Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2

Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO₂ in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO₂ insertion reactions were typically carried out in the temperature range of 343 to 403 K at 0.6 MPa CO₂ pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts.     

Methodologies for chemical utilization of CO2 to valuable compounds through molecular activation by efficient catalysts

The reactions of CO₂ with oxirane to produce cyclic carbonate, and with aziridine to afford oxazolidine have been of interest as a useful method for its fixation by a chemical process. Highly efficient processes employing recyclable CO₂-phlilic homogeneous catalyst were devised for environmentally benign synthesis of cyclic carbonates and oxazolidinones under supercritical CO₂ without any organic solvent. These processes represent pathways for greener chemical fixations of CO₂ to afford industrial useful materials such as organic carbonates and oxazolidinones with great potential applications.     

Use of carbon dioxide as feedstock for chemicals and fuels: homogeneous and heterogeneous catalysis

CO₂ is considered to play a key role in an eventual climate change, due to its accumulation in the atmosphere. The control of its emission represents a challenging task that requires new ideas and new technologies. The use of perennial energy sources and renewable fuels instead of fossil fuels and the conversion of CO₂ into useful products are receiving increased attention. The utilization of CO₂ as a raw material for the synthesis of chemicals and fuels is an area in which scientists and industrialists are much involved: the implementation of such technology on a large scale would allow a change from a linear use of fossil carbon to its cyclic use, mimicking Nature. In this paper the use of CO₂ as building block is discussed. CO₂ can replace toxic species such as phosgene in low energy processes, or can be used as source of carbon for the synthesis of energy products. The reactions with dihydrogen, alcohols, epoxides, amines, olefins, dienes, and other unsaturated hydrocarbons are discussed, under various reaction conditions, using metal systems or enzymes as catalysts. The formation of products such as formic acid and its esters, formamides, methanol, dimethyl carbonate, alkylene carbonates, carbamic acid esters, lactones, carboxylic acids, and polycarbonates, is described . The factors that have limited so far the conversion of large volumes of CO₂ are analyzed and options for large‐scale CO₂ catalytic conversion into chemicals and fuels are discussed. Both homogeneous and heterogeneous catalysts are considered and the pros and cons of their use highlighted. © 2013 Society of Chemical Industry     

2,2',2'-Terpyridine-Catalyzed Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide under Solvent-Free Conditions

An efficient coupling reaction of epoxides with CO₂ affording cyclic carbonates with the use of 2,2'',2''''-terpyridine as catalyst under solvent-free conditions has been developed.     

Poly(4‐vinylphenol)/tetra‐n‐butylammonium iodide: Efficient organocatalytic system for synthesis of cyclic carbonates from CO2 and epoxides

An efficient polymer‐based catalytic system of poly(4‐vinylphenol) and tetra‐n‐butylammonium iodide was developed for the synthesis of cyclic carbonates from epoxides and CO₂. Owing to the synergistic effects of hydroxyl groups and iodide anions, this commercially available and metal‐free system was highly active for the reaction of various terminal epoxides under environmentally benign conditions, at 25 to 60 °C and atmospheric pressure of CO₂, without the use of any organic solvents. The catalyst system can be easily separated by adding ether, and its ability was recovered by treating it with 40% CH₃CO₂H aq. The recyclability was investigated in detail for three substrates, epichlorohydrin, 1,2‐epoxyhexane, and styrene oxide, using ¹H nuclear magnetic resonance analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45189.     

Copolymerization of epoxides and carbon dioxide by using double metal cyanide complex (DMC) with high crystallinity

Zn₃ [Co(CN)₆]₂ based double metal cyanide complex(Co-Zn DMC) is synthesized and characterized by element analysis, FT-IR, TG-FTIR, XRD and TEM. The composition of Co-Zn DMC summarized by elemental analysis has been confirmed by TG-FTIR. The catalyst has high crystallinity according to strong crystalline peaks shown in XRD and diffraction spot observed by TEM. Copolymerization of epoxides and carbon dioxide are successfully catalyzed by Co-Zn DMC. The efficiency of catalysts is as high as 7488 g polymer/g catalyst for CO₂/propylene oxide (PO), 1100 g polymer/g catalyst for CO₂/ethylene oxide (EO), which are higher than that reported ever before. The effects of various reaction conditions such as amount of the catalyst, reaction time and temperature on the copolymerization are investigated. The results show that insertion of CO₂ into chains is significantly affected by the catalyst quantity and ambient temperature. The weight percentage of byproduct cyclic carbonate can be easily controlled to be less than 5% while the molar fraction of CO₂ in backbone (f_co2) is more than 30%.     

