REVERSIBLE DEALKYLATION OF PROTONATED TERT-BUTYLBENZENE - POSITION OF THE EQUILIBRIUM

tert-Butylbenzene (Id) is protonated in HF-TaF5, but in contrast with the behavior reported in HF-SbF5 or FSO3H-SbF5, it does not form any significant amount of tert-butyl cations (3) by dealkylation between -60 and -10 °C. A dealkylation-realkylation equilibrium is established under these conditions, as indicated by partial disproportionation to di-and tri-ferf-butylbenzene and benzene and by trapping 3 with CO, but the equilibrium is displaced virtually completely toward the alkylated material. Cation 3 prepared from tert-butyl chloride is stable in HF-TaF5 under these conditions. 1, 3, 5-Tri-tert-butylbenzene (5) is protonated in HF-TaF5-SO2 solutions with very little side reactions. Dealkylation of Id in HF-SbF5 or FSO3H-SbF5 is due to complete protonation of the dealkylation product benzene. The HF-TaF5 system has an acidity which is high enough to stabilize tert-butyl cations and protonate monoalkylbenzenes virtually completely, but which is not sufficient to protonate benzene completely. © 1979, American Chemical Society. All rights reserved.