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.     

The Baeyer-Villiger oxidation of ketones with Oxone in the presence of ionic liquids as solvents

Cyclic and linear ketones were readily oxidised with Oxone^® at 40 °C in ionic liquids as solvents and short times (2.5-20 h), affording their corresponding lactones and esters in high yields (65-95%). Both, aprotic and protic ionic liquids were used. The best conversion of ketones and the highest yields of products were obtained with 1-buty-3-methylimidazolium tetrafluoroborate and 1-methylimidazolium acetate as solvents. These ionic liquids were also efficiently recycled in the Baeyer-Villiger reaction without significant loss of activity. Several factors, such as the partial solubility of KHSO₅ in the ionic liquid, its viscosity and the presence of a proton in protic ionic liquids, have an influence on the course of the reaction.     

Superbase-derived protic ionic liquids with chelating fluorinated anions

Eighteen new protic ionic liquids were synthesized in one step from five organic superbases and five commercially available fluorinated β-diketones. Physical properties of the ionic liquids, including thermal decomposition temperature were determined. Nine of the ionic liquids were examined as extraction media for La³⁺, with some very large distribution coefficients obtained.     

The Synthesis of Poly(Vinyl Alcohol) Grafted with Fluorinated Protic Ionic Liquids Containing Sulfo Functional Groups

There has been an ongoing need to develop polymer materials with increased performance as proton exchange membranes (PEMs) for middle- and high-temperature fuel cells. Poly(vinyl alcohol) (PVA) is a highly hydrophilic and chemically stable polymer bearing hydroxyl groups, which can be further altered. Protic ionic liquids (proticILs) have been found to be an effective modifying polymer agent used as a proton carrier providing PEMs’ desirable proton conductivity at high temperatures and under anhydrous conditions. In this study, the novel synthesis route of PVA grafted with fluorinated protic ionic liquids bearing sulfo groups (–SO₃H) was elaborated. The polymer functionalization with fluorinated proticILs was achieved by the following approaches: (i) the PVA acylation and subsequent reaction with fluorinated sultones and (ii) free-radical polymerization reaction of vinyl acetate derivatives modified with 1-methylimidazole and sultones. These modifications resulted in the PVA being chemically modified with ionic liquids of protic character. The successfully grafted PVA has been characterized using ¹H, ¹⁹F, and ¹³C-NMR and FTIR-ATR. The presented synthesis route is a novel approach to PVA functionalization with imidazole-based fluorinated ionic liquids with sulfo groups.     

Comparative Investigation of the Ionicity of Aprotic and Protic Ionic Liquids in Molecular Solvents by using Conductometry and NMR Spectroscopy

Electrical conductivity (σ), viscosity (η), and self‐diffusion coefficient (D) measurements of binary mixtures of aprotic and protic imidazolium‐based ionic liquids with water, dimethyl sulfoxide, and ethylene glycol were measured from 293.15 to 323.15 K. The temperature dependence study reveals typical Arrhenius behavior. The ionicities of aprotic ionic liquids were observed to be higher than those of protic ionic liquids in these solvents. The aprotic ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmIm][BF₄], displays 100 % ionicity in both water and ethylene glycol. The protic ionic liquids in both water and ethylene glycol are classed as good ionic candidates, whereas in DMSO they are classed as having a poor ionic nature. The solvation dynamics of the ionic species of the ionic liquids are illustrated on the basis of the ¹H NMR chemical shifts of the ionic liquids. The self‐diffusion coefficients D of the cation and anion of [HmIm][CH₃COO] in D₂O and in [D₆]DMSO are determined by using ¹H nuclei with pulsed field gradient spin‐echo NMR spectroscopy.     

Synthesis of functionalized chiral ammonium,imidazolium, and pyridinium-based ionic liquids derived from (−)-ephedrine using solvent-free microwave activation. Applications for the asymmetric Michael addition

An efficient procedure for the synthesis of functionalized chiral ammonium, imidazolium, and pyridinium-based ionic liquids derived from (1R, 2S)-ephedrine using solvent-free microwave activation has been described. Good yields were obtained in very short reaction time. These chiral ionic liquids were used as chiral reaction media for the asymmetric Michael addition, giving good yields and moderate enantioselectivities.     

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.     

Protic metal-containing ionic liquids as catalysts: Cooperative effects between anion and cation

HCo(CO)₄ is known to be the active species in the cobalt-catalyzed hydroformylation reaction. Although it is known that the anion [Co(CO)₄]⁻ is catalytically inactive, some cobalt carbonyl-containing ionic liquids are surprisingly able to catalyze hydroformylation reactions. However, only ionic liquids with protic cations demonstrate activity, whilst aprotic cations such as BMIM⁺ result in a completely inactive compound. The four applied cobalt-containing ionic liquids differ only by the cation component. Their different performance in catalytic activity allows the presumption of cooperative effects between the cation and the anion. These fundamental influences of the cation on the hydroformylation kinetics give hints for the reaction mechanism of biphasic hydroformylation reactions as well as on the reaction pathways of the conventional hydroformylation reaction under different reaction conditions.     

