Synthesis of 1,3-dialkylurea from ethylene carbonate and amine using calcium oxide

Several basic metal oxide catalysts were tested for the synthesis of 1,3-disubstituted urea from ethylene carbonate (EC) and amine. Among the catalysts used, CaO has been found to be an excellent recyclable catalyst for the reaction. It has been suggested that strongly basic property of CaO results in its high activity. Disubstituted ureas are obtained from propylamine and butylamine with high yields at 100 °C. Slightly higher reaction temperatures are necessary for obtaining good yields from amines having larger molecular weights and urea is not produced from dibutylamine as a secondary amine. Propylene carbonate can be used instead of EC for the reaction. A reaction mechanism was proposed, which involves reaction between EC and amine giving a carbamate followed by catalytic reaction between the carbamate and amine, yielding 1,3-disubstituted urea. It is suggested that the latter reaction is the rate-determining step. On the basis of this reaction mechanism, the synthesis of unsymmetric urea was also examined. 2-Hydroxyethyl butylcarbamate is selectively produced from EC with butylamine in the absence of the catalyst at a low temperature and reacts with benzylamine producing 1-butyl-3-benzylurea along with symmetric dialkyl ureas.