Catalysts For Synthesis Of Cyclic Carbonates Research Articles

Cycloaddition of CO2 to Epichlorohydrin over Pyridine, Vinylpyridine, and Poly(vinylpyridine): The Influence of Steric Crowding on the Reaction Mechanism

The cycloaddition of CO2 with epoxides is a 100% atom economical reaction that utilizes CO2 and produces valuable cyclic carbonate products. Organic bases are attractive catalysts for this reaction because of their green characteristics, such as low cost and low toxicity. However, further catalyst development is required to achieve acceptable yields at mild temperatures and pressures. This work aims to establish catalyst structure–performance relationships to accelerate the rational design of high performance organic base catalysts for the cycloaddition reaction. Toward this end, we investigate the influence of steric crowding at the ring nitrogen atom of a series of pyridine-based catalysts on the reaction mechanism and catalyst performance using batch reactor measurements at a mild temperature (57 °C) and atmospheric pressure under solventless conditions combined with in situ infrared spectroscopic characterization of the catalysts. We show that steric crowding at the ring nitrogen atom has a significant influence on the reaction mechanism and catalyst performance. Catalysts with unhindered access to the ring nitrogen atom, such as pyridine, 4-vinylpyridine, 3-vinylpyridine, and poly(4-vinylpyridine), are completely transformed during the cycloaddition reaction by quaternization from the epoxide reactant, producing zwitterionic pyridinium-epoxide adducts and ammonium salts that precipitate out of solution. Catalysts with hindered access to the ring nitrogen atom, such as 2-vinylpyridine and poly(2-vinylpyridine), resist quaternization from the epoxide reactant due to the high degree of steric hindrance at the ring nitrogen atom. The poly(2-vinylpyridine) catalyst in particular displayed high stability, high product selectivity, and high activity for cyclic carbonate synthesis. These molecular-level insights have significant implications for the rational design of active, stable, and metal-free catalysts for cyclic carbonate synthesis by tuning the steric crowding at the active site.

Group 13 salphen compounds (In, Ga and Al): a comparison of their structural features and activities as catalysts for cyclic carbonate synthesis.

Many complexes based on group 13 elements have been successfully applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2 and to date these have provided some of the most active catalysts developed. It is notable that most reports have focused on the use of aluminium-based compounds likely because of the well-established Lewis acidity of this element and its cost. In comparison, relatively little attention has been paid to the development of catalysts based on the heavier group 13 elements, despite their known Lewis acidic properties. This study describes the synthesis of aluminium, gallium and indium compounds supported by a readily prepared salphen ligand and explores both their comparative structures and also their potential as catalysts for the synthesis of cyclic carbonates. In addition, the halide ligand which forms a key part of the compound has been systematically varied and the effect of this change on the structure and catalytic activity is also discussed. It is demonstrated that the indium compounds are actually, and unexpectedly, the most active for cyclic carbonate synthesis, despite their lower Lewis acidity when compared to their aluminium congeners. The experimental observations from this work are fully supported by a Density Functional Theory (DFT) study, which provides important insights into the reasons as to why the indium catalyst with bromide, [InBr(salphen)], is most active.

Rational engineering of single-component heterogeneous catalysts based on abundant metal centers for the mild conversion of pure and impure CO2 to cyclic carbonates

