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Things I Won't Work With

The Higher States of Bromine

Chemists have a familiarity with many elements and many compounds, from having worked with them or studied them in the literature. You get a feel for what’s “normal” and for what’s unusual, and there are quite a few degrees of the latter. Take compounds of bromine, for example. Most any working chemist will immediately recognize bromine (there are exceptions) because we don’t commonly encounter too many opaque red liquids with a fog of corrosive orange fumes above them in the container. Which is good. That’s bromine in oxidation state zero, elemental, and then you have bromide (oxidation state -1), one of the most common anions around. “Chlorides are rabble”, said Primo Levi in one of my favorite lines from The Periodic Table, and he was right about that, but bromides are not of much higher social standing. Every cation has a bromide salt, and it’s usually one of the cheaper ones in the catalog.

So far, so good. But bromine can also go up to +3 and +5 oxidation states, and there things start to get interesting. You can have various mixed-halogen things, all of which are reactive and toxic and are distinguished by their various degrees of vileness. And you can get all sorts of bromine-oxygen species, ranging from the pretty well-known ones like bromate ion (BrO3) all the way up to. . .well, to the stuff described in this new paper., from Konrad Seppelt at the Freie Universität Berlin. It contains a whole list of new compounds that send my chemical intuition completely off the rails.

I have no “feel” for them whatsoever except a strong desire never to prepare any of them. Prepare any of them? I don’t even want to make the starting material. You know you’re in for a bumpy ride when your work needs something like bromine fluorine dioxide (bromyl fluoride, BrO2F); no one can claim that they weren’t warned. There hasn’t even been a reliable synthesis of that stuff until now – Seppelt describes a new one, from the aforementioned sodium bromate, which is fine, and bromine pentafluoride, which is not fine, because it’s a hideous oxidizing and fluorinating agent fit to fluorinate you right into the afterlife and whose attempted use in liquid rocket propellent mixtures was abandoned because it was too foul to work with, and, oh yeah, redistilled pure hydrogen fluoride, which is also about as far from “fine” as you can get. The SI of the paper casually mentions that you can use double vacuum distillation in a metal line to get your HF sufficiently anhydrous for the reaction, and you can go ahead and get cranking on that without waiting for me to show up.

You condense the latter two reagents onto a solid charge of the bromate at liquid nitrogen temperatures, and then let it warm all the way up to -78C, at which point a “vigorous” reaction sets in. Imagine running these things for the first time, waiting for said reaction and wondering if it’s going to stay inside your apparatus or invigorate itself all over the ceiling. Once you have made your bromyl fluoride, you raise the temperature a bit more to -40 and pump off the excess HF and pentafluoride, and you will want an extremely capable trap on the other end of that process, which according to the paper can take several hours, and probably had better. Finally, you sublime off the product from the solid residue in the tropical warmth of -10 or so and seal off that part of the tube.

You have now prepared the colorless solid bromine fluorine dioxide. What to do with it? Well, what you don’t do is let it warm up too far past +10C, because it’s almost certainly going to explode. Keep that phrase in mind, it’s going to come in handy in this sort of work. Prof. Seppelt, as the first person with a reliable supply of the pure stuff, set forth to react it with a whole list of things and has produced a whole string of weird compounds with brow-furrowing crystal structures. I don’t even know what to call these beasts: how, for example, do you refer to the cation in Br3O6+ triflate? What’s the name for the compound shown at right? Very few of us will have the need to name it, though – you make that one by condensing trifluoroacetic anhydride onto the bromyl fluoride at -196C, then warming and recrystallizing the solid from liquified freon to give yellow crystals. Those melt at -12C, and according to the paper and its SI, “The molten red liquid starts to gas slowly” and “inevitably explodes upon further warming“. Further experimentation runs a risk of exposure to further inevitabilities, and I’m glad that Prof. Seppelt’s expertise in the lab got him through all this.

The SI strongly warns readers that the preparations therein must not under any circumstances be scaled up, and that is clearly the advice of someone who has has your best interests at heart. Even at the amounts described, you will want an excellent and well-maintained vacuum line, access to noncommon nonhousehold reagents like the aforementioned bromine pentafluoride, a willingness to do things like redistill anhydrous HF, and you will at all times want to be suited up like you’re going to going to spay a velociraptor. Ah, the halogen chemist’s life for me, me hearties, yo-ho-ho and a barrel of. . .well, we still don’t know what to name it. Dang.

119 comments on “The Higher States of Bromine”

  1. A Nonny Mouse says:

    ….and a barrel of. . .

