Kinetics of Cycloaddition of CO ₂ to Ethylene Oxide in Ionic Liquids: A Conceptual Density Functional Theory Approach

We briefly discuss herein the molecular mechanism for the cycloaddition of CO₂ to ethylene oxide in a wide variety of ionic liquids (ILs) that include classical ILs based on ammonium, imidazolium, and pyridinium cations and combinations that incorporate (poly)-nuclear ILs as well as ILs based on inorganic complexes. We show that even with strong structural differences, all five cases examined share a common activation step characterized by the formation of a precursor complex followed by its activation toward a common rate-determining-step transition state structure. We additionally show that all these cases can nicely be described within a common quantum mechanical model based on the conceptual density functional theory. It is found that the dominating effect of the activation hardness, Δη^‡, drives the intrinsic reaction barrier in all five cases examined, a result that seems to be governed by the maximum hardness principle, an empirical rule that appears to still remain valid for its application in the chemistry in complex liquids: a promising and stimulating result.