• Novel, inexpensive heterogeneous catalysts for cyclic carbonate synthesis were prepared by readily accessible strategies. • The catalysts enabled the cocatalyst-free cycloaddition of CO 2 to several epoxides under mild conditions. • Besides pure CO 2 , diluted and impure CO 2 could successfully be used as feedstocks. • Recyclability and deactivation of the catalysts were studied. The development of fully heterogeneous catalysts for the widely investigated cycloaddition reaction of CO 2 to epoxides is crucial to achieve the sustainable synthesis of cyclic organic carbonates as useful emerging intermediates and building blocks. Nevertheless, relatively few fully heterogeneous catalytic systems exist for the title reaction with the ability to convert CO 2 to carbonates under atmospheric pressure and mild temperatures especially when using diluted and/or impure CO 2 as found in real case scenarios. Moreover, such catalysts are generally constituted by organic or metal–organic frameworks whose preparation generally involves the use or synthesis of expensive building blocks. In this work, we devised a convenient strategy to prepare single-component heterogeneous catalysts based on readily available metal halides and quaternary ammonium halide-based ionic liquids that started from a systematic evaluation of the corresponding homogeneous binary catalysts. This was followed by the preparation of silica-supported heterogeneous systems with different loadings of both catalytic components whose nature and composition were carefully studied through several characterization techniques (elemental analysis, FT-IR, ICP-OES, SEM and TEM microscopies, TGA analysis and XPS). The thus prepared catalysts showed the ability to carry out the cycloaddition of CO 2 to several epoxide under atmospheric pressure at mild temperatures (25–40 °C) including when using diluted CO 2 mixtures resembling low-calorific landfill gas with or without poisoning additives (H 2 S). Finally, the fate of the catalysts after reaction and their deactivation through the catalytic cycles is discussed.

Identification and tuning of active sites in selected mixed metal oxide catalysts for cyclic carbonate synthesis from epoxides and CO2

The reaction of CO2 with epoxides to produce cyclic carbonate is one of the important transformations of CO2 which has commercial applications. In this study, several mixed metal oxides were explored as potential catalysts for CO2 cycloaddition reaction with epoxides. The catalytic activities of these catalysts were correlated with their physicochemical properties. It is found that the catalytic activity in terms of cyclic carbonate yield has a good correlation with the number of weak and medium acid-base sites irrespective of type of metal oxides used indicating that a combination of acidity and basicity is an important factor for this reaction. Among, different mixed metal oxides, Mn-Ba and Sn-Ni mixed metal oxides were found to be effective solid catalysts for the synthesis of cyclic carbonate from epoxide and CO2. These mixed metal oxides showed higher activity compared to individual oxides and physical mixture of respective metal oxides. Different compositions of mixed metal oxides and the effect of calcination temperature of the catalyst on cycloaddition of epoxide and CO2 were studied. Mn-Ba oxide and Sn-Ni oxide catalysts with metal ratios of 4.3:1 and 1.5:1 respectively, showed better activity compared to other compositions. The effect of various reaction parameters was studied to know the influence on the conversion and yield. Under optimized reaction conditions, Mn-Ba and Sn-Ni mixed oxides gave 96.0 and 90.2% yield respectively for propylene carbonate. Thus, mixed oxides were shown to be highly efficient catalysts with good recyclability for propylene oxide and CO2 reaction and also can be applied to some other epoxides effectively to make cyclic carbonates.

Synthesis of helical aluminium catalysts for cyclic carbonate formation.

Helical aluminium complexes [Al2X4(μ-nbptam)] (X = Me 1, Et 2), [Al2X4(μ-fbpam)] (R = Me 3, Et 4), [Al3X7(μ-nbptam)] (X = Me 5, Et 6) and [Al3X7(μ-fbpam)] (X = Me 7, Et 8) have been prepared by treatment of scorpionate ligand precursors with two or three equivalents of the corresponding trialkylaluminium derivative. The structures of these complexes have been determined by spectroscopic methods and the X-ray crystal structure of complex 1 has also been established. These complexes have been studied as catalysts for the chemical fixation of carbon dioxide into cyclic carbonates displaying good catalytic activity. When cyclohexene oxide was used as a substrate, polyether-polycarbonate was obtained in a ratio which is highly dependent on the cocatalyst and the catalyst to cocatalyst ratio used.

