Metal-free protic ionic liquids as catalysts: High-yield synthesis of cyclic carbonates from CO2 without high pressure and temperature

A series of protic ionic liquids (PILs) were synthesized using inexpensive amine and acid materials, and their density, viscosity, and thermal properties were investigated. The PILs exhibited excellent CO2 absorption capacity and efficient catalytic activity for the coupling of epoxides and CO2, without the need for any metal catalyst and solvent. These reactions were carried out under mild conditions, including mild temperature, short reaction time, and ambient pressure. The thermal stability of all the PILs was found to be good at temperatures up to 373.2 K. The rate constants were determined as a function of reaction temperature in the range of 303.2-333.2 K, and the activation energy was calculated to be 92.6 kJ & sdot;mol-1. The kinetic equation for the synthesis of butylene carbonate catalyzed by [DMEDAH][Prop]/[DBUH]Br was also obtained. Furthermore, [DMEDAH][Prop]/[DBUH]Br maintained its efficient catalytic activity even after five cycles. A possible mechanism for the synthesis of cyclic carbonates from CO2 and epoxides was also proposed.