Sciencemadness Discussion Board

Double bond ox. cleavage to aldehyde with CuO

underground - 17-1-2025 at 03:02

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]

Texium - 17-1-2025 at 06:54

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.

6dthjd1 - 17-1-2025 at 08:15

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?

Keras - 6-4-2025 at 23:11

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.

Boffis - 7-4-2025 at 09:53

@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.

Keras - 7-4-2025 at 22:04

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?

Texium - 8-4-2025 at 08:06

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.


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.

clearly_not_atara - 9-4-2025 at 09:34

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

dicyanin - 27-4-2025 at 21:13

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.

clearly_not_atara - 28-4-2025 at 16:25

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]

clearly_not_atara - 6-5-2025 at 15:30

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]

chempyre235 - 7-5-2025 at 10:30

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]