Bifunctional Aluminum Catalysts for the Chemical Fixation of Carbon Dioxide into Cyclic Carbonates

Bifunctional aluminum complexes supported by novel zwitterionic NNO-donor scorpionate ligands were found to be efficient bifunctional catalysts for cyclic carbonate synthesis from terminal and internal epoxides in good yields and with broad substrate scope. Neutral scorpionate ligands (1–2) were designed and used as precursors to obtain two novel zwitterionic NNO-heteroscorpionate ligands (3–4). Reaction of 3 or 4 with [AlX3] (X = Me, Et) in a 1:1 or 1:2 molar ratio afforded the mononuclear and dinuclear cationic aluminum complexes [AlX2{κ2-mbpzbdmape}]I2 (X = Me (5), Et (6)), [AlX2{κ2-mbpzbdeape}]I2 (X = Me (7), Et (8)), [{AlX2(κ2-mbpzbdmape)}(μ-O){AlX3}]I2 (X = Me (9), Et (10)), and [{AlX2(κ2-mbpzbdeape)}(μ-O){AlX3}]I2 (X = Me (11), Et (12)) with elimination of the corresponding alkane. These complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide in the absence of a co-catalyst. Complex 7 was found to be the most active catalyst for cyclic carbonate form...

Catalytic Performance of Dicationic Ionic Liquids and ZnBr2 in the Reaction of Epichlorohydrin and Carbon Dioxide: Kinetic Study

Cyclic carbonate synthesis is an attractive route to utilize CO2 and reduce green house gas. Numbers of studies have been reported on catalytic synthesis of cyclic carbonate, however, very few studies reported on kinetic analysis of cycloaddition reaction. Present study reports a kinetic analysis for coupling reaction of epichlorohydrin (ECH) and carbon dioxide catalyzed by various dicationic ionic liquids (DILs) and zinc bromide. Effects of structural change of DILs on its catalytic activity towards cycloadditiion reaction have also been explored. In addition an attempt has also been made to discuss the plausible reaction mechanism at optimal reaction conditions for coupling of ECH and CO2. At a catalyst loading of 0.5 mmol% C6 (mim) (mim) Br2 and 0.25 mmol% ZnBr2, ECH conversion of 98% can be obtained at 90 °C and 3 MPa in 40 min. Maximum conversion efficiency (98%) and minimum activation energy (20 kJ/mol) was associated with catalytic system comprising of C6 (mim) (mim) Br2 and ZnBr2. Thus, from industrial application point of view C6 (mim) (mim) Br2 and ZnBr2 are potential catalysts for cyclic carbonate synthesis.

Rh(0)/Rh(iii) core–shell nanoparticles as heterogeneous catalysts for cyclic carbonate synthesis

Rh(0)/Rh(iii) core-shell nanoparticles were prepared by surface oxidation of Rh nanoparticles with N-bromosuccinimide. They were employed as heterogeneous catalysts for cyclic carbonate synthesis from propylene oxide and CO2, and exhibited high activity and excellent recyclability due to Lewis acidic Rh(iii) species on the shells.

Dinuclear Aluminum Poly(phenolate) Complexes as Efficient Catalysts for Cyclic Carbonate Synthesis

A series of dinuclear aluminum complexes 1–4 stabilized by amine-bridged poly(phenolato) ligands have been synthesized, which are highly active in catalyzing the cycloaddition of epoxides and CO2. In the presence of 0.3 mol % complex 3 and 0.9 mol % NBu4Br at 1 bar CO2 pressure, terminal epoxides bearing different functional groups were converted to cyclic carbonates in 60–97% yields. Complex 3 is one of the rare examples of Al-based catalysts capable of promoting the cycloaddition at 1 bar pressure of CO2. Moreover, reactions of more challenging disubstituted epoxides also proceeded at an elevated pressure of 10 bar and afforded cyclic carbonates in 52–90% yields.

ChemInform Abstract: Advancements in the Conversion of Carbon Dioxide to Cyclic Carbonates Using Metal Organic Frameworks as Catalysts

AbstractReview: 55 refs.

