Carbon dioxide uptake as ammonia and amine carbamates and their efficient conversion into urea and 1,3-disubstituted ureas

Solid mixtures of ammonium carbamate and bicarbonate originating from the CO2 capture by NH3 in water–ethanol solution were converted into urea by heating to 428 K for 60–90 min. The yield of urea was up to 53% on molar basis. An analogous technique was employed to capture CO2 with 1-aminobutane, 1- amino-2-methylpropane, 2-amino-2-methylpropane, 1-aminooctane, aminocyclohexane and 1,4- diazacyclohexane, in organic solvents as amine carbamates which were separated in the solid state and thermally converted at 423 K for 15–16 h into 1,3-disubstituted ureas with 30–40% yield on molar scale. The formation of 1,3-disubstituted ureas was 100% selective. The rate of the conversion reaction was significantly improved in the presence of copper catalysts. The identification and quantification of the products in the reaction mixtures were obtained by 13C NMR analysis.