Polymer- and Carbon Nanotube-Supported Heterogeneous Catalysts for the Synthesis of Carbamates from Halides, Amines, and CO₂

Abstract: A series of tetraalkylammonium catalysts immobilized on polystyrene or carbon nanotubes were investigated in a reaction between alkyl halides, amines, and CO₂. The yield of carbamates was up to 85 % at 100 °C and 1 MPa of CO₂ after 3 h (first stage 25 °C, 1 h) in the presence of Cs₂CO₃ and DMF as a solvent. The best results were achieved in the case of large ammonium substituents (C₄ and C₆) in the catalyst, benzyl amine, and benzyl chloride as reagents. The catalysts retained their activity after at least five cycles when carefully dried between cycles. Both polymer and carbon nanotube supports were equally effective, but the latter were less prone to deactivation. Graphical Abstract: [Figure not available: see fulltext.]