Preparation of mono-, di-, and trisubstituted ureas by carbonylation of aliphatic amines with S,S-dimethyl dithiocarbonate

General procedures are reported to prepare N-alkylureas, N,N'-dialkylureas (both symmetrical and unsymmetrical), and N,N,N'-trialkylureas by carbonylation of aliphatic amines, employing S,S-dimethyl dithiocarbonate (DMDTC) as a phosgene substitute. All reactions were carried out in water. Symmetrical disubstituted ureas were prepared directly working at 60 degrees C with a molar ratio of DMDTC:amine = 1:2, preferably under nitrogen. Unsymmetrical ureas were prepared in two steps via S-methyl N-alkyl-thiocarbamate intermediates, which are formed selectively in the first step at room temperature. These intermediates react in the second step with ammonia or various aliphatic amines, both primary and secondary, at temperatures varying between 50 and 70 degrees C. All the target ureas were obtained in high yields (28 examples, average yield 94%) and with very high purity (generally > 99.2%). Also to be noted is the recovery of a co-product of industrial interest, methanethiol, in an amount of two moles for each mole of DMDTC, with complete exploitation of the reagent.