Calcium-Based Catalytic System for the Synthesis of Bio-Derived Cyclic Carbonates under Mild Conditions

Construction of a series of pH stable Ca-based MOFs, their CO2 adsorption and catalytic activity

In this study, three different solvent systems have been employed to investigate the effect of reaction parameters on the synthesis of four alkaline earth metal-based MOFs namely [Ca(0.5 1,4-phenyl diacetic acid)2(H2O)DMF]∞ (Ca-MOF-1), [Ca(1,4-naphthalene dicarboxylate)DMF]∞ (Ca-MOF-2), [Ca2(0.5 1,2,4,5-benzene tetracarboxylate)2(H2O)3DMF]∞ (Ca-MOF-3) and [Ca2(2,6-naphthalene dicarboxylate)2(H2O)6]∞ (Ca-MOF-4). The crystal structures of these four MOFs have been resolved through single crystal X-ray analysis and the bulk phase purity of these MOFs was assessed using PXRD and FT-IR analysis. To check the stability of these MOFs, thermogravimetric analysis (TGA) was carried out. To analyze the robustness of these MOFs, the PXRD of the samples was also collected at different pH levels. These MOFs were further explored as Lewis acid catalysts for the alcoholysis of epoxides and the activity of these catalysts depend on the open metal sites present in the MOFs. The catalytic activity follows the order: Ca-MOF-2 > Ca-MOF-4 > Ca-MOF-1 > Ca-MOF-3. The activity was also checked with various epoxide substrates using Ca-MOF-2. Density functional theory (DFT) calculations also support this trend with the help of the thermodynamic feasibility of epoxide binding, considering model MOF structures. The weak interaction between the epoxide oxygen and the metal centre of the most stable MOF structure has also been clarified by computational studies.

Catalytic Strategies for the Cycloaddition of CO2 to Epoxides in Aqueous Media to Enhance the Activity and Recyclability of Molecular Organocatalysts

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.

Silicon Oxycarbide (SiOC)-Supported Ionic Liquids: Heterogeneous Catalysts for Cyclic Carbonate Formation

Silicon oxycarbides (SiOCs) impregnated with tetrabutylammonium halides (TBAX) were investigated as an alternative to silica-based supported ionic liquid phases for the production of bio-based cyclic carbonates derived from limonene and linseed oil. The support materials and the supported ionic liquid phases (SILPs) were characterized via Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption, X-ray photoelectron spectroscopy, microscopy, and solvent adsorption. The silicon oxycarbide supports were pyrolyzed at 300-900 °C prior to being coated with different tetrabutylammonium halides and further used as heterogeneous catalysts for the formation of cyclic carbonates in batch mode. Excellent selectivities of 97-100% and yields of 53-62% were obtained with tetrabutylammonium chloride supported on the silicon oxycarbides. For comparison, the catalytic performance of commonly employed silica-supported ionic liquids was investigated under the same conditions. The silica-supported species triggered the formation of a diol as a byproduct, leading to a lower selectivity of 87% and a lower yield of 48%. Ultimately, macroporous monolithic SiOC-SILPs with suitable permeability characteristics (k1 = 10-11 m2) were produced via photopolymerization-assisted solidification templating and applied for the selective and continuous production of limonene carbonate with supercritical carbon dioxide as the reagent and sole solvent. Constant product output over 48 h without concurrent catalyst leaching was achieved.

Synthesis of cyclic carbonates from CO2 cycloaddition to bio-based epoxides and glycerol: an overview of recent development

Anthropogenic carbon dioxide (CO₂) emissions contribute significantly to global warming and deplete fossil carbon resources, prompting a shift to bio-based raw materials. The two main technologies for reducing CO₂ emissions are capturing and either storing or utilizing it. However, while capture and storage have high reduction potential, they lack economic feasibility. Conversely, by utilizing the CO₂ captured from streams and air to produce valuable products, it can become an asset and curb greenhouse gas effects. CO₂ is a challenging C1-building block due to its high kinetic inertness and thermodynamic stability, requiring high temperature and pressure conditions and a reactive catalytic system. Nonetheless, cyclic carbonate production by reacting epoxides and CO₂ is a promising green and sustainable chemistry reaction, with enormous potential applications as an electrolyte in lithium-ion batteries, a green solvent, and a monomer in polycarbonate production. This review focuses on the most recent developments in the synthesis of cyclic carbonates from glycerol and bio-based epoxides, as well as efficient methods for chemically transforming CO₂ using flow chemistry and novel reactor designs.

