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 C-13 NMR analysis. (C) 2015 Elsevier Ltd. All rights reserved.