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The cycloaddition of CO2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO2. One of the main focuses of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of CO2 to epoxides is provided in this work along with recommendations for possible future developments. [ABSTRACT FROM AUTHOR]

Rising carbon dioxide (CO2) levels in the atmosphere are recognized as a threat to atmospheric stability and life. Although this greenhouse gas is being produced on a large scale, there are solutions to reduction and indeed utilization of the gas. Many of these solutions involve costly or unstable technologies, such as air‐sensitive metal–organic frameworks (MOFs) for CO2 capture or "non‐green" systems such as amine scrubbing. Conjugated microporous polymers (CMPs) represent a simpler, cheaper, and greener solution to CO2 capture and utilization. They are often easy to synthesize at scale (a one pot reaction in many cases), chemically and thermally stable (especially in comparison with their MOF and covalent organic framework (COF) counterparts, owing to their amorphous nature), and, as a result, cheap to manufacture. Furthermore, their large surface areas, tunable porous frameworks and chemical structures mean they are reported as highly efficient CO2 capture motifs. In addition, they provide a dual pathway to utilize captured CO2 via chemical conversion or electrochemical reduction into industrially valuable products. Recent studies show that all these attractive properties can be realized in metal‐free CMPs, presenting a truly green option. The promising results in these two fields of CMP applications are reviewed and explored here. [ABSTRACT FROM AUTHOR]

This study introduces an efficient strategy for synthesizing polyhydroxyurethane-based multicomponent hydrogels with enhanced rheological properties. In a single-step process, 3D materials composed of Polymer 1 (PHU) and Polymer 2 (PVA or gelatin) were produced. Polymer 1, a crosslinked polyhydroxyurethane (PHU), grew within a colloidal solution of Polymer 2, forming an interconnected network. The synthesis of Polymer 1 utilized a Non-Isocyanate Polyurethane (NIPU) methodology based on the aminolysis of bis(cyclic carbonate) (bisCC) monomers derived from 1-thioglycerol and 1,2-dithioglycerol (monomers A and E, respectively). This method, applied for the first time in Semi-Interpenetrating Network (SIPN) formation, demonstrated exceptional orthogonality since the functional groups in Polymer 2 do not interfere with Polymer 1 formation. Optimizing PHU formation involved a 20-trial methodology, identifying influential variables such as polymer concentration, temperature, solvent (an aprotic and a protic solvent), and the organo-catalyst used [a thiourea derivative (TU) and 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU)]. The highest molecular weights were achieved under near-bulk polymerization conditions using TU-protic and DBU-aprotic as catalyst–solvent combinations. Monomer E-based PHU exhibited higher M w ¯ than monomer A-based PHU (34.1 kDa and 16.4 kDa, respectively). Applying the enhanced methodology to prepare 10 multicomponent hydrogels using PVA or gelatin as the polymer scaffold revealed superior rheological properties in PVA-based hydrogels, exhibiting solid-like gel behavior. Incorporating monomer E enhanced mechanical properties and elasticity (with loss tangent values of 0.09 and 0.14). SEM images unveiled distinct microstructures, including a sponge-like pattern in certain PVA-based hydrogels when monomer A was chosen, indicating the formation of highly superporous interpenetrated materials. In summary, this innovative approach presents a versatile methodology for obtaining advanced hydrogel-based systems with potential applications in various biomedical fields. [ABSTRACT FROM AUTHOR]

Nowadays there is an urgent need for mitigating CO2 emissions through clean energy and the development of new carbon capture and utilization (CCU) technologies. Among others, the use of bifunctional ionic liquids (ILs) addressed simultaneously CO2 capture and conversion steps, having applied successfully to the propylene carbonate production case. In this work, a systematic evaluation of all representative cyclic carbonate literature was made, covering ethylene, propylene, butylene, hexylene, cyclohexene, and styrene cyclic carbonates, in order to guide the product role within the integrated CCU (ICCU) concept. The multiscale strategy combining molecular simulation (DFT -Density Functional Theory-, COSMO -COnductor-like Screening MOdel-), process simulation (COSMO/Aspen methodology), and life cycle assessment (LCA) was used to set up, simulate and evaluate the processes. ICCU configuration is the best approach when compared with sequential configuration for energy consumption analysis (reduction of 28, 28, 22, 11 and 6 %, respectively, for ethylene, propylene, butylene, hexylene, and cyclohexene cases) and CO2 emissions associated (reduction of 38, 40, 31 and 14 %, respectively, for ethylene, propylene, butylene, and hexylene cases). The main variable of the results is the boiling point of the cyclic carbonate since heavy products impose technical limitations and even discard ICCU alternative. The ICCU concept works since all cyclic carbonates’ reaction enthalpies are higher than that of the IL-CO2 one, which reduces heating requirements. Finally, energy demand can be slightly further reduced, partially recycling the cyclic carbonate to the capture unit.

The conversion of CO2 with epoxides into the corresponding cyclic carbonates represents a green approach to transform a waste into value-added products. To promote this conversion, a catalyst in needed. This study presents the synthesis of two cross-linked materials composed of magnesium phthalocyanine and imidazolium bromide moieties: MgPc-BIBI-Br and MgPc-SIBI-Br. Magnesium phthalocyanines are cost-effective and versatile catalysts, synthesized in high yield from low-cost precursors and can be easily modified for specific needs. Imidazolium bromide groups play a crucial role as well, acting as a nucleophile source essential to promote the ring-opening process of the epoxide. The materials have been extensively characterized through analytical and spectroscopic techniques and tested as catalysts in the conversion of epichlorohydrin into 4-chloromethyl-1,3-dioxalan-2-one. They both achieved excellent catalytic performance (maximal TON values of 3070 for MgPc-SIBI-Br and 1903 for MgPc-BIBI-Br) and recyclability (both recyclable at least for 4 cycles). The reported results represent an improvement if compared to similar materials already reported in the literature in which the addition of external nucleophilic species (e.g. TBAB, BMIM-Br, etc.) is needed. To the best of our knowledge, this work is the first example in which imidazolium bromide and magnesium phthalocyanine moieties are combined in bifunctional polymeric materials that convert CO2 into cyclic carbonates via heterogeneous catalysis.

This study introduces a straightforward synthesis method for producing a hybrid material composed of halloysite and kojic acid, which catalyzes carbon dioxide (CO2) conversion processes. Kojic acid, derived from malted rice fermentation, exhibits inherent chelating properties that facilitate the introduction of copper ions onto the material’s surface. Copper ions, an economically viable alternative to noble metals, catalyze CO2 conversion reactions effectively. The hybrid catalyst was evaluated for two distinct CO2 conversion pathways: photocatalytic methane production under simulated sunlight and CO2 fixation into cyclic carbonates via epoxide reactions. The hybrid material demonstrates remarkable catalytic activity under mild conditions, achieving high conversion efficiencies at 45 °C for methane production and 70 °C for carbonate fixation at atmospheric pressure. Conversion of 31 % and 89 % were achieved for the photocatalytic CO2 reduction and the carbonate fixation, respectively. FT-IR spectra confirmed the functionalization of the material. Additionally, its organic/inorganic hybrid nature is complemented by excellent thermal stability, as studied by TGA. It enables repeated utilization, maintaining a 25 % catalytic activity for methane production and 70 % for carbonate fixation after the fourth reuse. This research highlights the potential of using naturally derived materials for sustainable CO2 mitigation.

