As an organic chemist, I am willing to deal with the occasional bang or kapow in the lab, as long as things don’t get too out of hand. You’re supposed to know enough to be on guard against the sorts of compounds most likely to do that and be ready for them in case they decide to make the thermodynamic cliff dive all of a sudden. That said, like most chemists, I don’t actually sit around thinking up ways to make things blow up, so reading the energetic-materials literature is always an interesting experience – it’s a world where people are happily walking up the same staircase that everyone else is frantically sliding down.
Take this paper from Jean’ne Shreeve’s group at Idaho, a lab that has certainly given us all some alarming compounds over the years. If you or I (’cause we’re sensible, right?) look at a well-known crater-maker like dinitropyrazolopyrazole, we’ll probably decide that it has pretty much all the nitrogens it needs, if not more. But that latest paper builds off the question “How do we cram more nitro groups into this thing?”, and that’s something that wouldn’t have occurred to me to ask. Saying “this compounds doesn’t have enough nitro groups” is, for most chemists, like saying “You know, this lab doesn’t have enough flying glass in it” – pretty much the same observation, in the end. The way to stuff in more nitros, in case you’re wondering, is to hang hemiaminals off the NH groups and then nitrate those. (Edit: or, as shown at right, make the N-amino compounds and nitrate that). Why not? Round-bottom flasks, rota-vaps, and balances aren’t supposed to last forever, right?
The nitrated nitros shown in the paper are less thermally stable than the starting material – who’da thunk – although from reading the experimental section, it appears that Shreeve’s group – who definitely know what they’re doing in this field – did not experience any explosions while making them. The Supporting Information does mention that you definitely want to avoid any operations that involve scratching or scraping the solid products. Solid advice, that, and I can guarantee that the very thought has given any experienced chemist reading this part the shivers. Yeah, digging those last bits off the outer rim of the sintered-glass funnel to increase the yield is definitely not recommended here.
That paper, though, bracing though it is for people who like their glassware unpulverized and their eardrums intact, is not the only eyebrow-raiser that’s shown up recently in Angewandte Chemie. Try this paper out, from the Matzger group at Michigan. It’s on the delightful hexanitroisowurtzitane compound (CL-20) that I wrote about here. Now, if you complain that this one doesn’t have enough nitro groups in it then there’s something wrong with you, but apparently there are still those who look at this structure and say “Dang, not explosive enough”. Recall that this is the compound whose cocrystal with TNT is actually less dangerous than the pure starting material itself, and yeah, I know that sounds like the guy at the pet store packing a starved Komodo dragon into the carrier with your new dog, just to calm him down some. But there it is.
Making this compound even worse by nitrating it further isn’t practical, though, even by the expansive definition of “practical” that obtains in this field. It’s already nitrated to hell and gone by most standards anyway, and the classic methods, which involve forgiving reagents like hot red fuming nitric acid, are not enough. So how do you make it more dangerous? (I know that’s kept me up at night).
Well, the chemists in the crowd will be familiar with compounds forming hydrates – those are when one or more molecules of water crystallize along with a compound. It’s something that you have to think about (for example) when you’re formulating a drug candidate, because the hydrate will have different properties than the original substance (melting point, solubility, stability), and it might be better, might be worse. Hydrates of CL-20 are known, but as the paper points out, why wouldja do such a thing, because dousing the crystal’s unit cell with water just hurts all its properties from a blowing-stuff-up (BSU) perspective. (My acronym, not theirs).
The crystal’s unit cell looks like it could accommodate something else, though, so why not. . .anhydrous hydrogen peroxide? So I have to congratulate these folks; they’ve managed to combine two of my Things I Won’t Work With entries into the same flippin’ substance. All you have to do is take the hexanitroisowurtzitane, which you have to have military connections to get ahold of apparently, or at least I should hope so, and some 98% hydrogen peroxide, no thank you, and co-crystallize from acetonitrile. This is apparently the first time anyone’s done this “peroxate” solvate trick with any energetic material, and no doubt others in the field are slapping their heads while reading this paper – gently, though, so as not to set off the stuff next door.
The experimental section of the paper is worth a read, and again, you can tell that Matzger’s group has good technique because everyone made it intact to the writing of the manuscript. There are pictures of the crystals themselves, which are very nice, until you realize that they’re plotting to blow you into the ceiling crawl space at the first opportunity. It says that “no unplanned detonations were encountered” during the work, which is a nice distinction. For most of us in the lab, every detonation has a spontaneous zing to it, a je ne sais quoi that you really just have to experience, because words are insufficient. It expands your horizons while it expands your fume hood, and if the sensation is not to your taste, you may find yourself expanding your employment possibilities to, say, a relaxing job wrangling Komodo dragons for the better class of pet store. I might consider that myself if I had to repeat this paper – I don’t want any CL-20 (pretty sure about that), I don’t want to handle any 98% hydrogen peroxide (very sure about that indeed), and once I’ve crystallized the two together, which is the sort of thing most people would consider a very unfortunate accident, I most definitely do not want to take the powder X-ray diffraction spectrum of the stuff by “finely grinding and packing the material” into a sample holder. Who the hell got to be the first person to try that, and what were they wearing while they did it?
I’d be dressed up like the first person to set foot on Venus, I can tell you (“That’s one. . .small. . .step for a foolhardy moron. . .”) and while I picked up the mortar and pestle (assuming my suit allowed me that much mobility) and muttered a brief prayer to Cthulhu (edit: spelled his name wrong; I’m toast now), I’d be thinking that if I’d only planned my career with more attention that I could be wrestling a hungry carnivorous six-foot lizard instead. Mom always wanted me to go into reptile-wrangling, should have listened while I had the chance. . .