Quote:Tetrazole derivatives have featured several times here in "Things I Won't Work With", which might give you the impression that they're invariably explosive. Not so - most of them are perfectly reasonable things. A tetrazole-for-carboxyl switch is one of the standard med-chem tricks, standard enough to have appeared in several marketed drugs. And that should be recommendation enough, since the FDA takes a dim view of exploding pharmaceuticals (nitroglycerine notwithstanding; that one was grandfathered in). No, tetrazoles are good citizens. Most of the time.
It's when they get put in with the wrong sort of company that they turn delinquent. What with four nitrogens in the ring and only one carbon, they do have a family history of possible trouble - several sections of this blog category could just as accurately be called Things That Suddenly Want To Turn Back Into Elemental Nitrogen. And thermodynamically, there aren't many gently sloping paths down to nitrogen gas, unfortunately. Both enthalpy and entropy tilt things pretty sharply. A molecule may be tamed because it just can't find a way down the big slide, but if it can, well, it's time to put on the armor, insert the earplugs, and get ready to watch the free energy equation do its thing right in front of your eyes. Your heavily shielded eyes, that is, if you have any sense at all.
Nitro groups are just the kind of bad company I mean, since they both bring their own oxygens to the party and pull electrons around in delightfully destabilizing ways. So nitrotetrazole is already not something I'd feel good about handling (its metal salts are primary explosives), but today's paper goes a step further and makes an N-oxide out of a nitrogen on a nitrotetrazole ring. This both adds more oxygen and tends to make the crystal packing tighter, which raises the all-important kapow/gram ratio. (There is, of course, little reason to do this unless you feel that life is empty without sudden loud noises). The paper mentions that "Introducing N-oxides onto the tetrazole ring may . . . push the limits of well-explored tetrazole chemistry into a new, unexplored, dimension.", but (of more immediate importance) it may also push pieces of your lab equipment into unexplored parts of the far wall.
I love this guy. XD
I just want to quote again - "The all-important kapow/gram ratio." Because somehow, some way, I'm going to steal that and use it. The line, I mean. Not the kapow. ^_^;;