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Things I Won't Work With

Things I Won’t Work With: Straight Dimethyl Zinc

Organometallic reagentss come from large tribes, and there are always wild cousins up in the hills. A good place to look for the livelier ones is in the simplest alkyl derivatives, and you should go all the way down to the methyls if you want to know their real character. Ignore the halides. Methylmagnesium bromide you can get in multiliter kegs; they might as well sell it in Pottery Barn.
Dimethylmagnesium, though, is not an article of commerce. I’ve made it myself. So although it’s definitely something you want to keep an eye on, I can’t very well say that I won’t work with it. And the other metals? Dimethyl mercury I will not get within yards of, for very well-founded reasons. Trimethylaluminum is a flamethrower extraordinaire, with a solid reputation among pyromaniacs. I’ve used the stuff, although I wasn’t whistling while I was syringing it out. Handling it in solution, as I did, is less stressful than using the pure stuff – I’d definitely want to sit down and think about that one.
But neat dimethyl zinc. . .no, I don’t think so. A colleague of mine made some in graduate school, and came down the hall to us looking rather pale. He’d disconnected a length of rubber tubing from his distillation apparatus and seen it go up in immediate, vigorous flames. “This stuff makes t-butyllithium look like dishwater” is the statement I remember from that evening. You can buy the pure stuff from Alfa, if you’re inclined to run a head-to-head comparison. Do make sure to post the video on YouTube; that’s as close as I want to get.
One problem is that it’s a pretty volatile compound, boiling at 46C, so there’s plenty of vapor around to start a party. The diethyl analog is a bit better, but it’s nearly as pyrophoric. The Library of Congress discovered this in the 1980s and 1990s, during a long-running project to deacidify old documents. The diethyl zinc reacts with the acid in aged wood-pulp papers, neutralizing it, lightening the color, and stiffening the paper, so you’d think it would be ideal. Well, except for the instant-bursting-into-ravenous-flames part. Making sure that all the reagent was gone before opening the hatch, that was rather important. The pilot plant for this process suffered from some regrettable explosive bonfires before the whole idea was abandoned. Interestingly, one of the biggest problems seems to have been that the treated books were (at least at first) rather odorous, and some colored book covers were initially affected. You can sense a certain testiness about these issues in the Library’s final report on the subject:

It has also been established that tight or loose packing of books; the amount of alkaline reserve; reactions of DEZ with degradation products, unknown paper chemicals and adhesives; phases of the moon and the positions of various planets and constellations do not have any influence on the observed adverse effects of DEZ treatment.

You’ll notice that the LOC didn’t even bother with the dimethyl compound, and I think I’ll take a tip from them.

36 comments on “Things I Won’t Work With: Straight Dimethyl Zinc”

