Theoretical discussion on the mechanism of binding CO₂ by DBU and alcohol

Abstract

Quantum chemical studies on the reaction of binding CO₂ by amidine base diazabicyclo [5.4.0]-undec-7-ene (DBU) and alcohol were carried out at the B3LYP/6-31g(d) level in order to find the reaction mechanism. The structures of reactants and product were optimised, and thermodynamic analyses were also carried out using the single point energy calculation and frequency analyses. It is noted that the reaction of binding CO₂ by DBU and propanol is thermodynamically feasible and qualitatively in accordance with the experimental observations. The results of thermodynamic and kinetic analyses demonstrate that the possible reaction mechanisms can be a two-step bimolecular reaction and a one-step trimolecular reaction. In the two-step bimolecular mechanism, the first step is the formation of intermediate by DBU and CO₂, and the second step is the nucleophilic attack of propanol on the intermediate. In the one-step trimolecular mechanism, O and H atoms of hydroxyl in propanol form an O–C bond with CO₂ and an H–N bond with DBU, respectively. The one-step trimolecular reaction seems a more reasonable mechanism because of the consideration of kinetic parameters.

Keywords::

• CO₂ absorption
• quantum chemistry
• reaction mechanism
• trimolecular reaction

Acknowledgements

We acknowledge the financial support from the National Natural Science Foundation of China (20976182) and Foundation for Innovative Research Groups of the National Natural Science Foundation of China (20821092).