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Author: Subject: Vanillin Demethylation
Arsole
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[*] posted on 23-3-2012 at 19:44
Vanillin Demethylation


I have read that vanillin can be demethylated using (Pyridine or Triethylamine) and AlCl3 in DCM.

http://www.erowid.org/archive/rhodium/chemistry/methylenatio...

The site also describes a method using nitrobenzene and AlBr3.

Am I correct in saying that that the Nitrogen containing groups are being used as catalysts for the formation of MethylAlCl2 and the Protocatechualdehyde.

Would it be possible to use AlCl3 in the second reaction instead of AlBr3.

This reaction Mech. Is driving me nuts. It is a fridel-crafts reaction but I cannot straighten it out.

Thank you for the help.

[Edited on 3-24-2012 by Arsole]




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Nicodem
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[*] posted on 24-3-2012 at 04:47


Quote: Originally posted by Arsole  
Am I correct in saying that that the Nitrogen containing groups are being used as catalysts for the formation of MethylAlCl2 and the Protocatechualdehyde.

No, I don't think you are correct, because what you say does not make sense chemically. Do you have any references about MeAlCl<sub>2</sub> formation?
Quote:
This reaction Mech. Is driving me nuts. It is a fridel-crafts reaction but I cannot straighten it out.

No, it is not a Friedel-Crafts reaction. There is no C-alkylation or C-acylation of any aromatic system occurring, so I'm puzzled at how you came at such a conclusion.
The mechanism of demethylation of anisols was already discussed on the forum. It is just an SN2 substitution. Please UTFSE for more details and references.
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Would it be possible to use AlCl3 in the second reaction instead of AlBr3.

AlCl<sub>3</sub> is not AlBr<sub>3</sub>. That is kind of obvious already from its formula. What they have in common is their relatively similar acidity. However, their Pearson's hardness is different, the nucleophilicity of their halogenide part is quite different, and so is their solubility (though AlCl<sub>3</sub> is also soluble in nitrobenzene). So your question can only be answered by empirical data, though the only certainty is that the reaction kinetics would in any case differ significantly. I suggest you to do the most obvious thing to do, to read the full paper of the reference 2. Depending on the focus of the article, it might have information in this regard. Otherwise, you can always do a literature search or an experiment.
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Rich_Insane
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[*] posted on 24-3-2012 at 10:10


Not long ago, there was a patent speaking of O-demethylation using thiourea and AlCl3. There was also a thread here on Sciencemadness.

Here are the links: Process for Preparation of Phenolic Hydroxy-Substituted Compounds (Patent)

The thread: http://www.sciencemadness.org/talk/viewthread.php?tid=11607

They reported 81.4% yields with vanillin. There was also a Chinese publication about O-Demethylation... I think Google will yield the result by searching "O-demethylation".
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Arsole
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[*] posted on 25-3-2012 at 00:20


Rich - I had read that paper already and thought it was interesting. (That is how I stumbled upon these reactions). That post you are talking about is like fifty pages back in the form I read it a while ago when I first joined and spent a day reading all of the old posts lol.

Nicodem - Thank you for responding. I am only part way through my organic chem and and was just looking over Friedel-Crafts.

When you are just starting out and all you have is a hammer everything looks like a nail I guess.

I will do some more reading. I sat down for about 2 hours one night and could not figure out the reaction mechanism. It was driving me nuts so I posted looking for some tips.

Was this the right area to post in or does something like this go into beginnings?

Thank you for the quick response.

I just found the reaction mechanism for Pyridine and HCl (Really that simple?). In this reaction does AlCl3 react the same way as HCl does.

What is the purpose of the pyridine/Triethylamine? Certainly more that solvent?

[Edited on 3-25-2012 by Arsole]




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Rich_Insane
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[*] posted on 27-3-2012 at 11:28


I'm no expert, but I think pyridine will accept the methyl group to form methyl pyridinium.
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niertap
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[*] posted on 2-4-2012 at 04:40


Have you considered going balls to the wall and microwaving an aqueous solution for a min or 2? The microwaves apparently break aromatic methyl esters really easily and quickly.



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Nicodem
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[*] posted on 2-4-2012 at 06:23


Quote: Originally posted by niertap  
Have you considered going balls to the wall and microwaving an aqueous solution for a min or 2? The microwaves apparently break aromatic methyl esters really easily and quickly.

Whenever you propose something that makes no apparent sense, you are expected to give the reference! It's called science, you know. For example, it makes no sense that I actually have to point to this as a necessity, when already the title of this forum is Sciencemadness and says it all. Consequently, I have to refer you to the forum posting guidelines.

Besides, vanillin is not even an ester.
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Arsole
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[*] posted on 3-4-2012 at 19:48


I guess I will have to do an experiment and find out.

Producing the triethylamine may be a little tricky although still possible unlike the pyridine <--- (for me anyway).

I have read the AlCl3 threads and it should be fairly straight forward to produce a few grams using the hot method.

I have already extracted DCM from stripper.

I was planning on EtOH ---> NaBr/H2SO4 ---> Ethylbromide ---> NH3(g) ---> Triethylamine (Mono, Di also) ---> Fractional distillation (Boiling Points suggest it is quite possible)

Any other suggestions.

I could just buy the TEA however I would learn mountains working through it's synthesis.

Nitrobenzene is a fairly straightforward. Thank you Myst32YT

I do not however, feel safe in producing AlBr3 (at least not yet).




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