The Role of Water Revisited and Enhanced: A Sustainable Catalytic System for the Conversion of CO₂ into Cyclic Carbonates under Mild Conditions

Abstract

The role of water as highly effective hydrogen‐bond donor (HBD) for promoting the coupling reaction of CO2 with a variety of epoxides was demonstrated under very mild conditions (25–60 °C, 2–10 bar CO2). Water led to a dramatic increase in the cyclic carbonate yield when employed in combination with tetrabutylammonium iodide (Bu4NI) whereas it had a detrimental effect with the corresponding bromide and chloride salts. The efficiency of water in promoting the activity of the organic halide was compared with three state‐of‐the‐art hydrogen bond donors, that is, phenol, gallic acid and ascorbic acid. Although water required higher molar loadings compared to these organic hydrogen‐bond donors to achieve a similar degree of conversion of CO2 and styrene oxide into the corresponding cyclic carbonate under the same, mild reaction conditions, its environmental friendliness and much lower cost make it a very attractive alternative as hydrogen‐bond donor. The effect of different parameters such as the amount of water, CO2 pressure, reaction temperature, and nature of the organic halide used as catalyst was investigated by using a high‐throughput reactor unit. The highest catalytic activity was achieved with either Bu4NI or bis(triphenylphosphine)iminium iodide (PPNI): with both systems, the cyclic carbonate yield at 45 °C with different epoxide substrates could be increased by a factor of two or more by adding water as a promoter, retaining high selectivity. Water was an effective hydrogen‐bond donor even at room temperature, allowing to reach 85 % conversion of propylene oxide with full selectivity towards propylene carbonate in combination with Bu4NI (3 mol %). For the conversion of epoxides in which PPNI is poorly soluble, the addition of a cyclic carbonate as solvent allowed the formation of a homogeneous solution, leading to enhanced product yield.

Facile synthesis of crystalline viologen-based porous ionic polymers with hydrogen-bonded water for efficient catalytic CO2 fixation under ambient conditions

“…Besides, it is worthy to note that the HBD cocatalyst Hbonded water molecules in VIP-Br play a vital role in activating and enhancing the CO 2 /ECH coupling by forming Hbonds with the oxygen atom of ECH. 4,14,64,65 Fortunately, the high selectivity (99%) of the product cyclic carbonate were still achieved together with high yields catalyzed by the inherent water-contained VIP-Br, indicating that no byproduct diol was formed via a possible hydrolysis process. In this work, no additional water was considered to enhance the conversion of the epoxide, because the selectivity for the product would decrease due to the ring opening of ECH to 3-chloro-1,2propanediol by hot water.…”

“…First, the epoxide substrate was electrophilically activated by the hydrogenbonding interaction between the oxygen atoms from epoxides and the free -OH groups within H-bonded water, thus inducing the ring opening of the epoxide via the C-O bond polarization. 65,69 Second, the nearby nucleophilic Br À anion will attack the less hindered b-carbon atom of the activated epoxide, leading to the formation of an oxyanion intermediate that can be stabilized by the available multiple -OH groups from the Hbonded water. 69,70 Subsequently, the insertion of CO 2 into the oxyanion intermediate will create the OH-stabilized alkylcarbonate anion intermediate.…”

Recent developments in organocatalysed transformations of epoxides and carbon dioxide into cyclic carbonates

“…89 However, care must be taken with the addition of water as this can lead to diol formation and poor selectivity. In 2019, Pescarmona and Alassmy 90 revisited the role of water in cyclic carbonate formation under mild reaction conditions (25-45 o C and 10 bar of carbon dioxide). When the reaction was catalysed by tetrabutylammonium iodide (3 mol%) at room temperature at 10 bar of carbon dioxide for 48 h, the addition of water increased the conversion of propylene oxide from 17 to 85%, whilst retaining 99% selectivity for cyclic carbonate formation.…”

One‐pot Fixation of CO2 into Glycerol Carbonate using Ion‐Exchanged Amberlite Resin Beads as Efficient Metal‐free Heterogeneous Catalysts

“…However, the utilization of CO 2 as building block in the production of useful chemicals is a challenging task due to its high thermodynamic stability. This limitation can be overcome by the reaction of CO 2 with compounds that have high free energy, such as epoxides [5–8] . The chemical fixation of CO 2 with epoxides to produce cyclic carbonates has been widely investigated (Scheme 1), because of the extensive range of applications found by cyclic carbonates, e. g .…”