Green Polymerization of Phenol in Ionic Liquids

Physical properties of phosphonium ionic liquid and its mixtures with dodecane and water

During the last decade there has been an explosion of interest in ionic liquids. If the keywords “ionic liquid” or “ionic liquids” are used for a literature research in the Web of Science, more than seven thousand entries can be found for 2011. That is a tenfold increase in the number of publications dealing with ionic liquids over the past decade, and the field shows no signs of slowing down. Ionic liquids have changed from a lab curiosity to materials of tremendous academic and industrial interest. This new and remarkable liquid substance with unique and fascinating properties offers a phenomenal opportunity for new science and technology. The interest in these new materials is due to their wide range of possible applications as solvents for reaction and material processing, as extraction media or as working fluids in mechanical applications. Originating in the field of electrochemistry and based upon their wide electrochemical windows and good conductivities, ionic liquids have found useful applications in sensors, solar cells, solid-state photocells, batteries, separation devices and as thermal fluids, lubricants, hydraulic fluids, ionogels and fuels. The generally accepted definition of an ionic liquid is a salt composed solely of ions with melting points below 100 °C. New combinations of ions provide changing physical properties and thus novel potential applications for this class of liquid material. To a large extent, the structure and properties of ionic liquids are determined by the intermolecular interaction between anions and cations. In particular, the subtle balance between Coulomb forces, hydrogen bonds, π stacking and repulsion–dispersion forces is of great importance for understanding the properties of ionic liquids. All the important properties such as structure, diffusion, viscosity, conductivity or melting points depend on these interactions between cations and anions in ionic liquids. Thus, an important goal is to develop a fundamental understanding of their chemical and physical properties at the molecular level. Reliable structure–property relationships can help us to synthesize ionic liquid compositions with the desired set of properties. Since 2005 a number of research programs have been set up worldwide to advance ionic liquids research. Among those, the Japanese Priority Area “Science of Ionic Liquids” running from 2005 to 2009 and the priority programme SPP 1191 “Ionic Liquids” implemented by the German Science foundation (DFG) in 2006 and finished at the end of this year may be the most prominent ones in the academic arena. The efforts and developments achieved in ionic liquids research from these and other programmes are presented in this special issue. On the occasion of the International Bunsen Meeting 2012 in Leipzig, we put together a collection of almost forty articles that show the growing diversity within the field. In this special issue of ChemPhysChem, developments in experiment, theory and simulations for investigating ionic liquids are presented. The articles highlight the interaction within ionic liquids between anions and cations studied by a variety of experimental and theoretical methods including spectroscopy, ab initio simulations, classical molecular dynamics simulations and quantum molecular dynamics simulations. A particular focus is put on hydrogen bonding and dispersion forces, which are often assumed to be unimportant in Coulomb systems but are absolutely crucial to understanding ionic liquids. The critical review of theoretical and simulation approaches for describing the properties of ionic liquids is an important issue in this respect. Another topic is the interaction of ILs with water and organic solvents leading to modified local structures and polarities (Figure 1). In general, IL mixtures with water, alcohols and amines allow interesting tuning of important IL physical properties, including structural and transport properties such as diffusion coefficients, viscosities and conductivities. Walden plots, which compare the molar conductivity as a function of fluidity (inverse viscosity), show deviations from ideal, linear behaviour derived from well-understood aqueous solutions. Ionic liquids in its pure state (left) and in a mixture with an organic solvent (blue). Why not consider mixing ILs themselves to change properties? Thus another focus is put on mixtures of ILs including different anion–cation combinations. By varying the cation or the anion only, structure and interaction strength can be modified in the desired way. Several examples are given for structure–property relations in ionic liquids, which may allow predictions for physical properties for a set of specially synthesized ILs. Chemical reactions and coordination in ionic liquids are also attracting increasing interest. In several articles the effects on physical properties of other materials such as gels and micelles in IL environments are reported. ILs have also become increasing important in biology. The behaviour of biomolecules, such as the folding and unfolding of proteins, are developing into an important facet in ionic liquids research. Of course, after having an idea about the origin of the physical properties, new ionic liquids need to be synthesized and characterized. New and special ionic liquids and their properties are introduced in some of the contributions. An important aspect in and of itself is the liquid/gas or the liquid/liquid interface of ionic liquids (Figure 2). How do these interfaces look like with respect to the polar and hydrophobic parts of anions and cations? How do the IL properties change at the interfaces? Combinations of experimental and theoretical methods try to provide answers to these questions. Ion-pair evaporating from the surface of an imidazolium-based ionic liquid. All these fundamental issues are addressed in this special issue of ChemPhysChem. We hope that this compilation improves our understanding of the fascinating physical chemistry of ionic liquids. An understanding at the molecular level opens new potential for fundamentals and applications. Ralf Ludwig 1 Ed Maginn 1 Bala Sundaram 1

