Carbamate synthesis via transfunctionalization of substituted ureas and carbonates

Synthesis of carbamates from substituted ureas and organic carbonates has been demonstrated using di-n-butyltin oxide (DBTO) as a catalyst. Reactivity pattern of ureas indicated that substituents on ureas have no significant effect on the carbamate yields. While, the carbonate reactivity pattern seems to be following the rule that is expected based on the leaving group ability of alkoxides and phenoxide to form carbamate observed in aminolysis of carbonates, it has been shown that basicity of reacting urea plays a vital role in the catalytic activity of this reaction. The effect of reaction parameters such as temperature, catalyst loading, solvent, concentration of reactants, etc. were investigated for synthesis of methyl methyl carbamate (MMC). The Arrhenius activation energy for the reaction between dimethyl urea (DMU) and dimethyl carbonate (DMC) was found to be 7.57 kcal/mol. A reaction mechanism has been postulated explaining the role of DBTO in the synthesis of carbamate from urea and carbonate. (C) 2004 Elsevier B.V. All rights reserved.