Catalysis in Ionic Liquids

Recent Developments on 1,3-Dipolar Cycloaddition Reactions by Catalysis in Green Solvents

The use of eco-compatible synthetic procedures in organic reactions and, in particular, in 1,3-dipolar cycloaddition reactions, has recently received a great deal of attention and considerable progress has been achieved in this area in the last years. This review summarizes the approaches currently employed to synthesize heterocyclic compounds by catalyzed 1,3-dipolar cycloadditions in green solvents in the last six years. Our choice to do a selection of the literature from 2014 to 2019 was made considering the absence of a recent review about this period, to our knowledge. Several examples to construct heterocycles by 1,3-dipolar cycloadditions will be discussed in this work subdivided in function of the most important class of non-conventional and green solvents, i.e., ionic liquids (ILs), deep eutectic solvents (DES), and water.

Expanding the Electrochemical Window: New Tunable Aryl Alkyl Ionic Liquids (TAAILs) with Dicyanamide Anions

A set of new tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl imidazolium motif has been synthesized, in which the following variables were systematically changed: alkyl chain length, aryl substitution (group and position), and counter ion. TAAILs with dicyanamide (DCA) and bis(trifluoromethylsulfonyl)imide (N(SO₂ CF₃ )₂ , NTf₂ ) anions showed remarkable differences of their physical properties: NTf₂ ionic liquids were found to have high decomposition temperatures and viscosities well below those of the DCA TAAILs. In contrast, the dicyanamide anion increased the electrochemical stability leading to TAAILs with an extremely wide electrochemical window of up to 7.17 V. Additionally, both classes of TAAILs extract transition metals from aqueous solutions: TAAILs with the DCA anion extract both platinum and copper while TAAILs with the NTf₂ anion are selective towards platinum. This demonstrates that minor changes of the molecular structure lead to TAAILs with drastically changed physicochemical properties.

A Brønsted Acidic Ionic Liquid as an Efficient and Selective Catalyst System for Bioderived High Molecular Weight Poly(ethylene 2,5-furandicarboxylate)

Green synthesis of bioderived high-molecular-weight poly(ethylene 2,5-furandicarboxylate) (PEF) over metal-free catalysts is a significant challenge. This study focuses on PEF prepared from ethylene glycol and 2,5-furandicarboxylic acid (FDCA) through a direct esterification method with ecofriendly metal-free ionic liquids (ILs) as catalysts. The catalytic activities of a series of imidazolium cations in the presence of various anions are systematically investigated and found to be mainly governed by the anions. Among the ILs studied, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂ MIM]BF₄ ) is identified as the best catalyst, showing excellent catalytic activity, selectivity, and stability, even at low catalyst loadings (0.1 mol % w.r.t. FDCA). Optimization of the polymerization parameters enables [C₂ MIM]BF₄ -catalyzed production of PEF with a high number-average molecular weight (M_n =5.25×10⁴  g mol^-1 ). The relationship between Brønsted acidity and catalytic activity is also investigated and the results show that the trend in catalytic activity is in good agreement with that in Brønsted acidity, as determined by the Hammett method. Additionally, on the basis of experimental results and density functional theory calculations, an electrophilic activation mechanism induced by hydrogen bonds is proposed. This strategy of adjustable acidity and anion structure in ILs provides an opportunity to develop other ILs for bio-based polyesters through green synthesis pathways.

Low-Melting Manganese (II)-Based Ionic Liquids: Syntheses, Structures, Properties and Influence of Trace Impurities

The synthesis of more than 10 new magnetic ionic liquids with [MnX₄]^2- anions, X = Cl, NCS, NCO, is presented. Detailed structural information through single-crystal X-ray diffraction is given for (DMDIm)[Mn(NCS)₄], (BnEt₃N)₂[Mn(NCS)₄], and {(Ph₃P)₂N}₂[Mn(NCO₄)]·0.6H₂O, respectively. All compounds consist of discrete anions and cations with tetrahedrally coordinated Mn (II) atoms. They show paramagnetic behavior as expected for spin-only systems. Melting points are found for several systems below 100 °C classifying them as ionic liquids. Thermal properties are investigated using differential scanning calorimetry (DSC) measurements. The physicochemical properties of density, dynamic viscosity, electrolytic conductivity, and surface tension were measured temperature-dependent of selected samples. These properties are discussed in comparison to similar Co containing systems. An increasing amount of bromide impurity is found to affect the surface tension only up to 3.3%.