Room temperature ionic liquids (RTILs), considered as designers' solvents, are attracting a great attention because of their possibility to be tailored based on property requirements. The ionic liquids designed and synthesized for carrying out specified task are referred as functionalized ionic liquids, which show great application potential in various processes. The efforts to produce functionalized ionic liquids, characterize them, and evaluate their properties and applications are presented in this thesis. In chapter 1 the recent developments in ionic liquid functionalization are highlighted. Chapter 2 describes the synthesis and characterization of imidazolium salts in which a nitrile group is attached to the alkyl side chain (single-armed as well as double-armed). The nitrile group was chosen as it is a promising donor to transition metals such as palladium and platinum. The physicochemical properties of these new ionic liquids are described and it is shown how the length of the alkyl unit linking the imidazolium ring and the CN group influences the melting point of the ionic liquid. The third chapter describes palladium complexation reactions with the nitrile functionalized imidazolium ionic liquids (prepared as described in Chapter 2). Their application in C-C coupling and hydrogenation reactions are described. It will be shown that the palladium complexes serve as precursors to nanoparticle catalyst reservoirs and are very efficiently stabilized by the nitrile-functionalized ionic liquids. In chapter 4, the synthesis of a series of nitrile functionalized ionic liquids based on the N-butylnitrile pyridinium cation is reported and their suitability as solvents for palladium-catalyzed biphasic Suzuki and Stille coupling reactions is demonstrated. TEM images reveal that nanoparticles are formed in situ in Stille reactions and show that the nitrile-functionalized ionic liquid exert a superior nanoparticle-stabilizing effect compared to non-functionalized ionic liquids. This allows excellent catalyst lifetimes. In the fifth chapter the synthesis and characterization of a series of ionic liquids incorporating the allyl functionality and some nascent reactions that they undergo, indicating that they are useful precursors to a wide range of other functionalized ionic liquids, will be described. Chapter 6 reports on a concept of dual-functionalized ionic liquids. Specifically imidazolium cations with various functionalities are combined with the nitrile functionalized anion [CH3CH(BF3)CH2CN]-, aiming at reducing the melting point and visocity of ionic liquids. In the final chapter the ionic liquid, 1-methyl-3-(4-vinylbenzyl)-imidazolium chloride, is prepared and polymerized to form a macromolecule that is subsequently used as a transition metal nanoparticle stabilizer. A methodology that enables transition metal nanoparticle transfer between liquid phases, via surface modification of the nanoparticles by anion exchange, is described.

The colloidal stabilities of dispersions of unmodified and surface-functionalized SiO2 nanoparticles in hydrophobic and hydrophilic imidazolium-based ionic liquids were studied with advanced rheology at three temperatures (25, 100, and 200 °C). The rheological behavior of the dispersions was strongly affected by the ionic liquids hydrophilicity, by the nanoparticles surface, by the concentration of the nanoparticles in the dispersion as well as by the temperature. The unmodified hydrophilic nanoparticles showed a better compatibility with the hydrophilic ionic liquid. The SiO2 surface functionalization with hydrophobic groups clearly improved the colloidal stability of the dispersions in the hydrophobic ionic liquid. The temperature increase was found to lead to a destabilization in all studied systems, especially at higher concentrations. The results of this study imply that ionic liquids with tailored properties could be used in absorbers directly after reactors for gas-phase synthesis of nanoparticles or/and as solvents for their further surface functionalization without agglomeration or aggregation.

