ROLE OF THE MACROCYCLIC POLYETHER IN THE SYNTHESIS OF N-ALKYLCARBAMATE ESTERS FROM PRIMARY AMINES, CO2 AND ALKYL-HALIDES IN THE PRESENCE OF CROWN-ETHERS

Primary amines, RNH2 1, and CO2 easily afford monoalkylammonium N-alkylcarbamates, [RNH3][O2CNHR] 2, that have been reacted with alkyl halides, R'X, in the presence of crown-ethers to give organic carbamates in good yield. We report here the synthesis and spectroscopic characterization of some alkylammonium carbamates 2, where R = benzyl 2a, allyl 2b, ter-butyl 2c, cyclohexyl 2d, and discuss their stability in solution and the conditions in which they can react with alkyl halides to give organic carbamates, RNHC(O)OR'. The role played by the macrocyclic ligand in modifying the reactivity of monoalkylammonium carbamates 2 towards R'X has been rationalized and the influence of parameters such as solvent, temperature and CO2 pressure on the yield and selectivity of the process leading to organic carbamates has been also settled.