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How Not to Do It

How Not to Do It: Distilling Benzene

Summer students are showing up at academic and industrial labs around the country right about now. A certain percent of them will blow something up within the next three months, and that percent will be several standard deviations above the ka-boom rate of the other lab members. I’m not trying to say mean things about summer students. I merely speak the truth.
I had a summer undergraduate working with me for a while in grad school, and he taught me several lessons, of varying utility. One day he needed some dry benzene for a reaction, so I helped him set up a still in my hood. One-liter round-bottom flask, some benzene, a little sodium. My intern, who I’ll refer to as Toxic John, put a heating mantle on the thing and turned it on.
A little while later, I walked past my hood and noticed that the stuff was boiling merrily. A bit too merrily, actually – it was really hopping around in there. I turned down the Variac (basically a big dimmer-switch type AC transformer that’s used to step down the voltage to equipment like heaters) and went on my way. But I came back a little while later, and it was still rolling away in there.
If anything, it was worse. I turned down the Variac again, wondering just what was going on, and why my guess about the inital setting had been so wrong. A few minutes later, things hadn’t improved much. The benzene was really leaping around, splattering and erupting. I looked a little more closely at the Variac this time, and noticed something that had escaped me: the heating mantle wasn’t plugged into the damn thing at all.
Nope, it was plugged right into the wall socket, as some of my experienced readers will have guessed. As soon as I noticed that, I dropped the lab jack that was holding the heating mantle, which gave me a good look at the glowing red coils showing through the woven glass lining. I could feel it on my face like a sun lamp. Cursing, I pulled the thing out of my hood and heaved it into the hallway, right into a shopping cart that we kept out there for visits to the stockroom.
I went looking for Toxic John as the mantle popped and clicked. It was cooling down, but I wasn’t. “John!”, I shouted (I was pretty crabby back in grad school), “you plugged the mantle into the wall! No wonder it looked like a volcano in there!”
“What’s the matter,” he asked me. “Benzene doesn’t burn, does it?” “Doesn’t. . .burn. . .” I said slowly, as a nearby post-doc put a warning hand on my shoulder. “Well,” said John, making his case, “it’s inert to bromination!” That line of reasoning didn’t impress me much, and as I recall, I told him that if he had any more insights like that we were going to find out if he was inert to bromination himself. Then I went off looking for the professor who’d just taught him sophomore organic chemistry, to let him know that his work, once again, had been in vain.

10 comments on “How Not to Do It: Distilling Benzene”

  1. Sigivald says:

    So, uh, for us non-chemists, what was narrowly avoided? The specifics of the boom, that is?

  2. Derek Lowe says:

    Well, benzene really does burn nicely, which is why I wanted to strangle my summer student. And that heating mantle was getting mighty toasty.

    I suspect that the cold-water condenser on top of the still would have become overwhelmed with the volume of hot benzene vapors it had to deal with, and benzene would have started venting out the drying tube on top. When that dripped down to the blazing hot apparatus below, then Whoomph.

    There’s always the possibility that the fuse wire that the heating mantles are furnished with would have melted and shut off the current, but it didn’t show any signs of doing that. Makes you wonder how hot they have to get before they give way. . .

  3. SRC says:

    As a new faculty member I had an undergraduate in my lab who decided to “simplify” a literature procedure. I’d had my back to him while he was weighing stuff, and turning back to continue the directions, I saw, to my horror, that he was proposing to pour the solvent over the solid reactants in a round bottom flask!
    Not only that, but he had taken the carboy by the fingerhold and, holding it on his arm and shoulder moonshiner-style, was about to pour an indeterminate amount of solvent onto the mixture of reactants.
    Needless to say, he was gently but quickly set on a library project. Some people just don’t have the common sense to be allowed into a laboratory.

  4. PsychicChemist says:

    One of my fellow postdocs down the hall, had the bright idea to use his cigarette lighter to soften the tygon tubes on the THF and ether stills. Fortunately, someone got there in time to stop him from blowing himself up.
    On the other extreme, a second year graduate student insisted on attaching a reflux condensor to every reaction she ran – even if the reaction was being run at room temperature.

  5. Bill Tozier says:

    You just set this up so you could collect stories, right?
    OK. Here you go. You can explain the scary inside information to the laymen. [Laymen: this is all very very scary.] So one colleague, back in my organellar DNA isolation days, decided to distill phenol. In a laminar flow hood. Wearing sandals. Speeding it up with a bunsen burner. And the flask broke. And spilled on the floor. And his feet.
    Guys in white suits were crawling all over the brand new building for hours, and I had the sad/pleasant duty of escorting my idiot colleague, who ended up with about 10 mls of very pure phenol on his feet, to the hospital, and watching the look on his face when they told him how close he’d come to real quick permanent death. From just that little bit that spilled on his skin.
    Shoes, people.
    Then there’s the intern who decided to sonicate a 2-liter culture of papillomavirus-infected cells, when I was doing time at ThreeNamed Drug Company in Pennsylvania. And not in any hood at all. He’s probably dead from that, by now; the rest of us were all pretty close to just locking the door in order to let the air settle, regardless of what happened to him.
    But my favorite — and it’s not even the one that resulted in the hundred-thousand tiny fragments of polystyrene that are still embedded in the skin and muscles of my hands and forearms — was Back In The Day when there was this new method for prepping electron microscope samples using liquid propane. There was a demo going on in [another] lab across the hall, and all of a sudden the door slammed open and all the students and the instructor ran out yelling “Run!”. We all ran. Apparently the procedure (still in its early days) involved just pouring the liquid propane into an open styrofoam ice chest. And as the instructor was dipping some samples into it, it “turned blue”, indicating that just the wrong mix of atmospheric oxygen had dissolved into it to make it into a Big Nasty Bomb.
    White suits again, that time. But the smart instructor did a very cunning and foolish thing: she ran down the hall, decanted out some liquid nitrogen, and went back in the lab and used that to de-oxygenate the propane. Saving the top two floors of the building, apparently….

  6. Phil-Z says:

    I’m not that old, but I remember seeing a co worker eluting a chromotography column with a mix of hexane and ether while Bogarting a cig.
    My boss used to heat water for tea on the hotplate we used to develope TLC plates in the hood.
    I caught another boss, a new PHD, weighing out about an ounce of DCC outside the hood.
    Thats when I switched to the mass spec lab.

  7. pyrokinetics says:

    this little post makes workin in a lab sound extremely dangerous. So what’s the mean life span of a chemist these days?

  8. Novice Chemist says:

    Here at the National Organic Symposium, Jerrold Meinwald put up a photo (during his talk) of Woodward and a colleague looking at a distillation apparatus while wearing suits and ties. Woodward has (apparently) the ever-present cigarette in his mouth. My, how times have changed.

  9. Derek Lowe says:

    I should do a post on life expectancy of chemists, which is actually quite high. But if you spent your entire career around clueless undergrad summer students, that might cut into it a bit. . .

  10. Colby Cosh says:

    Even a non-chemist with a good spider-sense might have suspected the problem (and the point of the story). Benzene… Benz… early internal-combustion engines (emphasis on the “combustion” bit)… geddit?

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