    More like a thimble of, I would say (and probably too much there)

    1. metaphysician says:

      Indeed, I wouldn’t want to be in the same building as a “thimble full” of any of these compounds. Of course, I doubt this would be an issue, since pretty soon the building wouldn’t have said thimble of doom ( due to explosion ), nor me either ( due to fire alarms and evacuation ).

  2. Jacob Valentine says:

    Looks like some delicious bromyl trifluoroacetate on the right.

  3. Druid says:

    At least in the States you can have potassium bromate added to the flour in your bread. In the over-regulated EU, we have no fun at all.

  4. enl says:

    Thanks for posting this. Now I don’t even need to read the paper to have the nightmares.

  5. anon says:

    more like..Things I Won’t Work With!

    1. myma says:

      Yes! Things I won’t work with is back!

  6. TroyBoy says:

    > What’s the name for the compound shown at right?

    ChemDraw calls it: bromic 2,2,2-trifluoroacetic anhydride.

    1. Martin says:

      I would prefer something like:
      (pronounce in an alarmed tone, as if your “Bro” had just showed you a flask with 50 mL of that stuff)

  7. smurf says:

    Pointless science.

    1. dollarita says:

      ya bro only liek 1 substrait? #weak. is that yield only n=1 also? you need more better yealds for science and nature

    2. fred says:

      There. Is. No. Pointless. Science.
      [ad hominem attack expunged. seriously, you know better. – ed.]

      To quote a solid science author:
      [For example] “agriculture”.

      The minute you look at this, apparently clear-cut view of things, you see the holes. I mean, look at the tractor. Oh sure, it worked in the fields. But is it part of the history of agriculture? or… a dozen other things? The steam engine. The electric spark. Petroleum development. Rubber technology. It’s a countrified car! …and the fertilizer that follows: It doesn’t follow. That came as much as anything else, from a fellow trying to make artificial diamonds.

      James Burke, “Connections”, S01E10

      The trio of series, but most especially the first one, is one long series of arguments and examples as to why those two words “Pointless Science” transcends the embarrassing wrongness of the flat earth proponents and anti-vaxxers. They at least attempt to use science and research their positions. Though for them it is like grabbing the wrong end of a sword. It isn’t even the fractured logics of the mad and the drug addled. It is willfully idiotically wrong.

      Sorry. Either caffeine hasn’t kicked in, the ethanol has kicked out, or both. But, that one just put my hackles up.

    3. Hap says:

      Pointless engineering, maybe, because you probably can’t do anything with any of the compounds. But science is about finding out things, and you don’t know what will be useful and what won’t so you go looking and tell people what you find. Even showing that you can do something that’s done before isn’t pointless – it may not be exciting, and most people don’t need it, but it’s not useless. It also makes cost-benefit analyses difficult because you don’t know the value of a piece of information before people have it.

      All things considered, I’d rather have this work than a synthesis of maitotoxin – someone might (with sufficient absence of self-preservation instincts) repeat this work and use it, and it costs less, but I don’t know for sure.

  8. Mad Chemist says:

    “. . . We don’t commonly encounter opaque red liquids. . .”
    True that.
    The only lookalike I can think of for bromine is chromyl chloride, but the list of chemists who’ve encountered that liquid is likely very short indeed.

    1. C_B says:

      “. . . We don’t commonly encounter opaque red liquids. . .”

      Someone needs to spend more time wading in the blood of their enemies, sounds like.

      1. Mad Chemist says:

        Perhaps so. Still, orcs and other goblinoids don’t tend to have red blood, so that won’t help as much.

      2. metaphysician says:

        Hey, I bet goblin alchemists would *love* this stuff. I mean, violently toxic, corrosive, and flammable compounds that explode at temperatures you won’t see on the coldest Antarctic night? Sounds like fun? 🙂

        ( Especially if you have expendable “lab assistants” do the grunt work. If you survive, you get your degree. *eg* )

    2. KazooChemist says:

      Phenyl sulfenyl chloride (Ph-S-Cl) is another viscous dark red oil. It doesn’t fume like elemental bromine, but it has the “advantage” of horrendous smell to more than compensate. While no where near as unstable as the compounds of interest in the article being discussed, it does have the propensity to revert to diphenyl disulfide and chlorine even when stored in the freezer. The chlorine gas usually destroys the container in the process leaving a mess of the disulfide. Derek has a post about just this, but I can’t figure out how to resurrect it. I have had the misfortune to prepare this substance on several occasions, starting with early in my graduate school days. We would distill it and divide it into small aliquots for storage in the freezer with the containers well wrapped with towels. The attrition rate was high. One of my first successes in grad school was finding a way to avoid the use of the reagent as well as a very nasty singlet oxygen reaction conducted at -78C. Ahh, those were the days!