The fixation of carbon dioxide with epoxides is one of the most attractive methods for the green utilisation of this greenhouse gas and leads to many valuable chemicals. This process is characterised by 100% atom efficiency; however, an efficient catalyst is required to achieve satisfactory yields. Metal–organic frameworks (MOFs) are recognised as being extremely promising for this purpose. Nevertheless, many of the proposed catalysts are based on ions of rare elements or elements not entirely safe for the environment; this is notable with commercially unavailable ligands. In an effort to develop novel catalysts for CO2 fixation on an industrial scale, we propose novel MOFs, which consist of aluminium ions coordinated with commercially available 1,4-naphthalene dicarboxylic acid (Al@NDC) and their nanocomposites with gold nanoparticles entrapped inside their structure (AlAu@NDC). Due to the application of 4-amino triazole and 5-amino tetrazole as crystallization mediators, the morphology of the synthesised materials can be modified. The introduction of gold nanoparticles (AuNPs) into the structure of the synthesised Al-based MOFs causes the change in morphology from nano cuboids to nanoflakes, simultaneously decreasing their porosity. However, the homogeneity of the nanostructures in the system is preserved. All synthesised MOF materials are highly crystalline, and the simulation of PXRD patterns suggests the same tetragonal crystallographic system for all fabricated nanomaterials. The fabricated materials are proven to be highly efficient catalysts for carbon dioxide cycloaddition with a series of model epoxides: epichlorohydrin; glycidol; styrene oxide; and propylene oxide. Applying the synthesised catalysts enables the reactions to be performed under mild conditions (90 °C; 1 MPa CO2) within a short time and with high conversion and yield (90% conversion of glycidol towards glycerol carbonate with 89% product yield within 2 h). The developed nanocatalysts can be easily separated from the reaction mixture and reused several times (both conversion and yield do not change after five cycles). The excellent performance of the fabricated catalytic materials might be explained by their high microporosity (from 421 m2 g−1 to 735 m2 g−1); many catalytic centres in the structure exhibit Lewis acids' behaviour, increased capacity for CO2 adsorption, and high stability. The presence of AuNPs in the synthesised nanocatalysts (0.8% w/w) enables the reaction to be performed with a higher yield within a shorter time; this is especially important for less-active epoxides such as propylene oxide (two times higher yield was obtained using a nanocomposite, in comparison with Al-MOF without nanoparticles). [ABSTRACT FROM AUTHOR]

2–(1H–1,2,4–Triazol–3–yl)phenol (CAT–1) was used as an organocatalyst for the coupling reaction of CO2 and epoxides at an ambient temperature and atmospheric CO2 pressure (1 bar). This compound has a structure in which a hydrogen bond donor, a hydrogen bond acceptor, and another hydrogen bond donor are adjacent in sequence in a molecule. The binary catalytic system of CAT–1/nBu4NI showed TON = 19.2 and TOF = 1.60 h−1 under 1 bar CO2 at room temperature within 12 h using 2–butyloxirane. Surprisingly, the activity of CAT–1, in which phenol and 1H–1,2,4–triazole are chemically linked, showed a much greater synergistic effect than when simply mixing the same amount of phenol and 1H–1,2,4–triazole under the same reaction conditions. In addition, our system showed a broad terminal and internal epoxide substrate scope. [ABSTRACT FROM AUTHOR]

The novelty of this work consists of synthesizing and exploiting a heterogeneous catalyst containing ammonium chloride as part of the polymeric sponge sites for CO2 capture. To this aim, the polymerization of 2-acryloyl(oxyethyl)trimethylammonium chloride was performed in cryo-condition, in the presence of a crosslinking agent, obtaining a lightweight macroporous freestanding material. Its efficiency in converting aromatic and aliphatic epoxides to the corresponding carbonates was successfully proved by using proton Nuclear Magnetic Resonance (1H NMR). Remarkably, the conversion of styrene oxide (SO) to styrene carbonate (SC) reached a yield of 99 % after 24 h of reaction. The calculated yield versus the aliphatic cyclohexene oxide is 71 %. Similar results were obtained by substituting the resin counter anion with Br−, although the conversion kinetic was slower than the chloride. It is worth noticing that reactions took place in the mixture without adding the tetrabutylammonium bromide (TBAB), typically used as a co-catalyst to convert epoxides into carbonates. The recyclability of the as-prepared catalyst was evaluated for four reaction cycles, evidencing stable properties without significant depletion of CO2 capture efficiency. Most importantly, the post-cleaning of the catalytic sponge is not required to be reused. Finally, the green chemistry metrics applied to the process demonstrated that our approach significantly mitigates risks and reduces environmental impact, thus elevating the overall cleanliness of our proof of concept.

The cycloaddition reaction of CO2 with epoxides such as limonene epoxide (LE) to form cyclic carbonates is considered a promising alternative for reducing CO2 emissions. In this work, CO2 fixation on LE to produce cyclic carbonates was carried out over Zn/SBA-15 with tetrabutylammonium bromide (TBAB) as co-catalyst and over NH3X-Zn/SBA-15 (X= Cl, Br, or I) catalysts. The catalysts were characterized by FT-IR, XRD, N2 adsorption–desorption isotherms, TEM, NH3-TPD, XPS, TGA and Py-FTIR. The Zn/SBA-15 support mainly presents Lewis’s acid sites of medium acidity; the surface area was 512 m2/g and 378 m2/g and the pore size were 9 nm and 7.2 nm, for Zn/SBA-15 and NH3Cl-Zn/SBA-15, respectively. The functionalization of Zn/SBA-15 was verified by FTIR, UV-vis, and XPS analysis. It was found that when Zn/SBA-15 was used as catalyst that reaction time had a significative effect on LE conversion and in the case of limonene carbonate selectivity, co-catalyst concentration variation had the main effect. Zn/SBA-15 catalyst can be reused up to 5 times without significant changes neither in conversion nor in limonene carbonate selectivity. The best LE conversion and limonene carbonate selectivity was 33% and 93%, respectively (1 M LE, 200 mg Zn/SBA-15, 7% TBAB; 30 bar, 18 h, 700 rpm and 20 mL diethyl carbonate). The reported catalytic system is a promising system for obtaining limonene carbonate using a heterogeneous catalyst.