Biocompatible and recyclable amino acid binary catalyst for efficient chemical fixation of CO2

In this work, the cycloaddition reactions of CO₂ with various epoxides to form five-membered cyclic carbonates catalyzed by an efficient amino acid based biocompatible catalyst were investigated. It was found that the activity of amino acid could be obviously enhanced in the presence of alkali metal salts, and the l-tryptophan catalytic system was the most efficient among the catalysts employed. Based on the result, a possible mechanism for the synergetic effect of catalyst was proposed. The process reported here represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy catalyst recycling.     

Synthesis of organic carbonates from alcoholysis of urea: A review

Organic carbonates are green compounds with a wide range of applications. They are widely used for the synthesis of important industrial compounds including monomers, polymers, surfactants, plasticizers, and also used as fuel additives. They can be divided into two main classes: cyclic and linear carbonates. Dimethyl carbonate (DMC) and diethyl carbonate (DEC) are the important linear carbonates. Carbonyl and alkyl groups present in DMC and DEC make them reactive and versatile for synthesizing various other important compounds. Ethylene carbonate (EC), glycerol carbonate (GC) and propylene carbonate (PC) are well-known cyclic organic carbonates. Phosgenation of alcohols was widely used for synthesis of organic carbonates; however, toxicity of raw materials restricted use of phosgenation method. A number of new non-phosgene methods including alcoholysis of urea, carbonylation of alcohols using CO₂, oxy-carbonylation of alcohols, and trans-esterfication of alcohols and carbonates have been developed for synthesizing organic carbonates. Carbonylation of alcohols is preferred as it helps in utilization and sequestration of CO₂, however, poor thermodynamics due to high stability of CO₂ is the major obstacle in its large scale commercialization. Oxy-carbonylation of alcohols offers high selectivity but presence of oxygen poisons the catalyst. Recently, alcoholysis of urea has received more attention because of its inexpensive abundant raw materials, favorable thermodynamics, and no water-alcohol azeotrope formation. Also, ammonia evolved in this synthesis route can be recycled back to urea by reacting it with CO₂. In other words, this method is a step towards utilization of CO₂ as well. This article reviews synthesis of DMC, DEC, GC, PC, and EC from urea by critically examining various catalysts used and their performances. Mechanisms have been reviewed in order to give an insight of the synthesis routes. Research challenges along with future perspectives have also been discussed.     

Carbon dioxide: a renewable feedstock for the synthesis of fine and bulk chemicals

The syntheses of carbon dioxide (CO₂) based industrially important chemicals have gained considerable interest in view of the sustainable chemistry and “green chemistry” concepts. In this review, recent developments in the chemical fixation of CO₂ to valuable chemicals are discussed. The synthesis of five-member cyclic carbonates via, cycloaddition of CO₂ to epoxides is one of the promising reactions replacing the existing poisonous phosgene-based synthetic route. This review focuses on the synthesis of cyclic carbonates, vinyl carbamates, and quinazoline-2,4(1H,3H)-diones via reaction of CO₂ and epoxide, amines/phenyl acetylene, 2-aminobenzinitrile and other chemicals. Direct synthesis of dimethyl carbonate, 1,3-disubstituted urea and 2-oxazolidinones/2-imidazolidinones have limitations at present because of the reaction equilibrium and chemical inertness of CO₂. The preferred alternatives for their synthesis like transesterification of ethylene carbonate with methanol, transamination of ethylene carbonate with primary amine and transamination reaction of ethylene carbonate with diamines/β-aminoalcohols are discussed. These methodologies offer marked improvements for greener chemical fixation of CO₂ in to industrially important chemicals.     

Synthesis of Polycarbonate Precursors over Titanosilicate Molecular Sieves

A novel catalytic application of titanosilicate molecular sieves (TS-1 and TiMCM-41), in the synthesis of polycarbonate precursors like cyclic carbonates and dimethyl and diphenyl carbonates, avoiding toxic chemicals like phosgene or CO, is reported. Cyclic carbonates were prepared, over TS-1 and TiMCM-41, in high yields, by cycloaddition of CO₂ to epoxides, like epichlorohydrin, propylene oxide and styrene oxide, at low temperatures and pressures. Further, transesterification of the cyclic carbonates with methanol and phenol, over TiMCM-41, yielded other polycarbonate precursors like dimethyl carbonate (DMC) and diphenyl carbonate (DPC). The cyclic carbonates could also be synthesized from the olefins in the same reactor by reacting the olefins, in the presence of TiMCM-41, with a mixture of an epoxidizing agent (like H₂O₂ or tert-butyl hydroperoxide) and CO₂.     