    3. Nick K says:

      Actually, I made a few grams while still at high school as a demonstration at an Open Day. The experiment was carefully supervised by the teacher, of course. (the late Rev Richard Mabel, RIP).

    4. Chris says:

      And here I’ve just recently stumbled onto this guy insane enough to synthesize it himself:

      1. Nameless says:

        The insane part is actually his “clean up” video. He has a container filled 95% with a nearly boiling, aqueous, acidic Cr 6+ waste and throws in more and more sodium hydroxide. Of course it boils and sputters red liquid everywhere after every addition but that doesn’t stop him from adding more.

        1. Carl Sampson says:

          To be fair, he did title that video “My chromyl chloride cleanup was a disaster”…

    5. BirdMan says:

      chromyl chloride is apprently now being made for on youtube in a non professional lab

  9. Some idiot says:

    “… and fluorinating agent fit to fluorinate you right into the afterlife… ”
    That’s what I call a career change… From chemist to a non-stick spirit…

    1. Buckaroo Banzai says:

      I was ionized, but I’m okay now.

    2. Peter Kenny says:

      I quoted that line several hours ago in a tweet and I’m still chuckling. It’s always great fun when Derek spits feathers.

    3. Sok Puppette says:

      So, quantitatively, how fluorinated do I have to be to reach the afterlife?

      1. David DeLaney says:

        I’m pretty sure just one would do it, if applied with sufficient velocity and given time quant. suff. to work with.

        –Dave, NOT volunteering

  10. David A. Van Baak says:

    Non-chemist here, one supposing that BrO2F is a substituted version of the notorious FOOF, another thing not to work with. How many other XOOX variants are known? are stable? are safe to work with?

    1. Hap says:

      I don’t know the first answer. I suspect none for the second (O-O bonds aren’t really good, and if X is a halogen atom, X-O bonds aren’t great, either, so having three unhappy bonds next to each other in the same molecule is not a recipe for the molecule’s stable existence).

    2. Algirdas Velyvis says:

      Not a chemist either, but I think your supposition is wrong. BrO2F being discussed here is bromyl fluoride where bromine is in +5 oxidation state. Look at the image of bromyl triflate that Derek included in the post. You are thinking about somethig like Br-O-O-F, which I suspect should be even less stable than bromyl fluoride.

      1. Ian Malone says:

        Does that put Br-O-O-F in the rare class of onomatopoeic compounds?

        1. Algirdas Velyvis says:

          Ha ha, yes based on Derek’s article on FOOF, I imagine BrOOF would be just as onomatopoeic. I daresay many of the words elicited by these compounds from the experimentalist working on them are what linguists technically refer to as “F-words”…

          This got me thinking: how do you suppose, which class of compounds does F-O-O-B=Ar would belong to 😉?

    3. Jim Mowreader says:

      You’re thinking more on the lines of BrO2F. What makes FOOF a thing of beauty and a joy forever is the peroxide group stuck right in the middle of it. (All my Material Safety Data Sheets at work have a field for “will this product form explosive peroxides?” It is good that none of them will.) BrOF2, at least in theory, should be a stable molecule.

      I’m trying to imagine how you could make BrO2F. You make FOOF by heating a mixture of oxygen and fluorine to 700 degrees C. If you tried that little trick with a mixture of bromine, fluorine and oxygen you would probably wind up with a mixture of FOOF and Br2O2.

      You really don’t want to let the stuff anywhere around anything that could oxidize because O2F is a powerful oxidizing agent and adding another halogen to the side of it will only make it more so.

  11. Aubry Miller says:

    Thanks for this post Derek. You had me laughing out loud. It even got my wife (a biologist) to chuckle a bit when I read it to her.

    1. John says:

      I can one up you. I read some to my wife who is a Pilates instructor and choreographer and she laughed as well. I then said I didn’t understand why anyone would do this work and she asked me what the most important thing in science is. I said “explosions” to which she shook her head and said “curiosity”. Maybe that is why it is better I am in regulatory affairs now.

  12. gippgig says:

    Note the reaction with MoF5: BrO2F + MoF5 -> Cl2BrO6+Mo3O3F13-.
    I wonder if it would be possible to substitute the not-as-nasty BrF7 for BrF5.
    Ph-S-Br might (educated guess) be a better Br analog.
    BrO2F is not a substituted version of FOOF. In FOOF the O atoms are attached to each other (F-O-O-F in a (crooked) line) but in BrO2F both O atoms (& the F) are attached (only) to the Br.

    1. Nick K says:

      You may need to re-examine the stoichiometry of the molybdenum(V)fluoride reaction. It’s not clear to me where the chlorine is coming from.

