A DFT study on mechanisms of CO2 coupling with propargylic alcohols using alkali carbonates |
| |
Authors: | Weiyi Li Geng Leng Caiqin Li Yajing Lyu |
| |
Institution: | 1. School of Science, Research Center for Advanced Computation, Xihua University, Chengdu, Sichuan, People's Republic of China;2. School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu, People's Republic of China;3. School of Chemistry and Chemical Engineering, Shanxi Datong University, Datong, People's Republic of China |
| |
Abstract: | The mechanisms of CO2 coupling with the propargylic alcohol using alkali carbonates M2CO3 (M = Li, Na, K, Cs) have been investigated by means of density functional theory calculations. The calculations reveal that the target product tetronic acid (TA) is yielded through two stages: (a) the formation of the α-alkylidene cyclic carbonate (αACC) intermediate via Cs2CO3-mediated carboxylative cyclization of the propargylic alcohol with CO2, and (b) the conversion of the αACC intermediate with Cs2CO3 to produce the cesium salt of the TA. Since the overall kinetic barriers for the two stages are comparable and affordable, the excellent chemoselectivity to the TA should be primarily originated from the high thermodynamic stability of the cesium salt of the TA. Moreover, relative to the TA, the possibility to yield the by-product acyclic carbonate can be excluded due to the both kinetics and thermodynamic inferiority. This result is different from the organic base-mediated reaction. Alternatively, our calculations predict that CsHCO3 together generated with the cesium salt of the TA might also be an available mediating reagent for the incorporation of CO2 with the propargylic alcohol. Compared to other alkali carbonates M2CO3 (M = Li, Na, K), the stronger basicity of Cs2CO3 and the lower ionic potential of cesium ion can raise the effective concentration of the αACC intermediate, and thus the conversion of the αACC intermediate into the cesium salt of the TA can be achieved with high yield. |
| |
Keywords: | alkali carbonates chemoselectivity CO2 fixation density functional theory reaction mechanism |
|
|