Abstract Rising carbon dioxide (CO2) levels in the atmosphere are recognized as a threat to atmospheric stability and life. Although this greenhouse gas is being produced on a large scale, there are solutions to reduction and indeed utilization of the gas. Many of these solutions involve costly or unstable technologies, such as air‐sensitive metal–organic frameworks (MOFs) for CO2 capture or “non‐green” systems such as amine scrubbing. Conjugated microporous polymers (CMPs) represent a simpler, cheaper, and greener solution to CO2 capture and utilization. They are often easy to synthesize at scale (a one pot reaction in many cases), chemically and thermally stable (especially in comparison with their MOF and covalent organic framework (COF) counterparts, owing to their amorphous nature), and, as a result, cheap to manufacture. Furthermore, their large surface areas, tunable porous frameworks and chemical structures mean they are reported as highly efficient CO2 capture motifs. In addition, they provide a dual pathway to utilize captured CO2 via chemical conversion or electrochemical reduction into industrially valuable products. Recent studies show that all these attractive properties can be realized in metal‐free CMPs, presenting a truly green option. The promising results in these two fields of CMP applications are reviewed and explored here.

We report on the metal-free and rapid catalytic conversion of carbon dioxide into cyclic carbonates under solventless conditions utilizing novel bifunctional fluoroalcohol-based ionic liquids (FBILs) as catalsyts. In the presence of 2.5 mol% 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl) phenyl trimethylammonium iodide (FBIL-1), under 0.1 MPa and 90 °C, excellent yield of propylene carbonate(>95%) was achieved in 1 h, which significantly shortens the reaction time, compared with the conventional catalysts. DFT calculations reveal that FBILs with fluorine-substituted hydroxyl groups exhibit stronger hydrogen bonding with epoxides compared to ILs lacking fluorine substitutions. The hydrogen bond length for ILF/PO is 1.658 Å, shorter than that for IL/PO (1.813 Å). This characteristic contributes to reducing the activation energy for the ring-opening reaction of epoxides. In the ILF/PO system, the reaction barrier is 88.72 kJ·mol−1, lower than the 101.46 kJ·mol−1 barrier for IL/PO, allowing the former to more rapidly facilitate the fixation of carbon dioxide into cyclic carbonates. Besides high catalytic efficiency, these FBILs have the characteristics of a facile synthesis route and easy post-reaction recovery.

Porous polymeric frameworks have received great interest over the past few years because of their nonstop growth as crystalline porous polymeric materials connected through covalent bonds and versatile utilities in diverse fields. The production of high-value organic compounds via sustainable and environment-friendly methods is an uphill struggle for researchers. The elegant strategy of using carbon dioxide as a C1 building block is an intriguing platform owing to its non-toxicity, easy accessibility, natural abundance, recyclability, non-flammability, and cheapness. Additionally, CO2 levels are regarded as the main contributor to the greenhouse effect (the most abundant greenhouse gas across the globe) and the aforementioned strategy needs to mitigate CO2 emissions. This present study describes the synthesis of silver nanoparticles (AgNPs) embedded in a porous polymeric framework, a reusable heterogeneous catalyst (recyclable over 5 times), TpMA (MC)@Ag. The synthesized catalyst is characterized by using FT-IR, PXRD, XPS, FE-SEM, TEM, EDAX, TGA DTA, and N2 sorption studies. Additionally, the catalysts can be easily recycled to generate the desired α-alkylidene cyclic carbonates and oxazolidinone compounds under solvent-free conditions. This research demonstrates the potential of nanoporous 2D porous polymeric framework-based materials in the area of catalysis, specially, in CO2 capture and chemical fixation. These findings offer a promising approach for the chemical fixation of CO2 into α-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols utilizing AgNPs embedded in a 2D catalyst, which functions as a potential heterogeneous catalyst under mild conditions (e.g., solvent-free approach). [ABSTRACT FROM AUTHOR]

In this study, we report a successful strategy for the generation of palladium nanoparticles on porous P-doped carbon spheres with a high surface area. The synthesized Pd/P-CS was used in the CO2 fixation reaction with various epoxides under solvent-free conditions. The prepared Pd0/P-CS nanocatalyst was affirmed by different analysis, including TEM, FE-SEM, EDS, BET, FT-IR, XRD, and ICP-OES. The aforesaid nanocatalyst with a unique porous structure was an outstanding catalytic performance on different substrates toward produce of cyclic carbonates under solvent-free condition with high yields of final products. The catalytic activity of Pd0/P-Cs could be maintained efficiently after recycling up to five consecutive runs under the optimized reaction conditions. [ABSTRACT FROM AUTHOR]

The coupling reaction of carbon dioxide and highly-substituted epoxides derived from renewable resources such as fatty acids and waste vegetable oils (cooking oils derived from olive and sunflower) leads to the synthesis of new bio-derived cyclic carbonates using efficient metal-free bifunctional organocatalysts under mild and solvent-free reaction conditions. Once cyclic carbonates derived from biobased sources were synthesized, the design of non-isocyanate polyurethanes (NIPUs) with different chemical structures was investigated by their reaction with a broad substrate scope of diamines. The NIPUs materials were characterized by spectroscopic techniques (NMR and IR) and their molecular weights and polydispersities were determined by GPC studies. Finally, thermal properties of the polymers were studied by DSC and TGA analyses.

The cycloaddition of CO2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO2. One of the main focuses of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of CO2 to epoxides is provided in this work along with recommendations for possible future developments.

A novel approach is reported to prepare 3D-printed polymers that incorporate metal-organic frameworks (MOFs) through a one-pot growth process, involving covalent grafting and growth onto 3D polymeric surfaces. The resulting hybrid materials were subjected to comprehensive characterization using techniques such as SEM, XRD, FTIR, Raman, and XPS. The findings demonstrated an excellent dispersion of the inorganic units on the polymer matrix while preserving their metal-organic structure. The hybrid materials exhibited the presence of Lewis acid and basic groups within the MOF. The catalytic performance of these hybrid materials was evaluated in the mild cycloaddition reaction of carbon dioxide (CO2) to epoxides. Notably, the polymers incorporating UiO-67 MOFs displayed remarkable activity, even at low CO2 pressures and in the absence of auxiliary co-catalysts or additives. The catalytic activity of these hybrid materials exhibited a significant improvement, up to two orders of magnitude higher than analogous bulk MOFs. This observation highlights the superior performance of the 3D-printed polymer/MOF hybrids in this catalytic transformation.