Densities, viscosities and derived thermophysical properties of water-saturated imidazolium-based ionic liquids

Recent advances for sustainable production of levulinic acid in ionic liquids from biomass: Current scenario, opportunities and challenges

Due to their unique physiochemical properties that may be tailored for specific purposes, ionic liquids (ILs) have been investigated for various applications, including chemical separations, catalysis, energy storage, and space propulsion. The different cations and anions comprising ILs may be selected to optimize a range of desired properties, such as thermal stability, ionic conductivity, and volatility, leading to the designation of certain ILs as designer "green" solvents. The effect of counterions on the properties of ILs is of both fundamental scientific interest and technological importance. Herein, we report a systematic experimental and theoretical investigation of the size, charge, stability toward dissociation, and geometric/electronic structure of 1-ethyl-3-methyl imidazolium (EMIM)-based IL clusters containing two different atomic counterions (i.e., bromide [Br-] and iodide [I-]). This work extends our studies of EMIM+ cations with atomic chloride (Cl-) and molecular tetrafluoroborate (BF4-) anions reported previously by Baxter et al. [Chem. Mater. 34, 2612 (2022)] and Zhang et al. [J. Phys. Chem. Lett. 11, 6844 (2020)], respectively. Distributions of anionic IL clusters were generated in the gas phase using electrospray ionization and characterized by high mass resolution mass spectrometry, energy-resolved collision-induced dissociation, and negative ion photoelectron spectroscopy experiments. The experimental results reveal anion-dependent trends in the size distribution, relative abundance, ionic charge state, stability toward dissociation, and electron binding energies of the IL clusters. Complementary global optimization theory provides molecular-level insights into the bonding and electronic structure of a selected subset of clusters, including their low energy structures and electrostatic potential maps, and how these fundamental characteristics are influenced by anion substitution. Collectively, our findings demonstrate how the fundamental properties of ILs, which determine their suitability for many applications, may be tuned by substituting counterions. These observations are critical in the sub-nanometer cluster size regime where phenomena do not scale predictably to the bulk phase, and each atom counts toward determining behavior.

Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids with the outstanding mechanical characteristics of polymers. This special mix of features might help to circumvent the key limitations of low molecular weight ionic liquids, namely, leakage and poor mechanical properties while utilizing their outstanding characteristics such as low vapor pressures, wide liquidus ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. PolyILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices, among others. Despite their promising prospects as ideal polymer electrolytes, the role of molecular structure, morphology, and polymer dynamics on charge transport in PolyILs remains poorly understood. According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and structural dynamics. Although this prediction has been shown to hold reasonably well for low molecular weight aprotic ionic liquids, it fails for PolyILs. In addition, the impact of morphology on charge transport is not considered within the framework of these theories. This talk will focus on new insights obtained from experimental studies employing broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, rheology, and scattering techniques to elucidate the impact of morphology on charge transport and structural dynamics in systematic series of polymerized ammonium- and imidazolium- based ionic liquids. Detailed analyses reveal strong decoupling of these processes in the PolyILs, implying the limitation of the classical theories in describing charge transport and molecular dynamics in these materials, in contrast to low molecular weight systems. In addition, the strong correlation observed between ionic conductivity from dielectric experiments and morphologies from scattering and computational studies will be discussed.

Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids with the outstanding mechanical characteristics of polymers [1,2]. This special mix of features might help to circumvent the key limitations of low molecular weight ionic liquids, namely, leakage and poor mechanical properties while utilizing their outstanding characteristics such as low vapor pressures, wide liquidus ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. PolyILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices, among others. Despite their promising prospects as ideal polymer electrolytes, the role of molecular structure, morphology, and polymer dynamics on charge transport in PolyILs remains poorly understood. According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and structural dynamics. Although this prediction has been shown to hold reasonably well for low molecular weight aprotic ionic liquids, it fails for PolyILs [2,3]. In addition, the impact of morphology charge transport is not considered within the framework of these theories. The first part of this talk will focus on new insights obtained from experimental studies employing broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, rheology, and scattering techniques to elucidate charge transport and structural dynamics in a systematic series of bulk polymerized ammonium- and imidazolium- based ionic liquids. Detailed analyses reveal strong decoupling of these processes in the PolyILs, implying the limitation of the classical theories in describing charge transport and molecular dynamics in these materials, in contrast to low molecular weight systems (4,5). In addition, the strong correlation observed between ionic conductivity from dielectric experiments and morphologies from scattering studies will be reviewed. In the second part of this talk, our recent results from a new approach to dielectric experiments yielding details about ion dynamics in ultrathin films of polymerized ionic liquids down to sub-5nm film thicknesses will be discussed. While the characteristic charge transport rates remain bulk-like down to about 5 nm film thicknesses, ionic-liquid/substrate interactions play an increasingly significant role in determining ion dynamics in confined polymerized ionic liquids (5). These results will be considered within the context of recent models of charge transport and polymer dynamics under confinement. References 1) Mecerreyes, D. Progress in Polymer Science 2011, 36, 1629. 2) Sangoro, J. R. and Kremer, F. Accounts of Chemical Research 2012, 45, 525 3) Sangoro, J. R. et al., Soft Matter 2014, 10, 3536. 4) Wojnarowska, Z. et al., Macromolecules 2015, 48 (23), 8660-8666. 5) Heres, M. F. et al., Submitted.