Sustainable cycloaliphatic polyurethanes: from synthesis to applications

Polyurethanes (PUs) are a versatile and major polymer family, mainly produced via polyaddition between polyols and polyisocyanates. A large variety of fossil-based building blocks is commonly used to develop a wide range of macromolecular architectures with specific properties. Due to environmental concerns, legislation, rarefaction of some petrol fractions and price fluctuation, sustainable feedstocks are attracting significant attention, e.g., plastic waste and biobased resources from biomass. Consequently, various sustainable building blocks are available to develop new renewable macromolecular architectures such as aromatics, linear aliphatics and cycloaliphatics. Meanwhile, the relationship between the chemical structures of these building blocks and properties of the final PUs can be determined. For instance, aromatic building blocks are remarkable to endow materials with rigidity, hydrophobicity, fire resistance, chemical and thermal stability, whereas acyclic aliphatics endow them with oxidation and UV light resistance, flexibility and transparency. Cycloaliphatics are very interesting as they combine most of the advantages of linear aliphatic and aromatic compounds. This original and unique review presents a comprehensive overview of the synthesis of sustainable cycloaliphatic PUs using various renewable products such as biobased terpenes, carbohydrates, fatty acids and cholesterol and/or plastic waste. Herein, we summarize the chemical modification of the main sustainable cycloaliphatic feedstocks, synthesis of PUs using these building blocks and their corresponding properties and subsequently present their major applications in hot-topic fields, including building, transportation, packaging and biomedicine.

Chemoselective cycloadditions to epoxide derivatives of erucic acid with CO2 and CS2: controlled access to value-added bio-derived compounds

The potential for application of bio-derived molecules in our everyday lives is attracting vast interest as attention moves towards development of a truly circular and sustainable economy. Whilst a large number of molecules are naturally available and contain a variety of functional groups, few of these compounds are able to be immediately transferred to applications where they can directly replace established oil-derived species. This issue presents both a challenge and an opportunity for the synthetic chemistry community. This study demonstrates how erucic acid, a molecule containing an olefin and a carboxylic acid, which is readily available from commonly cultivated rapeseed oils, can be used as a platform to be chemoselectively converted into a range of value-added compounds using established and high yielding synthetic procedures. In particular, the work showcases approaches towards the chemoselective (and in cases regioselective) oxidation with m-CPBA and incorporation of cyclic carbonate and cyclic dithiocarbonate functionalities which have potential to be employed in a range of applications. Expedient routes to unusual derivatives containing both cyclic carbonate and cyclic dithiocarbonates are also presented taking advantage of the distinct reactivities of the two different epoxides in the intermediate compounds. This work also provides a rare example of the synthesis of internal cyclic dithiocarbonates. These new products have potential to be applied as monomers in the growing field of bio-based non-isocyanate polyurethane synthesis.

Continuous Formation of Limonene Carbonates in Supercritical Carbon Dioxide

We present a continuous flow method for the conversion of bioderived limonene oxide and limonene dioxide to limonene carbonates using carbon dioxide in its supercritical state as a reagent and sole solvent. Various ammonium- and imidazolium-based ionic liquids were initially investigated in batch mode. For applying the best-performing and selective catalyst tetrabutylammonium chloride in continuous flow, the ionic liquid was physisorbed on mesoporous silica. In addition to the analysis of surface area and pore size distribution of the best-performing supported ionic liquid phase (SILP) catalysts via nitrogen physisorption, SILPs were characterized by diffuse reflectance infrared Fourier transform spectroscopy and thermogravimetric analysis and served as heterogeneous catalysts in continuous flow. Initially, the continuous flow conversion was optimized in short-term experiments resulting in the desired constant product outputs. Under these conditions, the long-term behavior of the SILP system was studied for a period of 48 h; no leaching of catalyst from the supporting material was observed in the case of limonene oxide and resulted in a yield of 16%. For limonene dioxide, just traces of leached catalysts were detected after reducing the catalyst loading from 30 to 15 wt %, thus enabling a constant product output in 17% yield over time.

