[poorstudent83]

I'm working with calixarenes and know that de-tert-butylation at the upper rim is achieved using AlCl3 and phenol in toluene. I have searched everywhere for a mechanism for this reaction and have been unsuccessful. I'm guessing that the toluene "accepts" the tert-butyl anion but am not sure what the role of phenol is. I have attached the reaction....any ideas would be greatly appreciated!

[kiwi]

Look at it this way; what's more electron-rich, phenol or toluene?

[poorstudent83]

Phenol is more electron rich...the OH group is electron donating compared to the toluene CH3 group.

[UnintentionalChaos]

Phenol is more electron rich...the OH group is electron donating compared to the toluene CH3 group.

Basically, you want to do the FC alkylation mechanism completely backwards. This reaction is always in equilibrium, which makes it sythetically challenged. An FC acylation on the other hand is irreversible and selective, giving it greater synthetic utility. Since phenol is more electron rich than the substrate you're removing the tert-butyl group from, it is preferentially alkylated.

Is dry HCl gas also a part of the reaction? Typically, the AlCl3 complexes with the Cl of the HCl, stripping electron density away from the proton. The moderately "naked" proton protonates the aromatic ring, and the tert-butyl cation is expelled to restore aromaticity. This is promptly trapped by phenol.

[poorstudent83]

No, HCl gas is not used in the reaction. I completely understand the mechanism of the reaction, but I'm just not sure what kicks it off, does that make any sense?!?!!

[UnintentionalChaos]

No, HCl gas is not used in the reaction. I completely understand the mechanism of the reaction, but I'm just not sure what kicks it off, does that make any sense?!?!!

I suspect that the phenol groups are acidic enough (with the electron-rich phenolate anion complexed to the AlCl3) to temporarily "donate" a proton for the reaction to proceed. Since it's in equilibrium, but the removal of the tert-butyl groups from the phenols is unfavorable, they will all gradually be shuffled off of your substrate.