5/17/2007

stupid undergrad-in-lab moment

Synthetic chemistry is one of those disciplines in which there is no substitute for experience. Frequently, something arises for which there is no accepted procedure, so a high degree of resourcefulness is required.[1] No one is particularly good at it when they start (usually as an undergrad), so a few fuckups are more or less expected. Some people make more mistakes than others, and some mistakes are more serious than others. Derek Lowe has a fantastic collection of these stories, not all about undergrads, and I highly recommend that you read them.

I've been a bit on the cautious side in the lab, and I usually think about what I'm doing, so I don't have too many stories of my own to share.[2] But here is something that happened to me very, very recently. Remember my craptacular oil bath? Well, those Sonogashiras were in tiny little flasks, and the original level of oil in my bath wasn't quite high enough to effectively heat them. So I decided to add a little more. These were oil baths I'd inherited from the last guy who was in my hood, so I'd never had to fill or refill them. I knew we used PEG (poly(ethylene glycol)) for this, so I grabbed a bottle off the shelf and dumped some in, then turned up the heat a little and let it melt into the oily mess that was already there. The cute little Sonogashiras worked beautifully, but I had something else to set up that was in a 1L flask, so I poured some of the oil back into an empty bath and stuck the flask in there.


Well, after I worked that up, and the oil had cooled back to room temperature, I was confronted with this:
The PEG had solidified. What I didn't know was that the PEG we usually use for oil baths was not quite the same as the white crystalline-looking PEG that I had added to mine. When a labmate pointed out the greasy-looking carbowax PEG, I knew what I had done. The molecular weight on the correct PEG was around 600, but the crystalline stuff was around 8000. Quite a difference.[3]


[1] Often, this requires fixing things around the lab when they break. I am always looking for an excuse to break out the screwdrivers.
[2] I think being cautious drives my boss a little nuts. He's very much a cowboy chemist.
[3] For any non-chemists out there, PEG is a polymer, so the molecular weight depends on how long the polymer chain is. As the molecular weight increases, the polymer will go from liquid to glassy oil to wax to kinda-crystalline solid.

18 comments:

Mitch said...

Classic, but it really could of happened to anyone. And now, hopefully, you'll never make that mistake again. I wonder if I too would be considered a cowboy chemist at times. Hmmm....

Mitch

Excimer said...

Let's talk about how awesome t-BuLi is, if we're talking about stupid moments. I was putting a syringe in a bottle of the stuff and I pulled too hard and the syringe pump came off. The stuff in the syringe spilled on the floor (about 0.5 mL) and promptly caught the floor on fine. The nitrogen line I had in it was still in there, and the hole in the sureseal bottle from the other syringe needle was spewing out drops of t-BuLi (and thus fire).

Undergrad moment? Nope. That happened about a month ago. Yeah. Oh and the reaction didn't work either. Balls.

(I love the term cowboy chemistry. I use it when I'm doing something I'm fairly certain won't work.)

Mitch said...

You mean you pulled the plunger out too far?

Mitch

Excimer said...

both. I was really yanking on it hard and it kinda flew off, turning a bad situation into a worse one. Good times.

Propter Doc said...

Ah, wonderful! I've never heard of PEG being used as an oil bath before.
Dr R has a particular fondness for using t-BuLi when there is a new undergrad in his lab. He enjoys using a fine needle and making a miniflame thrower out of it, or alternately setting his glove on fire briefly to scare the hell out of said student so they take good care from then on.

My best was running a column using 90% diethylether (and 10 % something else, can't remember what) and not realizing that some bugger had turned off the fume hood. Stoned, completely stoned by lunchtime. Ended up sitting outside the building, sitting on the curb, watching dust blowing along the carpark. Then my supervisor appeared...lets just say my head hurt a great deal a few hours later. You'd think I would have learned my lesson when I knocked myself unconscious at high school whilst treating those annoying little fruit flies with diethyl ether to knock them out to study them. I was out cold.