Multi-component synthesis of piperidines and dihydropyrrol-2-one derivatives catalyzed by a dual-functional ionic liquid

N,N,N’, N’-tetramethyl- N,N’-bis(sulfo)ethane-1,2-diaminium mesylate ([TMBSED][OMs]2) was employed for the synthesis of piperidines and dihydropyrrol-2-ones via one-pot multi-component reactions in simple and green processes. This pseudo five-component reaction of aromatic aldehydes, anilines and alkyl acetoacetates was carried out under reflux conditions in ethanol to afford substituted piperidines. Also, dihydropyrrol-2-one derivatives were synthesized by means of four-component reactions of various amines, dialkyl acetylenedicarboxylates and formaldehyde in ethanol at room temperature. The present approaches have several advantages such as good yields, easy work-ups, short reaction times, and utilize mild and clean reaction conditions.

Diffusion of Radical Ions in Ionic Liquids Having Long Alkyl Chains

Magnetic field effects on a radical ion pair have been studied to investigate the diffusion of the radical ions generated by a photoinduced electron transfer reaction in ionic liquids having short and long alkyl chains. The yield of an escaped radical ion was evaluated by using a nanosecond laser flash photolysis under various magnetic fields. The magnitude of the magnetic field effect on the yield of the escaped radical was linearly increased with increasing solvent viscosity. Such solvent viscosity dependence of the magnetic field effect can be explained with the solvent viscosity dependence of the escape rate of the radical ions from the pair. In the time window (>20 ns) of our measurements, the effect of long alkyl chain aggregation on the dynamics of the radical ions was not clearly observed.

Poly(ionic liquid)-Modified Magnetic Janus Particles for Dye Degradation

The Fe₃O₄@SiO₂ paramagnetic Janus particles with phenyl groups and amino groups segmented on two different sides were fabricated by the Pickering emulsion method. Then, the poly(ionic liquid)s were selectively modified onto the amino side via in situ induced ATRP polymerization. Different anions were introduced onto the poly(ionic liquid)s region by exchanging anions to adjust the wettability of the side. Meanwhile, after the PW₁₂O₄₀^3- anions were employed, the poly(ionic liquid)-modified Fe₃O₄@SiO₂ Janus particles can be used as a catalytic solid emulsifier and degraded water-soluble dyes with the aid of stabilizing emulsion.

Effect of Ionic Composition on Physicochemical Properties of Mono-Ether Functional Ionic Liquids

Tunable properties prompt the development of different "tailor-made" functional ionic liquids (FILs) for specific tasks. FILs with an ether group are good solvents for many organic compounds and enzymatic reactions. However, ionic composition influences the solubility by affecting the physiochemical properties of these FILs. To address the structure effect, a series of novel FILs with a mono-ether group (ME) based on imidazole were prepared through cationic functionalization and anionic exchange reactions, and characterized by NMR, mass spectroscopy, and Thermogravimetric analysis (TGA). The effect of ionic composition (cationic structure and anions) on density, viscosity, ionic conductivity, electrochemical window, and thermal properties of these ME-FILs were systematically investigated. In general, the viscosity and heat capacity increases with the bigger cationic volume of ME-FILs; in particular, the 2-alkyl substitution of imidazolium enhances the viscosity remarkably, whereas the density and conductivity decrease on the condition of the same [NTf₂]^- anion; For these ME-FILs with the same cations, the density follows the order of [NTf₂]^- > [PF₆]^- > [BF₄]^-. The viscosity follows the order of [PF₆]^- > [BF₄]^- > [NTf₂]^-. Ion conductivity follows the order of [NTf₂]^- ≈ [BF₄]^- > [PF₆]^-. It is noted that the dynamic density has a good linear relationship with the temperature, and the slopes are the same for all ME-FILs. Furthermore, these ME-FILs have broad electrochemical windows and glass transition temperatures in addition to a cold crystallization and a melt temperature for ME-FIL7. Therefore, the cationic structure and counter anion affect the physicochemical properties of these ME-FILs together.

