Direct synthesis of <i>N</i>-methylurethanes from primary amines with dimethyl carbonate

Tundo, Pietro; Bressanello, Salima; Loris, Alessandro; Sathicq, Gabriel

doi:10.1351/pac200577101719

Pure Appl. Chem., 2005, Vol. 77, No. 10, pp. 1719-1725

http://dx.doi.org/10.1351/pac200577101719

Direct synthesis of N-methylurethanes from primary amines with dimethyl carbonate

Pietro Tundo, Salima Bressanello, Alessandro Loris and Gabriel Sathicq

Dipartimento di Scienze Ambientali, Università Ca' Foscari Venezia, Italy and Consorzio Interuniversitario Nazionale La Chimica per l'Ambiente, Dorsoduro 2137-30123 Venezia, Italy

Abstract:

The mechanism of the reaction between amines with dimethyl carbonate (DMC) has been investigated. Whereas in the absence of bases, they give methylation and carboxymethylation reactions without selectivity (B_Al2 and B_Ac2 mechanisms, respectively), in the presence of bases, the B_Ac2 mechanism prevails. The carbamate already formed reacts further with DMC via the B_Al2 mechanism to give the corresponding N-methyl derivative. Such pronounced double selectivity has been explained in terms of Pearson's Hard-Soft Acid-Base (HSAB) theory.

Accordingly, N-methylcarbamates have been prepared from primary aliphatic and aromatic amines, either at reflux temperature of DMC (90 °C) or at 230 °C in autoclave. The reaction can be carried out in one step or through the isolation of the carbamate and the subsequent methylation reaction with DMC. This method is the direct synthesis, in high yield and selectivity, of secondary N-methylamines from the corresponding primary amines.