This is from the same source that the preparation of 3,5-diMeO-4-OH-propenylbenzene, which i recently posted into Methods discourse - see Post 293193 (https://www.thevespiary.org/talk/index.php?topic=9755.msg29319300#msg29319300)
(Antoncho: "2,6-diMeO-4-allylphenol", Methods Discourse).
Edit: the original info comes from Patent US2516412 (http://l2.espacenet.com/dips/viewer?PN=US2516412&CY=gb&LG=en&DB=EPD)
I'm not sure if this hasn't been discussed bee4 - i just couldn't construct an accurate query on TFSE :) . But i think it hasn't since - why then no one ever thought of possibility of applying this to piperic acid?
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... What do you think?
One thing that confuses me is - AFAIK, Fehling's liquid is a Cu++/NH3 complex - which will certainly decompose at 100 C, with all ammonia going out of solution. What could they mean?
Antoncho