Development of an effective catalytic system for the cycloaddition of carbon dioxide to epoxides for the preparation of cyclic carbonates under mild conditions is of great importance. Herein, a mixture of zinc iodide, metal chlorides, and strong organic bases is demonstrated to be a useful catalytic system that works at room temperature under atmospheric pressure. The most efficient combination, zinc iodide-niobium chloride-7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (1.2-0.3-3.0 mol%), gave styrene carbonate (95%) from styrene oxide and CO2 (balloon) at 25 °C for 24 h. Another combination, zinc iodide-zinc chloride-1,8-diazabicyclo[5.4.0]undec-7-ene (1.2-0.8-4.0 mol%), kept the catalytic activity for the preparation of propylene carbonate until the fourth run. Therefore, the reaction system was operationally simple, highly efficient, and proceeded under ambient conditions. The catalyst is composed of readily available reagents and is reusable. Thus, the method presented is a powerful tool for utilizing CO2 as the starting material for the production of valuable chemicals. [ABSTRACT FROM AUTHOR]

The present work focuses on developing heterogeneous catalysts for conversion of CO2 and mono-/di-epoxides to mono-/bis-cyclic carbonates. To achieve this purpose, two types of recyclable solid catalysts, namely polyurethane (PU-BTP) and polyurethane modified on silica gel-solid support (SG-AU-BPT), are synthesized. On these catalysts, the key promoter CaI2 is pre-absorbed. Both catalysts show high catalytic activity under mild conditions. For example, phenyl glycidyl ether (PGE) can be converted to 4-(phenoxymethyl)− 1,3-dioxolan-2-one at 60 °C within 6 h under 1 atm pressure of CO2. PU-BTP and SG-AU-BPT can be recollected by suction filtration and reused for eight times with conversion larger than 81% and 95% respectively. These results indicate that the degree of CaI2 leaching out from the catalysts in each cycle and loss is low.

The development of efficient methods for the cycloaddition of CX2 (carbon dioxide (X${=}$O) or carbon disulfide (X${=}$S)) with fluorinated epoxides to produce five-membered cyclic carbonates (CCs) or cyclic xanthates (XAs) is a very attractive topic. In this work, the cycloaddition of CX2 with hexafluoropropene oxide (HFPO) was performed in the presence of a lithium bromide (LiBr) catalyst and optimized in terms of temperature, solvent, pressure, and reaction time. Then, the optimized conditions were tried in the cycloaddition of CX2 with 2-(trifluoromethyl)oxirane (TFEO) for reproducibility, leading to the corresponding products in high yields. Finally, two original fluorinated five-membered bis-CCs and bis-XAs were synthesized in high yields (85 and 87%) by reacting CX2 with 1,4-bis($2^{\prime }{,}3^{\prime }$-epoxypropyl) perfluorobutane (BEPFB). All of the resulting compounds were characterized by FTIR, 1H, 19F, and 13C NMR spectroscopy.

This study introduces an efficient strategy for synthesizing polyhydroxyurethane-based multicomponent hydrogels with enhanced rheological properties. In a single-step process, 3D materials composed of Polymer 1 (PHU) and Polymer 2 (PVA or gelatin) were produced. Polymer 1, a crosslinked polyhydroxyurethane (PHU), grew within a colloidal solution of Polymer 2, forming an interconnected network. The synthesis of Polymer 1 utilized a Non-Isocyanate Polyurethane (NIPU) methodology based on the aminolysis of bis(cyclic carbonate) (bisCC) monomers derived from 1-thioglycerol and 1,2-dithioglycerol (monomers A and E, respectively). This method, applied for the first time in Semi-Interpenetrating Network (SIPN) formation, demonstrated exceptional orthogonality since the functional groups in Polymer 2 do not interfere with Polymer 1 formation. Optimizing PHU formation involved a 20-trial methodology, identifying influential variables such as polymer concentration, temperature, solvent (an aprotic and a protic solvent), and the organo-catalyst used [a thiourea derivative (TU) and 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU)]. The highest molecular weights were achieved under near-bulk polymerization conditions using TU-protic and DBU-aprotic as catalyst–solvent combinations. Monomer E-based PHU exhibited higher Mw¯ than monomer A-based PHU (34.1 kDa and 16.4 kDa, respectively). Applying the enhanced methodology to prepare 10 multicomponent hydrogels using PVA or gelatin as the polymer scaffold revealed superior rheological properties in PVA-based hydrogels, exhibiting solid-like gel behavior. Incorporating monomer E enhanced mechanical properties and elasticity (with loss tangent values of 0.09 and 0.14). SEM images unveiled distinct microstructures, including a sponge-like pattern in certain PVA-based hydrogels when monomer A was chosen, indicating the formation of highly superporous interpenetrated materials. In summary, this innovative approach presents a versatile methodology for obtaining advanced hydrogel-based systems with potential applications in various biomedical fields.

The fixation of carbon dioxide with epoxides is one of the most attractive methods for the green utilisation of this greenhouse gas and leads to many valuable chemicals. This process is characterised by 100% atom efficiency; however, an efficient catalyst is required to achieve satisfactory yields. Metal–organic frameworks (MOFs) are recognised as being extremely promising for this purpose. Nevertheless, many of the proposed catalysts are based on ions of rare elements or elements not entirely safe for the environment; this is notable with commercially unavailable ligands. In an effort to develop novel catalysts for CO2 fixation on an industrial scale, we propose novel MOFs, which consist of aluminium ions coordinated with commercially available 1,4-naphthalene dicarboxylic acid (Al@NDC) and their nanocomposites with gold nanoparticles entrapped inside their structure (AlAu@NDC). Due to the application of 4-amino triazole and 5-amino tetrazole as crystallization mediators, the morphology of the synthesised materials can be modified. The introduction of gold nanoparticles (AuNPs) into the structure of the synthesised Al-based MOFs causes the change in morphology from nano cuboids to nanoflakes, simultaneously decreasing their porosity. However, the homogeneity of the nanostructures in the system is preserved. All synthesised MOF materials are highly crystalline, and the simulation of PXRD patterns suggests the same tetragonal crystallographic system for all fabricated nanomaterials. The fabricated materials are proven to be highly efficient catalysts for carbon dioxide cycloaddition with a series of model epoxides: epichlorohydrin; glycidol; styrene oxide; and propylene oxide. Applying the synthesised catalysts enables the reactions to be performed under mild conditions (90 °C; 1 MPa CO2) within a short time and with high conversion and yield (90% conversion of glycidol towards glycerol carbonate with 89% product yield within 2 h). The developed nanocatalysts can be easily separated from the reaction mixture and reused several times (both conversion and yield do not change after five cycles). The excellent performance of the fabricated catalytic materials might be explained by their high microporosity (from 421 m2 g−1 to 735 m2 g−1); many catalytic centres in the structure exhibit Lewis acids’ behaviour, increased capacity for CO2 adsorption, and high stability. The presence of AuNPs in the synthesised nanocatalysts (0.8% w/w) enables the reaction to be performed with a higher yield within a shorter time; this is especially important for less-active epoxides such as propylene oxide (two times higher yield was obtained using a nanocomposite, in comparison with Al-MOF without nanoparticles).

