Antoncho previously wrote-up a Syringaldehyde prepn. via the oxidization of 3,5-dimethoxy-4-hydroxypropenylbenzene, using alkaline CuO: R-CH=CH-CH
3 + 4CuO
__> RCHO + CHO-CH3 + 2Cu
2O
Post 293365
(Antoncho: "Double bond ox. cleavage (to aldehyde) with CuO", Chemistry Discourse) taken from the
US Patent US2516412
(
http://l2.espacenet.com/dips/viewer?PN=US2516412&CY=gb&LG=en&DB=EPD)
3,5-dimethoxy-4-hydroxypropenylbenzene ... added to a cupric oxide mixture freshly prepared from ... copper sulfate, ... sodium hydroxide, and ... water and the resulting mixture is heated to boiling under reflux for eight hours
He asked: "why then no one ever thought of possibility of applying this to piperic acid?"
Maybe they have but it didn't work so they never bothered to report their results. It seems likely that people wouldn't report failures.
I would be worried about a Cannizzaro side-reaction under the alkaline conditions with piperonal reacting with the glyoxal (aka: ethanedial, CHO-CHO) which we should also expect to get from piperic acid.
So Piperic acid Oxn: R-CH=CH-CH=CH-COO2H + 8CuO __> R-CHO + CHO-CHO + CHO-COOH, (R- = 3,4-MD-phenyl-)
Possible Cannizzaro: R'-CHO + R"-CHO + H2O __> R'-CH2OH + R"-COOH (usual conditions 50% alkali).
eg. CHO-CHO + H2O __> HOCH2-COOH
or (for piperonal): R-CHO + R-CHO + H2O __> R-CH2OH + R-COOH
Could gylcollic acid, HOCH2-COOH then react with piperonal in an Aldol side reaction?
Aldol Rxn: R-CHO + HOCH2-CHO __> R-CH=C(OH)-CHO - H2O (usual conditions warm concn. alkali).
My questions are:
1) Do people think this oxidation Piperic acid is possible without the alkali? i.e. by filtering the CuO, produced from CuSO4 + NaOH, and then using that under neutral conditions. Or do you think that the reaction would then not go at all?
I suppose that those side reactions would be even more possible in the original reactions, given in Antoncho's post and the patent, so I suppose things should be OK.
2) Do people think that 8 hours would be too long for piperic acid?, given that piperic acid is much more soluble in aq. alkali than 3,5-dimethoxy-4-hydroxypropenylbenzene.
3) I can't understand the remark about Fehling's Solution made in the patent [Other alkaline copper oxidizing agents such as Fehling's Solution ... may be used with the same results.]. Finar (vol 1, 5e, p185) says: "Aldehydes reduce Fehling's Solution to red cuprous oxide. The aldehyde is oxidised to the corresponding acid." Any comments on that?
I didn't want to start a new thread but the previous one seems to be closed.