Wednesday, February 6, 2013

14 thoughts you might have during a (somewhat) unexpected exotherm

Credit: Exotherm
Based on a compilation of events. 

1. Will this reaction ever initiate?
2. Maybe I should wait a bit before I add this next bit of iodine...
3. Will this reaction ever initiate?
4. Maybe I should wa - [dump]
5. [turns back to reaction]
6. Check out that delta-T!
7. Man, I should keep my hood cleaner.
8. I wonder if I should tell my lab -- hey, guys! Didn't see you sneak up on me there.
9. You know, I'm pretty sure that temp is above the boiling point of this solvent.
10. That ice bath I put under there is not doing a damn thing.
11. One of you folks want to get me a fire extinguisher?
12. And there come the hot solvent fumes out of the top of the condenser!
13. If it stays in my hood, it's not a near-miss, right?
14. Well, I guess we solved that initiation problem.

Elapsed time for said thoughts: ~30-45 seconds.

9 comments:

  1. Maybe a decade ago now so don't remember the exact reaction, but had one scary exotherm. Thankfully have more than one J-Kem temperature controller in my hood, so was able to monitor internal versus bath temperature. Scaled up a reaction initially run in a 4 mL vial in a heating block to a couple grams, so didn't know exotherm profile. Around 30 C internal temp started to rapidly exceed the bath temp, so I turned the bath off, closed the hood doors, exited my bay, and stood one bay over peering through the storage shelves at the J-Kem readout. Thankfully the reaction was small scale didn't reflux out the top of the condenser. Fun one to explain to the boss when she saw me hiding fearfully in another bay.

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  2. You mean the fountain out of the top of the condenser wasn't supposed to happen?

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  3. "When the internal thermo-probe reading goes from 22 to 260C in one second and the addition funnel suddenly flies by you, it usually marks an opportune moment to step outside the lab"

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  4. A classmate of mine was preparing (on molar scale) a cobalt complex in a large erlenmeyer. Said classmate missed the part in the experimental where they said to use a dropping funnel. Said classmate turned himself and the roof of his hood the most glorious shade of blue.

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  5. 1 mole borohydride addition went too fast - cue an hour of swaddling in ice, but I still got 80% out.

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  6. I've learned to do chemistry mostly on Grignards of various kinds (generating them and quenching afterwards), so I got pretty used to 'feeling them out' on the exotherm. My scariest one though, was first year in grad school, when I was doing that 1 liter of tBuLi reactions that I usually did to make my starting material. It has to be boiled in hexane for a week, then you get a huge ice bath and quench it. I was still too cocky from Grignards and was quenching it dropwise with water. Even a drop every five seconds was too much for that thing. I think I added two drops of water in the same five seconds, and it started boiling alarmingly, so I closed the sash and just stood back to watch. Half of it flew out the top of the condenser. Still manged to get about half of my starting material after work-up. From then on, I decided to start quenching those things with isopropanol or ethanol.

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  7. Back in grad school (1990's), I had to make my own SEM-Cl and I ran a >100 gm Reformatsky reaction, which didn't want to initiate. The heat gun and iodine would sometimes get it going, but it quickly started to reflux and get out of control. One of those times, half the contents in my 2L round bottom geysered out and into my hood. Unfortunately, the TMSCl was hydrolyzing to HCl and the lacrymator properties of bromo ethyl acetate prevented me from cleaning it up for 24 hr. Now, I just buy SEM-Cl.

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  8. Calcium Hydride never failed to surprise me at how quickly it went from "seemingly inert" to "depositing itself on the skylight of the hood"

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    1. I don't know the exact process you were using it for, but did you grind up the calcium hydride into a fine powder with a mortar? Otherwise it's basically a bunch of chunks that can react fast when the inside is finally exposed.

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