  1. RB Woodweird says:

    So it was that two such graduate students, both new to the game, stood together in the third-floor laboratory of Professor William Stringfellow, nervously eyeing an innocuous silvery canister. Neil Coit, a pudgy, shaggy-haired young man, was sweating much more than the temperature of the room demanded. He looked beseechingly at Jen Perrelli. She shrugged her shoulders. They had entered grad school together, last fall, and had independently cast their lot with Stringfellow. They had been assigned hoods in this lab, one of three small contiguous rooms in which the group worked, and they had each begun a small project related to Stringfellow’s palladium research, in which divalent palladium complexes were used to prepare otherwise inaccessible crowded carbons by insertion of metal-bound ligands into unactivated carbon-hydrogen bonds.
    They were hoping to use their preliminary results and their growing command of the chemistry to work on total syntheses of some of the natural products that their mentor had targeted, beautiful structures with exotic names like teleocidin B-4, neomangicol A and B, and combretastatin A-4. Instead, their boss had come into the lab bearing the silver can now resting on Neil’s benchtop and informed them that they were the vanguard of a glorious new chapter in the group’s storied history, for they were the shocktroops, the pioneers of the shining future of the preparation and synthetic uses of molybdenum ligand Mo(�2-C70)(CO)3(dppe) and its fellows. He had then plopped the canister down and departed, leaving the two to reset their calendars.
    They had gone to the library and dutifully investigated the synthesis of molybdenum ligands. What they had found was that they all sprang from the common precursor molybdenum hexacarbonyl, and molybdenum hexacarbonyl was profoundly toxic. Now, this should not have concerned either of them, for they had some experience with the safe manipulations of toxic chemicals. And they had hoods and gloves and goggles and aprons whenever they felt the need to don the same. Both had worked with cyanide and phosphine and hydrogen sulfide, all in their own right probably more deadly than molybdenum hexacarbonyl or any or its liganded relatives. Plus, many of the reactions which led from the hexacarbonyl to the various derivatives had to be done under argon, in air-tight glassware which itself furnished a primary safety barrier.
    What had spooked them was an article in an old Chemical and Engineering News that Jen had found while cleaning up a huge rotting pile of old magazines in the grad students lounge. When she read it, she got chills. When she gave it to Neil to read, he was pale for an hour.
    Sometime in August 1996, Karen Wetterhahn, a professor of chemistry at Dartmouth, was preparing a standard sample for an NMR. The standard was dimethylmercury. Already an international authority on the carcinogenicity of chromium, Professor Wetterhahn was undertaking the study of how organomercury compounds do their damage to cells and tissues. One warm New Hampshire day she put on latex gloves as usual – as everyone who worked with such compounds did – and in the protection of the hood prepared to transfer a minute amount of the liquid dimethylmercury into an NMR tube with a pipet. Jen and Neil had done this same operation a thousand times, minus the mercury. The NMR tube is as thin as a drinking straw. The pipet is fitted with a rubber bulb, and the airspace above the liquid is so large that liquids that are dense or have a low surface tension tend to run out the narrow tip of the pipet with little provocation. There should be a better way to do it, but the operator becomes comfortable with his tools, even flawed tools. Often drops of the liquid rush out, missing the NMR tube altogether. Unfortunately, the dimethylmercury was both dense and of low enough surface tension that a drop or two missed the tube and landed on Professor Wetterhahn’s gloved hand. She saw this, but was not overly concerned. Latex gloves were the accepted protection. She removed the gloves and disposed of them properly. If she was like Jen or Neil, she probably went promptly to the sink and washed her hands with plenty of soap just to be safe.
    Five months later, she began to slur her words. She stumbled on level ground and was having attacks of severe abdominal pain. It was her field of expertise, so she may have suspected the truth. Hospital tests showed that she had 80 times the lethal dose of mercury in her body. The drop of organomercury had penetrated her gloves and skin like a shot. Latex had been no protection – it was a scientific urban legend that it was a barrier at all. Just 22 days after the first symptoms, her eyes gave out, her ears quit working, and she could not make a sound. She died four months later without waking from her coma. She left a husband and two small children. Karen Wetterhahn was only 48.
    The moral of the story was too clear. Something you had dealt with safely for years could rise up and bite your ass off. Now the two had the silver canister in the lab, shining its evil and distorted vertical fisheye reflections of them like they were already trapped within its demonic grasp. It was a monolith, silent, dominant. Was this the one? Would they read the MSDS and follow all the rules, pull on nitrile gloves, slip goggles over their eyes, snap open the glass ampoule inside of a glovebag inside of a hood, never touching the stuff without layers of glass and plastic between them, only to find out in a month, a year, a decade that – oops, sorry: we were wrong. Our bad. Turns out that molybdenum hexacarbonyl seeps through those old things you were using. You should have been wearing Teflon gloves covered with stainless steel mittens. Hey, who knew? Too bad about the aggressively inoperable tumors, the paralysis, the dementia, the blindness. Told you to go to law school.
    But the culture of chemistry, in which Jen and Neil were being steeped, did not permit hesitation. Reasonable precaution, sure, but timidity was for the other eighty-five out of a hundred. Open the bottle! Run the reaction! Just do it! was the message, no matter how many safety seminars the University made them sit through. Results were the object, and results came from experimentation, and experimentation implied the running of reasonable risks. So Neil knew he would get out his can opener and cut open the cylinder, because he did not want to be seen by his peers – and especially Stringfellow – as less than gung-ho in all respects. And Jen would snap the vial, inside a glove bag inside a hood, because she would feel the need to prove to the male-dominated faculty and the male-dominated graduate students that lack of balls did not mean she lacked balls.

  2. Atom Recession says:

    One great use of dimethyl zinc: Take it into the glovebox and unseal the container. Judge the dryness of your box by the volume of smoke evolved from the bottle. Even the most rigorously dessicated boxes will produce some smoke!

