[shrikantvarma]

I have done demethylation of substituited methoxy benzene by using AlCl3/thiourea mixture (3:1) ratio
the process is working very well as compare to other reagents can anybody explain me what is role of thiorea in above combination?

[orgopete]

It's the nucleophile.

[moov]

Thiourea is acting like a weak nucleophile, just like a RSH, and attacking the CH3 group.
(Thiourea has two resonance forms as far as I know thiourea and isothiourea. The later has a positive charge on the sulfur atom, and a negative on one of the nitrogen atom.)

The reaction basically is AlCl3 -> electrons on oxygen of ether group
-> AlCl3 (-)-RO (+) CH3  ->  AlCl3 (-)-RO (+)  +  H4N2-C-S-CH3      ->  add HCL -> AlCl3 + ROH

[r_dengle]

Dear All,
I am trying demethylation using BBr3. substrate also contaion O-Bn, O- Bz, conjugated ester groups. I need an advice in this regard.

[orgopete]

I am trying demethylation using BBr3. substrate also contaion O-Bn, O- Bz, conjugated ester groups. I need an advice in this regard.

Although I would expect debenzylation to also occur, I don't know the selectivity. All reactions or virtually all reactions can be shown to have at least slightly different rates. If you simply attempt the dealkylation with one equivalent if BBr3, I would be surprised to find 50.0:50.0 ratio of deMe:deBn. (I would have thought debenzylation to be faster, but I do not have real knowledge or experience.)

[PhDoc]

BBr3 can be very brutal, and without knowing how sensitive your molecule is, I'd hesitate to offer any specific suggestions. You may find something useful by looking through a book on carbohydrate chemistry. Just about every demethylation procedure known has been through the hands of sugar chemists.

[zsinger]

Lennox,
I am a PhD student, but as you said, this is touchy stuff.  I've never tried to this.  Is there a good way to "de-methoxylate"?  If you are uncomfortable sharing on the forum, PM me, as I think you may be the only one with this knowledge?  Do you always end with an alcohol or can you end with just a hydrogen?
         Thanks,
            -Zack

[Benzene]

I was reading the patent: http://www.google.com/patents/EP1831144A2?cl=en

They are pretty broad (obviously  ) about the ratio of substrate to thiourea.

I assume the ratio of substrate to thiourea is 1:1
Is this correct?