Facile synthesis of [urea-Zn]I2 eutectic-based ionic liquid for efficient conversion of carbon dioxide to cyclic carbonates

Synthesis of metal-free benzimidazole-based catalysts and its application in CO2 cycloaddition

Ionic polymers functionalized with hydroxyl, carboxyl, and amino groups can enhance the catalytic activity of catalysts. However, the straightforward preparation of bifunctional ionic polymers containing abundant ionic active sites and hydrogen bond donors remains challenging. In this study, a series of porous ionic polymers (BZIs) containing different hydrogen bond donors (-NH2, -OH, -COOH) were prepared through a simple one-pot Friedel-Crafts alkylation using benzimidazole derivatives and benzyl bromide. The structures and properties of BZIs were characterized by various techniques such as Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state nuclear magnetic resonance, and scanning electron microscopy. Among the prepared catalysts (BZI-NH2, BZI-OH, and BZI-COOH), BZI-NH2 exhibited the highest catalytic activity and recyclability, achieving a yield of 97% in the CO2 cycloaddition. The synergistic effect of Br-, hydrogen bond donors (-NH-, -NH2), and N+ in BZI-NH2 was found to contribute to its superior catalytic performance. DFT calculations were employed to study the effect of hydrogen bonds, Br-, and N+ in BZI-NH2 and BZI-OH on the CO2 cycloaddition. Using BZI-NH2 as an example, a mechanism was proposed for the synergistic effect between amino groups and bromide ions in catalyzing the CO2 cycloaddition reaction.

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

In recent years, the chemical industry has put emphasis on designing or modifying chemical processes that would increasingly meet the requirements of the adopted proecological sustainable development strategy and the principles of green chemistry. The development of cyclic carbonate synthesis from CO₂ and epoxides undoubtedly follows this trend. First, it represents a significant improvement over the older glycol phosgenation method. Second, it uses renewable and naturally abundant carbon dioxide as a raw material. Third, the process is most often solvent-free. However, due to the low reactivity of carbon dioxide, the process of synthesising cyclic carbonates requires the use of a catalyst. The efforts of researchers are mainly focused on the search for new, effective catalysts that will enable this reaction to be carried out under mild conditions with high efficiency and selectivity. Recently, deep eutectic solvents (DES) have become the subject of interest as potential effective, cheap, and biodegradable catalysts for this process. The work presents an up-to-date overview of the method of cyclic carbonate synthesis from CO₂ and epoxides with the use of DES as catalysts.

Synthesis of Aliphatic Polycarbonates from Diphenyl Carbonate and Diols over Zinc (II) Acetylacetonate

APCs (aliphatic polycarbonates) are one of the most important types of biodegradable polymers and widely used in the fields of solid electrolyte, biological medicine and biodegradable plastics. Zinc-based catalysts have the advantages of being low cost, being non-toxic, having high activity, and having excellent environmental and biological compatibility. Zinc (II) acetylacetonate (Zn(Acac)₂) was first reported as a highly effective catalyst for the melt transesterification of biphenyl carbonate with 1,4-butanediol to synthesize poly(1,4-butylene carbonate)(PBC). It was found that the weight-average molecular weight of PBC derived from Zn(Acac)₂ could achieve 143,500 g/mol with a yield of 85.6% under suitable reaction conditions. The Lewis acidity and steric hindrance of Zn²⁺ could obviously affect the catalytic performance of Zn-based catalysts for this reaction. The main reasons for the Zn(Acac)₂ catalyst displaying a higher yield and M_w than other zinc-based catalysts should be ascribed to the presence of the interaction between acetylacetone ligand and Zn²⁺, which can provide this melt transesterification reaction with the appropriate Lewis acidity as well as the steric hindrance.

Arylamine organic dye-functionalized g-C3N4 formed through cycloaddition reactions and its application in photocatalytic hydrogen evolution

The arylamine organic dye grafted g-C3N4 by covalent azomethine ylide bonds via 1,3-dipolar cycloaddition is successfully prepared, which is the as-obtained g-C3N4/TPA-CNCHO photocatalyst with much enhanced photocatalytic activity for H2 production.

Efficient Conversion of CO2 via Grafting Urea Group into a [Cu2(COO)4]-Based Metal-Organic Framework with Hierarchical Porosity