The partition of various chlorinated and nitrated phenols between hydrophobic ionic liquids and aqueous solutions of different pH values was investigated at 298.2 K. Ionic liquids used are 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([BMIm][NTf2]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([BMPyr][NTf2]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)amide ([OMIm][NTf2]), and 1-methyl-3-octylimidazolium tetrafluoroborate ([OMIm][BF4]). Partition coefficients (PIL/W) of the electrically neutral form (ArOH) and the dissociated anionic form (ArO–) were determined. For a given phenol, the PIL/W(ArOH) value in the ionic liquid/water system is generally independent of the kind of the ionic liquid and smaller than that in the 1-octanol/water system. Exceptionally, the PIL/W(ArOH) value in the [OMIm][BF4]/water system is larger than those in the other ionic liquid/water systems and comparable to or greater than that in the 1-octanol/water system. The interaction energies of the ionic liquids with the phenolic hydroxyl group were evaluated. It is shown from the dependence of the interaction energy on the acid-dissociation constant of the phenol that the ionic liquid behaves as both an electron-pair donor and an acceptor like water rather than 1-octanol. The PIL/W(ArO–) value depends largely on the kind of ionic liquid, showing that an ionic liquid formed by a more hydrophobic cation and a more hydrophilic anion has a higher extractability for the phenolate anions. The substituent effects on PIL/W(ArO–) are also different from those on PIL/W(ArOH).

Ion dynamics and charge transport in 1-methyl-3-octylimidazolium ionic liquids with chloride, bromide, tetrafluoroborate, tricyanomethanide, hexafluorophosphate, triflate, tetrachloroaluminate, bis(trifluoromethylsulfonyl)imide, and heptachlorodialuminate anions are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. A detailed analysis reveals an anion and temperature-dependent separation of characteristic molecular relaxation rates extracted from various representations of the dielectric spectra. The separation in rates extracted from the electric modulus and conductivity formalisms is interpreted as an experimental signature of significant heterogeneity in the local ion dynamics associated with the structural glass transition, viscosity, and dc ion conductivity. It is further found that the degree of dynamic heterogeneity correlates with the strengths of slow dielectric and mechanical relaxations previously attributed to the dynamics of mesoscale solvophobic aggregates. Increasing local dynamic heterogeneity correlates with an increase in the strength of the slow, aggregate dielectric relaxation and a decrease in the strength of the slow, aggregate mechanical relaxation. Accordingly, increasing local dynamic heterogeneity, brought about by change in temperature and/or cation/anion chemical structure, correlates with an increase in the static dielectric permittivities and a decrease in the contribution of aggregate dynamics to the zero-shear viscosities. The established correlation provides a new ability to distinguish between the influence of mesoscale aggregate shape/morphology versus local and mesoscale ion dynamics on the transport properties of ionic liquids.

