ORBITAL-CONTROLLED REACTIONS CATALYZED BY ZEOLITES - ELECTROPHILIC ALKYLATION OF AROMATICS

The role of orbital control in product selectivity during electrophili c aromatic alkylation catalysed by zeolites was studied both theoretic ally and experimentally. In order to discuss this, the alkylation of t oluene and m-xylene by methanol was carried out on a series of large-p ore zeolites (HY). The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structural ly alike model clusters but containing different tetrahedral cations a round the active site. The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the cata lyst composition on the reactivity of the electrophilic reagent.