One-Pot Tandem Catalytic Epoxidation—CO2 Insertion of Monounsaturated Methyl Oleate to the Corresponding Cyclic Organic Carbonate

Conversion of unsaturated fatty acids, FAMEs or triglycerides into the corresponding cyclic organic carbonates involves two reaction steps—double-bond epoxidation and CO2 insertion into the epoxide—that are generally conducted separately. We describe an assisted-tandem catalytic protocol able to carry out carbonation of unsaturated methyl oleate in one-pot without isolating the epoxide intermediate. Methyl oleate carbonate was obtained in 99% yield and high retention of cis-configuration starting from methyl oleate using hydrogen peroxide and CO2 as green reagents, in a biphasic system and in the presence of an ammonium tungstate ionic liquid catalyst with KBr as co-catalyst.

Sustainable Synthesis of Cyclic Carbonates from Terminal Epoxides by a Highly Efficient CaI2/1,3-Bis[tris(hydroxymethyl)-methylamino]-propane Catalyst

The nonstopping increment of atmospheric carbon dioxide (CO₂) concentration keeps harming the environment and human life. The traditional concept of carbon capture and storage (CCS) is no longer sufficient and has already been corrected to carbon capture, utilization, and storage (CCUS). CCUS involves significant CO₂ utilization, such as cyclic carbonate formation, for its cost effectiveness, less toxicity, and abundant C1 synthon in organic synthesis. However, the high thermodynamic and kinetic stability of CO₂ limits its applications. Herein, we report a mild, efficient, and practical catalyst based on abundant, nontoxic CaI₂ in conjunction with biocompatible ligand 1,3-bis[tris(hydroxymethyl)-methylamino]-propane (BTP) for CO₂ fixation under atmospheric pressure with terminal epoxides to give the cyclic carbonates. The Job plot detected the 1:1 Ca²⁺/BTP binding stoichiometry. Furthermore, formation of a single crystal of the 1:1 Ca²⁺/BTP complex was confirmed by single-crystal X-ray crystallography. The bis(cyclic carbonate) products exhibit potentials for components in the non-isocyanate polyurethanes (NIPUs) process. Notably, this protocol shows attractive recyclability and reusability.

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

Oils and fats of vegetable and animal origin remain an important renewable feedstock for the chemical industry. Their industrial use has increased during the last 10 years from 31 to 51 million tonnes annually. Remarkable achievements made in the field of oleochemistry in this timeframe are summarized herein, including the reduction of fatty esters to ethers, the selective oxidation and oxidative cleavage of C-C double bonds, the synthesis of alkyl-branched fatty compounds, the isomerizing hydroformylation and alkoxycarbonylation, and olefin metathesis. The use of oleochemicals for the synthesis of a great variety of polymeric materials has increased tremendously, too. In addition to lipases and phospholipases, other enzymes have found their way into biocatalytic oleochemistry. Important achievements have also generated new oil qualities in existing crop plants or by using microorganisms optimized by metabolic engineering.

Metal-Cocatalyst Interaction Governs the Catalytic Activity of MII-Porphyrazines for Chemical Fixation of CO2

Chemical fixation of CO₂ to produce cyclic carbonates can be a green and atomic efficient process. In this work, a series of porphyrazines (Pzs) containing electron-withdrawing groups and central M^II ions (where M = Mg, Zn, Cu, and Co) were synthesized and investigated as catalysts for the cycloaddition of CO₂ to epoxides. Then, the efficiency of the Pzs was tested by varying cocatalyst type and concentration, epoxide, temperature, and pressure. Mg^IIPz bearing trifluoromethyl groups (1) showed the best conversion, producing, selectively, 78% of propylene cyclic carbonate (PCC), indicating that a harder and stronger Lewis acid is more effective for epoxide activation. Moreover, cocatalyst variation showed a notable effect on the reaction yields. Spectrophotometric titrations, MALDI-TOF mass spectra, and theoretical calculations suggest poisoning of the catalyst when tetrabutylammonium chloride (TBAC) and large amounts of tetrabutylammonium bromide (TBAB) were used in the system. The same was not observed for tetrabutylammonium iodide (TBAI), indicating that the metal-cocatalyst interaction may govern the reaction rate. In addition, two rare examples of crystalline structures were obtained, proving the distorted square pyramidal geometry with water molecule as axial ligand. This is one of the first studies reporting Pzs as catalysts for the chemical fixation of CO₂, and we believe that the intricate balance between cocatalyst concentration and conversion efficiency shown here may aid future studies in the area.

