Peptide synthesis in room temperature ionic liquids

We demonstrate that chemical peptide coupling using modern coupling agents is efficient in rt ionic liquids. This new approach presents some advantages, especially in the case of hindered amino acids, which are not easy to couple under standard conditions, since high purities for the crude peptides were observed with respect to coupling in classical solvents.     

Review of ionic liquids with fluorine-containing anions

Interest in ionic liquids has grown markedly in recent years. The syntheses, characterization and properties of quaternary alkyl-substituted ammonium, imidazolium, triazolium and pyridinium salts with a variety of fluorine-containing anions have been studied in detail; however, ionic liquids with other cations and anions continue to be discovered. This review is limited to the literature from 2000 to 2005 dealing with ionic liquids with fluorine-containing anions.     

Synthesis and physical properties of new layered double hydroxides based on ionic liquids: Application to a polylactide matrix

Ionic liquids based on tetraalkylphosphonium salts combined with different anions (decanoate and dodecylsulfonate) have been used as intercalating agents of layered double hydroxides (LDHs) by ion exchange. The synthesized phosphonium-treated LDHs display a dramatically improved thermal degradation and a significant increase in the interlayer distance as confirmed by thermogravimetric analysis (TGA) and X-ray Diffraction (XRD), respectively. To highlight the effect of thermostable ionic liquids, a very low amount of LDHs has been introduced within a polylactide (PLA) matrix and PLA/LDHs nanocomposites have been processed in melt by twin-screw extrusion. Then, transmission electron microscopy (TEM) analysis has been used to investigate the influence of ILs on the different morphologies of these nanocomposites. Even though the thermal stability of PLA matrix decreased, an excellent stiffness-toughness compromise has been obtained.     

First application of chiral ionic liquids in asymmetric Baylis-Hillman reaction

The first example of the use of chiral ionic liquids as reaction media in the asymmetric Baylis-Hillman reaction was described using N-alkyl-N-methylephedrinium salts. Good yields and significant enantiomeric excesses were obtained.     

Thermophysical properties and thermodynamic phase behavior of ionic liquids

The thermal stability of many tested ionic liquids (ILs) was investigated by the TGA and DTA curves over the wide temperature range from 200 to 780 K. The TGA curves have mainly a sigmoid shape, which can be split into three segments. The thermal decomposition of the samples was higher than 500 K. For the ammonium salts, C₂BF₄, or C₂PF₆, or C₂N(CN)₂, or C₄Br, the temperatures of the decompositions were 583.5, 556.1, 545.1 and 525.3 K, respectively. Generally, it was found that the temperature of decomposition of investigated ionic liquid is strongly depended on the type of cation and the anion. Phase equilibria and thermophysical constants were measured also for the dialkoxy-imidazolium ILs, [(C₄H₉OCH₂)₂IM][BF₄], [(C₈H₁₇OCH₂)₂IM][Tf₂N], [(C₁₀H₂₁OCH₂)₂IM][Tf₂N] and for pyridinium IL, [Pyr][BF₄].The characterization and purity of the compounds were obtained by the elemental analysis, water content (Fisher method) and differential scanning microcalorimetry (DSC) analysis. From (DSC) method, the melting points, the enthalpies of fusion, the temperatures and enthalpies of solid-solid phase transitions and the half C_p temperatures of glass transition of all investigated ionic liquids were measured.The phase equilibria of these salts with common popular solvents: water, or alcohols or n-alkanes, or aromatic hydrocarbons have been measured by a dynamic method from 290 K to the melting point of IL, or to the boiling point of the solvent in the whole mole fraction range, x from 0 to 1.These salts mainly exhibit simple eutectic systems with immiscibility in the liquid phase with upper critical solution temperatures (UCST), not only with aromatic hydrocarbons, cycloalkanes and n-alkanes but also with longer chain alcohols. For example the C₂BF₄ salt show simple eutectic system with water and simple eutectic systems with immiscibility in the liquid phase with upper critical solution temperature with alcohols.The solid-liquid phase equilibria, SLE curves were correlated by means of the different G^Ex models utilizing parameters derived from the SLE. The root-mean-square deviations of the solubility temperatures for all calculated data depend on the particular system and the equation used.     