Protic Imidazolium Polymer as Ion Conductor for Improved Oxygen Evolution Performance

Improving the electrocatalytic performance of oxygen evolution reaction (OER) is essential for oxygen-involved electrochemical devices, including water splitting and rechargeable metal–air batteries. In this work, we report that the OER performance of commercial catalysts of IrO₂, Co₃O₄, and Pt-C can be improved by replacing the traditional Nafion^® ionomer with newly synthesized copolymers consisting of protonated imidazolium moieties such as ion conductors and binders in electrodes. Specifically, such an improvement in OER performance for all the tested catalysts is more significant in basic and neutral environments than that under acidic conditions. We anticipate that the results will provide new ideas for the conceptual design of electrodes for oxygen-involved electrochemical devices.

A Multiphase Protocol for Selective Hydrogenation and Reductive Amination of Levulinic Acid with Integrated Catalyst Recovery

At 60-150 °C and 15-35 bar H₂ , two model reactions of levulinic acid (LA), hydrogenation and reductive amination with cyclohexylamine, were explored in a multiphase system composed of an aqueous solution of reactants, a hydrocarbon, and commercial 5 % Ru/C as a heterogeneous catalyst. By tuning the relative volume of the immiscible water/hydrocarbon phases and the concentration of the aqueous solution, a quantitative conversion of LA was achieved with formation of γ-valerolactone or N-(cyclohexylmethyl)pyrrolidone in >95 and 88 % selectivity, respectively. Additionally, the catalyst could be segregated in the hydrocarbon phase and recycled in an effective semi-continuous protocol. Under such conditions, formic acid additive affected the reactivity of LA through a competitive adsorption on the catalyst surface. This effect was crucial to improve selectivity for the reductive amination process. The comparison of 5 % Ru/C with a series of carbon supports demonstrated that the segregation phenomenon in the hydrocarbon phase, never previously reported, was pH-dependent and effective for samples displaying a moderate surface acidity.

How green are ionic liquids? - A multicriteria decision analysis approach

Due to various desirable physicochemical properties, ionic liquids (ILs) are still gaining in popularity. ILs have been recurrently considered green solvents. However, environmental, health and safety assessments of ILs have raised certain doubts about their benignness, and their greenness status is currently unclear. To clarify the situation on their greenness, we perform a comprehensive assessment of more than 300 commercially available ILs. We apply multicriteria decision analysis, the tool that allows ranking many alternatives according to relevant criteria. They are toxicity towards various organisms, biodegradability, hazard statements and precautionary measures during their handling. We incorporated organic solvents to rankings, as their greenness is better described, so they serve as greenness reference points. The ranking results obtained considering the whole set of criteria show that ILs are placed between recommended polar solvents and problematic/undesirable non polar organic solvents in terms of greenness. However, the exclusion of toxicity data due to unavailability of endpoints results in assessment of ILs as greener than most of organic solvents.

Choline Chloride-Based Deep Eutectic Systems in Sequential Friedländer Reaction and Palladium-Catalyzed sp3 CH Functionalization of Methyl Ketones

A volatile organic solvent-free and choline chloride (ChCl)-based deep eutectic system (DES)-mediated sp³-CH functionalization of acetophenones 1 with benzyl alcohols 2 to the corresponding α, β-saturated ketones 3 is accounted for. The domino dehydrogenation-aldol condensation (hydrogenation borrowing concept) has been successfully attempted with palladium-tetrakis(triphenylphosphine) [Pd(PPh₃)₄] catalyst-xantphos ligand combination. Furthermore, a sequential Friedländer reaction of 2-aminobenzophenone 4 and palladium-catalyzed α-alkylation of the quinolinyl methyl ketone with benzyl alcohols 2 in ChCl-based DES have been successfully investigated. The C-C bond formation through sp³-CH functionalization involves a wide scope of the substrates, high atom efficiency, chemoselectivity, and environmentally friendly strategy.