Efficient Synthesis of Cyclic Carbonates from Unsaturated Acids and Carbon Dioxide and their Application in the Synthesis of Biobased Polyurethanes

Bio-derived furan- and diacid-derived cyclic carbonates have been synthesized in high yields from terminal epoxides and CO₂ . Furthermore, four highly substituted terpene-derived cyclic carbonates were isolated in good yields with excellent diastereoselectivity in some cases. Eleven new cyclic carbonates derived from 10-undecenoic acid under mild reaction conditions were prepared, providing the corresponding carbonate products in excellent yields. The catalyst system also performed the conversion of an epoxidized fatty acid n-pentyl ester into a cyclic carbonate under relatively mild reaction conditions (80 °C, 20 bar, 24 h). This bis(cyclic carbonate) was obtained in high yields and with different cis/trans ratios depending on the co-catalyst used. An allyl alcohol by-product was only observed as a minor product when bis(triphenylphosphine)iminium chloride was used as co-catalyst. Finally, two cyclic carbonates were used as building blocks for the preparation of non-isocyanate poly(hydroxy)urethanes by reaction with 1,4-diaminobutane.

Cycloaddition of CO2 to epoxides by highly nucleophilic 4-aminopyridines: establishing a relationship between carbon basicity and catalytic performance by experimental and DFT investigations

New highly nucleophilic homogeneous and heterogeneous catalysts based on the 3,4-diaminopyridine scaffold are reported for the halogen-free cycloaddition of CO₂ to epoxides.

Self-Assembly of CDs@NH2-MOF(Ni)/n-Bu4NBr and its Catalytic Performance for CO2 Fixation with Epoxides

Metal–organic frameworks (CDs@NH2-MOF(Ni)) with carbon dots as the core were synthesised successfully by a one-pot method. The synthesised CDs@NH2-MOF(Ni) contain a large number of amine functional groups and a large surface area for capturing CO2. The FT-IR spectra showed that there exists a large number of carboxylate and amine groups on the surface of the carbon dots, and analysis by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric, and Brunauer–Emmett–Teller surface area analysis confirmed that the CDs had successfully entered the CDs@NH2-MOF(Ni). The cycloaddition reaction of propylene oxide (PO) and CO2 was carried out using CDs@NH2-MOF(Ni)/tetra-n-butylammonium bromide (TBAB) and NH2-MOF(Ni)/TBAB as catalytic systems, respectively. The reaction results showed that the two catalytic systems have good catalytic performance for the cycloaddition reaction of PO and CO2. Compared with that of the NH2-MOF(Ni)/TBAB system, both the conversion of PO and the yield of propylene carbonate (PC) are improved in the CDs@NH2-MOF(Ni)/TBAB system. Finally, the optimum catalytic reaction conditions, such as time, temperature, CO2 pressure, and five cycles of catalytic effect, were also discussed. Meanwhile, the mechanism of the catalytic system CDs@NH2-MOF(Ni)/TBAB in the cycloaddition reaction of PO and CO2 was proposed in this work.

Cycloaddition of carbon dioxide and epoxides catalyzed by rare earth metal complexes bearing a Trost ligand

Rare earth metal complexes containing Trost ligands were used to catalyze the cycloaddition reaction of epoxides with CO₂. A series of epoxides were successfully converted into the corresponding cyclic carbonates under mild conditions.

Conversion of dilute CO2 to cyclic carbonates at sub-atmospheric pressures by a simple indium catalyst

A simple indium halide with an ammonium salt catalyst can catalyze effectively the cycloaddition of epoxide and dilute CO₂. A detailed mechanistic investigation is conducted using kinetics, isotope labeling, and in situ NMR and IR experiments.

Formation of β-cyano-ketones through cyanide-promoted ring-opening of cyclic organic carbonates

In an unusual cascade process involving KCN, vinyl cyclic carbonates are converted into β-cyano ketones with the subsequent extrusion of carbon dioxide and acetonitrile facilitating a Michael addition to an intermediate α,β-unsaturated ketone.

