Carbon dioxide utilization in the efficient synthesis of carbamates by deep eutectic solvents (DES) as green and attractive solvent/catalyst systems

Abstract

A green and eco-friendly solvent/catalyst system based on a deep eutectic solvent (DES) was devised and developed for the simple synthesis of carbamates through three-component coupling of amines, alkyl halides and carbon dioxide (CO₂). It was found that choline chloride:zinc(II) chloride ([ChCl][ZnCl₂]₂) was very proficient and effective for the activation and utilization of CO₂ in carbamate formation reactions from a wide scope of amines. Surprisingly, this strategy provides the desired carbamates under atmospheric CO₂ pressure at room temperature. In particular, both aromatic and aliphatic amines were effective and demonstrated excellent yields. Besides, the [ChCl][ZnCl₂]₂ exhibited very high stability and also could be reused for at least five consecutive cycles without any significant loss of activity. It is worth noting that this is the first solvent/catalyst system which can be recycled successfully from the reaction mixture.