  3. Canuck Chemist says:

    I wish I could have witnessed it, but one of my old grad. school colleagues told me a tale of a plugged glass syringe containing dimethylzinc (can’t remember if it was neat or not). The solution to the problem, which actually would seem to be generally useful for cowboy chemistry, involved tying a hammer to some rope, fishing it over the monkey bars and under the fume hood sash, and dropping the hammer on the syringe with a tug of the rope. Cool to watch the fireball while safely behind the plexiglass…

  4. JAB says:

    I always wondered what happened to that Library of Congress project. They were supposed to put it here at Ft. Detrick…….

  5. Milo says:

    I used to work for a company that produced trimethylaluminum. The safety demonstration always included someone squiting a 1/2 ml sample of the stuff (neat no less!) in to a steel pail. Fun stuff indeed.

  6. Luke Weston says:

    A video of interest:
    Yes, it’s diethyl zinc, and not dimethyl, unfortunately.

  7. Philip says:

    I suspect that RB Woodweird owes an atribution unless he is, in fact, the real S. A. Scoggin.
    I will admit that I was quite spooked by the death of Professor Wetterhahn. Things that go boom with a ball of flame are sissy stuff compared to things that destroy your brain months later.

  8. Rhenium says:

    Excellent and entertaining post. 🙂

  9. Anonymous says:

    I once witnessed the evacuation of an entire chemistry building for several hours because a bottle (Not-So-Sure Seal) of neat diethyl zinc developed a crack in the glass while a grad student was cannulating it into an airfree flask. The fire department and the hazmat folks wanted nothing to do with that. The situation was finally resolved when someone manned up and went inside to finish the cannulation. I won’t mention any names or places–to protect the innocent and the guilty.
    Scary stuff. And a strong second to Derek’s point. Use the toluene solution — much safer.

  10. Greg Hlatky says:

    Polyolefin catalysts use triethylaluminum as activators. A plant engineer told me that they used neat TEA in the commercial process instead of a (non-pyrophoric) solution; much easier to handle, he said but did not elaborate. Presumably he wasn’t changing cylindars or purging lines.

  11. Anonymous says:

    What is the passage from the first post from?

  12. Arjun says:

    As Atom alludes to, cracking open a vial of diethyl zinc and looking for smoke is somewhat of a standard procedure for assessing the quality of your glovebox atmosphere. Diluting the reagent into a more volatile solvent actually increases the sensitivity of the test.
    And yes, it *is* possible to get your box into a condition where diethyl zinc will not smoke.

  13. Nick K says:

    Back in the 1850’s Edward Frankland made dimethyl and diethylzinc, and thus made some important deductions about valency. How the hell he did it without incinerating himself I don’t know. Trialkylboranes are equally pyrophoric, burning with a brilliant green flame. A possibly apocryphal story I heard at Imperial College was that the only way of disposing safely of these materials was to throw them off the roof of the Chemistry Building. Apparently the resulting sheets of green fire were extremely spectacular.

  14. milkshake says:

    Me3Al in toluene 1M soln is pretty tame stuff. (It is a great reagent for direct aminolysis of simple esters with amines). Pyrophoric stuff that always self-ignites at the tip of needle bothers me lot less than stuff that is supposed to be well-behaved, such as LAH or NaH except that sometimes it does not – when one gets a wrong batch that bursts in flames as soon as you open the can. Putting out 100g can flaming on the bench right next to your balances is no picnic.

  15. processchemist says:

    @ milkshake
    I completely agree, having experienced the self ignition of a 100 g closed bag of NaH 99% in my hands (probably caused by a minor damage to the bag).
    Two major lab accidents I witnessed were caused by small quantities of ether.

  16. RB Woodweird says:

    Philip: An oversight. I have blanket permission to extract S.A.’s material, but here is the attribution in the form of a link:
    Coming soon to Amazon for your prebound pleasure.

  17. CMCguy says:

    So after DEZ adventure at LOC did they come up with something else to accomplish this task of deacidification? Or as JAB implies did they make it someone else’s problem? (BTW wasn’t Ft Detrick a former ChemWarfare testing site?)
    As milkshake effectively notes it is frequently stuff one knows or think has control over than lead to biggest problems.

