Jinquan Wang

Chitosan functionalized ionic liquid as a recyclable biopolymer-supported catalyst for cycloaddition of CO2

Development of efficient, cheap and recyclable catalysts for a reaction under green reaction conditions is still a very attractive topic. In this work, the cycloaddition reactions of CO2 with various epoxides to form five-membered cyclic carbonates catalyzed by chitosan functionalized 1-ethyl-3-methyl imidazolium halides (CS-EMImX, X = Cl, Br) without additional solvent and metal co-catalyst were achieved in high yield and selectivity. The catalyst could be easily recovered and reused five times with high catalytic activity and selectivity. Besides, a possible catalytic cycle for the hydrogen bond assisted ring-opening of epoxide and activation of CO2 induced by the nucleophilic tertiary nitrogen of the chitosan was also proposed. The process represents a simple, ecologically safe and cost-effective route to synthesize cyclic carbonates with high product yield, as well as easy catalyst recycling.

Fixation of CO2 into cyclic carbonates catalyzed by ionic liquids: a multi-scale approach

Fixation of CO2 to cyclic carbonates is one of the most important reactions since it represents a much greener alternative to the traditional phosgene process. In this context, the transformation of CO2 with epoxides into cyclic carbonates with respect to the newly emerged ionic liquid (IL) technology is discussed from a multi-scale viewpoint, including (1) the mechanism considering the “cooperative effect” at the basic atom and molecule level; (2) the reactor configuration at the unit level; (3) and the related process integration at the system level.

Efficient Acid–Base Bifunctional Catalysts for the Fixation of CO2 with Epoxides under Metal‐ and Solvent‐Free Conditions

A series of acid-base bifunctional catalysts (ABBCs) that contain one or two Brønsted acidic sites in the cationic part and a Lewis-basic site in the anionic part are used as efficient catalysts for the synthesis of cyclic carbonates by cycloaddition of CO(2) to epoxides, without the use of additional co-catalyst or co-solvent. The effects of the catalyst structures and various reaction parameters on the catalytic performance are investigated in detail. Almost complete conversion can be achieved in 1u2005h for propylene oxide using [{(CH(2))(3)COOH}(2) im]Br under mild reaction conditions (398u2005K and 2u2005MPa). Furthermore, the catalyst can be recycled over five times without substantial loss of catalytic activity. This protocol is found to be applicable to a variety of terminal epoxides, producing the corresponding cyclic carbonates in good yields and high selectivities. A synergistic effect of the acidic and the basic sites as well as suitable hydrogen-bonding strength of ABBCs are considered crucial for the reaction to proceed smoothly. The activities of the ABBCs increase remarkably with increasing carboxylic-acid chain length of the cation. This metal- and solvent-free process thus represents an environmentally friendly process for BTC-catalyzed conversion of CO(2) into value-added chemicals.

Superbase/cellulose: an environmentally benign catalyst for chemical fixation of carbon dioxide into cyclic carbonates

An environmentally benign catalytic system consisting of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) and cellulose was developed for CO2 chemical fixation with epoxides under metal-free and halide-free conditions. Due to the dual roles played by DBU and cellulose on the activations of CO2 and epoxide, the reaction could be performed with high activity and selectivity. A possible catalytic cycle for the hydrogen bond assisted ring-opening of epoxide and the activation of CO2 induced by DBU was proposed. The process herein represents a simple, ecologically safe and efficient route for CO2 chemical fixation into high value chemicals.

Experimental and theoretical studies on hydrogen bond-promoted fixation of carbon dioxide and epoxides in cyclic carbonates

The hydrogen bond donor-promoted fixation of CO(2) and epoxides into cyclic carbonates was investigated through experimental and density functional theory studies. A highly effective homogeneous system of 1,2-benzenediol-tetrabutyl ammonium bromide (TBAB) and heterogeneous poly-ionic liquids were developed for the fixation of CO(2) into cyclic carbonates via hydrogen bond activation, based on the understanding of the reaction mechanism and catalyst design. The work hence provides a molecular level understanding of the reaction process and forms the basis for the rational design of catalytic systems for the fixation of CO(2) into useful organic compounds.