The assembly of mixed [1,1';3',1'']terphenyl-4,5',4''-tricarboxylic acid (H₃TPTC) and [1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂BPDC), 2,2'-diamino-[1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂BPDC-NH₂), or 6-oxo-6,7-dihydro-5H-dibenzo[ d, f][1,3]diazepine-3,9-dicarboxylic acid (H₂BPDC-Urea) with Cu²⁺ ion generated the corresponding copper-paddlewheel-based metal-organic framework (MOF) [Cu₅(TPTC)₃(BPDC)_0.5(H₂O)₅] (1), [Cu₅(TPTC)₃(BPDC-NH₂)_0.5(H₂O)₅] (1-NH₂), or [Cu₅(TPTC)₃(BPDC-Urea)_0.5(H₂O)₅] (1-Urea). They are isostructural with hierarchical porosity, consisting of zero-dimensional cage (19.2 Å × 18.9 Å) and one-dimensional pillar channel (29.7 Å × 15.1 Å) in a manner of face sharing. Platon analyses revealed the porous volume ratios are 80.2%, 80.0%, and 77.8% for 1, 1-NH₂, and for 1-Urea, respectively. Thermogravimetric measurements suggested 53, 51, and 48 wt % guest molecules in 1, 1-NH₂, and 1-Urea, respectively. 1-NH₂ and 1-Urea were precisely functionalized via the introduction of amino and urea functional groups into the pillar channels. The constructed MOF 1-Urea, incorporating both exposed copper active sites and accessible urea functional groups to substrates, presents high efficiency on catalytic CO₂ cycloaddition with propene oxide to produce cyclic carbonate in the yield of 98% with a TOF value of 136 h^-1 at 1 atm and room temperature. This synergic effect provides a new strategy for designing high-efficient catalysts for CO₂ chemical conversion under ambient conditions.

Choline chloride-based deep eutectic solvents for efficient cycloaddition of CO2 with propylene oxide

Choline chloride-based deep eutectic solvents (DESs) exhibited remarkable activity in the cycloaddition of CO₂ with propylene oxide (PO) in the absence of any additives under solvent- and metal-free conditions as well as recyclability.

Amino-Functional Ionic Liquids as Efficient Catalysts for the Cycloaddition of Carbon Dioxide to Yield Cyclic Carbonates: Catalytic and Kinetic Investigation

Various amino-functional ionic liquids were developed as homogeneous catalysts for the cycloaddition of carbon dioxide to different epoxides yielding the corresponding cyclic carbonates under metal- and solvent-free conditions. The effects of reaction temperature, reaction time, CO2 pressure, and the amount of catalyst on the cycloaddition reaction were investigated. The catalysts could be easily recovered after the reaction and then reused at least eight times without noticeable loss of activity and selectivity. Reaction kinetic studies were undertaken, the reaction was apparently first order with respect to the concentration of epoxide and catalyst. Furthermore, the rate constants were determined over a temperature range of 100–130°C and the activation energy was determined to be 45.9 kJ mol−1. Finally, a possible reaction mechanism was proposed. The amino-functional ionic liquids showed the advantage of high catalytic activity and were easily recyclable for CO2 chemical fixation into valuable chemicals.

Study of Superbase-Based Deep Eutectic Solvents as the Catalyst in the Chemical Fixation of CO₂ into Cyclic Carbonates under Mild Conditions

Superbases have shown high performance as catalysts in the chemical fixation of CO₂ to epoxides. The proposed reaction mechanism typically assumes the formation of a superbase, the CO₂ adduct as the intermediate, most likely because of the well-known affinity between superbases and CO₂, i.e., superbases have actually proven quite effective for CO₂ absorption. In this latter use, concerns about the chemical stability upon successive absorption-desorption cycles also merits attention when using superbases as catalysts. In this work, ¹H NMR spectroscopy was used to get further insights about (1) whether a superbase, the CO₂ adduct, is formed as an intermediate and (2) the chemical stability of the catalyst after reaction. For this purpose, we proposed as a model system the chemical fixation of CO₂ to epichlorohydrin (EP) using a deep eutectic solvent (DES) composed of a superbase, e.g., 2,3,4,6,7,8-hexahydro-1H-pyrimido[1,2-a]pyrimidine (TBD) or 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine (DBU), as a hydrogen acceptor and an alcohol as a hydrogen bond donor, e.g., benzyl alcohol (BA), ethylene glycol (EG), and methyldiethanolamine (MDEA), as the catalyst. The resulting carbonate was obtained with yields above 90% and selectivities approaching 100% after only two hours of reaction in pseudo-mild reaction conditions, e.g., 1.2 bars and 100 °C, and after 20 h if the reaction conditions of choice were even milder, e.g., 1.2 bars and 50 °C. These results were in agreement with previous works using bifunctional catalytic systems composed of a superbase and a hydrogen bond donor (HBD) also reporting good yields and selectivities, thus confirming the suitability of our choice to perform this study.

Synthesis of Ureas from CO2

Ureas are an important class of bioactive organic compounds in organic chemistry and exist widely in natural products, agricultural pesticides, uron herbicides, pharmaceuticals. Even though urea itself has been synthesized from CO₂ and ammonia for a long time, the selective and efficient synthesis of substituted ureas is still challenging due to the difficulty of dehydration processes. Efficient and economic fixation of CO₂ is of great importance in solving the problems of resource shortages, environmental issues, global warming, etc. During recent decades, chemists have developed different catalytic systems to synthesize ureas from CO₂ and amines. Herein, we focus on catalytic synthesis of ureas using CO₂ and amines.