One-Pot Synthesis of N,N′-dialkylureas via Carbonylation of Amines with CO2 Applying Y0.08Zr0.92O1.96 Mixed Oxide (YSZ-8) as a Heterogeneous Catalyst

One-pot synthesis of N,N′-dialkylureas were successfully achieved from catalytic carbonylation of aliphatic primary amines with CO2 as the carbon source and Y0.08Zr0.92O1.96 mixed oxide (Yttria-stabilized zirconia, YSZ-8) as the heterogeneous catalyst. The yield of the target product was obtained up to 80.60% from a 48 h reaction with an aliphatic primary amine and 3.0 MPa CO2 in N-methyl-2-pirrolidinone at 160 °C. A multi-pronged mechanistic study was carried out where factors that might influence the reaction efficiency were studied, including catalyst structure, substrates basicity, CO2 pressure, solvent polarity and reaction time. The presence of oxygen vacancies in YSZ-8 was found to be essential for the carbonylation process by creating additional reduction potential for the activation of CO2 which would lead to the key intermediate species.