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

Abstract

BackgroundCarbon 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. MethodsIn 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 (ESI-TOF MS). Significant findingsThe most active catalytic system is obtained by chemically interaction of 3-bromopropionic acid (BPA) with DMF at 80 °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 (ΔG‡) and negative value of activation entropy (ΔS‡) confirm a non-spontaneous, endergonic and kinetically controlled reaction.