A promising application of carboxymethyl cellulose (CMC), which is a congener of the cellulose family, as a supporting material for a variety of imidazolium based ionic liquid catalysts in the chemical fixation of CO 2 has been studied here. The ionic liquids immobilized on the carboxymethyl cellulose (CMIL) showed high catalytic activity and selectivity in the cycloaddition of carbon dioxide with propylene oxide (PO) resulting in propylene carbonate (PC) under mild and solvent free conditions. A new pathway was proposed based on the density functional theory (DFT) calculations performed at the B3LYP/6-31G (d,p) level, where the carboxyl and hydroxyl moieties on the CMC were found to act synergistically with the halide ions to eventuate in the cycloaddition reaction. The carboxyl group entities on the carboxymethyl cellulose support supposedly stabilize the product complex via strong hydrogen bonds, thereby promoting the reaction. The catalyst system also displayed good reusability. † Electronic supplementary information (ESI) available. See
Naturally occurring amino acids were identified as efficient co-catalysts for the alkali metal halide-mediated synthesis of cyclic carbonates from carbon dioxide and epoxides under mild, solvent free reaction conditions. The binary system of histidine/potassium iodide gave an appreciable turnover number of 535 for propylene oxide in 3 h. Detailed studies evaluating a variety of amino acids revealed that the basic amino acids afforded better conversion rates. The formation of a seven membered ring involving the zwitterionic ends of the amino acid, the metal halide, and the epoxide was considered to accelerate the catalysis rate. Density functional theory calculations were performed for the first time on amino acid co-catalyzed cycloaddition to provide further evidence for this hypothesis. The iodide ions of the alkali metal halide displayed excellent synergism with the hydrogen bonding groups of the amino acids in the production of cyclic carbonates, whereas bromide and chloride anions functioned less efficiently. The utilization of amino acids to enhance the catalytic activity of the cheap and eco-friendly alkali metal halides for cyclic carbonate synthesis represents a cost-effective, greener route towards the chemical fixation of carbon dioxide.
A novel application of alkanolamines, widely employed as CO2 scrubbers in catalyzing the insertion of CO2 into epoxides generating cyclic carbonates in excellent yield and selectivity via the synergistic activity of hydroxyl and amine groups, is unravelled along with computational studies.
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