Azole-Anion-Based Aprotic Ionic Liquids: Functional Solvents for Atmospheric CO 2 Transformation into Various Heterocyclic Compounds

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Efficient catalytic conversion of CO2 to quinazoline-2,4(1H,3H)-diones by a dual-site anion-functionalized ionic liquid: reconsidering the mechanism

In order to elucidate the reaction mechanism of ionic liquid-catalyzed CO2 with 2-aminobenzonitrile, [P4442]2[Hy] with two N- sites is designed for the efficient preparation of quinazoline-2,4(1H,3H)-diones. The results show that [Hy]2- can activate 2-aminobenzonitrile by hydrogen bonding with -NH2 in addition to activating CO2, and the key intermediate is revealed.

Tuning Ionic Liquid-Based Catalysts for CO2 Conversion into Quinazoline-2,4(1H,3H)-diones

Carbon capture and storage (CCS) and carbon capture and utilization (CCU) are two kinds of strategies to reduce the CO₂ concentration in the atmosphere, which is emitted from the burning of fossil fuels and leads to the greenhouse effect. With the unique properties of ionic liquids (ILs), such as low vapor pressures, tunable structures, high solubilities, and high thermal and chemical stabilities, they could be used as solvents and catalysts for CO₂ capture and conversion into value-added chemicals. In this critical review, we mainly focus our attention on the tuning IL-based catalysts for CO₂ conversion into quinazoline-2,4(1H,3H)-diones from o-aminobenzonitriles during this decade (2012~2022). Due to the importance of basicity and nucleophilicity of catalysts, kinds of ILs with basic anions such as [OH], carboxylates, aprotic heterocyclic anions, etc., for conversion CO₂ and o-aminobenzonitriles into quinazoline-2,4(1H,3H)-diones via different catalytic mechanisms, including amino preferential activation, CO₂ preferential activation, and simultaneous amino and CO₂ activation, are investigated systematically. Finally, future directions and prospects for CO₂ conversion by IL-based catalysts are outlined. This review is benefit for academic researchers to obtain an overall understanding of the synthesis of quinazoline-2,4(1H,3H)-diones from CO₂ and o-aminobenzonitriles by IL-based catalysts. This work will also open a door to develop novel IL-based catalysts for the conversion of other acid gases such as SO₂ and H₂S.

Understanding of the interactions between azole-anion-based ionic liquids and 2-methyl-3-butyn-2-ol from the experimental perspective: the cage effect

The interactions between azole-anion-based ionic liquids (AILs) and 2-methyl-3-butyn-2-ol (MBY) play an important role in AIL-promoted carboxylative cyclization of MBY with CO₂. To better understand the interactions between AILs ([P₆₆₆₁₄][Im], [P₆₆₆₁₄][4-MeIm], and [P₆₆₆₁₄][4-BrIm]) and MBY, a detailed investigation from the experimental perspective has been carried out in this study. The results show that the derivative of viscosity (η) with the mole fraction of AIL (x_AIL) of AIL + MBY mixtures appears to have the maximum value when x_AIL ≈ 0.3, while ¹H NMR chemical shifts of P-CH₂ of [P₆₆₆₁₄]⁺ reach the minimum value at x_AIL ≈ 0.3, indicating that [P₆₆₆₁₄]⁺ of AILs tend to self-aggregate. The interaction parameters (g_ji-g_ii) of the systems obtained from η by the Eyring-UNIQUAC equation are positive, and the difference between the bulk and local composition (x_i-x_ii) is always negative, indicating that AILs can interact with MBY. Moreover, excess molar volumes and isentropic compressibility deviations are all negative deviations and become more negative as the temperature increases, reaching a minimum value at x_AIL ≈ 0.30, indicating that azole-based anions can form H-bonds with MBY, and MBY molecules tend to enter the aggregates formed by AILs. Consequently, the cage effect is proposed to describe the interactions between AILs and MBY: MBY first enters the cage formed by the aggregation of [P₆₆₆₁₄]⁺, and then forms H-bonds with azole-based anions. Finally, the sizes of the particles of the [P₆₆₆₁₄][Im] + MBY mixture from dynamic light scattering increase first and then decrease with x_AIL, with the maximum of 122 nm at x_AIL ≈ 0.25, which confirms the rationality of the cage effect.

Exovinylene Cyclic Carbonates: Multifaceted CO2 -Based Building Blocks for Modern Chemistry and Polymer Science

Carbon dioxide is a renewable, inexhaustible, and cheap alternative to fossil resources for the production of fine chemicals and plastics. It can notably be converted into exovinylene cyclic carbonates, unique synthons gaining momentum for the preparation of an impressive range of important organic molecules and functional polymers, in reactions proceeding with 100 % atom economy under mild operating conditions in most cases. This Review summarizes the recent advances in their synthesis with particular attention on describing the catalysts needed for their preparation and discussing the unique reactivity of these CO₂ -based heterocycles for the construction of diverse organic building blocks and (functional) polymers. We also discuss the challenges and the future perspectives in the field.