2–(1H–1,2,4–Triazol–3–yl)phenol (CAT–1) was used as an organocatalyst for the coupling reaction of CO2 and epoxides at an ambient temperature and atmospheric CO2 pressure (1 bar). This compound has a structure in which a hydrogen bond donor, a hydrogen bond acceptor, and another hydrogen bond donor are adjacent in sequence in a molecule. The binary catalytic system of CAT–1/nBu4NI showed TON = 19.2 and TOF = 1.60 h−1 under 1 bar CO2 at room temperature within 12 h using 2–butyloxirane. Surprisingly, the activity of CAT–1, in which phenol and 1H–1,2,4–triazole are chemically linked, showed a much greater synergistic effect than when simply mixing the same amount of phenol and 1H–1,2,4–triazole under the same reaction conditions. In addition, our system showed a broad terminal and internal epoxide substrate scope.

A one-pot multicomponent green process is investigated for the synthesis of perfluoroalkylated cyclic carbonate which merges the photo-promoted Atom Transfer Radical Addition (ATRA) of a perfluoroalkyl iodide (Rf-I) onto allyl alcohols with the Lewis-base-promoted carboxylative cyclization. The evolution of the complex mixture during the reaction was monitored by in situ ATR-IR and Raman spectroscopies that provided insights into the reaction mechanism. The effect on the kinetics and the carbonate yields of key parameters such as the stoichiometry of reagents, the nature of the Lewis base and the solvent, the temperature and the pressure were evaluated. It was found that high yields were obtained using strong Lewis bases that played both the role of activating the allyl alcohol for the generation of the allyl carbonate in the presence of CO2 and promoting the ATRA reaction through the activation of C4F9I by halogen bonding. This protocol was also extended to various unsaturated alcohols. [ABSTRACT FROM AUTHOR]

[Display omitted] Fossil fuel has empowered a remarkable era of prosperity and development of the welfare of human society. However, the resulting large anthropogenic CO 2 emissions had an adverse impact on global temperature. Furthermore, the scarcity of limited fossil fuel resources will eventually force them to look for alternative carbon sources to sustain a sustainable economy. Chemical fixation of CO 2 into fuels and valuable chemicals via renewable energy sources has been attracting human society for not only alleviating CO 2 emissions but also reducing reliance on non-renewable energy sources and minimizing the impact on the environment from displaced fossil fuel fractions. Cyclic carbonate is a valuable CO 2 product that can be used as aprotic solvent, the electrolytic solvent in lithium batteries, degreasing solvents, and intermediates for the synthesis of polycarbonates, drugs, and cosmetics. It can be synthesized via cycloaddition of CO 2 with epoxide under the catalytic condition due to the low reactivity of CO 2 (thermodynamic as well as kinetic inert). An ideal catalyst for this conversion is composed of a Lewis acid to activate the epoxide ring and a Lewis base to open the epoxide ring. Efforts have been done to synthesize various catalytic systems for cyclic carbonate formation. The review is focused on metal-catalyzed cyclic carbonate formation. It begins with carbon capturing, storage, and utilization (CCSU) along with the importance of cyclic carbonate. The mechanism for cyclic carbonate formation was classified into two categories including binary and bifunctional systems based on the presence of nucleophilic moiety either as a separate entity or attached to a catalyst. Various metal catalysts such as metal salen, metal porphyrin, metal salts, metal–organic framework, and zeolitic imidazolate framework are discussed with recent progress in the development. It was believed that homogeneous catalysts showed high catalytic activity but difficult product separation whereas heterogeneous catalysts can be easily separated by simple filtration. Finally, the conclusion and the future outlook in the development of catalysts for cyclic carbonate formation are mentioned. [ABSTRACT FROM AUTHOR]

The cycloaddition of CO2 to epoxides to afford cyclic organic carbonates is an increasingly relevant non-reductive strategy to convert CO2 to useful products able to serve as high-boiling solvents, chemical intermediates, and monomers for the preparation of more sustainable polymers. The development of efficient and robust heterogeneous catalysts for such transformation is, therefore, crucial and can be carried out by several strategies that often require the preparation of sophisticated and/or expensive organic networks, linkers, or compounds. A different approach to the preparation of heterogeneous catalysts for CO2-epoxide coupling is by applying surface science methodologies to graft molecular fragments or single atoms on various supports leading to well-defined active sites. In this context, surface organometallic chemistry (SOMC), along with comparable methodologies, is a valuable approach for the preparation of efficient, single-site Lewis acids and catalysts for the target cycloaddition reaction on metal oxides, whereas, other grafting methodologies, can be applied to prepare analogous catalysts on different kinds of surfaces. Finally, we discuss very recent advances in the application of surface methodologies for the preparation of single atom catalysts as an increasingly relevant approach towards highly active Lewis acids for the cycloaddition of CO2 to epoxides. Overall, we show that Lewis acids and catalysts prepared by facile surface methodologies hold significant potential for future application in the synthesis of cyclic carbonates from CO2.

Novel mono- and bimetallic scorpionate aluminum compounds have been designed and characterized by spectroscopic methods. These organometallics complexes, in combination with tetrabutylammonium bromide as cocatalyst, displayed good catalytic activity for the cycloaddition of styrene oxide and CO2 under ambient conditions. Among the compounds tested, monometallic complex 3 featuring diethylamino groups showed the highest catalytic activity. This catalytic system catalyzed the formation of cyclic carbonate products from their corresponding epoxides at room temperature and 1 bar of CO2 pressure in the absence of a solvent in good yields and excellent selectivities.

Novel polyhydroxylated ammonium, imidazolium, and pyridinium salt organocatalysts were prepared through N-alkylation sequences using glycidol as the key precursor. The most active pyridinium iodide catalyst effectively promoted the carbonation of a set of terminal epoxides (80 to >95% yields) at a low catalyst loading (5 mol%), ambient pressure of CO2, and moderate temperature (75 °C) in batch operations, also demonstrating high recyclability and simple downstream separation from the reaction mixture. Moving from batch to segmented flow conditions with the operation of thermostated (75 °C) and pressurized (8.5 atm) home-made reactors significantly reduced the process time (from hours to seconds), increasing the process productivity up to 20.1 mmol(product) h−1 mmol(cat)−1, a value ~17 times higher than that in batch mode. [ABSTRACT FROM AUTHOR]

