Utilization of CO₂ via Catalysis in Ionic Liquids

Carbon dioxide, CO₂, is a molecule of intense current interest, as it is the primary chemical motor leading to the calamity of climate change. CO₂ is also a viable, sustainable, yet challenging C1 feedstock, and the preferred reagent over other C1 sources such as phosgene, COCl2, and CO. Fundamental catalytic studies for the development of CO₂ chemistry are needed for advancing chemical sustainability, which is particularly relevant where CO₂ can be used as a replacement for extremely toxic phosgene, which produces two equivalents of Cl-containing waste when used as a carbonylating agent. An industrially applicable target reaction is the production of an aromatic carbamate from CO₂, aniline, and an alcohol; related carbamates are potentially isocyanate precursors for the polyurethane industry. The only known CO₂-based catalysis relevant to this goal is the production of diphenylurea (DPU) from aniline and CO₂, which takes place with moderate yields in ionic liquids (ILs) and CsCO3 as catalyst. In order to investigate the potential of ILs in CO₂-utilization reactions, and to study a large variety of ILs systematically, we have initiated a program to screen with high-throughput technology a large parameter space of ILs and catalysts for the production of aromatic carbamates.Our studies have revealed a number of new catalyst/IL systems for the synthesis of diphenylurea or dibenzylurea from CO₂ and aniline or benzylamine, respectively. The nature and amount of various ILs affect not only the primary product distribution, but also the extent and type of byproducts. One system in particular shows higher turnovers for DPU than reported.This presentation will provide results based on data generated from a large array of catalyst/IL combinations, which will further elucidate the role of ILs in these reactions and which IL structural properties are most important.