Utilization of CO₂ via Catalysis with Ionic Liquids

While carbon dioxide, CO₂, is the primary motor of climate change, it is also a viable, sustainable, yet challenging, C1 feedstock. One application of CO₂ which can positively impact chemical sustainability is via its displacement of phosgene. Two industrially important chemicals where CO₂ utilization can have a significant impact on sustainability are the production of aromatic carbamates, which may be potential precursors of isocyanates for the polyurethane industry, and the production of dimethylcarbonate (DMC).  The former can be synthesized from CO₂, aniline, and alcohols, while the latter results from the reaction of CO₂ with methanol.  In both cases, water is also formed, and a significant problem with these reactions is low, equilibrium-limited product yields.  As ionic liquids (ILs) have shown promise for enhancing CO₂ reactivity and have tunable hydrophilicities, we have initiated a program to screen with high-throughput technology a large variety of ILs and catalysts for the improved synthesis of aromatic carbamates and DMC from CO₂.  This presentation will discuss the current results from this program, including only the second example of a catalytic system for the synthesis of diphenylurea, an intermediate in aromatic carbamate formation, from CO₂ and aniline.  Additionally, our investigations have shown that ILs are not necessarily innocuous bystanders in these reactions, but they rather can be responsible for undesirable byproducts.