Maize-like ionic liquid@polyaniline nanocomposites for high performance supercapacitor

In this study, ionic liquids (IL) containing carboxyl and different alkyl chains were fabricated and used to dope polyaniline (PANI). The results revealed that IL@PANI composites could be facilely obtained via template-free polymerization of aniline using ammonium persulfate as the oxidant. The as-prepared IL@PANI composites were measured by FT-IR, XPS, and SEM. Electrochemical performances of IL@PANI nanocomposites were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results indicate that the alkyl chains of ILs have an important influence on the morphology and capacitance performance of IL@PANI electrode materials. With the shorter alkyl group in ILs, IL@PANI materials presented higher specific capacitance. Especially, 1-vinyl-3-carboxymethyl-imidazolium chloride ([VCMIm]Cl)@PANI composite presented the highest specific capacitance. Cycling performance measurement demonstrated that 82% capacitance retention could be achieved after 1000 cycles in 0.5 M H2SO4 aqueous solution. Therefore, our strategy provides a new technique for PANI nanocomposites with tunable morphology and high performance.

Experimental Data of Fluid Phase Equilibria- Correlation and Prediction Models: A Review

The examples of phase equilibria in binary systems, solid/liquid (SLE), liquid/liquid (LLE), vapor/liquid (VLE), as well as liquid/liquid equilibria in ternary systems mainly containing ionic liquids (ILs), or the infragrance materials, or pharmaceuticals with molecular organic solvents, such as an alcohol, or water, or hydrocarbons, are presented. The most popular correlation methods of the experimental phase equilibrium data are presented, related to the excess Gibbs free energy models such as Wilson, universal-quasichemical, UNIQUAC and non-random two-liquid model, NRTL as well as several popular theories for the modeling of the phase equilibria and excess molar enthalpy, HE in binary or ternary mixtures are presented: the group contribution method (Mod. UNIFAC) and modified UNIFAC model for pharmaceuticals and lattice theory based on non-random hydrogen bonding (NRHB). The SLE, LLE, or VLE and HE of these systems may be described by the Perturbed-Chain Polar Statistical Associating Fluid Theory (PC-SAFT), or a Conductor-like Screening Model for Real Solvents (COSMO-RS). The examples of the application of ILs as extractants for the separation of aromatic hydrocarbons from alkanes, sulfur compounds from alkanes, alkenes from alkanes, ethylbenzene from styrene, butan-1-ol from water phase, or 2-phenylethanol (PEA) from water are discussed on the basis of previously published data. The first information about the selectivity of extrahent for separation can be obtained from the measurements of the limiting activity coefficient measurements by the gas–liquid chromatography technique. This review outlines the main research work carried out over the last few years on direct measurements of phase equilibria, or HE and limiting activity coefficients, the possibility of thermodynamic modeling with emphasis on recent research achievements and potential for future research.

Green chemical engineering in China

In China, the rapid development greatly promotes the national economic power and living standard but also inevitably brings a series of environmental problems. In order to resolve these problems fundamentally, Chinese scientists have been undertaking research in the area of green chemical engineering (GCE) for many years and achieved great progresses. In this paper, we reviewed the research progresses related to GCE in China and screened four typical topics related to the Chinese resources characteristics and environmental requirements, i.e. ionic liquids and their applications, biomass utilization and bio-based materials/products, green solvent-mediated extraction technologies, and cold plasmas for coal conversion. Afterwards, the perspectives and development tendencies of GCE were proposed, and the challenges which will be faced while developing available industrial technologies in China were mentioned.

Using an interpolation-based method (IDVequ) to predict the combined toxicities of hormetic ionic liquids

In the field of computational toxicology, predicting toxicological interaction or hormesis effect of a mixture from individuals is still a challenge. The two most frequently used model concentration addition (CA) and independent action (IA) also cannot solve these challenges perfectly. In this paper, we used IDV_equ (an interpolation method based on the Delaunay triangulation and Voronoi tessellation as well as the training set of direct equipartition ray design (EquRay) mixtures) to predict the toxicities of binary mixtures composed of hormetic ionic liquids (ILs). One of the purposes is to verify the predictive ability of IDV_equ. The other one is to improve the risk assessment of ILs mixtures especial hormetic ILs, because the toxicity reports of ILs mixtures are rarely reported in particular the toxicity of the hormetic ILs mixtures. Hence, we determined time-dependent toxicities of four ILs and their binary mixtures (designed by EquRay) to Vibrio qinghaiensis sp.-Q67 at first. Then, mixture toxicities were predicted and compared using the IDV_equ and CA. The results show that, the accuracy of IDV_equ is higher than the accuracy of CA. And, more important, to some mixtures out of the CA application, IDV_equ also can predict the mixture effects accurately. It showed that IDV_equ can be applied to predict the toxicity of any binary mixture regardless of the type of concentration-response curve of the components. These toxicity data provided useful information for researching the prediction of hormesis or toxicological interaction of the mixture and toxicities of ILs mixtures.

