We have studied the synthesis of five-membered cyclic carbonates through the cycloaddition
of CO2 to epoxides by using acyclic guanidinium salts. We have found that the cycloaddition
reactions proceed smoothly at ordinary temperatures and pressures and result in good
yields when acyclic guanidinium iodides are employed as catalysts. Both cation moiety
and anion moiety of the guanidinium salts play important roles in their catalytic
activity. It is essential to have active hydrogens on the cation moiety as well as
an iodide ion as the anion moiety so as to achieve good catalytic activity. Guanidinium
iodides with three or more active hydrogens give cyclic carbonates in high yields
in polar solvents such as 1-methylpyrrolidin-2-one, whereas the guanidinium iodides
with one or two active hydrogens show good catalytic activity in less polar solvents
such as 2-methyltetrahydrofuran.
Key words
CO
2
- guanidinium iodide - active hydrogen - cyclic carbonates - epoxides
