CO2 atmosphere enables efficient catalytic hydration of ethylene oxide by ionic liquids/organic bases at low water/epoxide ratios

Abstract

The development of an efficient and low-cost strategy for the production of monoethylene glycol (MEG) through hydration of ethylene oxide (EO) at low H₂O/EO molar ratios is an important industrial challenge. We have established that by using CO₂ as the reaction atmosphere, hydration of EO can be achieved at a low H₂O/EO ratio of 1.5 : 1 along with high yields (88–94%) and selectivities (91–97%) of MEG catalyzed by binary catalysts of ionic liquids and organic bases. The results are significantly better than those of experiments conducted under an atmosphere of N₂. Isotope labeling experiments revealed that CO₂ had altered the reaction pathway and participated in the reaction, in which cycloaddition of EO with CO₂ occurred first followed by the hydrolysis of ethylene carbonate (EC) to generate MEG and recover CO₂. The ionic liquids and organic bases synergistically catalyzed the one-pot two-step reaction. DFT calculations confirmed that this route is more kinetically favorable compared to the pathway of direct epoxide hydration.