I don't use diethyl ether much these days...

Ψ*Ψ said...

I love the ether. Anytime I see one of my labmates using a great deal of it out on the bench, I go hang out with them for a few minutes.

kiwi said...

certainly amusing stuff. the upside of dimwitted stuff like this is it is a vivid lesson that you don't forget, which in the long term is how you learn. and so you don't feel too stupid, an early lesson of mine involved the merits of throwing "quenched" sodium into a wet sink full of ethanol fumes. quite a warm lesson.

Ψ*Ψ said...

I thought it was more amusing than anything else. Besides, it was harmless, so it's a good opportunity for everyone who reads this to make fun of me. :)

milkshake said...

Silicone oil is quite expensive in the common grade ("for melting point apparatuses, (OSiMe2)n ) but there is one super-expensive for high temperature applications, (OSiMePh)n. The funny moment arrives when you need to refill the bath and find out that the two aren't miscible, and you have made an expensive silicone oil milkshake in your bath.

Uncle Al said...

Are you the least bit concerned that PEG pyrolysis gives ETO? What is wrong with paraffin oil? If you are clever with snail mail you can request a free sample quart of Mobil 1 base stock "to evaluate as inert working fluid in a heat exchanger application." Thereafter add 0.1% Irganox 1010 to taste. Flash point ~235 C.

A real man would use squalane, 10 torr vp @ 263 C. Flash point ~218 C. All natural!

Russ said...

There might be somme advantages to a 'wax bath' as opposed to an oil bath. Let the flasks cool, and then justpick off the solid wax instead of wiping (and discarding a small amount of) the oil. Also, no spills.

David Eaton said...

I did a few dumb things that caused explosions and/or fires as a grad student, but one stands out as the experience that taught me to be careful.

I had heard that a certain plastic film had free aldehydes sticking off it, and that one could prepare a Tollen's solution bath to plate silver onto it. I tried it, and it worked, so I tried various masking strategies. To make a long story short, I left my solution sitting a bit long- not for days, but all day at least. When I recognized what I had done, I recall thinking, aaah, dammit, I need to dispose of that. I picked up the vessel, to look into it to see how much was left, and BOOM, I had a face full of basic solution and silver ions.

The stuff got around my glasses. My ears were ringing, my eyes were glued shut (largely out of fear, probably) but I knew where my eyewash was and I shuffled that way, as someone grabbed my elbow and led me to it. I rinsed for several minutes, then stopped to check that I could still see. Luckily, I could. I had several bags of saline run into both eyes at the emergency room (ow, they were cold!). My eyes were blood red the rest of the day, and the silver ions gave me tiger stripes for a while. It didn't make me scared, but it woke me up to the fact that nature will bite given the chance.

It's a bit embarrassing, because I knew better than to leave Tollen's sitting. But it taught me how quickly a goofup can be made worse by not thinking clearly about how to fix it.

sam said...

I worked in an AFM lab. While setting up the AFM for a demo at a high school, I plugged a cable into the wrong plug and broke the AFM. We brought the AFM back to lab and tried to figure out the problem. In doing so, we repeated the exercise with our other AFM, breaking that one. Now our lab was without an AFM for a month. Oops.

LiquidC said...

Polymer chem lab in Moscow State uses Wood's metal as a bath.

Ψ*Ψ said...

Uncle Al appears to have missed the memo; in order for me to become a "real man," a considerable amount of surgery would be required.

Dave, that's a hell of an accident.

Chemgeek said...

Don't get Uncle Al going on gender or race issues. Yikes!

Excimer said...

Oh no, I'm not stopping him. It's funny. Few other people are as willing to use the hypothetical black lesbian transvestite named shaneequa with three kids on welfare in an argument against... anything, really. I love it.

Andrew said...

PEG as heating media? I've never heard that here in China...PEG...isn't it much less stable than PE (wax)?