Rheological Behavior of Polyarylsulfone 1‐Butyl‐3‐Methylimidazolium Chloride Solutions

Polyarylsufone polymers are engineering thermoplastics that can only be dissolved in polar solvents. We found that polyarylsufone has good solubility in ionic liquid (IL) with IL being a new kind of green solvent; thus, ILs are potential substitutes for conventional molecular solvents. However, the thermodynamics in ionic liquids are different then those in conventional solvents, so ILs as solvents have attracted enormous attention recently. Rheological behavior is an important factor in polymer material processing. The rheological behavior of polyarylsulfone (PASF) in both N, N,‐dimethylacetamide (DMAc) and ionic liquid 1‐butyl‐3‐methylimidazolium chloride [(Bmim) Cl] were studied in this paper as a function of concentration for concentrated solutions. It is interesting that the rheological behavior of the PASF/(Bmim) Cl solution is very different from that of PASF/DMAc solutions. In DMAc, as concentration increases viscosity increases, while the rheological behavior of the PASF/(Bmim) Cl solution exhibits a maximum in the viscosity‐concentration plots.     

Solvent effects on chemical processes: new solvents designed on the basis of the molecular–microscopic properties of (molecular solvent + 1,3‐dialkylimidazolium) binary mixtures

The purpose of this work was to analyze the microscopic feature of binary solvent systems formed by a molecular solvent (acetonitrile or dimethylformamide or methanol) and an ionic liquid (IL) cosolvent [1‐(1‐butyl)‐3‐methylimidazolium tetrafluoroborate or 1‐(1‐butyl)‐3‐methylimidazolium hexafluorophosphate]. The empirical solvatochromic solvent parameters E_T(30), π*, α, and β were determined from the solvatochromic shifts of adequate indicators. The behavior of the solvent systems was analyzed according to their deviation from ideality. The study focused on the identification of solvent mixtures with relevant solvating properties in order to select mixed solvents with particular characteristics. The comparison of the molecular–microscopic solvent parameters corresponding to the selected binary mixtures with both ILs considered at similar mixed‐solvent composition revealed that the difference is centered on the basic character of them. A kinetic study of a nucleophilic aromatic substitution reaction between 1‐fluoro‐2,4‐dinitrobenzene (FDNB) and 1‐butylamine (BU) developed in (acetonitrile or dimethylformamide + IL) solvent mixtures is presented in order to investigate and compare the solvent effects on a chemical process. For the explored reactive systems the solvation behavior is dominated by both the dipolarity/polarizability and the basicity of the media, contributing these solvent properties to accelerating the chemical process. Copyright © 2007 John Wiley & Sons, Ltd.     

Solvatochromism of 2‐(N,N‐dimethylamino)‐7‐nitrofluorene and the natural dye β‐carotene: application for the determination of solvent dipolarity and polarizability

The effects of solvents on chemical phenomena (rate and equilibrium constants, spectroscopic transitions, etc.) are conveniently described by solvation free‐energy relationships that take into account solvent acidity, basicity and dipolarity/polarizability. The latter can be separated into its components by manipulating the UV–vis spectra of two solvatochromic probes, 2‐(N,N‐dimethylamino)‐7‐nitrofluorene (DMANF) and a di‐(tert‐butyl)‐tetramethyl docosanonaen probe (ttbP9) whose synthesis is laborious and expensive. Recently, we have shown that the natural dye β‐carotene can be conveniently employed instead of ttbP9 for the determination of solvent polarizability (SP) of 76 molecular solvents and four ionic liquids. In the present work, we report the polarizabilities of further 24 solvents. Based on the solvatochromism of β‐carotene and DMANF, we have calculated solvent dipolarity (SD) for 103 protic and aprotic molecular solvents, and ionic liquids. The dependence of SD and SP on the number of carbon atoms in the acyl‐ or alkyl group of several homologous series (alcohols; 2‐alkoxyethanols; carboxylic acid‐ anhydrides, and esters, ionic liquids) is calculated and briefly discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

ESR studies on the pressure and temperature dependence of electron self-exchange kinetics between tetrathiafulvalene (TTF) and its radical cation in ionic liquids and organic solvents

