Reactivity descriptors and rate constants for electrophilic aromatic substitution: Acid zeolite catalyzed methylation of benzene and toluene

The acid zeolite catalyzed methylation of benzene and toluene with methanol to form toluene and ortho-, meta, or para-xylene is investigated at the B3LYP/6-31G* level of calculation with a T4 cluster representing the zeolite. After geometry optimization of reactants, transition states and products, reaction rate constants, entropy of activation. activation hardness, and local hardness are calculated and used to model the reactions. In general, the ortho and para products are favored over the meta and nonsubstituted products. Through calculation of rate constants and entropy of activation comparison between different reaction mechanisms has been carried out, indicating that the direct and consecutive mechanisms are competitive at higher temperature. The activation hardness correlates well with the activation energy and local hardness is a good parameter for describing intermolecular reactivity in charge controlled reactions.