Investigation of carbon-2 substituted imidazoles and their corresponding ionic liquids

The functionality at the C-2 position of the imidazole ring plays a key role in defining the chemical properties of the imidazoles and their corresponding ionic liquids. Imidazoles 1−6 with different C-2 functionality were synthesized and their corresponding ionic liquids were systematically investigated. Based on their physical properties the six imidazoles can be divided into three groups. (1) The imidazoles 2 and 3 are capable of self-polymerization to form poly(ionic liquid)s, and they are characterized with a strong leaving group at the C-2 position. (2) The imidazoles 4 and 5 can form ionic liquids, but they are very sensitive to moisture. (3) The imidazoles 1 and 6 can form stable ionic liquids, and their stabilities were influenced by the electronic effects of the substituents at the C-2 position.     

Chiral pool based synthesis of pyrrolidinium ionic liquids

Chiral ionic liquids show promising applications in various different fields. A series of pyrrolidinium-based chiral ionic liquids bearing a chiral cation, a chiral anion or both was prepared in good yields using an efficient, economic and simple pathway. The chirality was introduced using (l)-lactate and (l)-menthol derivatives. The resultant chiral compounds were characterized by both spectroscopy and polarimetry. We envision that these new chiral compounds can serve as effective reaction media and chiral catalysts for asymmetric reactions, which are presently being investigated in our lab.     

Scalable synthesis of ionic liquids: comparison of performances of microstructured and stirred batch reactors

A range of alkylpyridinium bromide ionic liquids have been synthesized in a stirred reactor at multigram scale and characterized by physical methods (viscosity, conductivity, melting point, electrochemical window, and water content). One ionic liquid, octylpyridinium bromide, was chosen to be synthesized in both macro and reduced scale reactors, in order to compare its performance and to afford evidence of the advantages of a cross channel micro reactor (channel width = 1 mm) compared to a stirred reactor.     

Tetraalkylphosphonium-based ionic liquids

Ionic liquids are salts that are liquid at or near room temperature. Their wide liquid range, good thermal stability, and very low vapor pressure make them attractive for numerous applications. The general approach to creating ionic liquids is to employ a large, unreactive, low symmetry cation with and an anion that largely controls the physical and chemical properties. The most common cations used in ionic liquids are N-alkylpyridinium and N,N′-dialkylimidazolium. Another very effective cation for the creation of ionic liquids is tetraalkylphosphonium, [PR₁R₂R₃R₄]⁺. The alkyl groups, R_n, generally are large and not all the same. The halide salts of several phosphonium cations are available as starting materials for metathesis reactions used to prepare ionic liquids. The large phosphonium cations can combine with relatively large anions to make viscous but free flowing liquids with formula mass greater than 1000 g mol⁻¹. Some other more massive salts are waxes and glasses. The synthesis and the physical, chemical, and optical properties of phosphonium-ionic liquids having anions with a wide range of masses were measured and are reported here.     

Direct polycondensation in ionic liquids

Ionic liquids (ILs) are subject to an enormous research effort due to their unique properties, such as non-volatility, high solution and reactivity ability, etc. For the first time ILs have been used as a solvent for preparing polymers via direct polycondensation. The influence of IL's nature and reaction parameters upon the polymer formulation has been investigated. It is shown that direct polycondensation is successfully proceeded in ILs and triphenyl phosphite (condensing agent) without any additional extra components, such as LiCl and pyridine, using in similar reactions in ordinary molecular solvents. Various polyamides (η_inh=0.11-1.10 dl/g), polyamide imides (η_inh=0.48-1.41 dl/g), -hydrazides (η_inh=0.56-0.60 dl/g) and polyhydrazides (η_inh=0.71-1.32 dl/g) have been obtained in quantitative yield and high molecular weight.     

Pyrylium sulfonate based ionic liquids

Pyrylium salts represent a new group of ionic liquids (ILs) containing a positive charge on the oxygen atom. The novel ILs were obtained starting with 4-pyrones from petroleum feedstock and renewable resources and sulfonic acids. The use of carboxylic acids instead of salts resulted in the formation of cocrystals. The synthesized pyrylium ionic liquids were stable in air and in contact with water and common organic solvents. The permanganate indices which are characteristic for prepared sulfonates were also investigated. The pyrylium ionic liquids were useful as immobilizers and dissolving agents in hydrosilylation reactions.     

New chiral imidazolium ionic liquids: 3D-network of hydrogen bonding

New hydrophobic chiral ionic liquids bearing an imidazolium core have been stereospecifically prepared from the chiral pool; their enantiomeric purity and 3D-network of hydrogen bonding were analysed by NMR and X-ray diffraction, respectively.     