The question whether chemical reactions and diffusion processes in ionic liquids are comparable with those taking place in classical organic liquids is a current issue in the literature. Pressure- and temperature-dependent investigations on simple electron self-exchange reactions between the two partners of a redox couple are good tools to get a better understanding of how the solvent influences such reactions. The electron self-exchange reaction between tetrathiafulvalene (TTF) and its radical cation has been investigated in two ionic liquids and two organic solvents using electron spin resonance (ESR) line broadening experiments at variable temperature and pressure. Rate constants are reported for the ionic liquids 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim⁺][Tf₂N^?]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim⁺][Tf₂N^?]) within a temperature range of 298 K ≤ T ≤ 368 K and a pressure range of 0.1 MPa ≤ p ≤ 100 MPa. The self-exchange reaction of the redox couple [TTF/TTF^?+] has been found to be diffusion-controlled in the used ionic liquids over the entire temperature range. The observed rate constants in ionic liquids at higher pressures are larger than those predicted by common diffusion, and suggest that the electron transfer takes place within a solvent cage. Also, the self-exchange reaction of the [TTF/TTF^?+] redox couple in classical solvents (dimethylphthalate (DMP) and acetonitrile) was investigated and compared to the results with those obtained in ionic liquids. The high viscosity of the ionic liquids makes it difficult to extract the electron transfer rate constants reliably, making interpretation within the framework of the Marcus Theory impossible.     

Quantitative generation of cation radicals and dications using aromatic oxidants: effect of added electrolyte on the redox potentials of aromatic electron donors

Redox titrations using robust aromatic oxidants allow for a quantitative analysis of redox and optical properties of organic electron donors in their oxidized states. Unlike spectroelectrochemistry, redox titrations can be performed without added electrolyte in relatively nonpolar solvents, affording quick access to the redox and optical properties of a given electron donor without the need of a complex electrochemical setup. However, the redox potentials obtained by the two methods are not the same. To establish the direction and magnitude of this discrepancy, we have performed a systematic case study using a set of tetraarylethylene donors and a tetrasubstituted hydroquinone ether cation radical (^THEO^+?) as a stable aromatic oxidant. We show that redox potentials (especially second and higher oxidation potentials) measured by electrochemical methods are systematically lower compared with the redox potentials obtained by redox titrations in the absence of electrolyte, because of the enhanced stabilization of dications and polycations by electrolyte. We have also uncovered that the smaller cation radicals (e.g., a para‐hydroquinone or ortho‐hydroquinone ether cation radicals) are much more effectively stabilized when compared with the cation radicals in which charge is delocalized over larger area (e.g., tetraarylethylene cation radicals) in the presence of electrolyte because of increased ionic strength of the solution. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiscale modelling strategies and experimental insights for the solvation of cellulose and hemicellulose in ionic liquids

ABSTRACT

The present study investigates the dissolution behaviour of cellulose and hemicellulose in potential ionic liquids (ILs) using both the quantum chemical and experimental validation. For converging upon the recommended IL, 1428 ILs consisting of 42 cations and 34 anions were studied with the conductor like screening model for real solvents (COSMO-RS) model. Based on the infinite dilution activity coefficient of the components in IL, the selected anions and cations were visualised by observing their interactions with cellulose and hemicellulose using interaction energies, natural bonding orbital analysis and molecular dynamics simulations. The dissolution order of cellulose and hemicellulose in ILs was primarily determined by the evaluation of hydrogen bonds between the oxygen atom of anion and hydroxyl proton of cellulose/hemicellulose. From this discernible fact, the anion of the IL was observed to play a leading role in the solvation process as compared to the cation. Eventually, acetate [OAc]^– anion and 1-ethyl-3-methylimidazolium [EMIM]⁺ cation were found to be good candidates for the dissolution of cellulose and hemicellulose. This was further confirmed by the measurement of solid-liquid equilibria with cellulose and hemicellulose. The regenerated cellulose powder was then characterised by Fourier transform spectroscopy(FTIR), X-ray diffraction (XRD) and Thermal gravimetric analysis (TGA).     

Temperature effect on the molecular interactions between two ammonium ionic liquids and dimethylsulfoxide

To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been performed over the whole composition range at temperature ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study included diethyl ammonium acetate ([Et₂NH][CH₃COO], DEAA) and triethyl ammonium acetate ([Et₃NH][CH₃COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed solvents, we predicted the excess molar volume (V^E), the deviation in isentropic compressibilities (ΔK_s) and deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u and η, respectively. Redlich-Kister polynomial was used to correlate the results. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMSO molecules and their structural factors.     