Highlights: PC synthesis was achieved over CaO-MgO as a catalyst. The effects of precipitating agent and Mg/Ca ratio was investigated. Best PC yield and selectivity of 96.8% and 99.8%, respectively were achieved. CaO-MgO catalyst revealed excellent reusability up to 6 cycles. A series of calcium oxide–magnesium oxide (CaO–MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active sites present on the surface of the CaO–MgO catalysts was carried out using the Hammett indicator method. The as-prepared mixed oxide samples were tested for propylene carbonate (PC) synthesis through the alcoholysis of urea with propylene glycol (PG). The effects of the catalyst composition, catalyst dose, reaction temperature, and contact time on the PC yield and selectivity were investigated. The maximum PC yield of 96%, with high PC selectivity of 99% and a urea conversion rate of 96%, was attained at 160 °C using CaO–MgO catalysts prepared using a Mg/Ca ratio of 1 and Na2CO3 as a precipitating agent. The best-performing catalysts also exhibited good reusability without any significant loss in PC selectivity. It is expected that the present study will provide useful information on the suitability of different precipitating agents with respect to the catalytic properties of the oxides of Ca and Mg and their application in the synthesis of organic carbonates. [ABSTRACT FROM AUTHOR]

Porous polymeric frameworks have received great interest over the past few years because of their nonstop growth as crystalline porous polymeric materials connected through covalent bonds and versatile utilities in diverse fields. The production of high-value organic compounds via sustainable and environment-friendly methods is an uphill struggle for researchers. The elegant strategy of using carbon dioxide as a C1 building block is an intriguing platform owing to its non-toxicity, easy accessibility, natural abundance, recyclability, non-flammability, and cheapness. Additionally, CO2 levels are regarded as the main contributor to the greenhouse effect (the most abundant greenhouse gas across the globe) and the aforementioned strategy needs to mitigate CO2 emissions. This present study describes the synthesis of silver nanoparticles (AgNPs) embedded in a porous polymeric framework, a reusable heterogeneous catalyst (recyclable over 5 times), TpMA (MC)@Ag. The synthesized catalyst is characterized by using FT-IR, PXRD, XPS, FE-SEM, TEM, EDAX, TGA DTA, and N2 sorption studies. Additionally, the catalysts can be easily recycled to generate the desired α-alkylidene cyclic carbonates and oxazolidinone compounds under solvent-free conditions. This research demonstrates the potential of nanoporous 2D porous polymeric framework-based materials in the area of catalysis, specially, in CO2 capture and chemical fixation. These findings offer a promising approach for the chemical fixation of CO2 into α-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols utilizing AgNPs embedded in a 2D catalyst, which functions as a potential heterogeneous catalyst under mild conditions (e.g., solvent-free approach).

Herein, we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV) or Zr(IV) centres (2a-3b) as homogeneous catalysts for the conversion of CO2 and epoxides into cyclic carbonates. The four complexes were synthesised, characterised and then evaluated in combination with tetrabutylammonium iodide, bromide or chloride as binary catalytic systems for the reaction of CO2 with 1,2-epoxyhexane as epoxide substrate at 12 bar CO2 pressure and 90 °C for 2 h. The catalytic systems comprising the two Ti(IV) complexes (2a and 2b) showed similar performance. One notable exception was the catalytic system consisting of titanium complex 2b, bearing an axial Cl-ligand, and tetrabutylammonium chloride, which displayed higher catalytic activity compared to other titanium-based systems. Even higher activity was achieved with Zr(IV) complex 3a, bearing an axial isopropoxide ligand, which reached turnover numbers (TONmetal) up to 1920 for the reaction of CO2 with 1,2-epoxyhexane at 12 bar CO2 pressure and 90 °C for 2 h. This performance is comparable with that of state-of-the-art catalysts for this reaction. The catalytic system consisting of complex 3a and tetrabutylammonium bromide was explored further by investigating its applicability with a broad substrate scope, achieving quantitative conversion of several epoxides with CO2 into cyclic carbonate products at 90 °C and 12 bar CO2 pressure for 18 h. The selectivity towards the cyclic carbonate products was ≥ 98% for all studied terminal epoxides and ≥ 80% for all examined cyclohexene-type 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. [ABSTRACT FROM AUTHOR]

One way to exploit CO2 is to use it as a feedstock for the production of cyclic carbonates via its reaction with organic epoxides. As far as we know, there is still no heterogeneous catalyst that accelerates the reaction in a selective, efficient and industrially usable way. Cobalt and zinc-based zeolitic imidazole frameworks (ZIFs) have been explored as heterogeneous catalysts for this reaction. In particular, we have prepared ZIF-8 and ZIF-67 catalysts, which have been modified by partial replacement of 2-methylimidazole by 1,2,4-triazole, in order to introduce uncoordinated nitrogen groups with the metal. The catalysts have shown very good catalytic performance, within the best of the heterogeneous catalysts tested in the cycloaddition of CO2 with epichlorohydrin. The catalytic activity is due ultimately to defects on the outer surface of the crystal, and varies in the order of ZIF-67-m > ZIF-67 > ZiF-8-m = ZIF-8. Notably, reactions take place under mild reaction conditions and without the use of co-catalysts. [ABSTRACT FROM AUTHOR]

Transforming CO2 into value-added chemicals has been an important subject in recent years. The development of a novel heterogeneous catalyst for highly effective CO2 conversion still remains a great challenge. As an emerging class of porous organic polymers, covalent organic frameworks (COFs) have exhibited superior potential as catalysts for various chemical reactions, due to their unique structure and properties. In this study, a layered two-dimensional (2D) COF, IM4F-Py-COF, was prepared through a three-component condensation reaction. Benzimidazole moiety, as an ionic liquid precursor, was integrated onto the skeleton of the COF using a benzimidazole-containing building unit. Ionization of the benzimidazole framework was then achieved through quaternization with 1-bromobutane to produce an ionic liquid-immobilized COF, i.e., BMIM4F-Py-COF. The resulting ionic COF shows excellent catalytic activity in promoting the chemical fixation of CO2 via reaction with epoxides under solvent-free and co-catalyst-free conditions. High porosity, the one-dimensional (1D) open-channel structure of the COF and the high catalytic activity of ionic liquid may contribute to the excellent catalytic performance. Moreover, the COF catalyst could be reused at least five times without significant loss of its catalytic activity. [ABSTRACT FROM AUTHOR]

A novel cobalt-based MOF nanoribbon with high catalytic activity and selectivity in the CO 2 cycloaddition reaction. [Display omitted] Chemical fixation of CO 2 with epoxides is an effective option to achieve sustainable synthesis of cyclic organic carbonates. Although metal–organic frameworks (MOFs) are promising catalysts for this reaction, their low stability in aqueous solutions makes this application infeasible. In an effort to overcome this limitation, cobalt-based metal–organic framework (Co(II)MOF) nanoribbons have been prepared by coordinating the Co(II) ions with a new ligand (C 16 H 12 N 4 O 4) full of oxygen and nitrogen moieties. Strong chemical interactions occur between the adsorbed CO 2 and oxygen/nitrogen atoms in this porous MOF structure. Co(II)-MOF nanoribbons with tetra- n -butylammonium bromide acted as cocatalysts with ∼97% yield of cyclic carbonate (reaction kinetic rate of 14.7 × 106 µmol g-1 h−1) upon the cycloaddition of epichlorohydrin (ECH) to CO 2 (>99% reaction selectivity under solvent-free reaction condition at 80 °C, 3 h and 1 MPa CO 2 pressure). This work may open a new avenue for chemical fixation of CO 2 by rational design of the components and morphology of MOF-based catalysts. [ABSTRACT FROM AUTHOR]