Advancements in the Conversion of Carbon Dioxide to Cyclic Carbonates Using Metal Organic Frameworks as Catalysts

Global warming has begun to show its impact on the environment, and it is time to take steps to manage CO2 emissions, so as to regain the balance of carbon cycle. In addition to various capture and sequestration techniques, conversion of CO2 to value added products is high relevant. However, the inertness of CO2 makes catalysts an indispensable part of the process. CO2 undergoes cycloaddition with epoxides to produce cyclic carbonates, which have utility in various applications. Considering the necessity for heterogeneity and activity under ambient conditions, metal organic framework (MOF) catalysts have recently emerged as prospective candidates for cyclic carbonate synthesis. These porous hybrid inorganic–organic crystals are also excellent materials for gas storage and separation, including CO2 gas. Thus, MOFs could efficiently capture CO2 and catalytically convert them to cyclic carbonates. In this review, we discuss the recent advancements in the design of MOF catalysts for cyclic carbonate synthesis.

ChemInform Abstract: Sustainable Solid Catalysts for Cyclic Carbonate Synthesis from CO2 and Epoxide

AbstractReview: 127 refs.

Sustainable Solid Catalysts for Cyclic Carbonate Synthesis from CO<sub>2</sub> and Epoxide

Sustainable Solid Catalysts for Cyclic Carbonate Synthesis from CO<sub>2</sub> and Epoxide

ChemInform Abstract: Ketone Synthesized Cobaloxime/Organocobaloxime Catalysts for Cyclic Carbonate Synthesis from CO2 and Epoxides: Characterization and Electrochemistry.

AbstractA new dioxime ligand is prepared and used for the synthesis of a series of mono‐ and trinuclear cobaloxime/organocobaloxime complexes (10 examples; detailed physical and physico‐chemical data).

Silica grafted ammonium salts based on DABCO as heterogeneous catalysts for cyclic carbonate synthesis from carbon dioxide and epoxides

DABCO based ammonium salts immobilized on functionalized silica proved to be an effective heterogeneous catalyst for the synthesis of cyclic carbonate from epoxide and CO2 without the utilization of any organic solvent and any additives.

The synthesis, characterization, and electrochemistry of molecular cobaloxime/organocobaloxime: catalysts for cycloaddition of carbon dioxide and epoxides

The new cobaloxime (1), organocobaloxime (2), and their intramolecular hydrogen (O–H⋯O) bridges replaced by Cu(II)-containing multinuclear cobaloximes (3–10) were synthesized and characterized by elemental analysis, 1H and 13C NMR spectra, FT-IR spectra, UV–vis spectra, LC-MS spectra, molar conductivity measurements, melting point measurements, and magnetic susceptibility measurements. Their electrochemical properties were investigated using cyclic voltammetric techniques in DMSO solution. The cobaloxime or organocobaloxime (1, 2) were used as precursors, replacing intramolecular O–H⋯O bridges, forming multinuclear complexes (3–10). Then, these compounds were used as homogeneous catalysts for cyclic carbonate synthesis from carbon dioxide (CO2) and epoxides. In the catalytic experiments, dimethyl amino pyridine (DMAP) was used as co-catalyst, since DMAP was a more active base with higher yield compared to other Lewis bases. It is not necessary to use solvent according to catalytic test results, important in green chemistry.

Ketone synthesized cobaloxime/organocobaloxime catalysts for cyclic carbonate synthesis from CO2 and epoxides: Characterization and electrochemistry