Solvophobic solvation and interaction of small apolar particles in imidazolium-based ionic liquids

We report results of molecular dynamics simulations characterizing the solvation and interaction of small apolar particles such as methane and xenon in imidazolium-based ionic liquids (ILs). The simulations are able to reproduce semiquantitatively the anomalous temperature dependence of the solubility of apolar particles in the infinite dilution regime. We observe that the "solvophobic solvation" of small apolar particles in ILs is governed by compensating entropic and enthalpic contributions, very much like the hydrophobic hydration of small apolar particles in liquid water. In addition, our simulations clearly indicate that the solvent mediated interaction of apolar particles dissolved in ILs is similarly driven by compensating enthalpic and entropic contributions, making the "solvophobic interaction" thermodynamically analogous to the hydrophobic interaction.     

Behavior of Nitroxide Biradicals with Acetylene Bridges in Organic Solvents and Ionic Liquids

Intramolecular electron spin exchange (IESE) in two nitroxide biradicals, R₆–C≡C–C≡C–R₆ (1) and R₆–C≡C–p-C₆H₄–C≡C–R₆ (2), is studied as a function of temperature and solvent properties. The effect of molecular solvents and ionic liquids (ILs, [1-methyl-3-butylimidazolium]⁺[PF₆]^?, bmimPF₆, and [1-methyl-3-octylimidazolium]⁺[BF₄]^?, omimBF₄) on the IESE in magnetically diluted solutions is investigated. Changes in electron paramagnetic resonance spectra are analyzed and the thermodynamic parameters of these changes are calculated. Geometry optimization and D-tensor calculations of biradicals 1 and 2 were carried out on the DFT/UB3LYP/cc-pVdz and DFT/ROPBE/N07D levels of theory. The probable differences in biradical behavior are discussed.     

Phase behaviors of ionic liquids attributed to the dual ionic and organic nature

Ionic liquids (ILs), also known as room-temperature molten salts, are solely composed of ions with melting points usually below 100 °C. Because of their low volatility and vast amounts of species, ILs can serve as ‘green solvents' and ‘designer solvents' to meet the requirements of various applications by fine-tuning their molecular structures. A good understanding of the phase behaviors of ILs is certainly fundamentally important in terms of their wide applications. This review intends to summarize the major conclusions so far drawn on phase behaviors of ILs by computational, theoretical, and experimental studies, illustrating the intrinsic relationship between their dual ionic and organic nature and the crystalline phases, nanoscale segregation liquid phase, IL crystal phases, as well as phase behaviors of their mixture with small organic molecules.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

Piperidine‐appended imidazolium ionic liquids as task‐specific catalysts: computational study,synthesis, and multinuclear NMR

Imidazolium ionic liquids (IMILs) with a piperidine moiety appended via variable length methylene spacers (with n = 1–4) were studied computationally to assess their potential to act as internal base for N‐heterocyclic carbene (NHC) generation. Proton transfer energies computed by B3LYP/6‐311+G(2d,p) were least endothermic for the basic‐IL with n = 3, whose optimized structure showed the shortest C₂‐H‐‐‐‐N(piperidine) distance. Inclusion of counter anion (Cl or NTf₂) caused dramatic conformational changes to enable close contact between the acidic C₂‐H and the anions. To examine the prospect for internal C₂‐H‐‐‐‐N coordination, multinuclear NMR data (¹H, ¹⁵N, and ¹³C) were computed by gauge independent atomic orbitals–density functional theory (GIAO‐DFT) in the gas phase and in several solvents by the PCM method for comparison with the experimental NMR data for the basic ILs (with n = 2–4) synthesized in the laboratory. These studies indicate that interactions with solvent and counter ion are dominant forces that could disrupt internal C₂‐H‐‐‐‐N coordination/proton transfer, making carbene generation from these basic‐ILs unlikely without an added external base. Therefore, the piperidine‐appended IMILs appear suitable for application as dual solvent/base in organic/organometallic transformations that require the use of mild base, without the necessity to alkylate at C‐2 to prevent N‐heterocyclic carbene formation. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of a perturbed hard-sphere equation of state for pure and mixture of ionic liquids