Highly Active CO2 Fixation into Cyclic Carbonates Catalyzed by Tetranuclear Aluminum Benzodiimidazole-Diylidene Adducts

A set of tetranuclear alkyl aluminum adducts 1 and 2 supported by benzodiimidazole-diylidene ligands L1, N,N’-(1,5-diisopropylbenzodiimidazole-2,6-diylidene)bis(propan-2-amine), and L2, N,N’-(1,5-dicyclohexyl-benzodiimidazole-2,6-diylidene)dicyclohexanamine were synthetized in exceptional yields and characterized by spectroscopic methods. These compounds were studied as catalysts for cyclic carbonate formation (3a–o) from their corresponding terminal epoxides (2a–o) and carbon dioxide utilizing tetrabutylammonium iodide as a nucleophile in the absence of a solvent. The experiments were carried out at 70 °C and 1 bar CO2 pressure for 24 h and adduct 1 was the most efficient catalyst for the synthesis of a large variety of monosubstituted cyclic carbonates with excellent conversions and yields.

Unlocking the Potential of Substrate-Directed CO2 Activation and Conversion: Pushing the Boundaries of Catalytic Cyclic Carbonate and Carbamate Formation

The unparalleled potential of substrate-induced reactivity modes in the catalytic conversion of carbon dioxide and alcohol or amine functionalized epoxides is discussed in relation to more conventional epoxide/CO₂ coupling strategies. This conceptually new approach allows for a substantial extension of the substitution degree and functionality of cyclic carbonate/carbamate products, which are predominant products in the area of nonreductive CO₂ transformations. Apart from the creation of an advanced library of CO₂ -based heterocyclic products and intermediates, also the underlying mechanistic reasons for this novel reactivity profile are debated with a prominent role for the design and structure of the involved catalysts.

NNC-Scorpionate Zirconium-Based Bicomponent Systems for the Efficient CO2 Fixation into a Variety of Cyclic Carbonates

Two new derivatives of the bis(3,5-dimethylpyrazol-1-yl)methane modified by introduction of organosilyl groups on the central carbon atom, one of which bearing a chiral fragment, have been easily prepared. We verified the potential utility of these compounds through the reaction with [Zr(NMe₂)₄] for the preparation of novel zirconium complexes in which an ancillary bis(pyrazol-1-yl)methanide acts as a robust monoanionic tridentate scorpionate in a κ³-NNC chelating mode, forming strained four-membered heterometallacycles. These κ³-NNC-scorpionate zirconium amides were investigated as catalysts in combination with tetra-n-butylammonium bromide as cocatalyst for CO₂ fixation into five-membered cyclic carbonate products. The study has led to the development of an efficient zirconium-based bicomponent system for the selective cycloaddition reaction of CO₂ with epoxides. Kinetics investigations confirmed apparent first-order dependence on the catalyst and cocatalyst concentrations. In addition, this system displays very broad substrate scope, including mono- and disubstituted substrates, as well as the challenging biorenewable terpene derived limonene oxide, under mild and solvent-free conditions.

A Phosphonium Ylide as a Ligand for [3 + 2] Coupling Reactions of Epoxides with Heterocumulenes under Mild Conditions

The potential of carbonyl-stabilized phosphonium ylides as ligands for novel catalysis was explored. We found that the combination of phosphonium ylides and metal halide salts efficiently catalyzed the reaction of epoxides with carbon dioxide under mild conditions. Five-membered cyclic carbonates, including disubstituted cyclic carbonates, were obtained in good yields with the use of 1 atm of carbon dioxide at 35 °C. Terminal epoxides could be converted to N-aryl oxazolidinones in the reaction with isocyanates under a similar catalytic system.

Organocatalytic Trapping of Elusive Carbon Dioxide Based Heterocycles by a Kinetically Controlled Cascade Process

A conceptually novel approach is described for the synthesis of six-membered cyclic carbonates derived from carbon dioxide. The approach utilizes homoallylic precursors that are converted into five-membered cyclic carbonates having a β-positioned alcohol group in one of the ring substituents. The activation of the pendent alcohol group through an N-heterocyclic base allows equilibration towards a thermodynamically disfavored six-membered carbonate analogue that can be trapped by an acylating agent. Various control experiments and computational analysis of this manifold are in line with a process that is primarily dictated by a kinetically controlled acylation step. This cascade process delivers an ample diversity of six-membered cyclic carbonates in excellent yields and chemoselectivities under mild reaction conditions.