Ionic liquid mediated carbonylation of amines: Selective carbamate synthesis

Abstract Reaction of amines with dialkylcarbonates serves the purpose of generating carbamates besides methylated products. Present work reports the selective synthesis of carbamates from amines using dimethylcarbonate as carbonylating agent, in the presence of imidazolium derived ionic liquids as catalysts. Imidazolium based mono and dicationic liquids generated carbamates with 100% selectivity in fairly good to excellent yields, without isolation of any other side product. The dicationic ionic liquids B[MIm]2[PF6]2, B[MIm]2Cl2 and B[MIm]2[NO3]2 exhibited better catalytic activity in comparison to monocationic ones, may be because of bifunctional nature. DFT calculations revealed that the acidic proton of imidazolium ionic liquids (flanked by two nitrogen atoms) interact with the oxygen of dimethylcarbonate, increases its nucleophilicity and thus catalyses the reaction. Ionic liquids were recovered easily and reused a number of times. The protocol thus possesses, advantageous features of being simple, cost-effective, solvent free and sustainable.