A perturbed hard-sphere equation of state (PHS EOS) was previously proposed to present the volumetric properties of ionic liquids by employing a variable parameter β being a function of acentric factor to justify the range of vdW dispersion forces (M. M. Papari, J. Moghadasi, S. M. Hosseini, F. Akbari, J. Mol. Liq. 158 (2011) 57–60). The main aim of the present study is to revise an attractive part of the preceding EOS by re-evaluating the above-mentioned variable parameter as well as the repulsive term. Two temperature-dependent parameters appearing in the revisited EOS have been determined from the corresponding states correlations using the interfacial properties of ILs, i.e., surface tension and liquid density, both at room temperature. The revisited EOS has been employed to model the volumetric properties of ionic liquids (ILs). The predictive power of the proposed model has been assessed by comparing the results obtained with 2189 experimental data points related to 24 ILs over a broad range of pressures and temperatures. The overall average absolute deviation (AAD) of the calculated densities from literature data was found to be 0.62 %. Furthermore, the revisited PHS EOS has been employed to model the volumetric properties of 23 mixtures including IL + IL and IL+ solvent over the vast range of temperatures. From 1580 data points of the binary mixtures of interest, the AAD of the correlated densities from the measurements was found to be 0.47 %.     

Molecular dynamics study of reaction kinetics in viscous media

Predicted by stochastic models and observed experimentally in a number of isomerization reactions, viscosity-induced solvent effects manifest themselves in a significant departure of the reaction rates from the values expected on the basis of transition state theory. These effects are well understood within the framework of stochastic models; however, the predictive power of such models is limited by the fact that their parameters are not readily available. Experiment and molecular dynamics (MD) simulations can provide such information and can serve as the testing grounds for various stochastic models. In real solvents, a change in viscosity is inevitably associated with variation of at least one of the three factors – temperature, pressure, or solvent identity, resulting in different solvent–solvent and solvent–solute interactions. A model is proposed in which solvent viscosity is manipulated through mass scaling, which allows one to maintain other factors constant for a series of viscosities. This approach was tested on MD simulations of the kinetics of two model isomerization reactions in Lennard–Jones solvents, whose viscosity was varied over three orders of magnitude. The results reproduce the Kramers turnover and a strong negative viscosity dependence of the reaction rates in the high viscosity limit, somewhat weaker than η ^?1.     

Probing solute-solvent interaction in 1-ethyl-3-methylimidazolium-based room temperature ionic liquids: A time-resolved fluorescence anisotropy study

Rotational diffusion of two organic solutes, coumarin153 (C153) and 4-aminophthalimide (AP) has been investigated in four ionic liquids (ILs), viz. 1-ethyl-3-methylimidazolium trifluoroacetate (EMIMTFA), 1-ethyl-3-methylimidazolium ethylsulfate (EMIMESU), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMTFB) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIMTCB), as a function of temperature. Between the two probes, AP can act as hydrogen-bond-donor to the solvents having hydrogen bond acceptor ability. The results indicate that the rotational dynamics of C153 is mainly governed by the viscosity of the medium. On the other hand, the rotational motion of AP is found to be significantly hindered in the ILs depending on the nature of anions of the ILs. Rotational coupling constant values for AP in the ILs follow the order TFA?>?ESU?>?TCB?>?TFB. The slower rotational motion of AP in these ILs has been attributed to the specific hydrogen bonding interaction between AP and anions of ILs.

Effect of alkyl chain length in protic ionic liquids: an AIMD perspective

In this study we have explored, by means of ab initio molecular dynamics, a subset of three different protic ionic liquids (ILs). We present both structural and dynamical information of the liquid state of these compounds as revealed by accurate ab initio computations of the interactions. Our analysis figures out the presence of a strong hydrogen bond network in the bulk state, that is more stable in those ILs characterised by a longer alkyl side chain. Indeed it becomes more long-lasting passing from ethyl ammonium to butyl ammonium, owing to the hydrophobic effects stemming from alkyl chain contacts. Furthermore, the relative free energy landscape of the cation–anion interaction exhibits a progressively deeper well as the side chain of the cation gets longer. The hydrogen bond interaction, as already mentioned in previous works, leads to loss of degeneracy of the asymmetric stretching vibrations of the nitrate anions. The resulting frequency splitting between the two normal modes is about 90 cm^?1.     

