A kinetic study of Zn halide/TBAB-catalysed fixation of CO 2 with styrene oxide in propylene carbonate

Synthesis of styrene carbonate (SC) via the fixation of CO2 with styrene oxide (SO) has been investigated using a combination of zinc bromide (ZnBr2) and tetrabutylammonium halides (TBAX) as acid-base binary homogeneous catalysts. The combination of ZnBr2 and TBAB had a synergistic effect, which led to about 6-fold enhancement in the rate of SC formation as compared to using TBAB alone as a catalyst. Propylene carbonate (PC) was chosen as a green solvent for a comprehensive study of reaction kinetics. The reaction followed a first-order kinetics with respect to SO, CO2, and TBAB, whereas a fractional order was observed for the ZnBr2 when used in combination with the TBAB. Arrhenius and Eyring's expressions were applied to determine the kinetic and thermodynamic activation parameters, where activation energy (E-a) of 233 kJ mol(-1) was obtained for the SC formation over the temperature range of 90-120 degrees C. The thermodynamic analysis showed that positive values for enthalpy (Delta H-double dagger = 18.53 kJ mol(-1)), Gibbs free energy (Delta G(double dagger) = 79.74 kJ mol(-1)), whereas a negative entropy (Delta S-double dagger = -162.88 J mol(-1) K-1) was obtained. These thermodynamic parameters suggest that endergonic and kinetically controlled reactions were involved in the formation of SC from SO and CO2.