Herein we report the synthesis and characterization of a new series of synthesized mono- and trinuclear cobaloxime/organocobaloximes from ketone that act as catalysts for cyclic carbonate synthesis from CO2 and epoxides under appropriate conditions (2 h, 100 °C and 1.6 MPa pressure). These reactions were carried out with and without co-catalyst, namely, 4-dimethylaminopyridine (DMAP), pyridine (py), triethyl amine (NEt3) or triphenyl phosphine (PPh3). In the catalytic experiments, the 4-dimethylaminopyridine (DMAP) was used as co-catalyst, since the DMAP was a more active base with higher yield compared to other Lewis bases. In addition, various factors influencing the cycloaddition reaction, such as co-catalyst, temperature, CO2 pressure and reaction time, were investigated. A dioxime ligand (LH2) (1) was obtained in two steps from 4-methylpropiophenone as ketone. Reaction of CoCl2.6H2O with the dioxime ligand (LH2) (1) and 4-tertbutyl pyridine afforded six-coordinate mononuclear cobaloxime or organocobaloxime (2–3) complexes. The mononuclear cobaloxime or organocobaloxime (2–3) complexes were used as precursors for building trinuclear cobaloximes or organocobaloxime (4–11) complexes. All compounds were fully characterized by 1H and 13C NMR spectra, FT-IR spectra, UV–Vis spectra, molar conductivity measurements, melting point measurements, magnetic susceptibility measurements, and LC-MS spectroscopic studies as well as by cyclic voltammetry.

Amino acid/KI as multi-functional synergistic catalysts for cyclic carbonate synthesis from CO2under mild reaction conditions: a DFT corroborated study

Naturally occurring amino acids were identified as efficient co-catalysts for the alkali metal halide-mediated synthesis of cyclic carbonates from carbon dioxide and epoxides under mild, solvent free reaction conditions. The binary system of histidine/potassium iodide gave an appreciable turnover number of 535 for propylene oxide in 3 h. Detailed studies evaluating a variety of amino acids revealed that the basic amino acids afforded better conversion rates. The formation of a seven membered ring involving the zwitterionic ends of the amino acid, the metal halide, and the epoxide was considered to accelerate the catalysis rate. Density functional theory calculations were performed for the first time on amino acid co-catalyzed cycloaddition to provide further evidence for this hypothesis. The iodide ions of the alkali metal halide displayed excellent synergism with the hydrogen bonding groups of the amino acids in the production of cyclic carbonates, whereas bromide and chloride anions functioned less efficiently. The utilization of amino acids to enhance the catalytic activity of the cheap and eco-friendly alkali metal halides for cyclic carbonate synthesis represents a cost-effective, greener route towards the chemical fixation of carbon dioxide.

Influence of Support and Linker Parameters on the Activity of Silica‐Supported Catalysts for Cyclic Carbonate Synthesis

AbstractSilica‐supported, bimetallic aluminium(salen) complexes bearing pendant quaternary ammonium groups catalyse the synthesis of cyclic carbonates from epoxides and carbon dioxide in both batch and gas‐phase flow reactors. The influence of particle and pore size of the silica support on catalyst activity was investigated with smaller particle sizes (<80 μm) being advantageous to catalyst activity, whereas the silica pore size had little effect on catalyst activity. The nature of the silica support also affected catalyst stability and the Fluorochem LC301 silica gave a catalyst with both the highest intrinsic activity and the lowest rate of deactivation. The catalysts are attached to the silica through a linker containing three or eleven carbon atoms. The longer linker was found give a catalyst loading three times higher than the shorter linker, but this was offset by a three times lower activity for the catalyst with the longer linker.

One-component bimetallic aluminium(salen)-based catalysts for cyclic carbonate synthesis and their immobilization

The development of one-component, bimetallic μ-oxoaluminium(salen) complexes as highly active catalysts for the synthesis of cyclic carbonates from terminal epoxides is described. The resulting homogeneous catalysts are used in batch reactions at room temperature and one atmosphere pressure. The catalysts have also been immobilized onto various support materials and used in either batch reactions or gas-phase flow reactions with ethylene and propylene oxides. Catalyst lifetime, deactivation and reactivation have been studied in both batch and flow reactions, and it has been shown that of the impurities present in power station flue gas, only sulfur trioxide deactivates the catalyst and at the concentrations of sulfur trioxide present in flue gas, this deactivation would require more than one years exposure of the catalyst to flue gas.