CeO2-Catalyzed Synthesis of 2-Imidazolidinone from Ethylenediamine Carbamate

CeO2 acted as an effective and reusable heterogeneous catalyst for the direct synthesis of 2-imidazolidinone from ethylenediamine carbamate (EDA-CA) without further addition of CO2 in the reaction system. 2-Propanol was the best solvent among the solvents tested from the viewpoint of selectivity to 2-imidazolidinone, and the use of an adequate amount of 2-propanol provided high conversion and selectivity for the reaction. This positive effect of 2-propanol on the catalytic reaction can be explained by the solubility of EDA-CA in 2-propanol under the reaction conditions and no formation of solvent-derived byproducts. This catalytic system using the combination of the CeO2 catalyst and the 2-propanol solvent provided 2-imidazolidinone in up to 83% yield on the EDA-CA basis at 413 K under Ar. The reaction conducted under Ar showed a higher reaction rate than that with pressured CO2, which clearly demonstrated the advantage of the catalytic system operated at low CO2 pressure or even without CO2.

Ionic-Liquid-Catalyzed Approaches under Metal-Free Conditions

ConspectusMetal-free catalysis is a promising protocol to access chemicals without metal contamination. Ionic liquids (ILs) that are entirely composed of organic cations and inorganic/organic anions have emerged as promising alternatives to molecular solvents and metal catalysts due to their unique properties such as structural tunability, the coexistence of multiple interactions among ions (e.g., electrostatic interaction, hydrogen bonding, van de Waals forces, acid/base interactions, hydrophilic/hydrophobic interactions, etc.), unique affinity for a wide range of chemicals, good chemical and thermal stability, and quite low volatility. ILs have shown potential applications in various chemical processes.In this Account, we systematically described our most recent work on IL-catalyzed approaches under metal-free conditions. The first section presents the IL-catalyzed strategies toward the transformation of CO2 to value-added chemicals, focusing on the CO2-reactive IL-catalyzed CO2 transformation to various heterocycles and the IL-catalyzed reductive transformation of CO2 to chemicals. In these approaches, we designed task-specific ILs that are able to chemically capture and activate CO2 via forming anion-based carbonate/carbamate or cation-based carboxylate/carbamate intermediates, thus further accomplishing its transformation to a series of heterocycles including quinazoline-2,4(1H,3H)-diones, cyclic carbonates, 2-oxazolidinones, oxazolones, and benzimidazolones under metal-free conditions. For the IL-catalyzed approaches to reducing CO2 with hydrosilanes to chemicals, we employed ILs capable of activating the Si-H bond in hydrosilanes and the N-H bond in amine substrates via H-bonding, thus achieving the reductive transformation of CO2 to formamides, benzimidazoles, and benzothiazoles via cooperative catalysis. The second section describes our finding on the IL-catalyzed hydration of the C≡C bond in propargylic alcohols. Azolate anion-based ILs that can chemically capture CO2 via the formation of carbamates could serve as robust nucleophiles to attack the C≡C bond in propargylic alcohols and then efficiently catalyze the hydration of propargylic alcohols to produce α-hydroxy ketones with the assistance of atmospheric CO2 gas under metal-free conditions. The third section unveils the cooperative catalysis strategy of hydrogen bond donors and acceptors of ILs for chemical reactions. In the hydrogen-bonding catalysis protocols, cations of the ILs act as H-bond donors and anions, as acceptors, forming H-bonds with the reactant molecules, respectively, in opposite ways, which can cooperatively catalyze the ring-closing C-O/C-O bond metathesis reactions of aliphatic diethers to O-heterocycles, the dehydrative etherification of alcohols to ethers, and direct oxidative esterification of alcohols to esters. We believe that these IL-catalyzed metal-free processes and strategies display promising practical applications, and their commercialization would bring great benefits to the production of the as-afforded value-added chemicals.

Metal-Free Synthesis of N-(Carboselenoate) Benzimidazolones by Cascade Cyclization of ortho-Diisocyanoarenes and Selenosulfonates

A facile synthesis of N-(carboselenoate) benzimidazolones through metal-free reactions of ortho-diisocyanoarenes with selenosulfonates is reported here. The desired products are obtained in moderate to good yields with good functional group compatibility. The ortho-diisocyanoarenes are applied to the construction of 2-benzimidazolone derivatives for the first time.

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C-N Bond Forming Reactions of Amines with CO2

Organocatalysts promote a range of C-N bond forming reactions of amines with CO₂ . Herein, we review these reactions and attempt to identify the unifying features of the catalysts that allows them to promote a multitude of seemingly unrelated reactions. Analysis of the literature shows that these reactions predominantly proceed by carbamate salt formation in the form [BaseH][RR'NCOO]. The anion of the carbamate salt acts as a nucleophile in hydrosilane reductions of CO₂ , internal cyclization reactions or after dehydration as an electrophile in the synthesis of urea derivatives. The reactions are enhanced by polar aprotic solvents and can be either promoted or hindered by H-bonding interactions. The predominant role of all types of organic and salt catalysts (including ionic liquids, ILs) is the stabilization of the carbamate salt, mostly by acting as a base. Catalytic enhancement depends on the combination of the amine, the base strength, the solvent, steric factors, ion pairing and H-bonding. A linear relationship between the base strength and the reaction yield has been demonstrated with IL catalysts in the synthesis of formamides and quinazoline-2,4-diones. The role of organocatalysts in the reactions indicates that all bases of sufficient strength should be able to catalyze the reactions. However, a physical limit to the extent of a purely base catalyzed reaction mechanism should exist, which needs to be identified, understood and overcome by synergistic or alternative methods.

