Thermodynamic and Catalytic Insights into Non-Reductive Transformation of CO₂ with Amines into Organic Urea Derivatives

Carbon dioxide (CO2) utilization as a carbonyl source is an attractive and promising approach to yielding value-added organic urea derivatives, which are currently produced with toxic reagents such as phosgene and carbon monoxide, along with the contribution to mitigating global warming. However, the direct intermolecular reaction between CO2 and amines into organic urea derivatives has thermodynamic limitations, and such obstacles need to be considered well in order to establish efficient reaction systems. Herein, this review describes the thermodynamic aspects for producing several organic urea compounds, viz., N,N'-dibutylurea, N,N'-di(tert-butyl)urea, 2-imidazolidinone (ethylene urea), N,N'-dimethyl-2-imidazolidinone, tetrahydro-2-pyrimidinone (propylene urea), and N,N'-diphenylurea, based on the results of computational calculations. Besides, a variety of the state-of-the-art reaction systems with/without catalyst for synthesizing such organic urea compounds operated under pressurized CO2 have been summarized and discussed to make not only advantages but also disadvantages clear. We have also overviewed the very recently reported approaches that employ alkylcarbamic acids as substrates and instead does not require external CO2. The thermodynamic and catalytic insights garnered here could be a fruitful guideline for fairly assessing each reaction system and further improving the efficiency of CO2 utilization as a carbonyl source.