THEORETICAL-MODEL OF THE N-PROPYLBENZENE FORMATION IN THE BENZENE ISOPROPYLATION OVER ZEOLITES - AN ANTI-MARKOVNIKOV-TYPE PROTON ADDITION PROMOTED BY THE STERIC EFFECT OF MFI AND MEL ZEOLITE CHANNELS

Proton-catalyzed bimolecular reaction of isopropylbenzene with benzene leading to n-propylbenzene was studied employing ab initio quantum ch emical calculations. The reaction complex was described by a complex o f protonated isopropylbenzene and the benzene molecule. Geometry optim izations were performed at the Hartree-Fock level of theory under two conditions: (i) full relaxation of the geometrical parameters, reflect ing the situation in nonrestricted reaction space; and (ii) imposing g eometrical constraints, representing the steric conditions at the chan nel intersection in zeolites of the MFI and MEL structural types. Comp utations on the fully relaxed complex of protonated isopropylbenzene a nd benzene showed that n-propylbenzene formation cannot be expected on catalysts with nonrestricted reaction space. Use of the constrained m odel verified existence of a reaction pathway leading to n-propylbenze ne formation, in agreement with the experimental observation.