Al[18F]F-HBED-CC-radiolabeling in a media of protic alkanolammonium ionic liquids

The possibility of Al¹⁸F-radiolabeling of molecules with the N,N'-bis[2-hydroxy-5-(2-carboxyethyl)benzyl]ethylenediamine-N, N'-diacetic acid motif in the medium of protic alkanolammonium ionic liquids is reported for the first time. Ionic liquids containing triethanolammonium or triisopropanolammonium cations proved to be the most promising. High values of radiochemical conversion were achieved using the minimum amount of the precursor.     

A green approach for efficient α-halogenation of β-dicarbonyl compounds and cyclic ketones using N-halosuccinimides in ionic liquids

Room temperature ionic liquids (ILs) are used as a green recyclable reaction media for the α-monohalogenation of 1,3-diketones, β-keto-esters and cyclic ketones with N-halosuccinimides in excellent yields in the absence of a catalyst. The recovered ionic liquid was reused five to six times with consistent activity.     

Reactive Oligomeric Protic Cationic Linear Ionic Liquids with Different Types of Nitrogen Centers

Reactive linear oligo(ethylene oxides) containing terminal secondary hydroxyl groups and secondary amino groups combined with nitrogen heterocyclic fragments are synthesized by the reaction of oligo(oxyethylene glycol) α,ω-diglycidyl ether (М = 1.0 × 10³) with 1-(3-aminopropyl)imidazole, 2-aminopyridine, or 2-amino-3-methylpyridine. Protonation of the synthesized compounds by ethanesulfonic acid and p-toluenesulfonic acid at their different ratios is studied. This process makes it possible to obtain oligomeric linear protic cationic ionic liquids capable of condensation. The proton conductivity of oligomeric ionic liquids is investigated under anhydrous conditions in the temperature range of 40–120°С. The highest conductivity (1.36 × 10^–3 S/cm) is attained in the case of methylpyridinium ethanesulfonate oligomeric ionic liquid at 120°С. These compounds are thermally stable to a temperature of 250–290°С. They show promise for the synthesis of polymeric analogs of block ionic liquids suitable in the production of electrochemical devices for various purposes.     

Asymmetric Mannich reaction catalyzed by N-arylsulfonyl-l-proline amides

Proline-derived N-sulfonylcarboxamides efficiently catalyze the asymmetric Mannich reaction of cyclic ketones with N-(p-methoxyphenyl)-protected iminoglyoxylate. Both classical organic solvents and ionic liquids were used as the reaction media. With cyclohexanone, the reaction proceeded with high enantioselectivity (99% ee). Enamine intermediates were investigated by DFT calculations.     

Basic ionic liquids. A short review

Basic ionic liquids as environmental-friendly solvents and catalysts with high activity and selectivity and easily recovered materials were used to replace traditional bases such as KOH, NaOH, K₂CO₃, NaHCO₃, NaOAc, triethylamine, or tetrabutylammonium acetate. Using the traditional bases generally suffered from disadvantages such as waste production, corrosion and environmental problems. Basic ionic liquids offering a new possibility for developing environmentally friendly basic catalysts due to the combination of the advantages of inorganic bases and ionic liquids. They are flexible, nonvolatile,noncorrosive, and immiscible with many organic solvents. Basic ionic liquids (BILs) have been used in base-catalyzed processes such as Michael addition, Markovnikov addition, Knoevenagel condensation, Henry reaction, Mannich reaction, oximation, Feist-Benary reaction and etc. In this short review, we wish to present an overview of the types, properties, synthesis and applications of basic ionic liquids.     

Fluorolactonization of unsaturated carboxylic acids with F-TEDA-BF4 in ionic liquids

Fluorolactonization of unsaturated carboxylic acids under action of the electrophilic reagent F-TEDA-BF₄ in ionic liquids (ILs) has been studied. This reaction proceeds in ILs faster and provides a better stereoselectivity in comparison to acetonitrile as reaction media. Gem-difluorinated γ-lactones have been synthesized by interaction of unsaturated carboxylic acids with F-TEDA-BF₄ in ILs.     

Atom transfer carbonylation using ionic liquids as reaction media

Photo-induced ATC reactions of RI, CO, and amines to produce amides, were examined using ionic liquids, such as [bmim]PF₆ and [bmim]NTf₂, as reaction media in the presence of a catalytic amount of a Pd–carbene complex. When the primary alkyl iodide was used, the yield of the amide was lowered due to competing S_N2 reactions between RI and amines, whereas the reaction of the tertiary alkyl iodides was dependent on the structure of the substrates. ATC reactions of a wide variety of secondary RI proceeded smoothly when ionic liquids were used as reaction media. The Pd-catalyst and ionic liquid could also be recycled.     