    2. gippgig says:

      Oops, my memory failed me. There is no BrF7, only IF7 (which, unless my memory is failing me again, is less nasty than IF5).

  13. anon says:

    And to think I was nervous that day in graduate school when I accidentally isolated chromatographed, and took an NMR of an ozonide

    1. A Nonny Mouse says:

      Kids stuff now; they are being developed as anti-malarial drugs instead of artemesin analogues.

      See OZ439

      1. loupgarous says:

        You mean “artemisinin”, right?

        1. A Nonny Mouse says:

          …..Current therapy is based on artemesin combination drugs for P. falciparum, plus chloroquine for other sensitive malaria forms (WHO, 2010a).

          Both are used quite extensively

    2. Hap says:

      At least one person I knew in grad school had a lovely metal apparatus attached to his wrist for a couple of months because of an ozonide. They’re probably OK to be nervous about (or better for someone else to be nervous about).

  14. rhodium says:

    The mention of chromyl chloride brought back thoughts of the Etard reaction, which shows you just how weird name reactions can get. Further, I am unaware of any name reaction for an explosion. Perhaps we experimentalists, in honor of “Things I Won’t Work With” can take up saying, when something blows, I just ran a Lowe reaction.

    1. loupgarous says:

      Sort of stunned that a when, say, an exotic mercury azide cooks off, that’s not called a “Klapotke reaction”.

    2. Sok Puppette says:

      Obviously the phrase “Lowe reaction” has to refer to one you WON’T run.

      1. loupgarous says:

        Derek gave us a good example of a prototypical “Lowe reaction” – one whose starting points include a

        “hideous oxidizing and fluorinating agent fit to fluorinate you right into the afterlife and whose attempted use in liquid rocket propellent mixtures was abandoned because it was too foul to work with, and, oh yeah, redistilled pure hydrogen fluoride.

  15. Fluorine Chemist says:

    TIWWW after quite sometime! Thanks Derek, that made my day! As usual, beautifully written and very informative and a bit scary too!

    “fluorinating agent fit to fluorinate you right into the afterlife”
    That. Is. Classic.

  16. BFB says:

    Typo spotted: “to spay a velociraptor”

    1. Lambchops says:

      It’s not a typo, I suggest you watch Jurassic Park 5: Jurassic Vets!

    2. Jim Mowreader says:

      ‘Going to going to” right before “spay a velociraptor” is what I found.

  17. Ken says:

    You have to admire the rocket propellant folks, who undoubtedly knew going in that there was no way any sane person would want to work with a BrF5 oxidizer, but nevertheless measured the optimum fuel ratio, temperature of combustion, specific impulse, and exhaust velocity. I think I’ll dig out my copy of Clark’s Ignition and see if he mentions it.

    1. Matthijs van Duin says:

      On the contrary, in the concluding chapter of Ignition! he still saw a bright future for ClF₅ (to be used with a hydrazine-type fuel) for short-range tactical missiles, and for deep space probes he concluded “The oxidizers will be OF₂, and possibly ONF₃ and NO₂F, while perchloryl fluoride, ClO₃F, would be useful as far out as Jupiter.”

      There’s not much mention of BrF₅, except that it’s outperformed by ClF₃ (which itself is outperformed by ClF₅): “Bromine pentafluoride, BrF₅ is very similar to ClF₃ as far as its handling properties are concerned, except that its boiling point (40.5°) is a little higher. Oddly enough, it never seems to perform as well as it should, and it’s much harder to get a reasonable percentage of its theoretical performance out of it on the test stand than it is with ClF₃. Nobody knows why.”

  18. milkshake says:

    we were tempted to try BrF5 as a fluorinating reagent, and what discouraged the purchase of a small tank was the fact that the stuff is used by geologists to get free O2 from SiO2 and silicates when you need to measure isotopic composition of oxygen in rocks

    1. anon says:

      If geologists can use it, what’s stopping chemists?

      1. Slarty says:

        Knowledge & experience.

      2. milkshake says:

        they geologists have a purpose-built apparatus from high nickel coppernickel alloy, for handling tiny quantities of the stuff for MS analysis of rocks, and the bought it as a complete package, they did not tinker around to build it. Their biggest risk of exposure is when they open the lecture bottle with BrF5, if there is a leaky connector

        1. anon says:

          That makes a lot of sense.

        2. Anonymous says:

          To the lay readers reading milkshake’s posts about “BrF5 … is used by geologists to get free O2 from SiO2.” Standard laboratory glassware (well, glass in general) is primarily silicon dioxide. You don’t want your chemicals dissolving your glass apparatus! Hence, the need for the specialized nickel – copper metal apparatus.

