Synthesis of TBAB‐based Deep Eutectic Solvents as the Catalyst in the Coupling Reaction between CO₂ and Epoxides under Ambient Temperature

Abstract

The development of an efficient, easily prepared, and environmentally friendly catalyst is important for the coupling reaction between CO 2 and epoxides. Herein, novel TBAB-based (tetrabutylammonium bromide, TBAB) deep eutectic solvents (DESs) have been applied in the transformation of CO 2 and epoxides into cyclic carbonates with exhibit high activity and selectivity under mild conditions (25 °C, 8 bar CO 2 ), The excellent activity and versatility of the TBAB-based DESs can be attributed to the hydrogen-bond interaction between the TBAB and citric acid. Due to hydrogen-bond interaction between À OH and Br À , the Br À becomes more flexible and facilitates the nucleophilic ring-opening process. The density functional theory (DFT) method has been used to explore the mechanism governing the CO 2 cycloaddition reaction. DFT results imply that intramolecular hydrogen bonding and the flexible nucleophilic Br À anion can significantly accelerate the ring-opening process. Hence, the ring-closure reaction may be the rate-determining step in the CO 2 cycloaddition reaction catalyzed by TBAB-based DESs. Both the experimental and computational results have demonstrated that the synergistic effect between the À OH and Br À in the TBAB-based DESs play a significant role in the acceleration of the ring-opening process of the CO 2 cycloaddition reaction.

Modulating H‐bond Strength to Enhance Reactivity for Efficient Synthesis of Cyclic Carbonates with Tetrabutylammonium Iodide‐based Deep Eutectic Solvents

“…The structural information of TBAI/PEG 200 DESs was analyzed by FT‐IR spectra as depicted in Figure 1a. The peak associated with the ‐CH 3 vibrational bond of TBAI appeared at 2958 cm −1 and a similar signal was detected in DESs [26] . It can be observed that the peak of −OH in PEG 200 is located at 3398 cm −1 .…”

“…The peak associated with the -CH 3 vibrational bond of TBAI appeared at 2958 cm À 1 and a similar signal was detected in DESs. [26] It can be observed that the peak of À OH in PEG 200 is located at 3398 cm À 1 . However, when TBAI was added to form DESs, the peak shifted to 3378 cm À 1 , which may be due to hydrogen bonding interaction between TBAI and PEG 200 .…”

“…However, it is worth noting that the release of phosphorus into the environment may contribute to ecosystem eutrophication, which runs counter to the principles of green chemistry. Wang et al [26] developed a tetrabutylammonium bromide (TBAB)/citric acid system and obtained excellent product yields, in which the À OH in citric acid interacted with TBAB and the reaction temperature was further reduced. The reaction system involving styrene oxide and carbon dioxide proved to be intricate, requiring the use of hazardous organic solvents, elevated CO 2 pressure, increased reaction temperature, and extended reaction durations, primarily due to the reduced reactivity of its carbon atom compared to propylene oxide.…”

“…However, it is worth noting that the release of phosphorus into the environment may contribute to ecosystem eutrophication, which runs counter to the principles of green chemistry. Wang et al [26] . developed a tetrabutylammonium bromide (TBAB)/citric acid system and obtained excellent product yields, in which the −OH in citric acid interacted with TBAB and the reaction temperature was further reduced.…”

Deep Eutectic Solvents as Catalysts for Cyclic Carbonates Synthesis from CO2 and Epoxides

“…Very recently, TBAB-based DESs were used as catalysts for cyclic carbonate synthesis [62]. Wang et al paid attention to the use of hydroxyl groups in the catalyst, as they can positively affect the reaction of hydrogen bonds.…”