  18. Hap says:

    Ft. Detrick used to be an US offensive biowarfare site, and now it’s a biodefense site. I think it still has active BL-4 labs, for example. I don’t know if it was a chem warfare site as well.

  19. Sili says:

    Oh. Dimethylzink. I had the cannister of the diethyl standing the hood next to mine for months until the org student took it back (not even sure what we had it down for).
    Scary stuff about the Mercury. Of course the antivax nuts don’t care that in that case it is methyl and not ethyl – they’ll whine and shout about that and “antifreeze”, “formaldehyde” and “ground up babies” no matter what. Personally, I’d hope that I was in a state to kill myself if I was in that situation. Luckily I don’t have dependants.
    I hope nothing of interest was lost in those LOC experiments.
    :sighs: I wish I hadn’t turned out to be such a bad chemist.

  20. Anonymous says:

    Sili, ethylmercury is less toxic than methylmercury, and its elimination is complete; it doesn’t accumulate. That’s why thiomersal is an ethylmercury compound.

  21. chemist says:

    Among other hot stuff, I’ve used neat DIBAL. It came in a metal cylinder from Alfa or Morton Thiokol, I think. You could watch the viscous, clear liquid ooze down the tygon transfer tube to the SS needle adapter / needle. I never had any bad incidents. Despite being pyrophoric, I also don’t recall any flames shooting out of the syringe needle during cleanup. Just smoke and very slow ignition (which was deliberately, carefully allowed to make sure that most of the excess was consumed before proper quenching … and because it was neat to watch).

  22. Anonymous says:

    @ 2, 12 re: box testing.
    Often both TMA and DMZ are reacting with trace ether or other lewis basic ligands in your box atmosphere. If you use THF or DME with the catalyst open then you’ll “always” have some floating around, thus always some smoke from your TMA or whatever. I’ve been told (possibly apocryphal) that TEA and DEZ don’t have as many problems with “false positives” due to solvent.
    It is possible to have a DRY box. Just inconvenient. My group uses a TON of TMA and even though you get a little smoke it’s not bad to handle in the box. It’s also so volatile and reactive that you can just let the box purge for a while and the material finds a nice place to make alumina (e.g. the transfer pipette residue). No fires when you remove stuff from the antechamber. That’s much nicer than some other organometallics. . . .

  23. Syn-Thesis says:

    @ chemist: I’ve used neat DIBALH too, it’s rather tame but takes a lot of patience to handle, it’s so viscous. I used to clean the needles straight after using them with some acetone, but once I forgot and used water – BANG – sounded like a gunshot and made the needle fly through half the lab…
    Dimethylmercury: We were once forced to take stock of all our chemicals due to a new online inventory system, when two friends of mine decided it was time to properly clean out the fridges. They found, in the very back of an old fridge, a small bottle of 100 ml dimethylmercury.
    It was then when they decided that this fridge had to be someone else’s problem…

  24. Hap says:

    As long as nothing happens to the fridge – then it becomes everyone’s problem, whether they wanted it or not. Hope your (ex-)group has good life insurance.

  25. Sili says:

    Sorry, I got my rant on.
    I know that ethylmercury is harmless (relatively). But the anti-vaxxers insist on confusing it with methylHg in one of those cases where I’m really not sure Hanlon’s razor applies. I don’t know who to credit but when it comes to that subject I think this corollary fits better: “Any sufficiently advanced stupidity is indistinguishable from malice”.

  26. Hap says:

    I don’t think the stupidity is really very advanced at all. It’s still really stupid – it’s just persistent (because the people believe that falsehoods will be treated as truths if one only repeats them often enough. Since it works for presidents, I guess they figure it’ll work for them, too.)
    I guess I would prefer “Sufficiently repeated stupidity is indistinguishable from malice”. The lack of a disproof or unrefuted logical flaw would probably constitute suffiency.

  27. Jas says: is a nice demonstration of why diethylzinc is scary and dimethylzinc is freaking terrifying.

  28. Jose says:

    Jas- BBr3 (neat) is *way* spookier, FWIW.

