Reactions In Ionic Liquids Research Articles

Monte Carlo QM/MM simulation studies of the Cannizzaro reaction in ionic liquids for improved biofuel production.

The conversion of biomass to 5-hydroxymethylfurfural (HMF) holds substantial promise as a renewable energy source. Notably, HMF can be transformed into 2,5-bis(hydroxymethyl)furan (BHMF), a crucial reactant in biofuel production, but requires harsh operating conditions, H2, and precious metal catalysts. A recently reported Cannizzaro reaction of HMF to BHMF, characterized by its efficiency, mild conditions, and eco-friendliness, instead employed ionic liquids (ILs) to achieve high yields. In this study, combined quantum mechanical and molecular mechanical (QM/MM) simulations in conjunction with Metropolis Monte Carlo statistical mechanics and free-energy perturbation theory utilized M06-2X/6-31+G(d), PDDG/PM3, and the OPLS-VSIL force field to uncover important solute-solvent interactions present in the HMF to BHMF reaction pathway. The Cannizzaro reaction was examined in water and in five ILs composed of the 1-butyl-3-methylimidazolium [BMIM] cation coupled to hexafluorophosphate, tetrafluoroborate, thiocyanate, chloride, and bromide. Energetic and structural analysis of the rate-determining hydride transfer between HMF and the hydride-donor anion HMFOH- attributed the enhanced reactivity to highly organized solvent interactions featuring (1) hydrogen bonding between the ring protons of [BMIM] and the negatively charged carbonyl oxygen atoms on the transition structure, (2) favorable electrostatic interactions between the IL anions and solute hydroxyl groups, and (3) beneficial π-π stacking interactions between [BMIM] and the two aromatic rings present in HMF and HMFOH-.

Ultra-short running-in period and robust lubricity constructed by dynamic disulfide and hydrogen bonds from ionic liquid polyethylene glycol lubrication

Polyethylene glycol (PEG) system behave the characteristics of non-toxic, non-irritating and good compatibility with various substances, so the improvement and stability of lubrication property and comprehensive performance is vital for PEG system under harsh working conditions. Here, highly reactive ionic liquids (ILs) are designed and introduced with a specifically designed molecular structure, the ultra-short running-in period and robust lubricity can be obtained by dynamic disulfide and hydrogen bonds from the constructed IL-PEG200 lubrication system. Combined with analytical techniques (XPS, FIB-TEM, Nanoindentation, Raman, TOF-SIMS), their interaction was explored to further clarify the interfacial self-assembly behavior. The superior bearing capacity is mainly ascribed to the synergistic effect of carbon-like film, dynamic disulfide bond, hydrogen bonding and interfacial tribochemical reaction.

On the"Staple" Effect in the d-Glucose Acetylation by Choline-Chloride Ethylene Glycol and Choline-Chloride Urea Deep Eutectic Solvents.

This work employs hybrid quantum mechanics molecular mechanics simulations coupled with an umbrella sampling technique to investigate the acetylation of d-glucose with acetic anhydride in two deep eutectic solvents (DESs): choline-chloride ethylene glycol (ChCl/Etg) and choline-chloride urea (ChCl/U). The reaction proceeds spontaneously, with activation free energy barriers of 18.19 ± 0.15 and 19.83 ± 0.15 kcal/mol for ChCl/Etg and ChCl/U, respectively. These values align with literature data for similar reactions in ionic liquids, highlighting the potential of DESs as green reaction media for wood modifications, while minimizing lignocellulosic matrix degradation. Energy pair distribution analysis, radial distribution functions, and noncovalent interactions reveal a more solvated transition state compared to the initial reactant state within ChCl/Etg, facilitating the acetylation reaction. Interestingly, combined distribution function analysis unveils a "staple" effect in both solvents, potentially hindering efficient product separation. The work further explores hydrogen bond networks and Kamlet-Taft solvatochromic parameters to elucidate the role of solvents in the reaction mechanism. It was observed that a notable decrease in activation energy is accompanied by increasing net basicity, along with a reduction in the "staple" effect. This suggests that solvent parameters could serve as an effective screening tool for identifying novel and efficient DESs for wood modifications.

