oxygen molecule in your body preventing your cells from working and form calcium fluoride in your bones?

How would a person not be killed by breathing perfluorocarbon? Is oxygen more soluble in perfluorocarbon? Does perfluorocarbon not even get into the blood and instead stay in the lungs? And even then, why wouldn't the oxygen coming in be turned into oxygen fluoride? Is it simply because oxygen fluoride has such a short half-life, especially at body temperature that it never forms in significant enough amounts? But even then you would still be breathing out fluorine gas of which some will come back in the next breath. Fluorine gas is toxic because it is such a powerful oxidizer that it will oxidize anything.

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  • $\begingroup$ At a guess, the fluorine in such molecules is in a stable enough state that it doesn't bind to haemoglobin. Perfluorocarbons have very high gas solubility. Perfluoromethylcyclohexane is one commonly studied for its gas solubility and potential use as an oxygen delivery system. There's a paper on this, but it's paywalled unfortunately. $\endgroup$
    – Polynomial
    May 22, 2018 at 21:37
  • $\begingroup$ Fluorine (or any atom) that's bound in a molecule has very different properties from the pure element. Consider common salt, composed of sodium, a highly-reactive metal that spontaneously bursts into flame on contact with water, and chlorine, a poisonous gas used in chemical warfare (WWI). Yet the combination is necessary for life. Or the fluorine atoms in such things as toothpaste & non-stick cookware, or any number of rocks: en.wikipedia.org/wiki/Category:Fluorine_minerals $\endgroup$
    – jamesqf
    May 23, 2018 at 4:52
  • $\begingroup$ I think that's a chemistry.stack quesiton... Toxic chemicals are absorbed differently depending on their organic chemistry compatibility with the body... you can hold 200g of pure mercury in your hand without any risk of death, all day, but the lethal dose of certain mercury compounds is 1 drop for a minute, because pure mercury is not absorbed, whereas certain organic mercury compounds are so reactive that they can't even by synthesized without killing the researchers. $\endgroup$
    – bandybabboon
    May 23, 2018 at 8:06

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In liquid breathing systems the perfluorocarbons are simply an inert carrier for dissolved oxygen. It turns out that oxygen and other atmospheric gasses readily dissolve in perfluorocarbons without chemically reacting with them. Some perfluorocarbons can carry over 300 times as much oxygen as the equivalent amount of water. Perfluorocarbons are incredibly stable under conditions compatible with life, they aren't being broken down into free fluorine in you lungs or blood, or reacting with your tissues much at all. The perfluorocarbons don't cross the lung-blood interface in significant amounts.

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