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How Not to Do It

How Not to Do It: Chromium Trioxide

Note: this was a post on my old blog site, and never made the migration over to the current “In the Pipeline”. I was reminded of it this morning, and thought I’d bring it more out into the light.
There are reports (updated here – DBL) that Mars may have hexavalent chromium compounds in its surface dust, which is already being brought up as a concern for future human exploration. I agree with comments I’ve seen that this is putting the cart in front of the horse a bit, but it also means that I probably wouldn’t be a good candidate for the expedition. I’ve already had my lifetime’s exposure to Cr(VI).
Back in grad school, I had an undergraduate assistant one summer, a guy who was pretty green. I’ll refer to him by an altered form of his nickname, henceforth as Toxic Jim. I shouldn’t be too hard on him, I guess: I was a summer undergrad in my time, too, and I wasn’t a lot of help to anyone, either. But TJ did manage to furnish me with some of my more vivid lab stories in his brief time in my fume hood.
One morning I showed him how to make PCC. That’s pyridinium chlorochromate for the non-organic chemists out there, an oxidizing agent that doesn’t seem to be used as much as it was 15 or 20 years ago. Even in ’85, you could buy it, but the freshly-made stuff was often better. It certainly looked nicer. Like all the Cr(VI) salts, it has a vivid color, in this case a flaming orange. I shouldn’t say “flaming;” that’s getting ahead of the story. . .
It’s not hard to make. You take chromium trioxide, a vicious oxidant in itself which comes as clumpy fine purple crystals, and dissolve it in 6N hydrochloric acid. That’s an easy solution to whip up, since it’s just concentrated HCl out of the jug cut 1:1 with water. I had Toxic Jim do all this – weighing out the chromium compound, making the HCl. During that part I couldn’t resist quoting the ancient adage, which works well in the East Arkansas accent of my youth: “Do like you oughter, add acid to water.” Most chemists either remember that one, or they remember the syrupy conc. acids splattering all over their arm when they did it (once!) the other way around.
We set up a three-neck flask with an overhead stirrer to run this in. That’s just a motor mounted above the flask, turning a shaft with a paddle on the end of it. Works well for really thick mixtures, which this was supposed to turn into. As things turned out, it was even thicker than planned, for a brief exciting interlude.
In went the HCl, out of a big Erlenmeyer flask, and in went the chromium trioxide. Here’s where the wheels began to come off. Instead of a vivid red-orange solution, the stuff got dark and began to thicken. I could tell it was getting hot, too, since you could see the clear wavery solvent vapors coming out of the open necks of the flask. And that was wrong, too – you don’t get that so much with water vapor. It’s the mark of organic solvent fumes, with their different density and refractive index.
And so it was. TJ had indeed grabbed the wrong Erlenmeyer. Not the one he’d just mixed up the HCl in, but one from another part of the bench that contained ethyl acetate from a big chromatography run the night before. Ethyl acetate is a pretty poor substitute for hydrochloric acid, most of the time, when you stop to think about it.
Then the overhead stirrer began to bog down, which takes a mighty thick mixture to achieve. I hadn’t added up what had happened at this point, but I knew that things were going wrong in all directions at once. I pulled the glass hood sash down some more, saying “I think you better stand back -” WHOOOOMPH!
And there it went! The whole reaction went up in a big fireball, which filled a good part of the hood and came roaring out of the gap in the front sash. I felt the heat roll over me, yelled something incoherent, and bolted for the safety shower. I didn’t have to run up Toxic Jim’s back, either: he was making for the door in championship time. Pulling the chain of the shower dumped a hundred gallons of ice water on me immediately, not that I needed any more waking up.
When I opened my eyes and took inventory, things weren’t as bad as I thought. Limbs and appendages all present, head and facial hair still attached – though lightly singed and frizzed – skin not even sunburnt, although it (along with my lab coat) was generously splattered with green. That was what remained of the chromium trioxide. It was now the Cr(III) oxide, having given up three oxidation levels by turning the ethyl acetate into carbon dioxide, most likely. There were a few orange-brown spots of the Cr(VI) stuff, but those were mostly confined to the front of the lab coat, in a vivid line that showed where the hood sash had gotten pulled down to.
My hood wasn’t looking its best. There was smoke hanging in the air, although that was getting pulled out. There was a huge stain of the green and brown chromium mixture all over the inside, thickest in the directions of the three open necks of the flask. Which was still intact – if I’d been foolish enough to set this up in a closed system, the whole thing would have gone up as Pyrex shrapnel. Even the ceiling had a line of gunk on it, from the thin gap in the hood sash assembly.
While I was taking this in, wondering what the hell had gone wrong, and wondering what I could possibly do to TJ that was worse than what he’d just gone through, the emergency crews arrived. It was a Saturday morning, but Bob across the hall saw the explosion and immediately dialed 911. In came the fire crews, trying to talk through their breathing apparatus: “Mumph heff deff umphh cafulteff. . ” “What?” “We hear there’s a casualty up here”
I put my hands on my hips, and gave them the full effect of my green spots, frizzed hair, and soaking wet lab coat: “That would be me.”