Effects of acetonitrile on electrodeposition of Ni from a hydrophobic ionic liquid

Solvation and rotational relaxation of coumarin 153 and 4-aminophthalimide in a new hydrophobic ionic liquid: Role of N–H…F interaction on solvation dynamics

Ionic liquids (ILs) have significant potential for eco-friendly extraction of uranium from aqueous solutions, which is critical for nuclear technology, fuel cycle management, and environmental protection. This study examines the impact of the adjustable hydrophobic/hydrophilic properties of ILs on the removal of uranium(VI) (UO22+) from aqueous solutions utilizing both a novel hydrophilic IL (1-butoxyethyl-1-methylmorpholinium butoxyethylphosphite - Mor1-2O4-BOEP) and 1-heptyl-1-methylmorpholinium heptylphosphite (Mor1-7-HP) as an example of a hydrophobic IL with a similar structure. The transfer mechanism of uranyl ions from water to organic or solid phases closely depends on the physicochemical properties of ILs, especially their hydrophobicity. The hydrophobic Mor1-7-HP extracts uranyl via neutral complex formation as UO2(NO3)2-(Mor1-7-HP)2. Conversely, hydrophilic Mor1-2O4-BOEP induced selective precipitation as UO2(NO3)-(BOEP), transferring uranyl to the solid phase. Optimization of the working parameters, in terms of acidity of the aqueous solution and amount of ILs used, allowed the extraction of over 98% of U(VI). The stoichiometry of the organic complex and the precipitate was determined using physicochemical techniques. These tunable H-phosphonate-based ILs have advantages over traditional solvent extraction and conventional ILs, allowing easier handling, improved selectivity, and lower environmental impact. This work advances uranium separation techniques with applications in hydrometallurgy, particularly in the treatment of wastewater and radioactive waste for sustainable uranium recovery.

<sec><p indent="0mm">Propylene is an important part of the petrochemical industry, and its global market size has exceeded $120 billion. However, the existing propylene production process is frequently observed with the presence of propane. The separation process of propylene and propane is one of the most energy consuming processes in industrial development because of the similar structure and physical and chemical properties between them. Traditional cryogenic rectification techniques are beset with limitations such as inadequate separation efficiency and high energy consumption. Given the carbon peaking and carbon neutrality goals, it is imperative to develop environmentally friendly separation materials for propylene/propane that not only conserve energy but also enhance separation efficiency. Ionic liquids (ILs), with their characteristics of adjustable physical and chemical properties of structure, lower volatility than other organic solvents and rich hydrogen bond network, have wide significant interest in gas separation applications. ILs exhibit a unique absorption ability, which can selectively separate between propylene and propane through strong hydrogen bonding interactions or via π complexation with transition metal salts. ILs have been recognized as a new generation of efficient separation materials for propylene/propane separation, offering significant advantages in propylene absorption capacity, selectivity and cycle stability, and more. </sec><sec> In this work, the current research on propylene/ propane separation processes by using ionic liquids was firstly summarized, focusing on the optimal design of ILs, composite methods involving transition metal salts, and the underlying adsorption mechanisms. Subsequently, the influences of the structure of ILs (including the groups on the cation and anion of ILs, the length of side chain alkyl chain of cation, and the combination with transition metal salts), the properties of ILs (viscosity and cycle stability) and absorption conditions (temperature, pressure, concentration of transition metal salts) on the separation performance were discussed in detail. The results showed that the use of unsaturated groups on cations and anions or the reduction of side chain length both strengthen selective absorption capacity for propylene. Simultaneously, better gas separation performance can be achieved by reducing viscosity, increasing absorption pressure and increasing transition metal content. </sec><sec> Secondly, this article also outlines two methods for researchers to explore ILs-based functional materials for the purpose of making full use of the gas separation performance of ionic liquids and overcoming the influence of viscosity on gas diffusion. The initial strategy is to be combined ILs with porous adsorbents (such as metal-organic frameworks (MOFs)) to enhance their dispersion. For the second approach, ILs is utilized as raw material for membrane preparation to achieve propylene/propane separation. These studies about membrane preparation by using ILs not only investigated the separation properties of different ionic liquid composites, but also revealed the potential mechanism of their application in gas separation processes. </sec><sec> Finally, propylene/propane separation and the feasibility study of industrial applications were reviewed, such as the design and synthesis of ILs, the design and preparation of ILs membrane materials, the development of MOFs material combination, the application research of screening simulation and machine learning technology and so on. Hoping to provide useful reference for propylene/propane separation by using ILs. This work illustrates that the application of ILs shows great potential in the field of propylene/propane separation. The feature research direction of propylene/propane separation materials was proposed. In our opinion, many new ILs materials will be made great breakthrough in propylene/propane separation and industrial application in the future. </sec>