Thermochemistry of ionic liquid-catalysed reactions. Isomerisation and transalkylation of tert-alkyl-benzenes. Are these systems ideal?

The chemical equilibrium of mutual interconversions of tert-alkyl-benzenes was studied in the temperature range (286 to 423) K using chloroaluminate ionic liquids as a catalyst. The knowledge of the activity coefficients is required in order to obtain the thermodynamic equilibrium constants Ka. A well established procedure, COSMO-RS, has been used to assess activity coefficients of the reaction participants in the liquid phase. Enthalpies of five reactions of isomerisation and transalkylation of tert-alkyl-benzenes were obtained from temperature dependences of the corresponding equilibrium constants in the liquid phase. For the sake of comparison, high-level ab initio calculations of the reaction participants have been performed using the Gaussian-03 program package. Absolute electronic energy values of the molecules have been obtained using B3LYP and G3MP2 level. Using these results enthalpies of reaction of isomerisation and transalkylation of tert-alkyl-benzenes in the liquid phase based on the first principles are found to be in good agreement with the data obtained from the thermochemical measurements.