Elder bees, please excuse my ramblings, you of course know all this - and this topic has been discused zillion times bee4 -i just want to somewhat summarize the known facts for the ones still unfamiliar. Comments,
please!There are basically three types of demethylating agents (all acidic, alkaline is also possible, but i'll leave that out):
- mineral acids (HBr, HCl, H2SO4)
- metal halides (AlBr3, FeCl3, etc)
- hydroclorides of organic bases (pyridinium*HCl, anilinium*HCl)
So.... 1st, eugenol unaturated side-chain is profoundly rich in electrons, thus, any Lewis or Broensted acid, xept the mildest ones like organic amine chlorhydrates, will do things to it.
I suggested use of aniline HCl earlier - which has been mentioned as a good demethylating agent for vanillin in one of old Russian textbooks. BTW, remember, those were the pre-microwave days!
OTOH, the side-chain of MVK (methyl vanillyl ketone) is very electron-poor (acidic) - so acids won't hurt it, but there's a major BUT: any Lewis-acidic metal chloride will serve as a Friedel-Crafts catalyst for it, providing an excellent "process for producing polymer" as they say it at USPatent database
That's actually the reason for low yields in FC-acetonylation (P2P via chloroacetone).
I don't know if mineral acids can serve in the same manner (Rh? Os?), but i do know ketones react with strong acids.
Vanillin. This one, once demethylated, will of course bee more of a problem to convert to the desired product. But the odds of successful demethylation are much higher, it seems to me.
1st, it
can bee demethylated w/H2SO4. There is a patent.... uh, lemme see....
I am awfully sorry to end my post so abruptly, but i just found something that definitely deserves a thread of it's own sorry.Antoncho