Synthesis of cyclic carbonates from epoxides and carbon dioxide by using organocatalysts.

Chemical fixation of carbon dioxide (CO 2 ) may be very important in the future as a solution for the problem of increased atmospheric CO 2 levels. Recent developments for chemical fixation of CO 2 to cyclic carbonate, dimethyl carbonate (DMC), cyclic urea and cyclic urethane are reviewed. Synthesis of cyclic carbonate via CO 2 addition to epoxide has been already applied on the industrial scale, but catalyst development continues. Direct oxidative carboxylation of olefin is preferable for the synthesis of cyclic carbonate, but requires the development of catalysts for the epoxidation step in the presence of CO 2 . Direct synthesis of DMC is not in practical use at present because of the reaction equilibrium and chemical inertness of CO 2 . The preferred alternative is transesterification of ethylene carbonate and methanol for converting CO 2 to DMC indirectly. Moreover, combination of this reaction with CO 2 addition to epoxide or reaction of ethylene glycol and urea to synthesize DMC is promising. Application of these ideas depends on the development and optimization of catalysts and reaction conditions. Synthesis of cyclic urea and urethane without catalyst should use either CO 2 or urea depending on the structures of diamine and amino alcohol.

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.

The direct transformation of carbon dioxide to organic carbonates over heterogeneous catalysts

Article title: Synthesis of 6-membered cyclic carbonates from 1,3-diols and low CO2 pressure : a novel mild strategy to replace phosgene reagents Authors: Georgina Gregory, Marion Ulmann and Antoine Buchard* DFT study: Optimised structures of local minima and transition states from the potential energy surface of the tosylation and cyclisation steps in the synthesis of cyclic carbonate (R)-4-Methyl-[1,3]-dioxan-2-one from CO2 and (R)-1,3-butanediol. Protocol: rωb97xD/6-31+g(d)/ SCRF=(cpcm,solvent= chloroform) Content: Potential Energy Surface diagram and Gaussian09 rev A.02 output files

Development in the green synthesis of cyclic carbonate from carbon dioxide using ionic liquids

For Abstract see ChemInform Abstract in Full Text.

The synthesis of cyclic carbonates from carbon dioxide (CO2) and epoxides is a 100% atom economical reaction and an attractive pathway for CO2 utilisation. Because CO2 is a thermodynamically stable molecule, the use of catalysts is mandatory in reducing the activation energy of the CO2 conversion. Considering environmental compatibility and the high-efficiency catalytic conversion of CO2, there is the strong need to develop green catalysts. Biomass-based catalysts, a type of renewable resource, have attracted considerable attention due to their unique properties—non-toxic, low-cost, pollution-free, etc. In this review, recent advances in the development of biomass-based catalysts for the synthesis of cyclic carbonates by CO2 and epoxides coupling are summarized and discussed in detail. The effect of biomass-based catalysts, functional groups, reaction conditions, and co-catalysts on the catalytic efficiency and selectivity of synthesizing cyclic carbonates process is discussed. We intend to provide a comprehensive understanding of recent experimental and theoretical progress of CO2 and epoxides coupling reaction and pave the way for both CO2 conversion and biomass unitization.

CO2 composes cheap, easily available and practically inexhaustible source of synthetic carbon (C1-synthon). Among the various transformations of carbon dioxide, synthesis of cyclic carbonates from epoxides and carbamates from aziridines can be referred to the priority areas in the development of contemporary chemical synthesis and catalysis. Cyclic carbonates found wide application in modern industry (electrolytes, solvents, reagents, polymers) and their use and production will be constantly increased. At the forefront of research appears the development of effective catalytic processes, allowing carry out the synthesis of carbonates under mild conditions (atmospheric pressure of CO2 or lower, temperature - 25°С) with low catalyst loads, which sustains its high activity for a long time and is affordable. In the current review we analyze the existing directions of research and catalytic systems based on salts of cheap and earth-abundant metals Al3+, Fe2+(3+) and Zn2+ for the preparation of cyclic carbonates from epoxides and carbamates from aziridines.

