Compensation between activation entropy and enthalpy in reactions of aromatic hydrocarbons catalyzed by solid acids

Reaction rates of toluene disproportionation (A) and cumene cracking (B) normalized by the number of Brønsted acid sites were analyzed on aluminosilicates. The activation entropy showed linear and compensatory relationship against the activation enthalpy. The slope of entropy-enthalpy plot was in the order of (B)>(A)>small alkane cracking, whereas the intercept on the horizontal axis was in the order of propane and isobutane cracking>linear C4–8 alkanes and iso-pentane cracking>(A)>(B). The former is consistent with the bulkiness of reactant, while the latter is consistent with intrinsic difficulty of formation of intermediate cations.