34 comments on “How Not to Do It: Chromium Trioxide”

  1. JRnonchemist says:

    After my second general chemistry, I realized I didn’t have the lab technique for chemistry. I decided to stick with my original major, and not take any more lab chemistry courses. In other words, I quit before I ended up a Toxic Jim.
    Any more Toxic Jim stories?

  2. The Aqueous Layer says:

    It’s probably now Dr. Jim, MD or Professor Jim, right?

  3. John Schilling says:

    Toxic Jim and the Absent-Minded Professor, with me playing the latter role even though I was only a senior grad student at the time.
    Toxic Jim was assembling a bit of vacuum apparatus, and for a piece intended only for temporary use the most expeditious way of getting a good seal was to apply what we colloquially referred to as “black wax” just outside all the seal interfaces. Apply vacuum and heat, pull the wax into the seal, and you’re done by five rather than pulling an all-nighter. Does require using a torch in close proximity to wax, but that’s not too bad in itself.
    And if you’re working combined metal-and-glassware, keeping the temperature uniformly in the molten-but-not-burning wax range is kind of tricky. If you’re really good, you can still do the job with a torch and a stick of black wax. On an off day, you’ll occasionally need a squirt bottle of water to pull heat from the metal.
    So there’s the Absent-Minded Professor hard at work at his own bench. Fully engrossed in what he is doing, with just a few spare neurons rattling off stray thoughts. Thoughts that are now burned into my memory with a clarity far out of proportion to the attention I gave them at the time. Specifically:
    “I wonder if Toxic Jim knows that bottle is full of acetone, not water?”
    “I wonder if Toxic Jim knows that acetone is flammable?”
    “I should probably tell Toxic Jim all this.”
    “As soon as I’m finished with this next bit…”
    Fwoomp. AAARRWWK!!!
    “Never mind.”
    Singed eyebrows, no other injuries, and I think we even salvaged the metal parts of the apparatus.
    I don’t know that I’ve ever experienced that peculiar level of detached awareness since, though possibly it is the sort of thing one only remembers when it blows up in your face. Or someone else’s.

  4. John Wayne says:

    I got my wet chemistry education in New England. The ‘acid to water’ catch phrase I was taught had a similar, but Boston spin to it, “Acid to watta, just like ya otta.”
    That phrase appears to work; no matter now much I want to, I can’t get it out of my head.

  5. Alex says:

    Ehhh, all these stories seem benign enough when compared to our labs in Ukraine.
    Compared to the western labs, our accidents tend to be rarer, but much more horrific.
    Once you witness a guy slicing an 8-kilo hunk of sodium (to transfer it to smaller containers with kerosene) on the floor 2 meters next to a guy doing lab dishes in a sink with a nasty irregularly splashing overpressured tap, everything starts to get a new perspective.
    Or when you hear that story which happened in nineties with a guy who tore the rusty threading off of a bit aged chlorine gas cylinder when unscrewing, couldn’t close it, and thought of nothing better as to THROW the fucking thing right out of the window. All 60 kilos, yeah. Happened on 4th floor, witnesses tell it fell with a nice greenish plume.
    We have a saying in our uni, by the way: “An organic chemist who lived till 30 will live eternally”.