The bimetallic aluminium(salen) complex [(Al(salen))2O] is known to catalyse the reaction between epoxides and heterocumulenes (carbon dioxide, carbon disulfide and isocyanates) leading to five-membered ring heterocycles. Despite their apparent similarities, these three reactions have very different mechanistic features, and a kinetic study of oxazolidinone synthesis combined with previous kinetic work on cyclic carbonate and cyclic dithiocarbonate synthesis showed that all three reactions follow different rate equations. An NMR study of [Al(salen)]2O and phenylisocyanate provided evidence for an interaction between them, consistent with the rate equation data. A variable-temperature kinetics study on all three reactions showed that cyclic carbonate synthesis had a lower enthalpy of activation and a more negative entropy of activation than the other two heterocycle syntheses. The kinetic study was extended to oxazolidinone synthesis catalysed by the monometallic complex Al(salen)Cl, and this reaction was found to have a much less negative entropy of activation than any reaction catalysed by [Al(salen)]2O, a result that can be explained by the partial dissociation of an oligomeric Al(salen)Cl complex. A mechanistic rationale for all of the results is presented in terms of [Al(salen)]2O being able to function as a Lewis acid and/or a Lewis base, depending upon the susceptibility of the heterocumulene to reaction with nucleophiles.

Treatment of aldehydes with sulfur ylide (CH2=SOMe2 or CH2=SMe2), in the presence of CO2 (1 atm) bubbled sequentially under mild conditions, produces cyclic carbonates in preparative yields. Sodium iodide formed in situ promotes the reaction between epoxide as intermediate and CO2 at ambient conditions, thus constituting a powerful metal-free synthesis of organic cyclic carbonates directly from aldehydes.

The utilization of CO2 for the production of useful chemicals is nowadays considered as a promising way to contribute to the reduction of greenhouse gases in the atmosphere, while valorizing at the same time this widely available resource. The synthesis of cyclic carbonates and polycarbonates via cycloaddition of CO2 to epoxides is part of the few processes already industrialized. In this field, a critical challenge is the activation of the CO2 molecule, which can be achieved by the use of effective catalysts. Catalytic systems based on metal complexes, ionic liquids or organic bases have been developed to this end. This review focuses on the different mechanisms proposed in the literature for the reaction of CO2 addition to epoxides. Better understanding of these mechanisms should allow the development of high-performance catalytic systems, able to answer industrial constraints in term of stability, separation, handling and reuse of the catalysts.

A silica-supported ionic liquid (Im-IL) was proven to be an effective heterogeneous catalyst for solventless synthesis of cyclic carbonate from allyl glycidyl ether (AGE) and carbon dioxide. Im-IL catalysts were prepared by sol-gel method. The synthesis of cyclic carbonate from AGE and CO2 was carried out in a batch autoclave reactor. Im-IL with shorter alkyl chain length showed the highest conversion of AGE, probably due to the steric hindrance for the formation of intermediate from the catalyst prepared by using longer alkyl chains and AGE. High temperature and high pressure were favorable for the conversion of AGE. Im-IL can be reused for the reaction up to two consecutive runs without any considerable loss of its catalytic activity.

New bifunctional aluminum complexes have been prepared with the aim of studying the effect of a counterion on the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2). Neutral ligand 1 was used as a precursor to obtain four novel mesylate, chloride, bromide, and iodide zwitterionic NNO ligands (2-5). The reaction of these ligands with 1 or 2 equiv of AlR3 (R = Me, Et) allowed the synthesis of mono- and bimetallic bifunctional aluminum complexes [AlR2(κ2-mbpzappe)]X [X = Cl, R = Me (6), Et (7); X = Br, R = Me (8), Et (9); X = I, R = Me (10), Et (11)] and [{AlR2(κ2-mbpzappe)}(μ-O){AlR3}]X [X = MeSO3, R = Me (12), Et (13); X = Cl, R = Me (14), Et (15); X = Br, R = Me (16), Et (17); X = I, R = Me (18), Et (19)] via alkane elimination. These complexes were studied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. Iodide complex 11 showed to be the most active catalyst for terminal epoxides, whereas bromide complex 9 was found to be the optimal catalyst when internal epoxides were used, showing the importance of the nucleophile cocatalyst on the catalytic activity.

Synthesis of cyclic carbonate from vinyl cyclohexene oxide and CO 2 using ionic liquids as catalysts

A monovacant Keggin‐type polyoxometalate‐supported trirhenium carbonyl derivate [(CH3)4N]5H23[(PW11O39){Re(CO)3}3(μ3‐O)(μ2‐OH)]4⋅24 H2O was synthesized. It was used as a catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides under mild reaction conditions with co‐catalyst pyrrolidinium bromide. The catalyst system was recycled 10 times with only a small decline in yield. The catalytic mechanism was hypothesized based on experimental results and the frontier orbitals computed by DFT calculations.