      3. Mike Andrews says:

        Sanity, one hopes.

  19. Mike Turner says:

    Manganese heptoxide is another interesting dark red liquid, though I’ve never heard of a practical use for it. Alegedly it has interesting colours (red by transmitted light and green by reflected light) and can survive for quite a while on ice.

  20. Isidore says:

    Vivere pericolosamente – in all its glory!

  21. Industry Guy says:

    you will at all times want to be suited up like you’re going to going to spay a velociraptor….

    made my weekend

  22. Uncle Al says:

    FINALLY! A good reason for NASA manned exploration of cryogenic Titan – hyperhalogen-based life.

  23. Noni Mausa says:

    Another non-chemist Pipeline fan here. And yeah, I’m mostly in it for the explosions.

    But a curious question you folks might answer: even before you make them you expect some compounds, like FOOF, these bromides, and all the nitrogen family reunions Derek has written about, to corrode, explode, or dissolve everyone within a league downwind, okay.

    Are there examples of compounds which, against all odds, end up being fairly stable, beyond what anyone would have predicted?

    1. Anonymous says:

      Noni Mausa, stable beyond predictions: There are some historical examples but not all would hold up to more modern predictions. If I could access the literature, I’d provide the actual quoted passages, but here goes:
      1. beta-lactams – It became increasingly important to determine the structure of Fleming’s penicillin discovery. Some proposed that it contained a beta-lactam but some higher authorities pronounced that beta-lactams were too unstable to exist. Then came the X-ray. Oops. It’s a beta-lactam. Likewise, when Sheehan set out to synthesize those beta-lactams in the lab (many others had tried and failed), he was warned that they would be too unstable to prepare by chemical synthesis (cf, milder biological synthesis). Oops. Carbonyl diimidazole to the rescue.

      2. Many talented people had been trying to synthesize cyclopentane-1,3-dione w/o success. Therefore, it was decided, it must be too unstable to exist. “Yet when it appeared on the scene, … it was produced by the action of boiling HCl and red phosphorus on a degradation product of aureomycin.” (RB Woodward, Perspectives in Organic Chemistry, 1956.)

      3. There are several autobiographical essays by HC Brown (Nobel Prize for boron chemistry). During World War II, while working with Hermann Irving Schlesinger, Brown discovered a method for producing sodium borohydride (NaBH4), They thought it would be useful for generating H2 which would be a useful fuel and help in the war effort. (It’s easier to store and transport solid NaBH4 and generate H2 as needed on site than to lug around heavy tanks of H2 gas.) They were successful to get representatives of the DoD to visit the labs where Brown had set up explosion shields and other safety equipment for the demo. (The rapid generation of H2 gas can lead to an explosion.) Brown released the NaBH4 into the tub(?) of water and !!! – zilch. It fizzed a bit (H2 gas) and then stopped. Now we know that the rate of NaBH4 reaction with water is slowed at higher pH (which happens as the first bits of NaBH4 reacts).
      (I have read that story in a few places. Does anyone really believe that they didn’t run the test / demo BEFORE inviting the Army to visit the labs? NaBH4 was relatively scarce and expensive back then, but … really?)

      Those probably aren’t the sort of examples you wanted. You wanted the REAL non-explosive explosives. TNT (see wikipedia) is certainly an energetic material but it is surprisingly, to some, shock stable.

      Others have mentioned the book “Ignition!” In The Pipeline. If you enjoy reading about explosions, planned, unplanned, and failed, you can probably find some good examples in there. I read it long ago so I’m not remembering any specific cases to include here.

      1. Hap says:

        Perchloryl fluoride is a lot more stable than it has a right to be, I think (from Ignition). These triazides were unexpectedly stable as well.

        1. Hap says:

          Noble gas compounds – a lot of them (the xenon fluorides, XeO3 for example) are stable, albeit explosive. KrF2 has a decent existence as well. (There was a long history of people saying that they couldn’t exist, until Bartlett noticed that Xe and O2 have similar oxidation potentials, and since O2+ PtF7? or Pt2F11-?) existed, maybe a Xe+ PtFn- could, too. I don’t know why Bartlett didn’t get a Nobel in Chemistry.) PtF6 (a red liquid, prepared from Pt filaments + F2 and cooled rapidly in LN2) seems like a potential TIWWW candidate as well.

    2. Skeptical says:

      “And yeah, I’m mostly in it for the explosions.”
      TIWWW is like NASCAR for the science-literate.