A new bifunctional heterogeneous catalyst system was introduced by immobilization of pyridinium-based ionic liquid on Zn-MOF-NH 2 to produce IL-supported Zn-MOF-NH 2 as an efficient catalyst for CO 2 -epoxide cycloaddition reactions under mild solvent-free conditions. [Display omitted] • A new bifunctional heterogeneous catalyst system via immobilization of pyridinium-based ionic liquid on Zn-MOF-NH 2. • Dual-functional one-component system (IL-supported Zn-MOF-NH 2). • Including both Lewis acid sites (Zn) and IL functional sites. • CO 2 -epoxide cycloaddition reactions under mild solvent-free conditions. • High catalytic activity for the CO 2 -epoxide cycloaddition reactions. • Efficient low-leaching catalyst system. • Reusable for four successive cycles without decrease in the catalytic activity. A new bifunctional heterogeneous catalyst system was developed by immobilization of pyridinium-based ionic liquid on Zn-MOF-NH 2 to produce an IL-supported Zn-MOF-NH 2 catalyst. The dual-functional one-component system, including both Lewis acid sites and IL functional sites, showed high catalytic activity for the CO 2 -epoxide cycloaddition reactions under mild solvent-free conditions. Different techniques such as FE-SEM, EDX, FT-IR, XRD, and BET were applied to characterize of the as-prepared catalyst. This efficient low-leaching catalyst system is separated by centrifugation and can be reused successfully for four successive cycles without altering the catalytic activity in CO 2 epoxidation to cyclic carbonates. Due to the wide variety seen in both metal–organic frameworks (MOFs) and ionic liquids (ILs), we believe that this research represents a significant step forward in the potential applications of synthetic modification methods within MOFs. [ABSTRACT FROM AUTHOR]

Nowadays there is an urgent need for mitigating CO 2 emissions through clean energy and the development of new carbon capture and utilization (CCU) technologies. Among others, the use of bifunctional ionic liquids (ILs) addressed simultaneously CO 2 capture and conversion steps, having applied successfully to the propylene carbonate production case. In this work, a systematic evaluation of all representative cyclic carbonate literature was made, covering ethylene, propylene, butylene, hexylene, cyclohexene, and styrene cyclic carbonates, in order to guide the product role within the integrated CCU (ICCU) concept. The multiscale strategy combining molecular simulation (DFT -Density Functional Theory-, COSMO -COnductor-like Screening MOdel-), process simulation (COSMO/Aspen methodology), and life cycle assessment (LCA) was used to set up, simulate and evaluate the processes. ICCU configuration is the best approach when compared with sequential configuration for energy consumption analysis (reduction of 28, 28, 22, 11 and 6 %, respectively, for ethylene, propylene, butylene, hexylene, and cyclohexene cases) and CO 2 emissions associated (reduction of 38, 40, 31 and 14 %, respectively, for ethylene, propylene, butylene, and hexylene cases). The main variable of the results is the boiling point of the cyclic carbonate since heavy products impose technical limitations and even discard ICCU alternative. The ICCU concept works since all cyclic carbonates' reaction enthalpies are higher than that of the IL-CO 2 one, which reduces heating requirements. Finally, energy demand can be slightly further reduced, partially recycling the cyclic carbonate to the capture unit. [Display omitted] • Sequential and integrated CO 2 capture and conversion processes were evaluated. • Integrated schemes are better in energy consumption in almost all the cases. • Neat emissions are highly improved in integrated processes. • Product's boiling point was found to be the optimization key in all scenarios. [ABSTRACT FROM AUTHOR]

The conversion of CO 2 with epoxides into the corresponding cyclic carbonates represents a green approach to transform a waste into value-added products. To promote this conversion, a catalyst in needed. This study presents the synthesis of two cross-linked materials composed of magnesium phthalocyanine and imidazolium bromide moieties: MgPc-BIBI-Br and MgPc-SIBI-Br. Magnesium phthalocyanines are cost-effective and versatile catalysts, synthesized in high yield from low-cost precursors and can be easily modified for specific needs. Imidazolium bromide groups play a crucial role as well, acting as a nucleophile source essential to promote the ring-opening process of the epoxide. The materials have been extensively characterized through analytical and spectroscopic techniques and tested as catalysts in the conversion of epichlorohydrin into 4-chloromethyl-1,3-dioxalan-2-one. They both achieved excellent catalytic performance (maximal TON values of 3070 for MgPc-SIBI-Br and 1903 for MgPc-BIBI-Br) and recyclability (both recyclable at least for 4 cycles). The reported results represent an improvement if compared to similar materials already reported in the literature in which the addition of external nucleophilic species (e.g. TBAB, BMIM-Br, etc.) is needed. To the best of our knowledge, this work is the first example in which imidazolium bromide and magnesium phthalocyanine moieties are combined in bifunctional polymeric materials that convert CO 2 into cyclic carbonates via heterogeneous catalysis. [Display omitted] • Efficient synthesis of highly cross-linked magnesium phthalocyanine-based catalysts. • New examples of entirely heterogeneous bifunctional catalysts for CO 2 valorisation. • Green and sustainable approach for the synthesis of cyclic carbonates. • Raising Br-/Mg ratio in the catalyst to increment the level of epoxide conversion. [ABSTRACT FROM AUTHOR]

This study introduces a straightforward synthesis method for producing a hybrid material composed of halloysite and kojic acid, which catalyzes carbon dioxide (CO 2) conversion processes. Kojic acid, derived from malted rice fermentation, exhibits inherent chelating properties that facilitate the introduction of copper ions onto the material's surface. Copper ions, an economically viable alternative to noble metals, catalyze CO 2 conversion reactions effectively. The hybrid catalyst was evaluated for two distinct CO 2 conversion pathways: photocatalytic methane production under simulated sunlight and CO 2 fixation into cyclic carbonates via epoxide reactions. The hybrid material demonstrates remarkable catalytic activity under mild conditions, achieving high conversion efficiencies at 45 °C for methane production and 70 °C for carbonate fixation at atmospheric pressure. Conversion of 31 % and 89 % were achieved for the photocatalytic CO 2 reduction and the carbonate fixation, respectively. FT-IR spectra confirmed the functionalization of the material. Additionally, its organic/inorganic hybrid nature is complemented by excellent thermal stability, as studied by TGA. It enables repeated utilization, maintaining a 25 % catalytic activity for methane production and 70 % for carbonate fixation after the fourth reuse. This research highlights the potential of using naturally derived materials for sustainable CO 2 mitigation. [Display omitted] • Hybrid halloysite-kojic acid material efficiently catalyzes CO 2 conversion processes. • Copper ions offer a cost-effective alternative to other metals. • Converts CO 2 to methane under simulated sunlight at 45 °C and atmospheric pressure. • Fixes CO 2 into cyclic carbonates with epoxides at 70 °C. • Facile synthesis and excellent thermal stability enhance practical utility. [ABSTRACT FROM AUTHOR]

