Efficient synergistic chemical fixation of CO2 by simple metal-free organocatalysts: Mechanistic and kinetic insights

Background: Carbon dioxide is a versatile, non-toxic, and renewable C1 building block source to produce valuable chemicals such as cyclic carbonates. The purpose of this research is development of efficient, metal free and affordable catalysts for cycloaddition reaction of CO2 with epoxides at mild conditions. Methods: In the present work, a group of novel bifunctional organocatalysts consisting of different hydrogen bond donors (HBDs) and halogen ion is simply synthesized. Under the optimized conditions, the reaction is kinetically and thermodynamically studied. Additionally, the catalytic active species are determined, and a mechanism is proposed with the help of electrospray-ionization time-of -flight mass spectrometry (ESITOF MS). Significant findings: The most active catalytic system is obtained by chemically interaction of 3-bromopropionic acid (BPA) with DMF at 80 degrees C (BPA-DMF). An excellent product yield of 98% and a high TOF value are obtained with 0.99 mol% of BPA-DMF, which is attributed to the synergistic effects of carboxyl functional groups and halide ions. The activation energy was found to be 50.75 kJ/mol. The positive value of Gibbs free activation energy (DGt) and negative value of activation entropy (DSt) confirm a non-spontaneous, endergonic and kinetically controlled reaction. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This research developed efficient and affordable bifunctional organocatalysts for the cycloaddition reaction of CO2 with epoxides, achieving high product yield and catalytic activity. The study provided insights into the kinetics and thermodynamics of the reaction, as well as proposed a mechanism. Analysis of activation energy and free energy confirmed a non-spontaneous, endergonic reaction controlled by kinetics.