Zirconium-based isoreticular metal-organic frameworks for CO<Subscript>2</Subscript> fixation via cyclic carbonate synthesis

Two highly stable isoreticular metal-organic frameworks comprising chains of zirconium coordinated with linkers of 1,4-H₂BDC (1,4-benzenedicarboxylic acid) and 4,4′-H₂BPDC (4,4′-biphenyldicarboxylic acid), denoted as MIL-140A and MIL-140C, were synthesized. The catalytic activity of these frameworks was studied for the coupling reaction of CO₂ and epoxides to produce cyclic carbonates under solvent-free conditions. Excellent activity was observed for both catalysts: they yielded high epoxide conversion with >99% selectivity toward the cyclic carbonate, and were fully reusable even after four cycles without any considerable loss of initial activity. The enhancement in the catalytic activity was explained based on acidity/basicity studies. The influence of various reaction parameters such as catalyst amount, reaction time, reaction temperature, and CO₂ pressure was also investigated. Reaction mechanism was proposed on the basis of experimental evidence and our previous DFT (density functional theory) studies.     

One-pot terpolymerization of CO2, cyclohexene oxide and maleic anhydride using a highly active heterogeneous double metal cyanide complex catalyst

This paper describes a convenient one-pot terpolymerization of CO₂, cyclohexene oxide (CHO) and maleic anhydride (MAH) to afford a poly (ester-carbonate) with a low content of ether units (2.9-4.3 mol%) using a highly active Zn-Co(III) double metal cyanide complex (DMCC) catalyst. Terpolymerization was carried out in tetrahydrofuran (THF) at 75-90 °C and 1.0-4.0 MPa and no cyclic carbonate was observed in NMR spectra. The number-average molecular weight (M_n) of the terpolymer was up to 14.1 kg/mol with a narrow molecular weight distribution of 1.4-1.7. The apparent efficiency of the catalyst was up to 12.7 kg polymer/g Zn, representing the highest catalytic activity for terpolymerization of CO₂, epoxides and cyclic anhydrides to date. THF dramatically inhibited polyether formation in this terpolymerization owing to its nucleophilicity towards the Zn²⁺ center of Zn-Co (III) DMCC. This presents the first example of solvent-assisted selectivity for inhibiting ether units in CO₂ polymerization catalyzed by a heterogeneous system. Kinetic analyses of MAH/CHO/CO₂ terpolymerization (MAH/CHO 0.2) suggested that polyester production was slightly faster than polycarbonate production in the early stage. A mechanism for this terpolymerization catalyzed by Zn-Co (III) DMCC catalyst was proposed. Moreover, addition of small amounts of MAH (MAH/CHO molar ratio ≤0.2) during CO₂/CHO copolymerization can improve the thermal properties of the resultant terpolymers.     

Incorporation of Metal Ions into Silica-Grafted Imidazolium-Based Ionic Liquids to Efficiently Catalyze Cycloaddition Reactions of CO<Subscript>2</Subscript> and Epoxides

Abstract  

A variety of imidazolium-based ionic liquids (ILs) have been widely developed to effectively catalyze the cycloaddition reactions of CO₂ and epoxides. To further improve the catalytic performance of those IL catalysts, we incorporated various metal chlorides (CoCl₂, NiCl₂, CuCl₂, ZnCl₂, and MnCl₂) into silica-grafted 1-methyl-3-[(triethoxysilyl)propyl] imidazolium chloride to produce a series of heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of such metal ions can significantly enhance the catalytic reactivity of the silica-grafted ILs towards cycloaddition reactions of CO₂ and epoxides that produce cyclic carbonates in solvent-free conditions. In addition, the effects on the catalytic reactivity of reaction parameters including reaction time, reaction temperature and CO₂ pressure were investigated.     

均相体系中酸碱协同催化二氧化碳与环氧化物的环加成反应

基于“可持续发展”和“绿色化学”的概念,近年来CO₂的捕获、储存及资源化利用在工业上和学术上一直备受关注。通过具有100%原子经济性特点的CO₂与环氧化物环加成反应合成五元环状碳酸酯是最有前景的方法之一。基于均相催化剂的设计思想与方法,以CO₂和环氧化物的活化本质出发,从催化剂结构的角度综述了均相体系中酸碱协同催化CO₂与环氧化物环加成反应合成环状碳酸酯的研究进展,包括简单二元催化体系、功能型一元催化体系和金属配合物催化体系等。     

Increasing carbon utilization in Fischer-Tropsch synthesis using H2-deficient or CO2-rich syngas feeds