    3. Baltic says:

      Bis(trifluoromethyl) peroxide – one would usually expect small dialkyl peroxides to be quite eager to, figuratively, divorce the oxygen-oxygen bond, and, significantly more literally, split the house in half in process. And trifluoromethyl groups are not exactly known for reducing the reactivity of whatever functional group they’re attached to, either. The bis-CF3 variety, however, is as tame as can be. I think Derek has written about this odd member of the peroxide family.

      1. gippgig says:

        Odd Peroxides Indeed – Feb. 14, 2019
        Then there’s [1.1.1]propellane.

  24. loupgarous says:

    BrF5 sounds like a logical candidate for another TIWWW article.

  25. Henry Rzepa says:

    Re But bromine can also go up to +3 and +5 oxidation states.

    The story of bromine in +7 oxidation state is also odd. Many had tried to make it, but failed. It was finally made by radiochemical transmutation of 83Se to Br. Only thereafter were several simple chemical syntheses discovered! See 10.1021/ja01009a040

    1. eub says:

      That’s a remarkable pathway!

      1. Dave Kielpinski says:

        Hey, Marie Curie did win a Nobel in *Chemistry*.

  26. All the single authors (oh oh oh) *singing says:

    Prof. Seppelt is single author on this work and only acknowledges two individuals for gift chemicals. Can we assume he is so passionate about this research that he decides to do all the practical work at a tender age of 75? This could of course be a write-up of older results (who knows what other data is waiting to be published), but I guess it was hard to convince somebody else to do it…

    1. DrOcto says:

      Perhaps he was too honourable to send someone with their whole life ahead of them into the lab to try this.

  27. EO says:

    i’m sure Baran is cooking one of those to use in his total synthesis

  28. Anonymous Researcher snaw says:

    I see the first reaction in their “Scheme 1” starts not only with BrO2F but ALSO with SbF6. Antimony being a toxic element, and ANYTHING Hexaflouride being highly reactive, the combination does not seem like something with which I would care to work.

    1. Pedwards says:

      See also: hexafluorophosphate anions

    2. loupgarous says:

      UF6, despite not being a docile beast like SF6 (which is used as an electrical insulating gas in substation transformers and buried high-tension lines), is the preferred form for enrichment of uranium toward greater fissionability. I’m sure if you could make fissionables and fissiles using any other uranium compound, that would be first choice, but UF6 is what there is.

      1. Nameless says:

        UF6 is the only uranium fluoride that is gaseous and Fluorine is monoisotopic so the whole mass difference is due to the uranium. You can’t get much better than that if you had a free wish.

        1. Barry says:

          UF6 is (unsurprisingly) pretty corrosive. One of the first (the first?) use made of teflon was in sealing gas-diffusion equipment to contain it. It was not the only candidate for gas-diffusion isotopic enrichment. Uranium borohydride was explored. Since its molecular weight is less than that of UR6, the isotopic discrimination should be better (fewer passes needed). But it was abandoned when teflon made the UF6 option feasible.

          1. loupgarous says:

            That, and you have two naturally-occurring isotopes of boron present in signifcant amounts (B-10 is 20% abundant and B-11 is 80% abundant).

            That would have complicated the mass spectrometry/separation process, right?

          2. Barry says:

            The borohydride was pursued because minimizing the molecular weight of the diffusing species would maximize the isotopic separation. If it were to spend part of its time as the dimer (as seems to be the case) that advantage is lost. And yes, the isotopic diversity was unattractive.

  29. Jim Mowreader says:

    A few people here have mentioned John D. Clark’s book Ignition. While reading Derek’s words of warning, I thought to myself, “it’s too bad Mike Pino (the man who tried to turn mercaptans into rocket fuel) and Engelbrecht (the man who invented perchloryl fluoride) aren’t still alive. They would love this compound.”

    1. Hap says:

      let alone sulfenamines that attracted flies…though if you attached the flies to the rocket, it might help at liftoff.

  30. Stuart says:

    A comment from a friend on a share I made of this: “Oh gods now waiting for someone to do some research on selenium nitrosulphate complexes of fluoro peroxides…”

    Who’s up for it? Honour and glory – or at the very least, some entertaining stories – await!

  31. Mike Andrews says:

    Utterly glorious! Bromine is beyond merely nasty, all by itself, thanks very much, and here these people go making Br compounds that make elemental Br look like a friendly, welcoming glass of red wine.

    When my wife the biochemist wakes in the morning, I shall read this to her, and I’m fairly sure that she will want to never sleep again.

    1. loupgarous says:

      Your wife will probably smile and be thankful for her choice of “branch of chemistry”.

