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Austin543
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[*] posted on 28-7-2020 at 16:16
Pyrazine Synthesis?


A few months ago, I stumbled upon a paper that described some copper complexes that exhibit a wide range of fluorescent colors, almost all the colors in the rainbow in fact (https://pubs.acs.org/doi/abs/10.1021/ic0510359). However, one of the major ligands used is pyrazine or its derivatives. After doing some research I've realized that such a simple molecule is a lot harder to synthesize than I would've imagined.

I've come across quite a few syntheses, all of which have disadvantages. The first one starts with ethyl acetoacetate and it seems like the best method so far, however with many steps comes a reduced yield. I've posted the the pathway and the paper that it's from below. It forms dimethylpyrazine, but according to another source I found, KMnO4 can be used to oxidize the methyl groups yielding a carboxylic pyrazine (bottom of page 8). In that source they oxidized tetramethylpyrazine, but I don't see why it wouldn't do the same for the dimethyl version. From there you could do a decarboxylation similar to the common pyridine synthesis from niacin (pyridine-3-carboxylic acid).

Another route involves the gas phase reaction of ethylene diamine over a copper catalyst. They mention copper chromite which is easily prepared as shown by Doug's Lab, however it is a gas phase reaction, which makes the apparatus quite a bit more complicated. My idea for the apparatus would be passing ethylene diamine vapor over a bed of catalyst similar to how Nile Red made SiCl4, but who knows how that would turn out.

I also thought of doing a simple ring forming reaction similar to the dioxane synthesis from ethylene glycol. Using glyoxal and ethylene diamine, but it seems that it might make piperazine-2,3-diol among other things and sources are questionable.

Anyway, that's everything that I've come across regarding a piperazine synthesis and I wanted to hear your thoughts and see if any of you guys have tried to make it before or know a better method :)

pyrazine synthesis pathway.png - 32kB

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Pumukli
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[*] posted on 29-7-2020 at 00:32


I doubt if those two methyl groups would make a big difference as a ligand. Just do the synthesis and report what you find! :-)

Even if failed to luminesce the dimethyl-pyrazine synthesis in itself would be a worthy reading. I think no one attempted such a synth on science-madness so far.

I can see that it was your first post, so welcome in the group. We need more budding amateur organic chemists, especially the ambitious type. ;-)
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Σldritch
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[*] posted on 29-7-2020 at 02:43
2,5-dimethylpyrazine route


I had a great idea how to make 2,5-dimethylpyrazine. It may even be possible as a one pot mix and leave synthesis but im not sure if the acetone oxidation works in ammonia nor under what conditions the oxidation to pyrazine works. There should be a thread with more information on the acetone oxidation somewhere on the forum. As for the oxidation to pyrazine, copper is a pretty good air oxidation catalyst in aqeous solution, even oxidizing ammonia to nitrate. It may even be possible to cheap out on Copper Chloride by using it as a catalyst in step one with air. Workup should be a simple distillation i believe, unless the presence of byproducts does not make it foam horribly (it probably will).

[Edited on 29-7-2020 by Σldritch]

DimethylPyrazine.png - 4kB
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Austin543
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[*] posted on 29-7-2020 at 06:58



Quote:

I doubt if those two methyl groups would make a big difference as a ligand. Just do the synthesis and report what you find! :-)


Thats a good point! It seems like most of these syntheses give dimethyl or trimethyl pyrazine so hopefully skipping the oxidation step would work.


Quote:

I had a great idea how to make 2,5-dimethylpyrazine. It may even be possible as a one pot mix and leave synthesis but im not sure if the acetone oxidation works in ammonia nor under what conditions the oxidation to pyrazine works. There should be a thread with more information on the acetone oxidation somewhere on the forum. As for the oxidation to pyrazine, copper is a pretty good air oxidation catalyst in aqeous solution, even oxidizing ammonia to nitrate. It may even be possible to cheap out on Copper Chloride by using it as a catalyst in step one with air. Workup should be a simple distillation i believe, unless the presence of byproducts does not make it foam horribly (it probably will).


I did some research and found a french paper that describes what you're talking about with the aminoacetone but it says you'd also need to react it with a carbonyl compound in order to isolate the cyclized ring. If you used formaldehyde it seems like you'd get trimethylpyrazine, which hopefully wont affect florescence, but if it does I can try the permanganate oxidation step.

unknown.png - 21kB
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