  6. Handles says:

    My grandma taught me “may her rest be long and placid, she added water to the acid. The other girl did as she oughta, and added acid to the water”.

  7. Anonymous says:

    I’m sorry, did you just say an 8 kilo piece of sodium?!

  8. InfMP says:

    Derek, was this your most dangerous accident witnessed in lab?

  9. milkshaken says:

    @ 8kilo brick of sodium: There is Wikipedia picture of a giant (size of an arm) ampoule holding 1.36 kilo of cesium metal, made in USSR. You see, the classless society cannot be built by faint-hearted cadres.

  10. Fond memories says:

    I performed my first oxidation in grad school with PCC. I loved the fierce orange appearance of it. Of course, PCC is obsolete and I prefer Swern and Dess-Martin, but I’ll always have a soft spot for PCC.
    Derek, didn’t Suggs (PCC discoverer along with Corey if I recall) comment on your blog long ago?

  11. Derek Lowe says:

    #2 – I would assume so! I haven’t tried to track him down, though. . .
    #8 – it’s the worst that I’ve been on the receiving end of. I’ve been down the hall from worse (or potentially worse), but this is my personal record, and may it stay that way.

  12. Clueless Undergrad says:

    I recently did a my first summer research internship as an undergrad. I’m about to start my first reaction for the day. I read the protocol.
    “5 grams of Yttrium Nitrate plus dopants and boil in nitric acid until dry.”
    I weigh out my compounds and put them in a beaker.
    I check the acid cabinet. Oh whats this? 15.8 N nitric acid? Seems reasonable. It does say boil in nitric acid right? ( I am not a smart man).
    I add enough nitric acid to cover my compound and stir it around with a glass rod.
    15 seconds later my hood is covered in rapidly hardening Yttrium goo and concentrated acid. Luckily, I closed the sash before the people standing behind me got splattered.

  13. newnickname says:

    @3: black wax for vacuum seals? Sounds like it could be Apiezon Q (or maybe W). I still have some; must be 20+ years old.

  14. AlphaGamma says:

    Handles @6: I remember something similar to that from my school chemistry teacher (with a Brummie accent).
    Derek: is Toxic Jim related to Toxic John of “benzene doesn’t burn” fame?

  15. rockhopper says:

    @7 @8: Bulk sodium is shipped in tank rail cars (= a few tons ingot). At destination it is heated above melting point (98 °C) so it can be pumped to holding tanks.

  16. Nick K says:

    Who said Chemistry is boring?

  17. Wheels17 says:

    With regards to handling sodium, there’s an interesting .pdf about a horrible accident at an H. C. Starck facility in Newton, MA. in 1993. It is the typical series of small mistakes, lack of proper information, and deviations from procedure that resulted in a disaster.
    It’s at .

  18. B says:

    @9: Spent a pretty extensive amount of time in undergrad performing reactions with pure Cesium metal. We were interested in studying the unique physical characteristics of the metal.
    Nothing quite like handling a 50g ampule as you walk over to load it in to the glove box. Don’t slip…

  19. Kent G. Budge says:

    You chemists have all the fun. The worst I experienced in physics lab was the invention of the noise-emitting diode.
    My old high school had a couple of Toxic Jims who decided to get into the chemistry lab and start mixing random chemicals during their lunch break. Their little game of Russian roulette reached the loaded chamber when they decided to add concentrated sulfuric acid to a beaker full of potassium permanganate. One of the guys lost three fingers off his hand, and the other was shook up pretty bad.

  20. Hap says:

    I’m guessing that went like this:
    TJ1: Cool purple color.
    TJ2: Hey, what’s that brown oil precipitating out?
    Teacher: What was that?

  21. John Schilling says:

    @13: Yes, almost certainly one of the Apiezon sealants; we had too many of their products to keep track of the proper names.