Fischer-Tropsch technology has become a topical issue in the energy industry in recent times. The synthesis of linear hydrocarbon that has high cetane number diesel fuel through the Fischer-Tropsch reaction requires syngas with high H₂/CO ratio. Nevertheless, the production of syngas from biomass and coal, which have low H₂/CO ratios or are CO₂ rich may be desirable for environmental and socio-political reasons. Efficient carbon utilization in such H₂-deficient and CO₂-rich syngas feeds has not been given the required attention. It is desirable to improve carbon utilization using such syngas feeds in the Fischer-Tropsch synthesis not only for process economy but also for sustainable development. Previous catalyst and process development efforts were directed toward maximising C₅₊ selectivity; they are not for achieving high carbon utilization with H₂-deficient and CO₂-rich syngas feeds. However, current trends in FTS catalyst design hold the potential of achieving high carbon utilization with wide option of selectivities. Highlights of the current trends in FTS catalyst design are presented and their prospect for achieving high carbon utilization in FTS using H₂-deficient and CO₂-rich syngas feeds is discussed.     

Cu/ZnO/AlOOH catalyst for methanol synthesis through CO<Subscript>2</Subscript> hydrogenation

Catalytic conversion of CO₂ to methanol is gaining attention as a promising route to using carbon dioxide as a new carbon feedstock. AlOOH supported copper-based methanol synthesis catalyst was investigated for direct hydrogenation of CO₂ to methanol. The bare AlOOH catalyst support was found to have increased adsorption capacity of CO₂ compared to conventional Al₂O₃ support by CO₂ temperature-programmed desorption (TPD) and FT-IR analysis. The catalytic activity measurement was carried out in a fixed bed reactor at 523 K, 30 atm and GHSV 6,000 hr^?1 with the feed gas of CO₂/H₂ ratio of 1/3. The surface basicity of the AlOOH supported Cu-based catalysts increased linearly according to the amount of AlOOH. The optimum catalyst composition was found to be Cu : Zn : Al=40 : 30 : 30 at%. A decrease of methanol productivity was observed by further increasing the amount of AlOOH due to the limitation of hydrogenation rate on Cu sites. The AlOOH supported catalyst with optimum catalyst compositions was slightly more active than the conventional Al₂O₃ supported Cu-based catalyst.     

The first synthesis of a cyclic carbonate from a ketal in SC-CO2

In this paper the synthesis of a cyclic organic carbonate by a halogen-free route is described. The ketal formed from cyclohexanone and 1,2-ethanediol was reacted with carbon dioxide, either in SC-CO₂ or in organic solvents under CO₂ pressure. Transition-metal complexes with functionalized fluorinated di-ketone ligands were used as catalyst. The synthetic methodology based on SC-CO₂ is effective for the synthesis of ethylene carbonate. The use of methanol as co-solvent in SC-CO₂ prevents the formation of the ethylene carbonate and only the alcoholysis of the ketal is observed. In organic solvents, no reaction takes place.     

Quantum Chemical Determination of Stable Intermediates on CO2 Adsorption Onto Metal(Salen) Complexes

Coupling reactions of CO₂ and epoxides to produce either cyclic carbonates or polycarbonates are environmentally friendly reactions that allow the use of an inexpensive and renewable feedstock while achieving carbon efficiency. In this study, density functional theory calculations were used to understand the role the metal(salen) catalyst on CO₂ adsorption. We have performed a systematic analysis of the plausible interactions of CO₂ with metal(salen) catalysts and ethylene oxide/metal(salen) complexes. Adsorption reactions were analyzed on six metal(salen) complexes: Co, Cr, Mn, Fe, Zn, and Al, using the unrestricted OPBE functional. Geometry optimizations were carried out beginning with a variety of different conformations and frequency calculations were used to verify that structures lie in an energy minimum. Our results demonstrate that CO₂ does not bind to the metal atom of the bare metal(salen). The adsorption of CO₂ onto metal(salen) complexes is an endothermic reaction and the lowest energy adsorbed complex involves the interaction of CO₂ with the adsorbed opened-epoxide.     

Direct conversion of CO2 with diols,aminoalcohols and diamines to cyclic carbonates,cyclic carbamates and cyclic ureas using heterogeneous catalysts

CO₂ has a large effect on global warming by greenhouse gases, and development of an effective technique for the reduction of CO₂ is a crucial and urgent issue. From the chemical viewpoint, CO₂ is regarded as a stable, safe and abundant C1 resource, and the transformation of CO₂ to valuable chemicals is promising not only for reduction of CO₂ but also for production of useful chemicals. This mini‐review focuses on the direct conversion of CO₂ with diols, aminoalcohols and diamines to cyclic compounds such as cyclic carbonates, cyclic carbamates and cyclic ureas, and in particular discusses the mechanisms for these reactions over heterogeneous catalysts. © 2013 Society of Chemical Industry