Kinetic and theoretical study of the effect of molecular sieve structure on the selectivity to propylbenzenes in alkylation of benzene with isopropyl alcohol

The alkylation of benzene with isopropyl alcohol was investigated over molecular sieves of different structural types and acidity by kinetic measurements and ab initio quantum chemical calculations. The formation of n-propylbenzene occurring via bimolecular transalkylation between isopropylbenzene and benzene is enhanced by the appropriate geometry of the reaction space and the acidity of molecular sieves, n-Propylbenzene was formed over medium and large pore molecular sieves with such inner channel architecture which enables the approach of isopropylbenzene and benzene to form the reaction complex. Mesoporous sieves of MCM-41 structure provided only isopropylbenzene with some amount of diisopropylbenzenes. For the fully relaxed complex consisting of protonated isopropylbenzene and benzene, the computations verified the transfer of propyl group from one benzene molecule to another forming again isopropylbenzene. When the geometrical conditions modelling the channel intersections of ZSM-5 and ZSM-11 structures were considered n-propylbenzene was formed. The anti-Markovnikov type of proton transfer from the arenium cation to the propene part of the complex is promoted by the steric constraints present in the channel intersections of ZSM-5 and ZSM-11 zeolites.