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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

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February 4, 2004

Our Friend, the Carbon-Aluminum Bond

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Posted by Derek

"Twenty-five years of being a laboratory chemist, says Gregory Hlatky today, and this is the first time I've had an incident." Hey, maybe he's been doing the wrong kind of chemistry. Some kinds can almost guarantee you an incident every month or two!

Actually, the kind of chemistry he does (organometallics) is already pretty lively, and I have to say that I'm impressed by his 25-year safety record in a field like that. But I'm not surprised that it was an organoaluminum compound that took off on him, because I've had several of them do the same thing to me (without injury, fortunately.)

And the most nerve-wracking part of them was the time delay. Most reactive compounds are very forthright about their reactivity. They burst into flame on exposure to air (like tertiary-butyllithium, or for the hard-core pyromaniacs, the dialkyl zincs.) Or they give off great clouds of choking fumes (I can recommend neat titanium tetrachloride for those who want to experience this special effect - the one molar solution in dichloromethane is for dilettantes,) or hiss and splatter violently if they encounter water (chlorosulfonic acid is a winner in that category.) At any rate, you know very quickly, if you didn't already, what kind of substance you're dealing with.

But the alkylaluminum compounds have their coy ways. I recall a large aluminum alkyne reaction that I set up in graduate school, one of the once-and-for-all reactions which get scaled up a little more than is prudent. I don't believe that I've told this story on the blog, so this one can go into the file with my other lab stories.

With this reaction, the fun started early. I first had to add a large amount of n-butyllithium, which is less reliably pyrotechnic than the tertiary kind, and I'd done that by running the solution into a Pyrex dropping funnel. That, for the non-chemists in the readership, is one of these. As the stuff dripped slowly into the reaction, the BuLi had dried into a crust on the glass tip of the funnel. At the end of the addition, I had to pour in a larger quantity of toluene and switch the funnel to another piece of glassware, so I just grabbed the thing and swapped it out. Whereupon it burst into lovely orange/purple flames.

Well, they went out shortly. But I was standing there, pouring my (flammable) toluene with one hand, and holding this flaming funnel with the other, thinking that this would be a good time for a member of the department safety committee to show up. After that, the next steps of the reaction went along relatively quietly, and eventually it was time to quench the reaction. I did that by very carefully adding a few drops of methanol to the liter or so of solution. Nothing. So I added a few more.

Nothing. I waited to see if anything would happen. Nothing did. A brief squirt of methanol this time. Zilch. I was starting to wonder if there was going to be any reaction at all - surely there was some leftover organoaluminum stuff that needed to be quenched. A longer, more vigorous squirt of methanol. No sign of life.

Then, at the very bottom of the flask, down near the magnetic stir bar, a bubble formed and rose to the surface. And another. Several more. A stream, several streams, a vigorous fizzing mass that came roaring and foaming up the sides of the flask - Well, I managed to catch most of it in a bucket. When the bubbling started to really roll along, I had bolted for something to catch things in, because it was clear that the reaction could be on its way to a spectacular conclusion. It didn't disappoint me.

Like most once-and-for-all reactions, I had to do that one again, eventually. But the next time, at least, I was ready for it.

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