This fine reagent was mentioned here (disparagingly) in the comments the other day, and I knew that it was time to add it to the list. I've had some other selenium entries before, and they're all here for the same reason: their unsupportable stenches. Everyone, even people who've never had a chemistry class in their lives, knows that sulfur compounds are stinky, of course, but it's a problem that continues as you move down Group XVI of the periodic table.
And it's not like plain phenol itself has no odor. It's strong, penetrating, and completely unmistakable. As soon as I get a whiff of the stuff, I'm immediately transported back to the Verser Clinic, the small hospital in the town I grew up in back in Arkansas. Phenol smells like an old-fashioned medical office; it was used for many years as a disinfectant (and was, in fact, introduced as such by Joseph Lister himself). If you move it down a notch to sulfur, you get thiophenol, which is easy to describe: burning rubber - the pure, potent, platonic ideal of burning rubber, bottled up and daring you to open the cap. I can't say that I won't work with thiophenol, since I have (very much to my regret, at times), but I've used it most reluctantly, and probably haven't touched it in at least fifteen years.
Ah, but move down one more element and you have selenophenol, and that's a more exotic reagent. I've never seen any, and after reading the descriptions, I never want to. Actually, let me take that back: I'd look at some from the other end of the lab. What I never want to do is open any of it up. The chemical literature has numerous examples of people who are at a loss for words when it comes to describing its smell, but their attempts are eloquent all the same. A few years ago, Gaussling at the Lamentations on Chemistry blog referred to it as "The biggest stinker I have run across. . .Imagine 6 skunks wrapped in rubber innertubes and the whole thing is set ablaze. That might approach the metaphysical stench of this material." So we'll start with that.
I believe that this lovely compound is commercially available (if you're anywhere close to anyone making it, you'll know about it). But should you wish to prepare it with your own hands, do violence to your own schnozz, and drape yourself out of your own window while you throw up into your own rhododendrons, feel free to use this reliable preparation from Organic Syntheses, circa 1944. This features the note that "it is frequently advisable to work with [selenium compounds] on alternate days", which I suppose is to give them time to work their way out of your nasal passages.
I'm not so sure. When I was a teaching assistant in grad school, I taught three labs a week one semester, and one of those labs, damn it all, was the phenyl Grignard reagent. We had them making it in diethyl ether, outside of the small and inadequate fume hoods, and the solvent fumes were fit to strip paint. By the end of the Monday lab, I was well saturated with ether and had a terrible headache, which returned as soon as I caught my first whiff of the stuff on Tuesday afternoon. I barely made it through that lab, mostly by holding my breath and using a lot of hand gestures, and I took the opportunity on Wednesday to get as much fresh air as I could. But when I came back for the Thursday session, the first first wave of ether vapor washed over me and nearly stretched me out on the tiles. I taught the entire lab from the hallway, shouting and waving like Monty Python's "Semaphore Version of Wuthering Heights". So in my mind, the choice between getting these things over with and stretching them out is still not settled.
That Org Syn prep also notes that it can produce small amounts of hydrogen selenide, which is very toxic indeed (and will give you a sore throat, too, apparently, before it kills you). This luckless graduate student from the 1920s got to experience both of these bracing selenium room fresheners in the course of his work:
Berzelius described the poisonous effect of hydrogen selenide quite impressively; "In order ta get acquainted with the smell of this gas I allowed a bubble not larger than a pea to pass into my nostril ; in consequence of its smell I so completely loss my sense of smell for several hours that I could not distinguish the odor of strong ammonia even when held under my nose. My sense of smell returned after five or six hours, but severe irritation of the mucous membrane set in and persisted for a fortnight' The writer has been working on the gas for some time and was also quite seriously affected once, the injury persisting for many days. That it is more poisonous than the hydrogen sulphide is well known."
So you have that to look forward to on your way to selenophenol. And at your destination? Assuming your nose is still attached to your face, you'll experience what few chemists ever have. I'll let this 1908 report from Wisconsin take over:
When benzeneselenonic acid in solution is treated with reducing agents such as hydrogen sulphide, sulphur dioxide, or, best, with zinc and hydrochloric, acid selenophenol is obtained as a yellow oil with an overpowering and most nauseating odor. . .The odor of diphenyl diselenide is extremely disagreeable but is not nearly so bad as that of selenophenol.
. . .The effect of selenophenol on the skin is very similar to that of thiophenol, forming blisters which itch intensely. After a time, these dry up, the skin scales off, and there appears to be a deposit of red selenium beneath it. The odor of selenophenol is very penetrating, and is nauseating beyond description.
Gloves, man, gloves. Unless, of course, you wish to be tattooed with elemental selenium while being nauseated beyond description. Should this be your idea of a fun Saturday night, I will not stand in your way.