Thermodynamics and catalysis: Non-reductive conversion of CO₂ with amines to produce value-added organic urea derivatives has been overviewed from the viewpoints of both thermodynamics and catalysis. The lessons described in this review could be helpful for the assessment of developed catalytic systems and further improvement of efficiency of CO₂ utilization.

Abstract

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.