Ionogels: Squeeze flow rheology and ionic conductivity of quasi-solidified nanostructured hybrid materials containing ionic liquids immobilized on halloysite

Ionogels are hybrid ion-conducting materials consisting of ionic liquids stabilized by inorganic or polymer fillers and having good prospects for application in solid-state and flexible electronics and energy storage devices. The work presents the results of studying the rheological properties and ionic conductivity of a series of ionogels based on halloysite nanoclay and bis(trifluoromethylsulfonyl)imide ionic liquids with EMIm⁺, BMIm⁺, BM₂Im⁺, BMPyrr⁺, BMPip⁺ and MOc₃Am⁺ cations and content of the dispersion phase of 43–48%. The obtained values are compared with the analogous characteristics of bulk ionic liquids. It has been established that the IL cation structural characteristics affect the viscoplastic properties of ionogels subjected to uniaxial quasistatic compression (20 °C), ionic conductivity and structural resistance coefficient of an inorganic filler (from ?20 to +80 °C). Additive models of conductivity in binary systems are applied to obtain correlations linking ionic conductivity of ionogels with that of pure ionic liquids.     

Confined rapid thermolysis/FTIR/ToF studies of imidazolium-based ionic liquids

Rapid scan FTIR spectroscopy and time-of-flight (ToF) mass spectrometry were utilized to study thermal decomposition of three imidazolium-based ionic liquids, with 1-ethyl-3-methyl-imidazolium (emim) as the cation, and NO₃⁻, Cl⁻, and Br⁻ as the anions. The thermal decomposition involved heating rates of 2000 K/s and temperatures to 435 °C in an ambient inert gas at 1 atm. Using sub-milligram quantities of each compound, examinations of the evolution of gas-phase species revealed that the most probable sites for proton transfer and subsequent secondary reactions were primarily the methyl group and secondarily the ethyl group. The ring appeared to remain intact, as there was no evidence of the formation of HCN, imines or related products. The most reactive compound is [emim]NO₃, since the nitrate group served as a strong oxidizer and reacted strongly with the methyl/ethyl groups at the elevated temperatures to produce common final products from combustion.     

Diels-Alder reaction in protic ionic liquids

Protic imidazolium ionic liquids have been tested as reaction media in the Diels-Alder reaction between cyclopentadiene and two dienophiles (dimethyl maleate and methyl acrylate). Good conversions and endo/exo selectivities were achieved. The activation of the dienophile by hydrogen bonding with protic imidazolium ILs was demonstrated.     

Changes in the physical properties of low bandgap polymer after interaction with ionic liquids

Over the past few years, polymers shown comprehensive utilization in optical devices, solar cells, sensors, and other such devices. However, the efficiency of these devices remains a problem. We have synthesized new thiophene based, lowband gap polymer, poly(2-heptadecyl-4-vinylthieno[3,4-d] [1,3] selenazole) (PHVTS) and investigated the interactions between the PHVTS and ionic liquids (ILs), in this study. We have used imidazolium- and ammonium-family ILs, and studied the interactions using various spectroscopic techniques such UV–visible, FTIR, and confocal Raman spectroscopies. Additionally, we studied surface morphology of the polymer-IL film. Spectroscopic studies show that both families of ILs can interact with the newly synthesized polymer poly(2-heptadecyl-4-vinylthieno[3,4-d] [1,3] selenazole). However, the imidazolium-family Ionic Liquid-polymer (IL-polymer) mixture films show higher conductivities than ammonium-family IL–polymer mixture films.     

Heck reactions of aryl halides in phosphonium salt ionic liquids: library screening and applications

The Heck cross-coupling of aryl iodides and bromides with olefins proceeds in the phosphonium salt ionic liquid trihexyl(tetradecyl)phosphonium chloride (THP-Cl) in excellent yields. Furthermore, it is shown that the counter anion matched to the phosphonium cation exerts a measurable effect on the overall yield.     

Microwave-promoted synthesis of polyhydroxydeoxybenzoins in ionic liquids

A microwave-promoted synthesis of polyhydroxydeoxybenzoins and -phenylpropanones has been developed, using bis{(trifluoromethyl)sulfonyl}amine (HNTf₂) or BF₃·OEt₂ in an ionic liquid solvent.