Urea-derived graphitic carbon nitride as an efficient heterogeneous catalyst for CO2 conversion into cyclic carbonates

In order to overcome existing solid catalysts disadvantages of low stability and activity, urea-derived graphitic carbon nitrides (u-g-C3N4) with higher stabilities and more active centers were prepared under different temperatures (550–450 °C). With a decrease in preparation temperature from 550 °C to 480 °C, a u-g-C3N4 of lower crystallinity with a smaller polymerization degree was obtained and found to have a higher catalytic activity for CO2 conversion into propylene carbonate. The higher activity of the u-g-C3N4 caused by decreasing the temperature might be ascribed to the lower crystallinity and polymerization degree, which led to more edge defects, wherein the incompletely-coordinated nitrogen atoms served as the main active sites in the cycloaddition reaction. Among all the prepared catalysts, that prepared at 480 °C (u-g-C3N4-480) showed the highest catalytic activity for CO2 conversion and exhibited great suitability for other epoxide substrates.

Efficient fixation of CO2 into organic carbonates catalyzed by 2-hydroxymethyl-functionalized ionic liquids

Several novel 2-hydroxymethyl-functionalized ILs act as the catalysts for synthesis of cyclic carbonates from CO2 and epoxides without the use of any co-catalysts or organic solvent. Moreover, the 2-hydroxymethyl-functionalized ILs were compatible with base, which combined with K2CO3 were used as effective catalytic system for green synthesis of dimethyl carbonate from CO2via ethylene carbonate without catalyst separation. Additionally, the mechanistic details of the fixation of CO2 into cyclic carbonate catalyzed by 2-hydroxymethyl-functionalized ILs were also elucidated by density functional theory. The process reported here represents a simple, ecologically safer, cost-effective and energy-saving route to organic carbonates from CO2.

Efficient fixation of CO2 into cyclic carbonates catalyzed by hydroxyl-functionalized poly(ionic liquids)

A series of hydroxyl-functionalized poly(ionic liquids) (PILs) were synthesized and employed as catalysts for the synthesis of cyclic carbonates from CO2 and epoxides without the use of any co-catalyst or organic solvent. It was demonstrated that hydroxyl and bromide anion had an excellent synergetic effect on promoting the reaction, and the PILs catalysed co-polymerization of 1-vinyl-3-carboxyethylimidazolium bromide with the cross-linker divinylbenzene (DVB) was observed to be the most efficient, with nearly a 99% yield of propylene carbonate and 100% selectivity. The effects of temperature, pressure and reaction time on the reaction were also investigated. Moreover, the catalysts can be easily recovered and reused more than five times with only a slight decline in catalytic activity. This process carries huge industrial applications due to the reactions high efficiency and the ease of catalyst separation and recycling, which could be profitably applied to the development of fixed-bed continuous flow reactors.

Carboxylation of terminal alkynes at ambient CO2 pressure in ethylene carbonate

The CuI-catalyzed carboxylation of terminal alkynes with CO2 and alkyl halides using ethylene carbonate as the solvent under mild conditions was studied. DFT calculations reveal that the energy barrier for CO2 insertion into the sp-hybridized Cu-C bond could be reduced by employing ethylene carbonate as the solvent. Notably, the procedure was conducted under ambient CO2 pressure without any external ligands. A broad range of substrates with electron-withdrawing groups or electron-donating groups gave the corresponding products in reasonable yields.

Synthesis of dimethyl carbonate catalyzed by carboxylic functionalized imidazolium salt via transesterification reaction

We investigated the dependence of cations and anions of ionic liquids (ILs) on catalytic activity for the synthesis of dimethyl carbonate (DMC) via the transesterification of ethylene carbonate (EC) with methanol (CH3OH), and demonstrated that an easily prepared carboxylic functionalized imidazolium salt exhibited higher activity, 82% yield of DMC together with 99% selectivity was obtained under the metal-free and halogen-free conditions. The reaction mechanism was also proposed according to experimental and DFT studies. In addition, in order to simplify the catalyst separation and evaluate the catalyst stability, we also covalently anchored the functionalized imidazolium salt onto a highly cross-linked polystyrene resin (PS) as a heterogeneous catalyst for DMC synthesis, and continuously performed the reaction in a fixed bed reactor for 200 h without obvious loss of activity, which would have potential applications in industry. The process thus represented an environmentally friendly pathway for the synthesis of DMC via a transesterification reaction.