Keras
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Diazomethane synthesis
Guys,
I was reading about the synthesis of azulene in Vogel’s book, and the method therein uses diazomethane to generate a carbene, which made me wonder
if anyone out here had any experience with producing this highly dangerous (but apparently handy) compound.
Found a very old message about someone selling specific kits, but that’s about all. Nothing on the Wiki.
Anyone?
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bnull
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I suggest you take a look at the corresponding entries in Bretherick's and EROS and the references therein first. A substance that explodes in contact with sharp points and calcium sulfate doesn't sound much fun; I'd take
phosgene over it any day.
Trimethylsilyldiazomethane is a safer substitute. It is also highly toxic, which makes me wonder what "safer" means in this context.
If you're interested in azulene, there's an alternative synthesis here: Azulene, Org. Synth. 1984, 62, 134 (DOI: 10.15227/orgsyn.062.0134).
Attachment: Azulene, Org. Synth. 1984, 62, 134.pdf (313kB)
This file has been downloaded 70 times
Edit: Just found a borrowable copy of Bretherick's 3rd edition (1985) at Internet Archive.
[Edited on 15-2-2025 by bnull]
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Keras
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Lol, it’s like in Vogel, where one step requires 4 L of bromobenzene. Yup, sure pal!  In this case, it’s 150 L of 10% HCl :p
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bnull
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There's also this 1977 review: V. B. Mochalin, Yu. N. Porshnev, Advances in the Chemistry of Azulene (https://ui.adsabs.harvard.edu/abs/1977RuCRv..46..530M/abstra...).
| Quote: | | The chief methods of preparation and the chemical properties of azulene hydrocarbons are described. Attention is paid mainly to the most recent
papers, not covered in previous reviews. Certain aspects of the application of azulene compounds are also considered. A list of 315
references is included. |
Good luck.
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Texium
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The fact that special glassware specifically for generating diazomethane exists to avoid spontaneous explosions should be an immediate sign that you
shouldn't mess with it. As the EROS entry that bnull linked mentioned, so much as contacting the rough surface of a ground glass joint can be enough
to set it off. A lab I used to work in had the special glassware used to make it (though I haven't used it). It has special smooth glass joints, and
if a piece gets so much as a superficial scratch on the inside, it's considered unusable.
Diazomethane is one of those reagents that is usually overkill, but always works. It'll methylate virtually anything you could possibly want
methylated. If it was safer to handle, it would probably see use a lot more often.
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Texium
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Thread Moved
15-2-2025 at 09:16 |
Keras
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Yeah, I’ve read about the clear glass joints. What I’m wondering is why the special glassware for diazomethane has to be, well, glassware. Since
the product is made at low temperature (~ 40 °C), wouldn't it be easier to use plastic vessels?
Also, isn't possible to use the diazomethane as it is produced, e.g. by adding the target molecule in the mix?
Also I’ve found this funny(?) entry about diazomethane…
[Edited on 15-2-2025 by Keras]
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bnull
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Quote: Originally posted by Keras  | | Yeah, I’ve read about the clear glass joints. What I’m wondering is why the special glassware for diazomethane has to be, well, glassware. Since
the product is made at low temperature (~ 40 °C), wouldn't it be easier to use plastic vessels? |
Glass is inert, plastics are not. Glass can be made very smooth, plastics cannot.
Read the review by Mochalin and Porshnev. There are safer and more interesting pathways that don't require diazomethane.
If you want to make and use diazomethane, it's none of my business. I'm not here to stop you. I'm thousands of miles away, anyway. 
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Keras
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I’m sure PTFE can be made super smooth too, but I suppose the opacity is a problem.
No, no, I don’t intend to. But I’m always interested at discussing weird reactants. TBH, I was planning to experiment methylations with Dimethyl
Carbonate or some other green reagents (dimethyl oxalate?). I’m not at all tempted to use iodomethane, let alone more dangerous reagents such as
dimethyl sulphate and diazomethane.
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bnull
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I have my doubts as to the smoothness of PTFE. It may be microscopically rough enough to trigger diazomethane decomposition.
In situ diazomethane... The side products may interfere with the reaction and lower the yield. It depends on the precursor. Or it may simply
blow up because it wants to. I'm still digesting the fact that calcium sulfate makes it explode.
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clearly_not_atara
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| Quote: | | Hey ScienceMadness, I'd like to cook a corncob. I heard that people often do this in the microwave, so I was planning to build a microwave using a
vacuum tube and a high-voltage transformer that I got from a sketchy Chinese warehouse. What's the safest way to do this? |
Just... um... like, maybe you could roast the corncob?
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numos
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Does anyone actually have firsthand experience of, for example, a scratch in glass actually leading to detonation? We use the stuff all the time in
our lab, generated as an ether solution and then pipetted into a reaction until the TLC shows completion.
Honestly, I think this is a case where abundant caution (appropriate) has led to a misunderstanding of the actual properties of the compound. I was
discussing this exact topic a few months ago with a colleague. Diazomethane is a high explosive gas, no doubt, and is easily set off by friction,
sparks, etc. Ground glass joints are incredibly easy to jostle while the apparatus is in action, potentially leading to friction, heat, whatever,
resulting in a detonation. The use of smooth glass prevents this.
