Mechanistic insights on CO₂ utilization using sustainable catalysis

Abstract

Caffeinium halides were used to catalyse the cycloaddition of CO2 to form cyclic carbonates. The reaction intermediates were isolated and characterized experimentally. The reaction mechanism has been confirmed by DFT calculations.

Utilization of CO2-Available Organocatalysts for Reactions with Industrially Important Epoxides

“…Apart from the above-mentioned, in the case of caffeine hydrobromide, potassium halides added to the reaction mixture as an additional source of nucleophiles were successfully tested. With the same reaction conditions, the enhanced efficiency of cyclic carbonate formation was observed utilizing equimolar quantities of KX and caffeine.HBr or even 2: 1 KX: caffeine.HBr using DMSO as the reaction solvent at 70 • C and 0.7 MPa CO 2 pressure [29,37]. The yield of cyclic carbonate increased following the trend KF < KCl < KBr < KI, which was in good agreement with nucleophilicity and nucleofugacity of the corresponding halide anions (Table 4, Entries 17-25).…”

“…above-mentioned non-nucleophilic amines (DBU.HA, N-methylimidazole (MIM.HA), N,N-dimethylaminopyridine (DMAP.HA)) and, alongside these, even triethanolamine, pyridine and caffeine (Figure 3), are quite catalytically active in the cycloaddition of CO2 with epoxides (Table 3, Entries [3][4][5][6][7][8][9][10][11][12][15][16][17][18][19][20][21][22][23][24]. Hydrogen halides in particular are the most active in comparison with corresponding free bases [29,30,32,[37][38][39] (Table 3, Entries 3-6, 8-12). The most active seems to be hydroiodides of the corresponding amines (Table 3, Entries 10, 18-24, 26-27).…”

CO2 fixation into cyclic carbonates catalyzed by single-site aprotic organocatalysts

“…The general activity of the imidazolium-based catalysts might be attributed to the acidic imidazolium proton present on the carbon between the two nitrogens (C2-H), which facilitates epoxide ring-opening upon coordination through hydrogen bonding; this interaction between the C2-H and the epoxide oxygen was demonstrated by ATR-FTIR and 1 H NMR in early work. 72,78 Therefore, to investigate and clarify the significance of C2-H, monosubstituted imidazolium structure 1 was blocked over C2 using 1,2-dimethylimidazole motif to get 2 (Fig. 1).…”

“…70 This attracted the attention of our research group and the CO 2 community to explore the utility of these compounds experimentally and theoretically. 31,71 Our research highlighted that the imidazolium family was not limited to synthetic polymers or biomaterial-based organocatalysts, 72,73 but this work could also be expanded into the use of IL precursors and their polymeric counterparts. Herein, a series of mono- and bi-functionalized homogeneous catalysts together with a heterogeneous imidazolium-based catalyst were synthesized and utilized for the cycloaddition reaction to yield CCs.…”

In situ activation of green sorbents for CO2 capture upon end group backbiting

“…31 Furthermore, they can also be synthesized using green carbonylating agents such as propylene carbonate, as innovated by our research group, 32 CO 2 , 33,34 or scCO 2 . 35 Our recent findings on bio-renewables/materials, [36][37][38][39] fine chemicals, 22,[40][41][42][43][44] and natural/synthetic polymeric materials [45][46][47][48][49][50] serving as scaffolds for CO 2 sequestration/utilization unveil a newly developed strategy that can develop mechanistic approaches for CO 2 capture. 51,52 Several research groups [53][54][55][56] have studied the thermolysis of urethane with its derivative, illustrated by three separate individual steps.…”