As such, DDT is an outstanding pesticide. I have seen it in action with my own eyes. Most impressive. Its use has however been banned in many Western countries for a long time now, because nature does not know what to do with it. It is very chemically stable and very lipophilic, leading to bioaccumulation in the food chain, and in the worst case cancer and death for us humans here at the top of the pyramid.

I know a thing or two about carbon-fluorine bonds as well. They are strong as hell. In fact, they are the strongest of all covalent bonds. As far as I am aware, carbon-fluorine bonds do not occur naturally. Probably for a good reason too. (UPDATE July 19: I was wrong! Check literature reference in the comments below.)

Chemists, and medicinal chemists in particular, love to introduce fluorine here and there. (I only wish I were the exception.) By taking a so-so good compound, we can “fine-tune” (cheesy, I know; we use this term without sarcasm) the properties of the said compound by introducing fluorines in various positions of the structure. We can, among many things, lower the pKa, increase the permeability (especially into the CNS), and toy around with the pharmacokinetics to increase the half-life (our liver enzymes are probably quite unsure how to handle carbon-fluorine bonds) and with the pharmacodynamics to squeeze the compound into the active site and thus make it much more active. Many, many, many marketed drugs now contain carbon-fluorine bonds.

This development is not without a risk. Way up in the atmosphere, simpler flurohydrocarbons (CFCs, Freons et al.) do nasty things to the ozone layer, and down here on Earth… well, we are not really sure yet. Except that once these bonds are created, we know that they will stick around for quite a while.

Back to George Olah. He has been one of my favorite chemists, all categories, for a long time. I mean, how can you not love the creator of the superacid? He is totally worthy of his Nobel Prize. Olah’s magic acid (fluoroantimonic acid) is so strong that it protonates methane (an extraordinary weak base), creating the pentavalent CH5+ ion, an act which violates one or two fundamental concepts of chemistry. Also, how can you not be flabbergasted by an acid that is 2×10^19 stronger than pure sulfuric acid?

The article of today’s ramblings is this: Org. Lett., Article ASAP. (DOI: 10.1021/ol201669a)

Dead bug
Graphical abstract. (Slightly improved by yours truly.)

I fully agree with the opening: “Organofluorine compounds have special properties…”, and some cool, new chemistry is presented throughout the paper (I did not even know fluoralhydrate existed before I read this), and all is fine and dandy until the very last sentence of the concluding remarks: “…fluoroanalogs of DDT, which are potentially biodegradable…”

Hate to say it, but I would be VERY surprised to learn that fluoro-DDT was biodegradable. Does anybody here think compound 4e will be our next, green pesticide? I do not.

P.S. Why not wrap this post up with a limerick that was posted a couple of days ago at Reddit? In other words, I stole it.

A mosquito was heard to complain
That a chemist had poisoned his brain;
The cause of his sorrow
Was paradichloro-
Diphenyltrichloroethane

 

16 Responses to Unsure if I agree with your concluding remarks, Nobel Prize winner George Olah

  1. Michael Barclay says:

    Was there not a reference to go with that claim? The biodegradable claim i mean.

  2. Michael Barclay says:

    Does sound like an unfounded statement. I’m sure he has some evidence for the claim but…. would be nice if he shared it with the rest of us meer mortals.

    • drfreddy says:

      I think a) a grad student wrote the manuscript, b) Olah took a quick look at it and said “looks OK to me” and c) the reviewer would never dare to correct a Nobel Prize winner

  3. schwarzweiss says:

    CF3 is a good (or rather not so bad) leaving group

  4. Michael Barclay says:

    This isn’t really my area at all… but as C-F bonds are very unreactive… what harm can be done if were to digest some of these CF3 groups?

    • drfreddy says:

      Stability and toxicity are two completely separate things. What we do know is that DDT is super-stable and that DDT is toxic. Since we also know that carbon-fluorine bonds are about as stable as they come, one could only imagine how NON-biogradable fluoro-DDT would be.

  5. Magnus Johnson says:

    Interesting remark! I thought of never hearing about a fluorine containing natural product so I made a quick search and found this interesting paper:

    “Fluorine-containing natural products”
    Journal of Fluorine Chemistry 100 (1999) 127-133

  6. Magnus Johnson says:

    Nice, great post, the graphical abstract is hilarious!

    And sorry, but I also cannot help myself from saying that I believe Si-F bonds are stronger than C-F bonds (when covalent).

    • drfreddy says:

      Thanks. And to my defense, I am an organic chemist and I don’t know anything about bonds not containing carbons 🙂

  7. Stephen Moratti says:

    DDT is fairly stable but is rapidly broken down by base (my MSc)or light. The products produced such as DDE are more stable, and are often detected as DDT-like compounds in the soil. One must be careful that any reported half lifes dont include the break-down products as well. However, under the right conditions (acidic soil, underground) there is no doubt that DDT can stay around for decades.

  8. Fang says:

    Although perfluoroalkylated compounds (>C4) are usually extremely stable, many lightly fluorinated organic compounds can still be feasibly degraded. Many chemists, outside the organofluorine community, simply believe that all fluorinated organics are more stable than analogous organic halides/hydrocarbons because C-F bonds are very strong. In fact, lots of fluoroorganics are “unexpectedly” labile compared with the corresponding non-fluorinated counterparts! For example, CF3Li has never been obtained, but CCl3Li can be prepared (it is not stable either). CF3OH rapidly decomposes to CF2O and HF, but CH3OH usually doesn’t degrade to CH2O and H2. Similarly, dehydrofluorination reaction (elimination of HF) can also occur in molecules containing H-C-C-F substructures under basic conditions. Fluoro-DDT analogs were found to readily degrade through this pathway under basic conditions. (Ref. Acta Chimica Hungarica, 1988, 125, 181-191 and Can. J. Chem. 1985, 63, 576-580). I guess that is why Fluoro-DDT’s were claimed to be “potentially biodegradable”.

    • drfreddy says:

      Dear Fang Wang (who, I should add, is a graduate student in the group of Prakash and Olah),

      First allow me to say that I am honored that you and your colleagues have taken the time and devotion to clarify the subject further, and that I am not just a little flattered that you even found my page in the first place.

      Secondly, I would perhaps not label myself as being “outside” the organofluorine community, given my background in advanced materials, medicinal chemistry and custom synthesis.

      Thirdly, elimination of HF seems very feasible to me; I am more concerned about what happens after that. How is nature eventually going to deal with the Ar-F bonds, for instance? This is in no way targeted at you and your research specifically, but more of a reminder to all chemists that we should perhaps spend more time thinking about the chemical traces we leave behind.

      Fourthly, you should not take anything I post here very seriously. This page is a just hobby project, disconnected from my professional career; more of an outlet for me to use a couple of tabloid-ish titles, phrases and words I cannot use while I carry out my regular scientific work.

      Finally, I sincerely hope there are no hard feeling between any of us. If the opportunity ever present itself, tell Olah that he in my humble opinion is one of the most respected chemists in the world, and that I will continue to be fascinated by the research you produce and publish.

    • Alex says:

      Dear Fang,

      I’m a just a stranger on this site, so don’t take this comment too seriously.

      I think, in this case there was an issue of assuming some area-specific facts (i.e. biodegradability of fluoro-DDTs) are known to a wider audience (all organic chemists – readers of Org.Lett.). Have you cited those two references next to the statement of biodegradability — this post would not exist.

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