Synthesis of chiral phosphine-functionalized ionic liquids and their application in asymmetric hydrogenation

Abstract The present report prepared three novel chiral phosphine-functionalized polyetherimidazolium ionic liquids through ion-exchange reactions of chiral sulfonated BINAP ligands and hydroxyl-functionalized polyetherimidazolium ionic liquids grounded on the phosphine ligand-ionic liquid integration. Using these synthetics, methyl acetoacetate was subjected to asymmetric homogeneous hydrogenation catalyzed by ruthenium. The structural characterization of the three chiral phosphine-functionalized polyetherimidazolium ionic liquids was conducted using 1H NMR, 13C NMR, and 31P NMR in combination with HR-MS. Compared with their precursor sulfonated BINAP, the prepared chiral phosphine-functionalized ionic liquids exhibited comparable or better catalytic activity and enantioselectivity.

Thermal properties and bromine addition reaction of ionic liquids containing vinyl-substituted bis-sulfonylamide anion

Ionic liquids (ILs) comprising alkylammonium cations and a bis(sulfonyl)amide anion with a vinyl substituent (SO2CF3-N–-SO2CH = CH2) were synthesized. Their thermal properties and water miscibility were investigated and compared with those of the corresponding Tf2N (= (SO2CF3)2N–) salts. Exposure of these ILs to bromine vapor produced bromine adducts, tribromide salts, and a small amount of a cyclic adduct derived from the anion. The reaction products and the potassium salt of the anion were characterized crystallographically.

Interfacial structures and dissociation reactions of protic ionic liquids on Li metal surface: A combined first-principles and ab initio molecular dynamics investigation

Interfacial structures and dissociation reactions of protic ionic liquids (PILs) comprising five protic cations with two common sulfonylimide anions on the Li(001) surface were investigated using first-principles calculations and ab initio molecular dynamics simulations. Both the anions rapidly decompose, yielding LiF, Li2O and Li2S species as well as large fragments, e.g. NSO2CF3 and NSO2. Particularly, the proton attached to the N atom generally segregates from the cations and generates LiOH with the O atom from the anions and the surface Li atom. In addition, detailed comparisons of reaction mechanisms between PIL-based and AIL-based systems were also made.

Biocatalytic hydrolysis of di-urethane model compounds in ionic liquid reaction media

The suitability of different enzymes to carry out the hydrolysis of two-different toluene-based urethane model compounds (i.e. bis(2-methoxyethyl) (4-methyl-1,3-phenylene)dicarbamate, and bis(2-methoxyethyl) (2-methyl-1,3-phenylene)dicarbamate) has been demonstrated for the first time by taking advantage of ionic liquid (IL) technologies. Toluene-based urethane compounds were prepared from usual substrates in polyurethane industrial synthesis. Afterwards, their carbamate groups were target of a biocatalytic hydrolysis by means of different commercial hydrolases (i.e. lipase, urease and proteases) in either water, hydrophilic organic solvents (i.e. ethylene glycol or 1,2-dimethyl-1,3-dioxolane-4-methanol, (solketal)), or hydrophobic ILs (e.g. [C4mim][NTf2], etc.) as reaction media. Because of the insolubility of these compounds in water, most of the enzymes were unable to catalyse the hydrolysis of the di-urethane substrates in pure water, being clearly improved (up to 31.6 mU/mg for the urease case) in solketal:water (90:10, v/v) reaction media. When hydrophobic ILs were added into this reaction medium, the urease activity increased by more than twice (74.1 mU/mg). The most promising results for the hydrolysis of these urethane compounds were obtained by combining lipase and urease biocatalysts in a IL:solketal:H2O (70:25:5, v/v/v) reaction medium. These results demonstrate a possible biocatalytic approach for the hydrolytic depolymerization of polyurethane foam wastes.