  22. Anonymous says:

    I remember a colleague making cyclopropanol, starting with sodium powder in dry ether. After deciding he didn’t get enough product he decided to scale up – to 1 mole. He did dry the ether and then started by adding a small amount of the sodium powder to the flask and standing back. Nothing happened so he added a little more. After deciding it was safe he added all the remaining sodium powder. The flask started to shake allowing him to pull the sash down a little before KERRRBOOOOOOM! He escaped with minor eyebrow/hair damage but now there was flaming ether on the floor and nearby benches. So he reached for the CO2 extinguisher he had placed nearby in case of trouble. With a couple blasts from the extinguisher he managed to blow all the flaming ether round the lab setting paper/benches/lab books etc on fire. We did get things under control by first removing him from the lab.
    Funnily enough he still works at the University concerned – all of his former colleagues have however left.

  23. B says:

    @22: Regardless of the questionable chemical protocol and the choice to use ether, he shouldn’t have been allowed to run that reaction in the first place with a CO2 extinguisher as safety precaution.
    Anyone that works with alklai metals should know to have a Class D fire extinguisher ( or Sand nearby at the bare minimum!

  24. rhodium says:

    PCC is fine, but real men (i.e. idiots) make chromyl trifluoroacetate. Any time you decide you need to oxidize methylene chloride or the surface of polyethylene (or most anything that is not glass) it is one of the easiest to make go-to reagents.
    And @10, I think sluggo still checks in from time to time.

  25. Derek Lowe says:

    #14 – I can see that I’m going to have to standardize my aliases! Yep, same guy.
    #24 – I’ve used chromyl acetate, which was quite reactive enough, thanks all the same.

  26. Esa Tuunanen says:

    That “detached awareness” thinking is funny thing.
    Some years ago I was setting fence posts in the middle of field. While making one hole with digger bar and looking downward I saw flash of light reflecting from ground and grass.
    After first “WTF?” there was instant recognization that it had been lightning bolt…
    Followed automatically by “Missed, no danger” thought and automatic start for counting how far it was, which ended little after “one” to sharp crash of thunder.
    After that it took still five seconds to proceed to thinking maybe it would be best to head inside fast and let go of that metal object in hand.
    Probably not the most logical thoughts for such situation. But what can you do when you’re stormchaser with some re-wiring done in brains?
    Actually that bolt hit some 450m away (and got documented for “Attachment of natural lightning flashes to trees” study) and wasn’t really that close.
    And power line 50m away would have probably attracted it if it had been targeting closer general area.
    Was that after or before it became smoke-emitting diode?
    Though it’s really resistors which give nice white-grey “pope election” smoke signals.

  27. イッテルビウム says:

    In my school the phrase was ” Always add the acid to the water, not the water to your ass.”
    I never became a chemist, but that tidbit has stuck with me for almost 50 yrs now.

  28. dsm says:

    Detached awareness:
    Back in my days of trying to be a paleontologist, first time “in the field” learning the basics, sitting with friends on the Inferno Anticline having lunch.
    First thought: “Hm, that’s just what a rattlesnake sounds like on TV.”
    Second thought: “And I’m in Utah, better look down.”

  29. Tobi says:

    In my undergrad, during a placement in a polymer lab in South Africa, there was this microbiology student that was trying to make some money in her sparetime as a lab assistent in our lab.
    One lovely friday afternoon, after just having finished a flash column with diethylether, she felt it was time to leave soon…. So she whipped out the heatgun and thought it would be efficient to dry the silica, in the column, with a prolonged blast from the heatgun. Well, there was a blast but it wasn’t the heatgun. The column had shattered by the violently expanding gaseous ether, which luckaly for her didn’t ignite and the only piece of column that was still holding together was the tiny piece she was holding in her hand. She was extremely lucky in not getting perforated!

  30. Robert says:

    One in my high school experience. Student on the other side of the room ignored the teacher’s instruction that projects must ALWAYS be plugged into the big grey power supply (isolation transformer on the AC outlets), and NEVER into the bench-front soldering iron outlets. A big “BANG” got the attention of the whole class. The hot side of the 120 VAC went through the power switch of his project (how he was able to put everything together without a premature reaction), a diode (looked like popcorn), an SCR (front blown off it), and into the ground connection of the oscilloscope probe (which is connected to the safety ground).
    Note that this is a different moron from the guy who tossed aluminum slugs (from the chassis punch) into the ferric chloride etchant bath.

