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

Abstract

Abstract Synthesis of styrene carbonate (SC) via the fixation of CO 2 with styrene oxide (SO) has been investigated using a combination of zinc bromide (ZnBr 2 ) and tetrabutylammonium halides (TBAX) as acid-base binary homogeneous catalysts. The combination of ZnBr 2 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, CO 2 , and TBAB, whereas a fractional order was observed for the ZnBr 2 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 23.3 kJ mol −1 was obtained for the SC formation over the temperature range of 90-120°C. The thermodynamic analysis showed that positive values for enthalpy (ΔH ‡ = 18.53 kJ mol −1 ), Gibbs free energy (ΔG ‡ = 79.74 kJ mol −1 ), whereas a negative entropy (ΔS ‡ = –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 CO 2 .