Ionic liquid-mediated removal of naphthenic acids from crude oil: Process modelling and optimization

The present study demonstrated the efficiency of ionic liquid in the removal of naphthenic acids from crude oil. The crude oil sample was obtained from Belema oil field in Southern Nigeria while tetramethyl ammonium hydroxide pentahydrate (TMAH) ionic liquid was commercially obtained. Liquid-liquid extraction was carried out and the reaction conditions were modelled and optimized using Box-Behnken design of the response surface methodology. Ionic liquid concentration (w/v%), reaction temperature (°C), and reaction time (mins) were selected as the factors while extraction efficiency (%) was selected as the response. The results of the study showed that the highest extraction efficiency of 96.67 % was achieved under reaction conditions of 3 w/v% ionic liquid concentration, 50 °C reaction temperature, and 45 mins reaction time. Owing to R2, adjusted R2, and predicted R2 values generally > 0.90, the model accurately described the deacidification reaction. Optimization results indicated that removal efficiency can reach over 96 % at 2.82 w/v% ionic liquid concentration, 48 °C reaction temperature, and 45 mins reaction time. The characterization of the original and deacidified oils using GC–MS showed reduced concentration of acidic species in the latter. Also, FT-IR of the ionic liquid showed minimal or no variations in functional groups before and after extraction, highlighting a possibility for regeneration of the ionic liquid. The findings of the study showed the use of ionic liquids as green alternatives in the removal of acidic species from crude oil.

Solvent effects on Diels–Alder reaction in ionic liquids: A reaction density functional study

Extensive experimental studies have been performed on the Diels–Alder (DA) reactions in ionic liquids (ILs), which demonstrate that the IL environment can significantly influence the reaction rates and selectivity. However, the underlying microscopic mechanism remains ambiguous. In this work, the multiscale reaction density functional theory is applied to explore the effect of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) solvent on the reaction of cyclopentadiene (CP) with acrolein, methyl acrylate, or acrylonitrile. By analyzing the free energy landscape during the reaction, it is found that the polarization effect has a relatively small influence, while the solvation effect makes both the activation free energy and reaction free energy decrease. In addition, the rearrangement of local solvent structure shows that the cation spatial distribution responds more evidently to the reaction than the anion, and this indicates that the cation plays a dominant role in the solvation effect and so as to affect the reaction rates and selectivity of the DA reactions.

Impact of ionic liquid's cation alkyl chain length and reaction time on cellulose nanocrystals preparation

Traditional methods to obtain cellulose nanocrystals typically involve mechanical and chemical processes and develop an improved process in terms of efficiency, sustainability, and the quality of CNCs produced are interesting. In this sense, we aimed to prepare cellulose nanocrystals (CNCs) from the hydrolysis of microcrystalline cellulose using protic ionic liquids (PILs), named 3-diethylamino-propylammonium hexanoate ([DEAPA][Hex]), 3-dimethylamino- 1-propylammonium hexanoate ([DMAPA][Hex]), and propylammonium hexanoate ([PA][Hex]) at different reaction times. The PILs demonstrated efficiency in producing cellulose nanocrystals, regardless of the cation size and reaction times. However, as expected the properties of the CNCs varied depending on the studied condition. The highest yield was observed in DMAPA[Hex], with a 34 % conversion. Crystalline indices decreased independent of the cation sizes and reaction times. Thermal stabilities were shifted to higher temperatures up to 92 ºC probably due to PILs cation sizes. In contrast, increasing reaction times decreased nanocrystals’ thermal stabilities up to 51ºC. So, protic ionic liquids (PILs) can be considered more environmentally friendly or sustainable solvents compared to traditional organic solvents for preparing cellulose nanocrystals. In the present work, it is reported an alternative method for obtaining CNCs and additionally provide the best preparation conditions for achieving important properties of this nanomaterial, with the potential for various applications.