  32. David Edwards says:

    Konrad Seppelt bears, thanks to this paper, a resemblance to Alexander Streng and his work with FOOF, though I can’t see any references to hair fluffing by an adoring wife in the Seppelt paper. 🙂

    Oh, and as for weird halogen peroxides, BrOOBr also has some onomatopeic possibilities for anyone wishing to try and synthesise it.

    Given the known rambunctious nature of interhalogen trifluorides including their propensity to make sand burst into flames, I suspect that pentafluoride versions are likely to be livelier still. Unless someone with relevant knowledge can tell me, and everyone else here, if the F5 compounds are slightly more restrained than the F3 compounds, and what reasons exist for this behaviour. Only thus far, ClF3 has been cited here as the King Of The Hill™ of nasty, toxic, vigorously fluorinating oxidisers, and if so, I’d love to know what imposes restraint upon the likes of ClF5 and BrF5 in comparison. Not that I suspect sane individuals would want to find themselves in close proximity to any of the fluorinated interhalogens.

    In the meantime, I’m still enjoying the Seppelt paper, and the revelation that he’s alighted upon molecules containing such wonders as three bromine atoms, all in different oxidation states. I can’t recall seeing other molecules boasting mutliple instances of an atom, with each in a different oxidation state from the others, unless someone here knows far better than me, and has some nice, curiosity piquing examples to present, at which point I’ll hunt for more papers to enjoy on the subject. 🙂

    Oh, and as a final plea to Derek … any chance of enabling subscript and superscript tags in submissions to your blog, along with HTML entities? This would massively improve the ability to post here, especially among the trained chemists.

    1. Peter Edwards says:

      Apparently ClF5 is less reactive than ClF3:
      DOI: 10.1126/science.141.3585.1039
      The only thing I can think of to why it’s less reactive would be the higher steric crowding around the chlorine, making it harder for nucleophiles to come in and take advantage of the energy involved in keeping fluorine bound to chlorine

    2. Anonymous says:

      DE, “I can’t recall seeing other molecules boasting mutliple instances of an atom, with each in a different oxidation state from the others.” The lay readers might not follow this, but just look at all of the C2 + O compounds from ethane CH3-CH3 (ox state of C = -3 and -3) up to oxalic acid HO-CO-CO-OH (+3 and +3) and all of the states in between. But I don’t think DE meant to include C. The various stable ox states of C make it very special.

      Artemisinin came up In The Pipeline recently and that has stable Os in the -2 and -1 ox state. Nitroaniline has an N+5 and an N-3. Thiosulfate S2O3 dianion has an S-2 and an S+6 (or S-1 and S+5 in some counts). Phospophosphates, boranoborates, etc.. This could be a fun exercise.

      1. David Edwards says:

        So I’ve accidentally provided the full time chemists with a new Xmas quiz? So my questions aren’t completely useless after all! 🙂

        I’m going to have fun looking some of these moieties up … 🙂

      2. Sean McDonough says:

        Another example would be nitrosylazide, ONN3, with four nitrogen atoms, one each in the -1, 0, +1, and +2 oxidation states.

  33. Jon says:

    HURRAH! Another entry in the best chemist blog on the net!

    Will you write that book already?

  34. Blackie says:

    Derek, we desperately need a book. Don’t leave us hangin’!

  35. Guy Gordon says:

    Just to mess with people, you could give them all beautiful, sweet names like ‘Cinamaborato’.

  36. Bob Albrecht says:

    The scary thing is, I actually have the skills to do all that vacuum line chemistry at low temperature. I am glad I don’t have to do that any more.

  37. Daniel Jones says:

    Higher states of Bromine?

    More like the (momentarily) United States of SMASH!

    (Blame My Hero Academia! for that one…)

  38. Scott K. says:

    I’ve known Konrad since I started working as a fluorine chemist in grad school; he’s an intrepid experimentalist, and–like most fluorine chemists–possesses marginal survival instincts. Since the money for fluorine chemistry in DOE evaporated years ago, I’ve moved on to less hazardous materials than FOOF, interhalogens, nitrogen fluorides, and the noble gas fluorides–high nitrogen explosives. Still, it’s great to see someone of Prof. Seppelt’s standing still fighting to get into the lab.

    1. David Edwards says:

      “I’ve known Konrad since I started working as a fluorine chemist in grad school; he’s an intrepid experimentalist, and–like most fluorine chemists–possesses marginal survival instincts.”

      The fact that he’s reached the age of 75, whilst handling reagents of the requisite lively nature, suggests to me that his survival instincts must actually be pretty decent. Simply surviving to the age of 75, while working with reagents of a nature that would induce prolapse-level terror in many here, tells me that he has some serious skill in this department. Unless of course you’re going to tell me in a subsequent post that he has bits missing.