CO2 Capture and in situ Catalytic Transformation

The escalating rate of fossil fuel combustion contributes to excessive CO₂ emission and the resulting global climate change has drawn considerable attention. Therefore, tremendous efforts have been devoted to mitigate the CO₂ accumulation in the atmosphere. Carbon capture and storage (CCS) strategy has been regarded as one of the promising options for controlling CO₂ build-up. However, desorption and compression of CO₂ need extra energy input. To circumvent this energy issue, carbon capture and utilization (CCU) strategy has been proposed whereby CO₂ can be captured and in situ activated simultaneously to participate in the subsequent conversion under mild conditions, offering valuable compounds. As an alternative to CCS, the CCU has attracted much concern. Although various absorbents have been developed for the CCU strategy, the direct, in situ chemical conversion of the captured CO₂ into valuable chemicals remains in its infancies compared with the gaseous CO₂ conversion. This review summarizes the recent progress on CO₂ capture and in situ catalytic transformation. The contents are introduced according to the absorbent types, in which different reaction type is involved and the transformation mechanism of the captured CO₂ and the role of the absorbent in the conversion are especially elucidated. We hope this review can shed light on the transformation of the captured CO₂ and arouse broad concern on the CCU strategy.

Synthesis of renewable acetic acid from CO2and lignin over an ionic liquid-based catalytic system

Renewable acetic acid can be synthesized from CO₂and lignin over an ionic liquid-based catalytic system containing Ru–Rh bimetal catalyst.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

Recent Advances in the Catalytic Synthesis of Imidazolidin-2-ones and Benzimidazolidin-2-ones

2-Imidazolidinone and its analogues are omnipresent structural motifs of pharmaceuticals, natural products, chiral auxiliaries, and intermediates in organic syntheses. Over the years, continuous efforts have been addressed to the development of sustainable and more efficient protocols for the synthesis of these heterocycles. This review gives a summary of the catalytic strategies to access imidazolidin-2-ones and benzimidazolidin-2-ones that have appeared in the literature from 2010 to 2018. Particularly important contributions beyond the timespan will be mentioned. The review is organized in four main chapters that identify the most common approaches to imidazolidin-2-one derivatives: (1) the direct incorporation of the carbonyl group into 1,2-diamines, (2) the diamination of olefins, (3) the intramolecular hydroamination of linear urea derivatives and (4) aziridine ring expansion. Methods not included in this classification will be addressed in the miscellaneous section.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.

Ionic Liquids Catalysis for Carbon Dioxide Conversion With Nucleophiles

Carbon dioxide, as a promising C₁ synthon, has attracted great interest in organic synthesis. Due to the thermodynamic stability and kinetic inertness of CO₂, developing efficient strategies for CO₂ activation and subsequent conversion is very crucial. In this context, Ionic liquids (ILs) show great potential for capturing and activating CO₂ owing to their unique structures and properties, making them become ideal alternatives to volatile organic solvents and/or catalysts for CO₂ transformation. This minireview aims at summarizing ILs-promoted reactions of CO₂ with N-nucleophiles (primary amines)/O-nucleophiles (primary alcohols, water). Two catalytic systems i.e., metal/ILs binary systems such as Cu/ILs systems and Ag/ILs systems as well as single ILs systems including anion-functionalized ILs and bifunctionalized ILs have been developed for CO₂ catalytic conversion, for instance, carboxylative cyclization of nucleophiles e.g., propargylic alcohols, amines, 2-aminobenzonitriles and o-aminobenzenethiol, and formylation of amines or 2-aminothiophenols with hydrosilanes to afford various value-added chemicals e.g., cyclic carbamates, unsymmetrical organic carbonates, α-hydroxyl ketones, and benzimidazolones. In a word, IL could provide a powerful tool for efficient CO₂ utilization.

Carbon Dioxide Utilisation for the Synthesis of Unsymmetrical Dialkyl and Cyclic Carbonates Promoted by Basic Ionic Liquids

An efficient and greener synthesis of unsymmetrical organic carbonates mediated by Hünig’s base-appended basic ionic liquids, via carbon dioxide conversion, is described here. These ionic liquids were found to be effective bases for the fixation of carbon dioxide by various alcohols and benzyl bromide, at room temperature. When the alcohol and the halide functionalities are present within the same substrate, the reaction cleanly produces a cyclic carbonate. These functionalised basic ionic liquids were fully recyclable with no loss product yields.