CO2-Triggered Hierarchical-Pore UiO-66-Based Pickering Emulsions for Efficient and Recyclable Suzuki-Miyaura Cross-Coupling in Biphasic Systems.

Hierarchical-pore metal-organic frameworks (H-MOFs) are considered to be emerging stabilizers for Pickering emulsion formation because of their hierarchically arranged pores, tailorable structures, and ultrahigh surface areas. However, stimulus-triggered Pickering emulsions built by H-MOFs have been seldom presented to date despite their great significance in diverse applications. Herein, by grafting Pd(OAc)2 on the hierarchical-pore zirconium MOF UiO-66, namely, H-UiO-66, with the aid of 1-alkyl-3-methylimidazolium 2-cyanopyrrolide salts ([CnMIM][2-CN-Pyr], n = 4, 6, and 8), a series of Pd(OAc)2-[CnMIM][2-CN-Pyr]@H-UiO-66 have been developed and utilized as emulsifiers for constructing CO2-switching Pickering emulsions. It was found that Pd(OAc)2-[CnMIM][2-CN-Pyr]@H-UiO-66 was able to stabilize the n-hexane-water mixture to form a Pickering emulsion even at an amount of 0.5 wt %. Upon alternate addition of CO2 and N2 at normal pressure, Pickering emulsions could be smartly converted between demulsification and re-emulsification. Through combining varieties of spectroscopic techniques, the mechanism of the switchable phase transformation lay in the acid-base reaction of ionic liquids with CO2 on H-UiO-66 and the creation of more hydrophilic salts, which reduced the wettability of the emulsifier and destabilized the emulsion. As an example of application, the stimulus-triggered Pickering emulsion was employed as a palladium-catalyzed Suzuki-Miyaura cross-coupling microreactor to achieve the combination of chemical reactions, isolation of products, and recovery of catalysts.

Preparation of a High-Performance Asymmetric Supercapacitor by Recycling Aluminum Paper and Filter Components of Heated Tobacco.

In this study, Al paper and cellulose acetate (CA) filters derived from heated tobacco waste were successfully converted into current collectors and active materials for a supercapacitor device. Typically, heated tobacco contains electrically discontinuous Al paper. First, Al was extracted from the tobacco waste using HCl to produce Lewis acid (AlCl3). This acid was then used in an Al electrodeposition process utilizing the chloroaluminate ionic liquid reaction between the acid and the base (RCl) at room temperature. To enhance the conductivity, a supplementary coating of Al metal was applied to the Al paper through electrodeposition, thus re-establishing the electrical continuity of the discontinuous parts and forming an Al-coated current collector. Moreover, the CA filters were carbonized under a nitrogen atmosphere, yielding carbon precursors (C-CA) for the supercapacitor electrodes. To further enhance the electrochemical performance, nickel oxide (NiO) was incorporated into C-CA, resulting in C-CA@NiO with pseudocapacitance. The specific surface area of CA increased with carbonization and the subsequent incorporation of NiO. The as-synthesized C-CA and C-CA@NiO materials were applied to an Al-coated current collector to obtain C-CA- and C-CA@NiO-based electrodes, exhibiting stable electrochemical behavior in the voltage range of -1.0 to 0 V and 0 to 1.0 V, respectively. An asymmetric supercapacitor (ASC) device was assembled with C-CA@NiO and C-CA as the positive and negative electrodes, respectively. This ASC device demonstrated a high specific capacitance of 40.8 F g-1, while widening the operating voltage window to 2.0 V. The high electrochemical performance of the device is attributed to the successful Al electrodeposition, which facilitates the electrical conductivity and increased porosity of the C-CA@NiO and C-CA materials. To the best of our knowledge, this is a pioneering study in regards to the conversion of biomass waste into current collectors and active materials to fabricate a practical ASC device. Our findings highlight the potential of reusing Al paper and CA filters from heated tobacco waste as essential components of energy storage devices.

