Disproportionation Mechanism of Alkylbenzenes lnduced by Aluminum Chloride-Hydrogen Chloride

The complex layer of C6H5R-AlCl3-HCl system was used repeatedly for the disproportionation reaction of alkylbenzene (EtPh and i-PrPh) by substituting the upper hydrocarbon layers with fresh alkylbenzene after each reaction. In the reaction at 2 C, the amount of disproportionate product decreased with each run and was negrigible after several reactions. However, the bubbling of HCl caused the complex layer to recover its initial activity (Fig.1). Reacting at highertemperatures (20-50 C), the products increased gradually with temperature and a decrease of the products was not observed with each reaction at 50 C (Figs.2 and3). During each reaction, the constituents of the complex layer were maintained constant at 2 C, but were changed slightly toward higher temperatures (Table 1). These results indicate that: (i) complex [1], postulated in our previous paper, did not initiate the reaction at 2 C without HCl (Eq.(2)) but (ii) the dissociation of complex [1] took place at higher temperatures and then the reaction proceeded without HCl along the Eq. (3) according to the "HSAB" rule.