Development of an effective catalytic system for the cycloaddition of carbon dioxide to epoxides for the preparation of cyclic carbonates under mild conditions is of great importance. Herein, a mixture of zinc iodide, metal chlorides, and strong organic bases is demonstrated to be a useful catalytic system that works at room temperature under atmospheric pressure. The most efficient combination, zinc iodide-niobium chloride-7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (1.2-0.3-3.0 mol%), gave styrene carbonate (95%) from styrene oxide and CO2 (balloon) at 25 °C for 24 h. Another combination, zinc iodide-zinc chloride-1,8-diazabicyclo[5.4.0]undec-7-ene (1.2-0.8-4.0 mol%), kept the catalytic activity for the preparation of propylene carbonate until the fourth run. Therefore, the reaction system was operationally simple, highly efficient, and proceeded under ambient conditions. The catalyst is composed of readily available reagents and is reusable. Thus, the method presented is a powerful tool for utilizing CO2 as the starting material for the production of valuable chemicals.

The development of bifunctional ionic polymers as heterogeneous catalysts for effective, cocatalyst- and metal-free cycloaddition of carbon dioxide into cyclic carbonates has attracted increasing attention. However, facile fabrication of such polymers having high numbers of ionic active sites, suitable types of hydrogen bond donors (HBDs), and controlled spatial positions of dual active sites remains a challenging task. Herein, imidazolium-based ionic polymers with hydroxyl/carboxyl groups and high ionic density were facilely prepared by a one-pot quaternization reaction. Catalytic evaluation demonstrated that the presence of HBDs (hydroxyl or carboxyl) could enhance the catalytic activities of ionic polymers significantly toward the CO2 cycloaddition reaction. Among the prepared catalysts, carboxyl-functionalized ionic polymer (PIMBr-COOH) displayed the highest catalytic activity (94% yield) in the benchmark cycloaddition reaction of CO2 and epichlorohydrin, which was higher than hydroxyl-functionalized ionic polymer (PIMBr-OH, 76% yield), and far exceeded ionic polymer without HBDs groups (PIMBr, 54% yield). Furthermore, PIMBr-COOH demonstrated good recyclability and wide substrate tolerance. Under ambient CO2 pressure, a number of epoxides were smoothly cycloadded into cyclic carbonates. Additionally, density functional theory (DFT) calculation verified the formation of strong hydrogen bonds between epoxide and the HBDs of ionic polymers. Furthermore, a possible mechanism was proposed based on the synergistic effect between carboxyl and Br− functionalities. Thus, a facile, one-pot synthetic strategy for the construction of bifunctional ionic polymers was developed for CO2 fixation. [ABSTRACT FROM AUTHOR]

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed. [ABSTRACT FROM AUTHOR]

Wehave recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA]2[ZnBr4] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h-1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2. [ABSTRACT FROM AUTHOR]

Nonisocyanate polyurethane materials with pending alcohol groups in the polymeric chain were synthesized by polyaddition reaction of bis(cyclic carbonates) onto diamines. For the platform molecule, 1,4-butanediol bis(glycidyl ether carbonate) (BGBC, 1) was used. The polyaddition reaction of 1 onto a wide range of diamines with different electronic and physical properties was explored. All PHUs were obtained quantitatively after 16 h at 80 °C temperature in MeCN as solvent. The low nucleophilicity of L-lysine has proven unable to ring-open the cyclic carbonate and, thus, no reaction occurred. The addition of DBU or TBD as the catalyst was tested and allows the obtention of the desired PHU. However, the presence of strong bases also led to the formation of polyurea fragments in the new PHU. The different poly(hydroxyurethane) materials were characterized using a wide range of spectroscopic techniques such as NMR, IR, MALDI-ToF, and using GPC studies. The thermal properties of the NIPUs were investigated by DSC and TGA analyses. Moreover, reactions employing different monomer ratios were performed, obtaining novel hydroxycarbamate compounds. Finally, sequential and one-pot experiments were also carried out to synthesize the PHUs polymers in one-step reaction. [ABSTRACT FROM AUTHOR]

We have recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA]2[ZnBr4] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h−1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2.

A one-pot multicomponent green process is investigated for the synthesis of perfluoroalkylated cyclic carbonate which merges the photo-promoted Atom Transfer Radical Addition (ATRA) of a perfluoroalkyl iodide (Rf-I) onto allyl alcohols with the Lewis-base-promoted carboxylative cyclization. The evolution of the complex mixture during the reaction was monitored by in situ ATR-IR and Raman spectroscopies that provided insights into the reaction mechanism. The effect on the kinetics and the carbonate yields of key parameters such as the stoichiometry of reagents, the nature of the Lewis base and the solvent, the temperature and the pressure were evaluated. It was found that high yields were obtained using strong Lewis bases that played both the role of activating the allyl alcohol for the generation of the allyl carbonate in the presence of CO2 and promoting the ATRA reaction through the activation of C4F9I by halogen bonding. This protocol was also extended to various unsaturated alcohols.

For the production of cyclic carbonates from the cycloaddition of CO2 with epoxides, halogen pollution and product purity are two of the most common problems due to the usage of homogeneous halogen-containing catalysts such as ammonium salt and alkali metal halide. Hence, the development of a novel, halogen-free and efficient catalyst for the synthesis of high-purity cyclic carbonates is significant. Here, a series of acid–base bifunctional Ce1-xZrxO2 nanorods were successfully prepared. The Ce1-xZrxO2 nanorods could catalyze the cycloaddition of CO2 with epoxides efficiently without any halogen addition. Especially for the Ce0.7Zr0.3O2 catalyst, a conversion of 96% with 100% 1,2-butylene carbonate selectivity was achieved. The excellent catalytic performance of Ce1-xZrxO2 nanorods is attributed to the formation of the CeO2-ZrO2 solid solution, which contributes to abundant moderate acidic–basic active sites on the catalyst surface. It is the synergistic effect of moderate acidic–basic sites that dominates the conversion of CO2 with epoxides, which will supply important references for the synthesis of efficient metal oxide catalyst for the cycloaddition of CO2 with epoxides. [ABSTRACT FROM AUTHOR]