The Role of Imidazolium 2-Cyanopyrrolide Ionic Liquid in Reduction of CO2 to CO, Formate, and Ethylene on Copper Electrode Revealed By SERS

Electrochemical conversion of CO2 over copper catalyst is known to produce higher value products such as methane, ethylene, formate and alcohols in aqueous electrolytes. Since CO2 is a stable molecule, the electrochemical reduction reaction requires significant overpotential (-1.9 V vs SHE) for the first electron transfer to form CO2 -. Ionic liquids (ILs) have high CO2 solubility and can be further functionalized to bind with CO2 such that CO2 can be brought to the electrode surface in a more reactive state. In this study, we studied electroreduction of CO2 over copper in non-aqueous electrolyte with the reactive IL 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]) in the concentration range of 0.1 to 1 M. The linear sweep voltammetry experiments show the absence of a noticeable Faradic current within the potential window of -1.8 to -2.2 V vs Ag/Ag+ under N2 demonstrating the stability of the imidazolium cation against electrochemical conversion, which is also confirmed by NMR analysis. In the presence of CO2, the onset potential of reduction is at -1.9 V vs Ag/Ag+ (-1.4 V vs. SHE) and does not change with IL concentration. By employing surface enhanced Raman spectroscopy (SERS), potential dependent changes in the interfacial microenvironment during CO2 reduction was revealed. Specifically, imidazolium enrichment and surface adsorbed CO formation were captured. These results confirmed the catalytic role of the IL by facilitating the transport of the reactive CO2 to the electrode surface via imidazolium in particular. On the other hand, surface coverage by imidazolium cations on the electrode seems to prohibit higher level of C-C couplings, thus limiting reaction products to C1 and C2 products. During 3 hrs of bulk electrolysis at -2.1 V (vs. Ag/Ag+) in an H-cell with non-aqueous negolyte containing the IL and an aqueous posolyte (proton source), gaseous products of CO and H2, liquid product of HCOO- and dissolved C2H4were determined by GC and NMR analysis, respectively. Oxidation of Cu electrode was separately captured by ex-situ XPS measurements after 3 hrs of bulk electrolysis. Even though high CO2 concentrations are achieved in ILs and they are stable at CO2 reduction conditions even after 3 hours on Cu surface, IL structure should be optimized to allow C-C coupling to obtain C2+ products.

Ionic liquid catalyzed thiol-Michael addition reaction in fluorescent probe

Rapid response is a significant goal in fluorescence analysis technology. However, the response rate is uncontrollable due to the response rate is primarily determined and limited by the response mechanism and the type of detection target. To accomplish this goal, catalysis was first incorporated into fluorescence analysis in this work. PNL-Br, a novel imidazole liquid functionalized polysiloxane, was synthesized and used as a reusable catalyst for the thiol-Michael addition reaction. PNL-Br had a higher potential for thiol-Michael addition catalysis. Notably, PNL-Br could be used as an efficient catalyst for dithiothreitol (DTT) detection by fluorescence analysis, which was the first example of a catalysis system for fluorescent probe detection reactions. This new methodology presented a generic route to enhancing the response reaction rate of fluorescent probes and brought new perspectives for fluorescent probes field.

Reusable Pd-polymetallic catalysts based on magnetic ferrites for Suzuki reaction in ionic liquid

Based on magnetic ferrites of iron (magnetite), cobalt and nickel modified with 3-aminopropyltriethoxysilane (APTES) hybrid materials Pd-Fe-Co-Ni/MFe2O4@Si-NH2@Pd (M = Fe, Co, Ni) with a protective palladium coating were synthesized. Due to the synergistic effect, new Pd-polymetallic composites exhibit high catalytic activity in the Suzuki reaction in an aqueous solution of an ionic liquid. The developed catalysts are easily removed from the reaction mixture by magnetic decantation and can be reused several times without loss of catalytic activity.