  31. navarro says:

    while i was getting my bachelor’s degree, which ended up being a double major in math and english, i ended up taking a lot of various science classes for elective credit. i almost got a minor in chemistry to add to my degree but organic turned out to be my great nemesis (i’ve never worked harder for an “f” in my life but that’s another story). anyway, i was taking advanced inorganic and in the lab portion we were assigned the synthesis of a metallocene. as luck would have it my partner and i drew cobaltocene and ended up being given the odd man in our class. our first prep was ruined when the plumbing in our building backed up into our reaction vessel. our second prep worked fine and my original partner and i were trying to decide if we needed to fill a bag with argon or if something less expensive would work when my partner started hyperventilating and then shouting. it turned out she had suddenly noticed that while we were going through references trying to figure out if the cobaltocene might react with carbon dioxide or nitrogen gas our add-on partner had taken the seal off of our vessel and dumped the contents into a petri dish which immediately glowed red and then white and cracked the dish for good measure. when we asked him whether he knew that cobaltocene was pyrophoric he told us “sure, but i didn’t know it was going to burn up as soon as i dumped it out.” it was almost too sadly funny to get mad about . . . almost. we got him moved over to the ferrocene group and tried again. this time things went well and we were able to put together enough product to try to characterize it. she managed to get a crystal through the x-ray and while it didn’t work out exactly right we knew we were close so we decided to run an ir on it. In the end we used the argon and i got a pretty good salt disc using a bag. then we bagged up the ir spectrometer and started to do a run. a group of grad students were next to us setting up a new high-performance liquid chromotography unit in the space next to us but we were staying out of each others’ way when all of a sudden there was a fire in the ir machine. about the same time i noticed that the guys next to us had accidentally cut our bag with the boxcutter they had been using and nobody was happy for a while. between the four of us we got the ir cleaned up and back in working order but we just didn’t have the heart, or the time, to do a fourth prep and ended up getting a d minus on that project. this all happened 30 years ago but i still occasionally do a google image search just to look at the pretty violet crystals of cobaltocene.

  32. Chris says:

    Our high school chemistry teacher was notoriously accident prone. One day he was showing us phosphorus, cut a small piece off the main chunk with his penknife and did [something I forget] with it. Went to cut another piece and he noticed a little bit left on the knife was starting to smoke. From then on events went with the insane logical inevitability of a Peter Sellers sketch – he burnt the little bit off on a handy Bunsen burner flame, went to cut another piece of P, which of course burst instantly into flames. With lightning reaction he shot the lot towards the bench sink, so fast it skated right over the sink and landed in flames on the floor, he grabbed the CO2 extinguisher and gave it a blast but of course each time he stopped it was still above ignition temperature and reignited. It took about six attempts to put it out, by which time the room was full of dense white smoke and we all had to feel our way out of the door. The whole science block was evacuated.
    We kids loved his lectures, they were always entertaining.

  33. stordoff says:

    Chris’ post reminds me a school demonstration reaction involving Bromine (or possibly a Bromine compound; I’m a little hazy on the details) that suddenly went awry, and the reaction started producing fairly sizeable clouds of a reddish-brown gas. In hindsight, the mystery gas between me and the only two exits from the room, plus the panicked look on my teacher’s face, probably should have been more concerning.

    AFAIK, it had no lasting effects, but my teacher did have brown stains on his fingers for the next few weeks if I recall correctly.

  34. Mike A says:

    A friend tells about the time another chemist in the Health Dept. lab dropped a small bottle (maybe 100ml) of BrCN on the floor. Everyone out of the 8-story building; then the guy who dropped it donned PPE, went back in, turned all the hood fans on and threw something (Na thiosulfate, I think) on the puddle. Nobody got so much as hurt, which was A Good Thing.

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