The Higher States of Bromine
Chemists are familiar with many elements and many compounds, having worked with them or studying them in literature. You get a sense of what is “normal” and what is unusual, and there are some degrees of that. Take bromine compounds, for example. Most chemists recognize bromine right away (there are exceptions) because we normally don’t encounter too many opaque red liquids with a mist of corrosive orange fumes in the container. What is good. That is bromine in the zero oxidation state, elemental, and then you have bromide (oxidation state -1), one of the most common anions. “Chlorides are rabble,” said Primo Levi in one of my favorite lines from the periodic table, and he was right, but bromides don’t have much higher social status. Each 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 that’s where things get interesting. You can have different mixtures of halogens, all of which are reactive, toxic, and characterized by their various degrees of meanness. And you can get all kinds of bromine-oxygen species starting from the pretty well known ones like bromate ions (BrO)3-) to. . Now to the things described in this new article by Konrad Seppelt at the Free University of Berlin. It contains a whole list of new compounds that completely throw my chemical intuition off track.
I have no “feel” for them at all, other than a strong desire never to prepare any of them. Are you preparing one of them? I don’t even want to do the raw material. They know you are waiting for a bumpy ride when your job calls for something like bromofluorine dioxide (bromyl fluoride, BrO2F). Nobody can say they weren’t warned. Until now, there hasn’t even been a reliable synthesis of this material – Seppelt describes a new one, made from the above-mentioned sodium bromate, which is fine, and bromine pentafluoride, which is not fine because it’s a hideous oxidizing and fluorinating agent, which goes well with Fluoriniere you to the afterlife and its attempted use in liquid rocket propellant mixtures was canceled because it was too lazy to work with, and oh yes, redistilled pure hydrogen fluoride, which is also as far from “fine” as possible. The SI of the paper casually mentions that you can use double vacuum distillation in a metal pipe to drain your HF sufficiently to react, and you can go ahead without waiting for me to show up.
You condense the last two reagents mentioned at temperatures of liquid nitrogen on a solid charge of the bromate and then allow it to warm to -78 ° C. At this point a “violent” reaction sets in. Imagine doing these things for the first time, waiting for this reaction, and wondering whether it will stay in your device or enliven all over the ceiling. Once you’ve made your bromyl fluoride, raise the temperature a little more to -40 ° C and pump off the excess HF and pentafluoride. At the other end of this process, you need an extremely powerful trap that paper says takes several hours and probably had better. Finally, sublimate the product from the solid residue in the tropical heat of around -10 and cap this part of the tube.
You have now made the colorless solid bromofluorine dioxide. What should you do with it? What you’re not doing is letting it warm up too far above + 10 ° C as it will almost certainly explode. Remember this phrase, it will come in handy in this type of work. Prof. Seppelt, as the first person with a reliable supply of the pure material, set out to react it with a whole list of things and made a number of strange connections with crinkly crystal structures. I don’t even know what to name these beasts: how do you relate to the cation in Br3O6 + triflate, for example? What is the name of the connection shown on the right? Very few of us need to name it, however – you make this by condensing trifluoroacetic anhydride on the bromyl fluoride at -196 ° C, and then heating and recrystallizing the solid from liquefied freon to give yellow crystals. These melt at -12 ° C and, according to the paper and its SI, “the melted red liquid begins to slowly gas” and “inevitably explodes when heated further”. With further experiments there is a risk that further inevitables will arise and I am glad that Prof. Seppelt went through all of this because of his expertise in the laboratory.
The SI strongly warns readers that under no circumstances should the preparations contained therein be expanded, and this is clearly the advice of someone who has your interests first. Even with the amounts described, you need an excellent and well-maintained vacuum line, access to unusual non-household reagents such as the bromopentafluoride mentioned above, a willingness to re-distill anhydrous HF for example, and you want to be suitable at all times as if you were neutering a Velociraptor. Ah, the halogen chemist’s life for me, me Hearties, Yo-Ho-Ho and a barrel. Well we still don’t know what to call it. Dang.