B.R.S.M. Home of Woodward Wednesdays

28Jul/124

Selenium: Include Me Out

No, thanks.

This week I noticed that J. Derek Woollins, head of Chemistry at the University of Saint Andrews and legendary selenium chemist, recently published a review of the research leading to the discovery of his eponymous reagent in Synlett. Although, for reasons of self preservation, I tend to lose interest in the chalcogens after the first row or two, I quite like personal accounts of research so I thought I’d give it a try. Unfortunately, being an organic chemist, I couldn't follow a lot of the inorganic chemistry but I did enjoy some of the stories of things going wrong:

“Paul Kelly also later extended this work by making M–Se–N complexes using tetraselenium tetranitride (Se4N4) as the starting material. This is a very sensitive material. Indeed the first time we prepared it (from a reaction in liquid ammonia), whilst washing the red solid with a solution of potassium cyanide, nitrogen was let into the flask fairly briskly. The resulting turbulence caused an explosion, which destroyed the flask embedding pieces of red selenium into the white shirt Paul was wearing; from a distance this looked like major bleeding. Bravery was not lacking in the group during that era, and Paul Kelly also carried out what remains as the only published reaction of (extraordinarily explosive) pentasulfur hexanitride (S5N6) to give a complex containing the [S2N3]– ligand.”

Ah, wacky fun! I’m quite sure that S5N6 falls into the category of things that shouldn’t really exist, and trying to force them to do so isn’t good for anyone’s nerves.[1] Actually, the group engaged in quite a lot of this kind of lunatic chemistry. Another great example:

“Leaning on our previous work on reactions in liquid ammonia, we prepared sodium selenide (Na2Se) by the simple reduction of selenium with sodium in liquid ammonia. The resulting material is much more soluble than that prepared by the solid state route, though it is worth noting that this wonderfully finely divided solid is also very pyrophoric – on one occasion, around 75 grams caught fire in the port of our glove box with rather unpleasant consequences.

I imagine that ‘rather unpleasant’ probably doesn’t cover it. I can think of few things that would evacuate a building faster than screaming the words ‘selenium fire!’.[2] Fortunately, my own experience of selenium is a lot less exciting - I used phenylselenyl bromide a bit during my Masters to make enones, and aside from a marked decrease in affection from my girlfriend at the time, I suffered few ill effects. In fact, I suspect that beyond the old trick for forming enones (and the related Grieco olefination), many organic chemists would struggle to even think of uses for selenium in the lab. I am aware of one more reaction you can do with it, though, and I'll quickly explain why you shouldn't bother.

Filed under: Current Literature, Fun, Lab, Named reactions | 11,746 views | 4 comments Continue reading
15Jul/126

A Belated Happy Birthday To KCN

Sorry this is quite late; real life and chemistry have been kicking my ass the past couple of weeks. Hopefully normal service, and more actual science, will resume shortly.

From Angew. Chem. Int. Ed., 2002, 41, 2678

The CP molecules are scary!

 

Without further ado, here is a roundup of my favourite colouring competition entries. In the end I didn't get that many, despite lots of people telling me this was a great idea. Most of the contributers have already posted their entries on their own blogs, so if you keep up with other chemistry blogs (and you should, because there are some that are much better than this one) you've probably seen these already. So, in chronological order:

Filed under: Fun | 9,803 views | 6 comments Continue reading
2Jul/1212

A New Coupling Agent, And Sandmeyer’s Other Reaction

I wrote this post a couple of weeks back, but wasn't happy with how rambling it was. Anyway, it's only getting more out of date, so I'm putting it up now. Someone might learn something.

 

I’ve always had a soft spot for hypervalent iodine reagents, especially iodine(III). In fact, they were the cornerstone of a methodology project that I worked on last year. You can imagine, then, that the rather usual looking iodosobenzene derivative above, which was published in Org. Lett. a couple of weeks back (DOI: 10.1021/ol301085v), immediately caught my eye. Such compounds tend to be very useful oxidants, and you can check out a few recent applications on the relevant organic-chemistry.com page. Surprisingly, though, this wonderful new reagent wasn’t being touted as an oxidant (although I’m sure it is)… apparently, it’s a great new coupling agent!

Filed under: Current Literature, Fun, Serious | 11,633 views | 12 comments Continue reading