      I’ll admit that my direct contacts with fluorine chemists are pretty mucn zero, but I do remember vividly watching one in action on YouTube, who was called upon to set up an experiment involving the direct reaction of elemental caesium with fluorine. Which was, apparently, to be conducted during the Royal Institution’s Christmas Lectures, with an audience of schoolchildren whose ages range from 8 to 18. Yes, we have an interesting approach to pedagogy here in the UK. Enjoy seeing that one here.

      Said reaction was fun to watch, in no small part because I live 100 miles or more from the laboratory where this was done, and any unhappy accidents involving fluorine are unlikely to affect me from that distance. Whether I would volunteer to occupy the laboratory in question during the conduct of said experiment, well … let’s just say that with age comes caution.

      1. perlhaqr says:

        Ok, I just watched that video. I actually laughed out loud at the “Eye Protection Required” sign on the door. In a “I don’t think that’s going to cut it” sort of way. 😀

  39. Sean McDonough says:

    Red fuming nitric acid ticks the “red[dish] liquid” and “corrosive orange fumes” boxes, but, IIRC, the liquid is rather too transparent.

    Then there’s iodine monochloride (ICl), which, apparently, looks and fumes very much like elemental bromine (not too surprising, if you think about it).

  40. perlhaqr says:

    If someone were to have simply come out and *told* me, before reading this section of blog posts, that reading about chemistry would make me laugh out loud this heartily and frequently, I’d not have believed them.

    So, good work!

    1. perlhaqr says:

      Also, since I just read your link at “I want a new nitro” and it mentioned nitromethane, and that (being me) made me think of drag racing, I wonder if there’s a place in “Things I Won’t Work With” for good ol’ hydrazine? 😀

      1. Derek Lowe says:

        Hah! Technically no, since I have worked with hydrazine many a time. Which I guess says something about the stuff that *is* on the list.

        1. perlhaqr says:

          Having read some of the articles circulating the motorhead scene about the horrors of hydrazine… yeah, that actually provides a pretty solid benchmark. 😀

  41. David Edwards says:

    Meanwhile, back to the subject of red gases … I’m told that platinum hexafluoride is a red gas. Has anyone here observed this first hand, or filmed it? That’s one I’d like to see, if from a safe distance of course, given that numerous hexafluorides are, to use one of Derek’s favourite words, lively.

    I also suspect that due to the mass of the platinum atom, that gas is going to be even more troublesome than nickel carbonyl, that Derek mentioned once as being capable of flowing out of your fume hood onto the floor in a molasses-like manner. (Or was it dimethylcadmium he described thus?) A gas that’s 50% heavier per mole than xenon sounds like fun to work with, possible toxicity issues aside. Though if it’s sufficiently bromine like in appearance, at least you’ll be able to see it misbehave if it escapes confinement.

    I’m now wondering if it’s possible to put together a spectrum of gases, with colours ranging all the way from red to violet, rainbow like. Another chemistry trivia challenge for the experts here? 🙂

    1. Hap says:

      Green and blue might be problems, but orange = NO2, yellow-green = chlorine, purple = I2 vapor or the trifluoromethyl nitrone cited in the purple compound post). There has to be an easy yellow gas, but I can’t remember offhand.

      1. David Edwards says:

        If I remember correctly from watching fluorine being liquefied in a Royal Society presentation, that’s more yellow than green as a gas, and is certainly a distinct yellow colour when liquefied. Though there are probably better candidates for a genuine yellow gas.

      2. David Edwards says:

        @Hap … Yellow gas? Of course – diazomethane!!!

        The fact that it’s a frisky and capricious explosive in the gaseous form, is the reason it’s usually made in solution on the occasions it’s needed for a reaction … though I gather there are less troublesome alternatives for actual lab preps now.

        As for blue … isn’t ozone a pale blue colour?

        How on Earth did I forget these?

        Though I suspect it would be far harder to find gases that exhibit strong, acrylic paint like colours in the requisite parts of the spectrum.

        1. Hap says:

          I think it’s tough to get color density in gases because they’re so dilute, but ozone is supposed to be blue as a condensed liquid. Hopefully in someone else’s lab.

  42. anatoly belilovsky says:


    longtime fan, first time poster, MD with undergrad chemistry degree, and SF writer/member of SFWA, here.

    Just wanted to say thanks for all the posts, especially “Things I won’t work with,” which served as inspirations to (1) not go back to the chem lab, and (2) this story, called “Halogen Nightmares,” published in Nature:

  43. Otto says:

    Great article, thanks. A minor point – surely molecular bromine has a valency of one?

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