I don't know how many of you out there like to form azides, but if you do, you've probably used (or thought about using) imidazole-1-sulfonyl azide hydrochloride. This reagent appeared in Organic Letters a few years ago as a safe-to-handle shelf-stable azide transfer reagent, and seems to have found popularity. (I've used it myself).
So it was with some alarm that I noted this new paper on the stability and handling characteristics of the reagent. It's a collaboration between the University of Western Australia (where the reagent was developed, partly by the guy whose lab bench I took over in grad school back in 1983, Bob Stick), the University of British Columbia, and the Klapötke group at Munich. That last bunch is known to readers of "Things I Won't Work With", as experts in energetic materials, and when I saw that name I knew I'd better read the paper pronto.
As it turns out, the hydrochloride isn't quite as optimal as thought. It's impact-sensitive, for one thing, and not shelf-stable. The new paper mentions that it decomposes with an odor of hydrazoic acid on storage - you don't want odors of hydrazoic acid, believe me - and I thought while reading that, "Hmm. My bottle of the stuff is white crystalline powder; that's strange." But then I realized that I hadn't looked at my bottle for a few months. And as if by magic, there it was, turning dark and gooey. I had the irrational thought that the act of reading this paper had suddenly turned my reagent into hazardous waste, but no, it's been doing that slowly on its own.
So if you have some of this reagent around, take care. The latest work suggests that the hydrogensulfate salt, and especially the fluoroborate, are less sensitive and more stable alternatives to the hydrochloride, and I guess I'll have to make some at some point. (They also made the perchlorate - just for the sake of science, y'know - and report, to no one's surprise, that it "should not be prepared by those without expertise in handling energetic materials"). But it needs no ghost come from the grave to tell us this.
So, back to my lab and my waste-disposal problem! And here's a note on the literature. We have the original prep of the reagent, a follow-up note on stability problems, and this latest paper on alternatives. But when you go back to the original paper, there is no mention of the later hazard information. Shouldn't there be a note, a link, or something? Why isn't there? Anyone at Organic Letters or the ACS care to comment on that?
Update: I've successfully opened my bottle, with tongs and behind a blast shield, just to be on the safe side, and defanged the stuff off by dilution.