Scalable Screening of Soft Matter: A Case Study of Mixtures of Ionic Liquids and Organic Solvents

Room-temperature ionic liquids (RTILs) are a class of organic salts that are liquid at room temperature. Their physiochemical properties, including low vapor pressure and wide electrochemical stability window, have driven their use as electrolytes in many electrochemical applications; however, the slow transport properties of many RTILs have limited their utility in some applications. This issue is often mitigated by solvating ionic liquids in neutral organic solvents. To date, however, solvent interactions have only been explored for a small number of solvents, particularly acetonitrile and propylene carbonate, at only a few compositions. In this work, we use molecular dynamics simulations in the context of a computational screening approach to study mixtures of ionic liquids in many different solvents at a range of concentrations. Building on prior work, we again find that ionic liquid diffusivity increases monotonically with greater solvent concentration. In contrast to prior work, we find that pure solvent diffusivity, not polarity, is the most influential solvent property on mixture behavior. We also explore the concentration dependence of ionic conductivity and find maxima at intermediate concentrations. Experimental conductivity measurements, inspired by the computational screening study, support this observation with qualitatively consistent results. These results can further guide the selection of solvents for electrochemical applications of RTILs.

Oxidation of a Levitated Droplet of 1-Allyl-3-methylimidazolium Dicyanamide by Nitrogen Dioxide

Understanding the reaction mechanisms of ionic liquids and their oxidizers is necessary to develop the next generation of hypergolic, ionic-liquid-based fuels. We studied reactions between a levitated droplet of 1-allyl-3-methylimidazolium dicyanamide ([AMIM][DCA]), with and without hydrogen-capped boron nanoparticles, and nitrogen dioxide (NO₂). The reactions were monitored with Fourier-transform infrared (FTIR) and Raman spectroscopy. The emergence of new structures in the FTIR and Raman spectra is consistent with the formation of functional groups including organic nitrites (RONO), nitroamines (R¹R²NNO₂), and carbonitrates (R¹R²C=NO₂^-). Possible reaction mechanisms based on these new functional groups are discussed. The reaction rates were deduced at various temperatures by heating the levitated droplets with a carbon dioxide laser. We thereby determined an overall activation energy of 38.5 ± 2.3 kJ mol^-1 for the oxidation of [AMIM][DCA] for the first time.

Absorption and thermodynamic properties of CO2 by amido-containing anion-functionalized ionic liquids

In this contribution, two kinds of amido-containing anion-functionalized ionic liquids (ILs) were designed and synthesized, where the anions of these ILs were selected from deprotonated succinimide (H-Suc) and o-phthalimide (Ph-Suc). Then, these functionalized ILs were used to capture CO2. Towards to this end, solubility of CO2 in the ILs was determined at different temperatures and different CO2 partial pressures. Based on these data, chemical equilibrium constants of CO2 with the ILs were derived at different temperatures from the "deactivated IL" model. The other thermodynamic properties such as reaction Gibbs energy, reaction enthalpy, and reaction entropy in the absorption were also calculated from the corresponding equilibrium constant data at different temperatures. It was shown that these anion-functionalized ILs exhibited high CO2 solubility (up to 0.95 mol CO2 mol-1 IL) and low energy desorption, and enthalpy change was the main driving force for CO2 capture by using such ILs as absorbents. In addition, the interactions of CO2 with the ILs were also investigated by 1H NMR, 13C NMR, and FT-IR spectroscopy.

Environmentally benign nucleophilic substitution reaction of arylalkyl halides in water using CTAB as the inverse phase transfer catalyst

An environmentally benign, scalable and highly selective C-arylalkylation of active methylene compounds is developed using CTAB as the inverse phase transfer catalyst. The methodology is also applicable to the regioselective synthesis of N-aralkyl/alkyl 2-pyridones.