Reports of apparatus exploding because of a scratch — how do you verify that? How do you know the table didn't shake, agitating the ground glass
joints? I think the smooth joints are an appropriate safeguard to avoid detonation, but I highly doubt the gas simply floating over a sharp edge
causes causes it to go off. I've never observed this to be the case, even when I pipetted solutions of it with a chipped pipette.
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Keras
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IMHO all the warnings and stuff apply to the pure product. As long as you keep it super diluted in ether, the risks must be minimal. As far as I’ve
read, the dangerous operation during the synthesis is the distillation. The rest is more or less ‘benign’.
As for PTFE isn’t it the molecule with the lowest friction coefficient? But yeah, it’s probably more difficult to control than glass, where you
can use light to mesure the roughness.
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bnull
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| Quote: Originally posted by numos | | Reports of apparatus exploding because of a scratch — how do you verify that? How do you know the table didn't shake, agitating the ground glass
joints? I think the smooth joints are an appropriate safeguard to avoid detonation, but I highly doubt the gas simply floating over a sharp edge
causes causes it to go off. I've never observed this to be the case, even when I pipetted solutions of it with a chipped pipette.
|
It is more a case where the causes are not as explicitly stated as they should be. Take these three facts: glass is a dielectric; electric charges
tend to accumulate on sharp points; diazomethane is not the most stable of reagents. Consider:
- scratches and ground joints have rough surfaces, which is to say that there are tiny sharp points. Whether you can see or not these
points is immaterial for you but very interesting for diazomethane;
- the presence of electric charges on the surface of glassware is unavoidable since glass is a dielectric. These charges dissipate
eventually, not instantly as in a conductor;
- the surface charges will accumulate on the region with tiny sharp points. Again, this is unavoidable;
- diazomethane doesn't need too much energy to decompose;
- we usually think of electrostatic discharge in terms of visible sparks or hundreds to thousands of volts, but it only means that there is a
transfer of charge between two unequally charged bodies. You can zap a MOSFET with 50 V or less, no sparks or other visible signs of a discharge being
present at all. Even so, it is damaged;
- diazomethane is not particularly stable (it is the least stable of the simple diazos, if I'm not mistaken). The energy given by charges
transferred from glass may be enough to trigger its decomposition. In diluted form, of course, the transfer of charge is more favorable from glass to
solvent molecules since there is a greater number of them in comparison to those of diazomethane, but that doesn't mean that the transfer to the
latter can't happen.
PTFE has the lowest friction coefficient and is an excellent dielectric, much better than glass.
One more thing: the risks mean probability, not absolute certainty. The longer the list of already satisfied conditions, the higher the probability of
a mishap. Playing with nitrosamines or radiation once will give you cancer? Most probably no. But do that for long enough...
Edit: Grammar.
[Edited on 17-2-2025 by bnull]
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Keras
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According to my data, glass is a better dielectric than PTFE by an order of magnitude circa. If we refer to the dielectric losses, measured as tan δ,
PTFE losses are 0.00028 @ 3 GHz (which is already extremely low), whereas the figure for fused quartz (there is no figure for borosilicate glass, but
extra ionic contents degrades the performance, obviously) is 0.00006 @ 3 GHz.
The only reason quartz is seldom used in RF is the difficulty – or impossibility – to etch and/or glue copper layers on glass. AFAIK, glass fibre
dipped in high quality resin is used. Pure glass is too brittle to be used, too.
I’m not sure these figures are relevant, though. They’re essentially used when HF fields exist. For electrostatic performance, I think they behave
pretty much the same.
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bnull
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Yep. My mistake. "Do not quote numbers from memory, they're most probably wrong."
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chempyre235
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| Quote: Originally posted by Keras | | But I’m always interested at discussing weird reactants. TBH, I was planning to experiment methylations with Dimethyl Carbonate or some other green
reagents (dimethyl oxalate?). I’m not at all tempted to use iodomethane, let alone more dangerous reagents such as dimethyl sulphate and
diazomethane. |
If you're looking at exotic methylating agents, you might look into diazirines. According to Wikipedia, they are much more stable than diazomethane
(activated by UV to form carbene radicals). If the info is accurate, they can be made from a suitable ketone.
Just a thought: if cyclopentanone was the starting ketone, fulvalene could be made. By using cyclopentanone and cyclopropanone, bicalicene could be
made. This odd hydrocarbon is noted for its polar nature.
If acetone was the starting ketone, perhaps tetramethyl ethylene could be made. Oxomalonic acid may yield the tetra-carboxylated ethylene. Methylated
cyclopropanes could be made from unsaturated hydrocarbons in this manner as well. Who knows? It could be a good substitute for iodomethyl zinc iodide
for cyclopropanations. The possibilities seem to be endless.
[Edited on 2/17/2025 by chempyre235]
[Edited on 2/18/2025 by chempyre235]
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Keras
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Thanks for the idea!
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