Magnetically Reusable Polymetallic Pd-Catalyst for Sonogashira Reaction in Ionic Liquid

Based on magnetite modified with 3-aminopropyltriethoxysilane (APTES) hybrid materials Pd-Fe-Co-Ni/Fe3O4@Si-NH2 and Pd-Fe-Co-Ni/Fe3O4@Si-NH2@Pd were synthesized. Due to the synergistic effect, new magnetic polymetallic composites exhibit high catalytic activity in the Sonogashira reaction in an ionic liquid medium, which makes it possible to perform catalysis efficiently in the presence of 0.5 mol% of palladium. The new catalysts are easily removed from the reaction mixture using an external magnet and can be used up to 5-6 times without any visible loss of activity.

Magnetically Reusable Polymetallic Pd-Catalyst for Sonogashira Reaction in Ionic Liquid

Magnetically Reusable Polymetallic Pd-Catalyst for Sonogashira Reaction in Ionic Liquid

Ru Nanoparticle Intercalated Montmorillonite Clay Catalytic System for the Reduction of Aliphatic/Aromatic Nitro Compounds

Abstract: The Ru exchanged MMT clay was synthesized with different Ru metal stacking using the wet impregnation method. All the developed materials were analyzed with advanced analytical techniques. All the data were found in good agreement with each other. Furthermore, all the catalysts were tested for the reduction of aromatic and aliphatic nitro compounds to the corresponding amines in conventional and ionic liquid reaction mediums. The amines were easily isolated with simple ether washing in ionic liquid medium, and the catalyst was recycled up to 8 times. Various amines were also synthesized using the proposed methodology, having direct importance as building blocks of several biologically active compounds.

Solvent Role of Ionic Liquids in Fundamental Chemical Reaction Dynamics Analyzed by Time-Resolved Spectroscopy.

Ionic liquids (ILs), which are used as solvents for chemical reactions, are different from conventional organic solvents owing to their designability. Physicochemical parameters of the ILs, such as polarity and viscosity, that affect chemical equilibria and reaction kinetics can be tuned by changing the combination of anions and cations or by varying the lengths of the alkyl chains present in the cations. We were interested in knowing how these physicochemical parameters affect fundamental chemical reactions in ILs. Therefore, in this personal account, we investigate our recent work on two different photochemical reactions in ILs, namely excited-state intramolecular proton transfer of hydroxyflavone and photodissociation of aminodisulfide, using time-resolved spectroscopic techniques. Interestingly, the roles of the ILs in these chemical reactions are quite different. The effect of the cationic species of the ILs (i. e., the head groups and number of alkyl carbons) on the solvation environment upon photoexcitation and reaction rate are discussed.

Process hazard assessment of energetic ionic liquid with kinetic evaluation and thermal equilibrium

With the continuous development of battery technology, there are new research investments in materials of various parts. In the field of electrolytes, ionic liquids (IL) are considered to be excellent electrolytes and have been widely studied in distinct energy fields. However, it is necessary to pay attention to the safety characteristics of ionic liquids at high temperature due to the application of energy, but there is little research on the reaction and kinetics of ionic liquids. To ensure the safety of ionic liquids, such as high temperature, the common ionic liquid 1-Ethyl-3-methylimidazolium nitrate ([Emim] NO3) was selected for analysis. The exothermic mode is obtained from the data of differential scanning calorimetry. The basic reaction parameters of [Emim] NO3 were determined with thermodynamic equation simulation. For ionic liquids in the actual situation, consider adding a heat balance model to estimate its temperature change pattern and find out the hazard temperature and related safety parameters. Temperature changes were estimated by constructing 25.0 g and 50.0 g packages to simulate material reactions and heat transfer in the external environment. The results showed that [Emim] NO3 had shorter TMRad and TCL (<1 day) when the temperature was above 180 °C.