underground
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Double bond ox. cleavage to aldehyde with CuO
From the patent US2516412A
https://patentimages.storage.googleapis.com/23/db/8f/1e3b03d...
| Quote: | EXAMPLE VII: Syringaldehyde from the isolated intermediate
Syringaldehyde may also be prepared by oxidizing the isolated 3,5-dimethoxy-4-hydroxypropenylbenzene of Example V with nitrobenzene in alkali or other
low potential oxidizing agents.
Thus 195 parts 3,5-dimethoxy-4-hydroxypropenylbenzene are added to a cupric oxide mixture freshly prepared from 1000 parts hydrated copper
sulfate, 660 parts sodium hydroxide, and 8000 parts of water and the resulting mixture is heated to boiling under reflux for eight hours. The
separated red cuprous oxide is filtered and washed with water. The alkaline filtrate and washings are acidified and extracted with ether. Bisulfite
purification of the ether extract should yield approximately 155 parts or 90% syringaldehyde.
Other alkaline copper oxidizing agents such as Fehling's Solution, Benedict’s Solution, may be used with the same results.
An alkaline copper oxidizing agent is particularly advantageous for replacing the propenyl group with the aldehyde group because the strength
of its action in changing from a cupric to a cuprous compound is definitely adequate to oxidize to the aldehyde, and at the same time insufficient to
continue the oxidation to the acid further or to destruction.
However, in large scale operation, it will be obvious that oxidizing agents having no such automatic action may be employed for reasons of economy,
and the extent of the reaction controlled by controlling the amount of the reagent. |
So if Cuo is able to ox. cleavage 3,5-dimethoxy-4-hydroxypropenylbenzene to syringaldehyde, i do not see the reason why it wont work with other
propenyl group. For example:
styrene-->benzaldehyde
cinnamic acid-->benzaldehyde
piperic acid-->piperonal
3bromocinnamic acid-->3bromobenzaldehyde
2hydroxy cinnamic acid-->salicylaldehyde
and so on
The procedure looks super simple and high yielding
[Edited on 17-1-2025 by underground]
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Texium
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Sounds nice, but patents can sometimes be complete bunk, so you’ll have to try it out to see if it actually works. I’d suspect that freshly
prepared CuO is essential, so if you try it, prepare it the way they described, don’t just use CuO off the shelf, as it probably won’t have the
same activity, just as freshly prepared MnO2 can do a lot more than junk from a pottery store.
There’s a couple other reasons the reaction may not be so general, though. The electron donating groups on the syringaldehyde precursor might also
help to activate the alkene for oxidation, so it may be that it will work on electron rich aromatics only. The propenyl double bond is also going to
be easier to oxidize than the one in a cinnamic acid. So while the molecules you list are superficially similar in structure, there’s a decent
chance they won’t react the same way. Still, it wouldn’t hurt to try.
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6dthjd1
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Quote: Originally posted by Texium  | Sounds nice, but patents can sometimes be complete bunk, so you’ll have to try it out to see if it actually works. I’d suspect that freshly
prepared CuO is essential, so if you try it, prepare it the way they described, don’t just use CuO off the shelf, as it probably won’t have the
same activity, just as freshly prepared MnO2 can do a lot more than junk from a pottery store.
There’s a couple other reasons the reaction may not be so general, though. The electron donating groups on the syringaldehyde precursor might also
help to activate the alkene for oxidation, so it may be that it will work on electron rich aromatics only. The propenyl double bond is also going to
be easier to oxidize than the one in a cinnamic acid. So while the molecules you list are superficially similar in structure, there’s a decent
chance they won’t react the same way. Still, it wouldn’t hurt to try. |
What could underlie the activity present in freshly prepared CuO?
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Keras
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| Quote: Originally posted by Texium | | Sounds nice, but patents can sometimes be complete bunk, so you’ll have to try it out to see if it actually works. |
Did you? I was looking for a convenient way to produce o-nitrobenzaldehyde (to make indigo), and one of the way would be nitration of styrene followed
by mild oxidation of the double bond.
