Investigations on the Synthesis of Chiral Ionic-Liquid-Supported Ligands and Corresponding Transition-Metal Catalysts: Strategy and Experimental Schemes

Ionic liquids have been utilized in numerous significant applications within the field of chemistry, particularly in organic chemistry, due to their unique physical and chemical properties. In the realm of asymmetric transition-metal-catalyzed transformations, chiral ionic-liquid-supported ligands and their corresponding transition-metal complexes have facilitated these processes in unconventional solvents, especially ionic liquids and water. These innovative reaction systems enable the recycling of transition-metal catalysts while producing optically active organic molecules with comparable or even higher levels of chemo-, regio-, and stereoselectivity compared to their parent catalysts. In this short review, we aim to provide an overview of the structures of chiral ionic-liquid-supported ligands and the synthetic pathways for these ligands and catalysts. Various synthetic methodologies are demonstrated based on the conceptual frameworks of diverse chiral ionic-liquid-supported ligands. We systematically present the structures and comprehensive synthetic pathways of the chiral ionic-liquid-supported ligands and the typical corresponding transition-metal complexes that have been readily applied to asymmetric processes, categorized by their parent ligand framework. Notably, the crucial experimental procedures are delineated in exhaustive detail, with the objective of enhancing comprehension of the pivotal aspects involved in constructing chiral ionic-liquid-tagged ligands and compounds for both scholars and readers. Considering the current limitations of such ligands and catalysts, we conclude with remarks on several potential research directions for future breakthroughs in the synthesis and application of these intriguing ligands.

Molecular oxygen-promoted sustainable synthesis of functionalized quinolines using catalytic glucose-derived ionic liquids and copper

An expedient one-pot sustainable synthesis of quinoline analogues was developed via protection-free chemo-selective oxidation of 2-aminobenzyl alcohols to form aldehydes, followed by annulation with various 1,3-dicarbonyl compounds or nitriles under mild reaction conditions in an acetonitrile-water medium using a copper catalyst and new hydrogen bond-rich glucose-based ionic liquids (GSILs). Overall, 40 functionalized quinolines were synthesized with up to 93% yields following significant green chemistry parameters. The developed GSILs were recyclable with not much decrease in the yields of the products and the reaction rate.

Ionic Liquids for the Chemical Recycling of Polymeric Materials and Control of Their Solubility

Plastics are wonderful materials that have modernized our daily life; however, importance of effective recycling of plastics is gradually recognized widely. In this account, we describe our discovery of new and efficient methods for the chemical recycling of plastics using ionic liquids (ILs). Since the chemical recycling usually requires high temperature conditions to breakdown chemical bonds in polymeric materials, we thought that less-flammability and non-volatility of ionic liquids are the most suitable physical properties for this purpose. Ionic liquids successfully depolymerized polyamides and unsaturated polyesters smoothly and corresponding monomeric materials were obtained in good yields. To the best of our knowledge, this was the first use of Ionic liquids for such reactions. However, we encountered another difficult problem-separation. To solve the problem, we developed solubility-switchable ionic liquids, a new type of ionic liquids in which solubility is readily changed using the chemistry of protective groups. Conversion between hydrophilic and lipophilic forms was readily achieved using a simple chemical treatment under mild conditions, and the complete separation of products was achieved by liquid-liquid-extraction. The robustness of either form unlocks their wide use as reaction solvents.

Betaine- and L-Carnitine-Based Ionic Liquids as Solubilising and Stabilising Agents for the Formulation of Antimicrobial Eye Drops Containing Diacerein

The therapeutic efficacy of topically administered drugs, however powerful, is largely affected by their bioavailability and, thus, ultimately, on their aqueous solubility and stability. The aim of this study was to evaluate the use of ionic liquids (ILs) as functional excipients to solubilise, stabilise, and prolong the ocular residence time of diacerein (DIA) in eye drop formulations. DIA is a poorly soluble and unstable anthraquinone prodrug, rapidly hydrolysed to rhein (Rhe), for the treatment of osteoarthritis. DIA has recently been evaluated as an antimicrobial agent for bacterial keratitis. Two ILs based on natural zwitterionic compounds were investigated: L-carnitine C6 alkyl ester bromide (Carn6), and betaine C6 alkyl ester bromide (Bet6). The stabilising, solubilising, and mucoadhesive properties of ILs were investigated, as well as their cytotoxicity to the murine fibroblast BALB/3T3 clone A31 cell line. Two IL-DIA-based eye drop formulations were prepared, and their efficacy against both Staphylococcus aureus and Pseudomonas aeruginosa was determined. Finally, the eye drops were administered in vivo on New Zealand albino rabbits, testing their tolerability as well as their elimination and degradation kinetics. Both Bet6 and Carn6 have good potential as functional excipients, showing solubilising, stabilising, mucoadhesive, and antimicrobial properties; their in vitro cytotoxicity and in vivo ocular tolerability pave the way for their future use in ophthalmic applications.

Applications of biomass-derived solvents in biomass pretreatment - Strategies, challenges, and prospects

Biomass pretreatment is considered a key step in the 2nd generation biofuel production from lignocellulosic biomass. Research on conventional biomass pretreatment solvents has mainly been focused on carbohydrate conversion efficiency, while their hazardousness and/or carbon intensity were not comprehensively considered. Recent sustainability issues request further consideration for eco-friendly and sustainable alternatives like biomass-derived solvents. Carbohydrate and lignin-derived solvents have been proposed and investigated as green alternatives in many biomass processes. In this review, the applications of different types of biomass pretreatment solvents, including organic, ionic liquid, and deep eutectic solvents, are thoroughly discussed. The role of water as a co-solvent in these pretreatment processes is also reviewed. Finally, current research challenges and prospects of utilizing biomass-derived pretreatment solvents for pretreatment are discussed. Given bioethanol's market potential and increasing public awareness about environmental concerns, it will be a priority adopting sustainable and green biomass pretreatment solvents in biorefinery.

Preparation and Hydrophilicity/Lipophilicity of Solubility-Switchable Ionic Liquids

Various solubility-switchable ionic liquids were prepared. Their syntheses were readily achieved in a few steps from glyceraldehyde dimethylacetal or its derivatives. Pyridinium, imidazolium, and phosphonium derivatives also exhibited solubility-switchable properties; acetal-type ionic liquids were soluble in organic solvents, while diol-type ones exhibited a preference for being dissolved in the aqueous phase. The solubility of the ionic liquids prepared in this study also depended on the number of carbon atoms in the cationic parts of the ionic liquids. Interconversion between the diol-type and the acetal-type ionic liquids was readily achieved under the standard conditions for diol acetalization and acetal hydrolysis. One of the prepared ionic liquids was also examined as a solvent for an organic reaction.

Cu-Catalysed tandem reactions for building poly hetero atom heterocycles-green chemistry tool

Of late, regio-selective tandem reactions are given much attention due to the formation of several multiple bonds in a single synthetic operation, avoids altering the reaction conditions, isolation of the intermediates during the reaction, reduces the production of toxic waste to the environment and can produce highly complex organic molecules with desired selectivity. Though, it requires the well-built knowledge for optimization of the process, it permits to make the complex organic molecules with least number of steps, and it has eventually made great interest and inspiration to the upcoming organic chemists. Presentation of current book chapter presents the Cu-Catalysed tandem reactions for building poly hetero atom heterocyclic compounds via green approach.