Dielectric Dispersion Study of Poly(vinyl Pyrrolidone)–Polar Solvent Solutions in the Frequency Range 20 Hz–1 MHz

Influence of polar solvents environment and polymer concentrations on the electrical properties (complex dielectric constant, ac electrical conductivity, complex electric modulus and complex impedance) of the solutions of poly(vinyl pyrrolidone) (PVP) in polar solvents, namely water, ethyl alcohol, ethylene glycol, diethylene glycol, poly(ethylene glycol), glycerol, dimethyl sulfoxide and dimethyl formamide, have been investigated in the frequency range 20 Hz–1 MHz at 25°C. Comparative analysis of the dielectric dispersion curves confirms that the solvent molecular size and number of its hydroxyl groups, and the solutions viscosity, are the major factors which governs the PVP chain segmental motion. The ionic conduction and electrode polarization phenomena has a dominant influence on the large increase of complex dielectric constant values of the solutions of PVP‐polar solvent in the lower frequency region. The values of relaxation times corresponding to these phenomena are also reported.     

Solvent effect in sonochemical synthesis of metal-alloy nanoparticles for use as electrocatalysts

Nanomaterials are now widely used in the fabrication of electrodes and electrocatalysts. Herein, we report a sonochemical study of the synthesis of molybdenum and palladium alloy nanomaterials supported on functionalized carbon material in various solvents: hexadecane, ethanol, ethylene glycol, polyethylene glycol (PEG 400) and Ionic liquids (ILs). The objective was to identify simple and more environmentally friendly design and fabrication methods for nanomaterial synthesis that are suitable as electrocatalysts in electrochemical applications. The particles size and distribution of nanomaterials were compared on two different carbons as supports: activated carbon and multiwall carbon nanotubes (MWCNTs). The results show that carbon materials functionalized with ILs in ethanol/deionized water mixture solvent produced smaller particles sizes (3.00 ± 0.05 nm) with uniform distribution while in PEG 400, functionalized materials produced 4.00 ± 1 nm sized particles with uneven distribution (range). In hexadecane solvents with Polyvinylpyrrolidone (PVP) as capping ligands, large particle sizes (14.00 ± 1 nm) were produced with wide particle size distribution. The metal alloy nanoparticles produced in ILs without any external reducing agent have potential to exhibit a higher catalytic activity due to smaller particle size and uniform distribution.     

氯铝酸离子液体的酸性及其催化烷基化反应研究

分别采用吡啶探针和乙腈探针红外光谱法研究了氯铝酸离子液体的酸性,结合固体酸表征方法,研究了离子液体的酸性对吡啶探针各振动模式的影响。发现当氯铝酸离子液体AlCl₃的摩尔分数x为0.4～0.5时,离子液体显弱Lewis酸性,强碱性吡啶探针分子能很好地表征离子液体的酸性,而弱碱性乙腈探针分子只适用于表征酸性较强的离子液体。考察了氯铝酸离子液体酸强度对苯与长链烯烃烷基化反应的影响,结果发现,AlCl₃的摩尔分数x≤ 0.5时,离子液体没有催化活性;x>0.55时,随着离子液体酸性的增强,烯烃转化率升高,但2位烷基苯选择性下降。结合离子液体的酸强度对烷基化反应机理进行初步分析认为具有催化活性的物质是强Lewis酸Al₂Cl-₇。     

Ionic liquids screening for desulfurization of natural gasoline by liquid–liquid extraction

Seventy five ionic liquids (ILs) were tested as a sequestering agent of sulfured compounds in natural gasoline (NG). Desulphurization of NG was performed by means of liquid–liquid extraction method at room temperature and atmospheric pressure. Experimental ILs containing imidazolium, pyridinium, and ammonium cations along with organic and inorganic anions were synthesized conventionally and under microwave and sonochemical conditions. The effect of the molecular structure of ILs on the desulfurization efficiency of NG with high sulfur content was evaluated. Analysis indicated that the anion type played a more important role than the cation on the desulphurization process. ILs based on halogen–ferrates and halogen–aluminates exhibited the highest efficiency in sulfur removal, and their efficiency is further improved when there is an excess of metallic salt in a ratio of at least 1:1.3 during the synthesis of the corresponding IL. An explanation for the ability of metallic ILs to remove sulfur-containing compounds from natural gasoline based on the ratio of the ionic charge to the atomic radius is proposed. Furthermore, a method to recover and reuse water-sensitive to halogenated precursors is described.