Abstract

Abstract 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 (Ea) 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 CO2.

Highlights

  • The results indicate that the order of halide

  • The order of halide anions activity varies depending upon the type of epoxide and second catalyst used for cycloaddition reaction [47,48,49,50]

  • This requires the use of a reaction solvent in order to vary the concentration of styrene oxide (SO), and these were selected from commonly used organic solvents such as toluene and polar aprotic solvents: N,Ndimethylformamide (DMF), acetonitrile (CH3CN) and propylene carbonate (PC) (Table 1)

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Summary

Introduction

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Materials and methods
Kinetic study of SC formation
Proposed reaction mechanism
Conclusions

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