Alkylation of toluene with cyclohexene over phosphotungstic acid: A combined experimental and computational study

Abstract

Abstract C C bond formation between an aromatic ring and cyclohexene is of great importance for the preparation of bicyclic hydrocarbons. In this work, alkylation of toluene with cyclohexene over phosphotungstic acid (HPW) has been investigated using both experimental reaction kinetics and ab initio density functional theory (DFT) methods. Kinetic models for the formations of o-cyclohexyltoluene, m-cyclohexyltoluene and p-cyclohexyltoluene have been established and used to fit the experimental kinetic data. The reaction rate constants and apparent activation energies for the formation of the three products have been calculated and compared. Based on DFT calculation, the energy profiles with relevant equilibrium and transition states have been determined for the adsorption of reactants, formation & deprotonation of the metastable states and desorption of the products. A metastable state of an adsorbed arenium ion on HPW has been demonstrated. The rate constants (k) for the major elementary steps at different temperatures have been calculated using DFT data. The apparent rate constants are further determined theoretically based on kinetic analysis. Results show that the theoretical calculation fits well with experimental data, both of which have similar tendency changing with temperature. Combined experimental kinetic results and DFT calculations suggest that both the formation and deprotonation of the metastable state play key roles in affecting the product selectivity.