Mechanism of the side-chain alkylation of toluene with methanol

The side-chain alkylation of toluene with methanol has been studied experimentally and a detailed mechanism of the reaction has been investigated by using quantum chemistry. Experimental results have shown that this reaction proceeds consecutively; styrene is primarily formed by the reaction of toluene with formaldehyde produced by the dehydrogenation of methanol, followed by the hydrogenation of styrene to form ethylbenzene. The quantum chemical calculations have shown that the presence of a basic site is indispensable to the side-chain alkylation of toluene, whereas the benzene-ring alkylation of toluene takes place on an acidic site, in accordance with experiments. Furthermore, the calculations have indicated that specific configurations of acidic and basic sites with steric restrictions are required for the side-chain alkylation of toluene. This might explain the experimental results that alkali-cation-exchanged X and Y zeolites exhibit a higher activity for this alkylation compared to the other catalysts employed.