For conversion of styrene oxide to styrene carbonate, high
reaction temperature, long reaction time, high CO2 pressure, and/
or solvent were required to obtain satisfied styrene carbonate yield
due to the less reactivity of b-carbon atom compared with
propylene oxide and ethylene oxide. Recently, Arai et al. found that
the catalyst system comprised of ZnBr2 and an ionic liquid [C4-
mim]Cl, could afford 93% yield with 100% selectivity for styrene
carbonate at 353 K for 1 h [102] instead of the lower activity for
ZnBr2 and [C4-mim]Cl. They also found that the type of metal
cations in metal halides which acted as co-catalyst had strong
effect on the carbonate yield. The type of anion as well as the length
of alkyl chain on the imidazolium cation had strong effects on the
conversion and selectivity. Besides, the [C4-mim]Cl/ZnBr2 ratio
also affected the carbonate yield.