  29. Marge says:

    Oh, this brings back memories of grad school!
    My thesis advisor told me to quantitatively transfer trimethylaluminum on a 1970’s-era glass high-vac line to methylate something (You can’t weigh AlMe3 out if the boss only allows solids in the glove box, so we used PV=nRT and an old-school mercury manometer to get the right amount.). I’d already put other groups on; he just wanted to complete the set with methyl.
    I refused to do it, and my thesis advisor was “not happy.” I’ve always been glad I stood my ground, though it cost me. Guess we all have to draw the line somewhere. For me, it volatile pyrophoric liquids and the potential for flying glass.

  30. AJB says:

    I’ve been reading “Ignition!” in my off-hours, and I just discovered a section that made my hair curl:
    “All sorts of efforts were being made, during the late 50’s, to increase propellant densities, and I was responsible (not purposely, but from being taken seriously when I didn’t expect to be) for one of the strangest.
    Phil Pomerantz, of BuWeps, wanted me to try dimethyl mercury, Hg(CH3)2, as a fuel. I suggested that it might be somewhat toxic and a bit dangerous to synthesize and handle, but he assured me that it was (a) very easy to put together, and (b) as harmless as mother’s milk. I was dubious, but told him that I’d see what I could do.
    I looked the stuff up, and discovered that, indeed, the synthesis was easy, but that it was extremely toxic, and a long way from harmless.
    As I had suffered from mercury poisoning on two previous occasions and didn’t care to take a chance on doing it again, I thought that it would be an excellent idea to have somebody else make the compound for me. So I phoned Rochester, and asked my contact man at Eastman-Kodak if they would make a hundred pounds of dimethyl mercury
    and ship it to NARTS.
    I heard a horrified gasp, and then a tightly controlled voice (I could hear the grinding of teeth beneath the words) informed me that if they were silly enough to synthesize that much dimethyl mercury, they would, in the process fog every square inch of photographic film in Rochester, and that, thank you just the same, Eastman was not interested. The receiver came down with a crash, and I sat back to consider the matter. An agonizing reappraisal seemed to be indicated.”
    Wow – a rocket fuel that would almost certainly kill everyone within 200 yards of a launch site. Great idea!

  31. MSU says:

    Dimethyl mercury?
    Are you nuts?
    Check the following URL.

  32. Hap says:

    That’s not the real problem with dimethylmercury – see the Wikipedia article about Professor Karen Wetterhahn.
    Volatile toxins that penetrate skin and have delayed action and no antidote are not a good idea for rocket propellants…or anything else, really.

  33. jthomas666 says:

    Back in the day when I was a chemistry major, I worked on a team for undergrad research credit. We were working on synthesizing liquid clathrates, and one of the things we were using in the synthesis was trimethyl aluminum.
    Our supervising professor had a meeting to review safety procedures–hoods, glove boxes, and the like. He liked to tell of the time that he was cleaning out some glassware from a hood and found a stoppered flask with a little water in the bottom. Then he removed the stopped and found out that the “water” was TMA.
    Someone asked what we should do if the glove box leaved while we were working w/ TMA; he just shrugged and replied, “Well, it’s just your time to go.”
    We ended up a most safety-conscious group.

  34. KShan81 says:

    Curious. I’m not in the industry, so no firsthand experience, but the NFPA-704 diagram for t-BuLi (3-3-4) and TMA (3-4-3) both make them more hazardous, in their own way, than DMZ (3-3-3). I’m guessing this is either an illustration of the problems inherent in classifying compounds with unique structures and behaviors in such rigid “it does this” categories, or simply one of those “it’s the government” things (to its credit, the HMIS rates DMZ a 3-4-3).

  35. Freek says:

    Cool post! I worked extensively with this stuff for the synthesis of II-VI semiconductor nanocrystals. Typically, to make MnSe we would dissolve manganese cyclohexanebuterate powder into tri-n-octylphosphine and then add this to Hexadecylamine at 310 oC. Into this hot fluid (while mixing), we’d directly inject dimethyl zinc. I never considered it a particularly dangerous thing to do, but then I am trained a physicist… 😉
    Oh, yeah: a good Ar-based glovebox with less than 1 ppm oxygen / water is a good idea.

  36. ARC says:

    For those looking for the Library of Congress report linked to and quoted in this entry, it’s now here:
    Note that the LOC dropped the DEZ deacidification process because the Texas company working on development decided to shut the pilot plant down.

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