Column VI of the periodic table doesn’t start out smelly, but that’s probably just because we run on its first element, oxygen. Animal ancestors of ours who felt woozy all the time from the stench of oxygen didn’t leave much of a legacy, so we’re all pretty positive about it. But when you start moving down into the next rows, everything changes.

Sulfur’s next, and its fame as a reeking element is well deserved. Skunks, rotten eggs, burning tires – they all have delightful sulfurous tang, and we have sulfur compounds in the lab that are worse yet. But most people don’t think about the elements to come.

The next heavier element in the series is selenium, which most people will have heard of primarily from its presence in health food stores. It is indeed an essential trace element, although I’d think that if your cuisine includes a reasonable amount of garlic (as it should!) then you’re getting all the selenium you need. You don’t want to overdo it, because this essential dietary factor is also a pretty efficient poison, which is a useful First Lesson in Toxicology right there. (And no, I don’t think it’s possible to get selenium poisoning from eating too much garlic; I think many other effects would kick in before you noticed any selenium-related problems.)

Selenium compounds are, if anything, more intrinsically noxious than sulfur ones. Imagine a sort of hyperskunk, scattering its enemies before it and making them carom off trees and dive into ponds. The heavier selenium atoms tend to make the compounds less volatile, though, so you don’t always get their full bouquet. The smaller compounds get in their licks, though. One of the simpler selenium-rich compounds, for example, is carbon diselenide, an exact homolog of the carbon dioxide in your breath and in your glass of soda. Instead of a gas, the selenide is an oily liquid with a higher boiling point than water. Most of us organic chemists have never seen it.

Which is just fine. The first report of the compound in the chemical literature is from a German university group from 1936, and it was a memorable debut. A colleague of mine had a copy of this paper in his files, and he treasured a footnote from the experimental section which related how the vapors had unfortunately escaped the laboratory and forced the evacuation of a nearby village. The authors stressed the point that its aroma was like nothing that they’d ever encountered.

The compound made a few appearances over the next couple of decades, but one of the next synthetic papers dates from 1963. (That’s Journal of Organic Chemistry 28, 1642, for you curious chemists.) The authors are forthright:

“It has been our experience that redistilled carbon diselenide has an odor very similar to that of carbon disulfide. However, when (it is) mixed with air, extremely repulsive stenches are gradually formed. Many of the reaction residues gave foul odors which were rather persistent (and) it should be noted that some of the volatile selenium compounds produced may be extremely toxic as well as foul.”

Something for everyone! At least it lets you know when it’s coming. Interestingly, in recent years, the compound has actually made a comeback, with more references to it in the past twenty years than in the fifty before. It’s been used to prepare a number of odd compounds that have shown promise as organic semi- and superconductors, and there’s actually a commercial source for the disgusting stuff (which may be a first.) I’d like to see what they ship it in.

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