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Boffis
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@Keras, does styrene nitrate in the 2 position of the benzene ring? Do you have a reference for this?
As far as the original posters question goes I doubt you will oxidise piperic acid or cinnamic acid with such mild reagents. My experience is that
they are fairly tough even with permanganate, periodate etc.
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Keras
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That’s what the Wikipedia article on 2-nitrobenzaldehyde suggests, yes: ‘Synthesis begins by nitration of styrene followed by oxidation of the
2-nitrostyrene…’
Of course I could probably use an Étard reaction of 2-nitrotoluene. But I’d like to avoid chromium as best I can. Yesterday I tried oxidising
toluene with a mixture of Oxone and table salt. This works fine for converting alcohols to aldehydes, but didn’t work in that case (maybe I ended up
with benzyl chloride, since Oxone and salt give off elemental chlorine. The toluene layer took a strong yellow tinge that faded after one hour or two,
but no smell of almonds.) Likewise I tried sodium chlorate in water as an oxidant, but that was inconclusive. Maybe I should’ve heated the solution
to toluene reflux. In any case, it didn’t work.
Now Oxone would probably epoxidise styrene, but I am at a loss to follow up to aldehyde. Ozonolysis is another path, but I have no ozone generator.
Manganese dioxide apparently could work from toluene, but I’m not sure mine is active enough. Bleach and nitrotoluene?
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Texium
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| Quote: Originally posted by Keras | | Quote: Originally posted by Texium | | Sounds nice, but patents can sometimes be complete bunk, so you’ll have to try it out to see if it actually works.
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Did you? I was looking for a convenient way to produce o-nitrobenzaldehyde (to make indigo), and one of the way would be nitration of styrene followed
by mild oxidation of the double bond. |
I never said I would try it.
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clearly_not_atara
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| Quote: | | So if Cuo is able to ox. cleavage 3,5-dimethoxy-4-hydroxypropenylbenzene to syringaldehyde, i do not see the reason why it wont work with other
propenyl group. |
It works only because of the resonance structure though. The para-hydroxy styrene moiety can isomerize to a quinoid thingy
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dicyanin
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| Quote: Originally posted by Texium | | Sounds nice, but patents can sometimes be complete bunk, so you’ll have to try it out to see if it actually works. |
I suspect the reaction will likely be limited to those substrates that form water-soluble salts in alkaline medium: the phenolic propenylbenzenes, the
cinnamic acids and piperic acid.
sic transit gloria mundi
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clearly_not_atara
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If it works on piperic acid that would be interesting. That's a big "if" though. Chromic acid worked on anisole but was too aggressive for piperic
acid (the rxn was not optimized). There are a couple of other soluble alkoxyphenylalkenes out there, too.
[Edited on 29-4-2025 by clearly_not_atara]
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clearly_not_atara
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Update: I found another paper in which, inter alia, various styrenes are cleaved to benzaldehyes without a phenol group, using a Cu2+ catalyst under
blue visible light:
https://pubs.rsc.org/en/content/articlelanding/2022/qo/d2qo0...
The Supporting Information is free and indicates that both benzaldehyde and p-anisaldehyde were successfully prepared by this method.
So maybe the OP method will work on piperic acid?
[Edited on 7-5-2025 by clearly_not_atara]
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chempyre235
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According to the article's abstract (the article itself is behind a paywall), this reaction involves a Cu2+-Cl-O cluster
[Cu4OCl6]. How is this cluster prepared? Or is it generated in situ?
[Edit]: Never mind. I found the supplementary packet. It is in situ. CuCl2 and water form the cluster. There seems to be a
catalytic amount of LiCl in most of the reactions, too. Interestingly, it looks like this reaction may be useful for more than styrenes.
[Edited on 5/7/2025 by chempyre235]
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