Chemistry for the Conversion of CO₂

Carbon dioxide is a sustainable C1 feedstock, although thermodynamics presents challenges for the conversion of CO₂ into value-added chemicals.  This presentation will give a brief overview of these challenges and the policy drivers for the transformation of CO₂ into industrially useful chemicals.  As a specific example, our work on the one-pot reaction of CO₂, aniline, and alcohols to aromatic carbamates will be emphasized.  This work utilizes high-throughput technologies to screen a large catalyst/ionic liquid parameter space. Our studies have revealed a number of new catalyst/IL systems for both the synthesis of diphenylurea from CO₂ and aniline and the first example of a one-pot synthesis of an aromatic carbamate from aniline, CO₂, and an alcohol. The catalyst systems are primarily based on Ni/ligand combinations. Data from batch-scale reproductions of selected high-throughput experiments suggest that carbamate yields are equilibrium-limited. Unfortunately, the ILs are not simply innocuous bystanders under the conditions employed (170 °C, 70 bar CO₂). Rather, the nature and amount of various ILs affect not only the primary product distribution, but also the extent and type of byproducts. These byproducts arise in general from an SN2 attack of aniline or the alcohol on an alkyl group of the IL.