Synthesis and characterization of new pyrrolidinium based protic ionic liquids. Good and superionic liquids

New pyrrolidinium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reactions between pyrrolidine and Br?nsted acids, HX, where X is NO 3 (-), HSO 4 (-), HCOO (-), CH 3COO (-) or CF 3COO (-) and CH 3(CH 2) 6COO (-). The thermal properties, densities, electrochemical windows, temperature dependency of dynamic viscosity and ionic conductivity were measured for these PILs. All protonated pyrrolidinium salts studied here were liquid at room temperature and possess a high ionic conductivity (up to 56 mS cm (-1)) at room temperature. Pyrrolidinium based PILs have a relatively low cost, a low toxicity and exhibit a large electrochemical window as compared to other protic ionic liquids (up 3 V). Obtained results allow us to classify them according to a classical Walden diagram and to determinate their "Fragility". Pyrrolidinium based PILs are good or superionic liquids and shows extremely fragility. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional inorganic acids.     

Dissociation pathways of protic ionic liquid clusters: Alkylammonium nitrates

Protic ionic liquids are promising candidates for many applications, including as spacecraft propellants. For both fundamental interest and understanding clustering and dissociation during electrospray‐based propulsion, it is useful to explore the dissociation pathways of protic ionic liquid clusters, as well as the factors affecting the relative contributions of each pathway to the observed MS/MS spectra. With that said, most of the published reports on ionic liquid cluster dissociation have focused on aprotic ionic liquids. The purpose of the current work is to explore the dissociation pathways (eg, loss of amine, nitric acid, or ion pair) of alkylammonium nitrates using energy‐resolved collision‐induced dissociation. Here, it was found that, in general, protic ionic liquids have multiple dissociation pathways—namely, protic ionic liquids can lose their neutralized cation (here, an alkylamine) or neutralized anion (here, nitric acid)—in addition to the ion pair dissociation familiar to aprotic salt and aprotic ionic liquid clusters. In general, increasing the basicity of the cation (here, through increasing the degree of alkylation) decreases the propensity to follow these alternative pathways. Interestingly, increasing the cluster size has a similar effect: as cluster size increases, nitric acid loss decreases. These results will help better model and design protic ionic liquids for electrospray‐based spacecraft propulsion and help provide a better understanding for the general behavior of protic ionic liquids versus aprotic ionic liquids within mass spectrometers.     

A metal-free route towards 1,5-disubstituted 1,2,3-triazolylmethylene linked disaccharides: Synthesis in a biodegradable hydroxyl-ammonium-based aqueous ionic liquid media

Suitably protected carbohydrates were joined together using 1,5-disubstituted 1,2,3-triazolylmethylene (1,5-DTM) linkers. The DTM linker was built by the 1,3-dipolar cycloaddition reactions of a series of sugar azides with vinyl sulfonylmethylene-modified furanose or pyranose under metal free conditions. Three different biodegradable hydroxylammonium based ionic liquids were studied in water as the reaction media. The N,N-dimethyl ethanolammonium formate-water mixture was found to be the best reaction medium because the reaction time was shortened considerably to generate a dozen new 1,5-DTM-linked disaccharides.     

Peptide bond formation catalyzed by α-chymotrypsin in ionic liquids

α-Chymotrypsin catalyzed peptide bond formation was studied in ionic liquids using the synthesis of a protected fragment of Leu-enkephalin, ZTyrGlyGlyOEt, as model reaction. MOEMIM·PF₆ was found to be the most favorable solvent among the six different 1-alkyl-3-methylimidazolium hexafluorophosphates and tetrafluoroborates ionic liquids screened. With MOEMIM·PF₆ as reaction media, several di- or tripeptide derivatives were successfully prepared in 68-75% isolated yields.     

Facile nucleophilic fluorination of primary alkyl halides using tetrabutylammonium fluoride in a tert-alcohol medium

Nonpolar protic reaction media such as t-amyl alcohol allow the aliphatic, nucleophilic fluorination reaction of primary haloalkane systems to fluoroalkanes, using tetrabutylammonium fluoride (TBAF), to proceed chemo-selectively at a reasonable reaction rate under mild conditions to afford the fluoro-product in high yield. As an example, the nucleophilic fluorination of 2-(3-iodopropoxy)naphthalene (1a) as the primary haloalkane model compound, with TBAF in acetonitrile as a polar aprotic solvent, CsF in t-amyl alcohol as a nonpolar protic solvent, and TBAF in t-amyl alcohol for 1 h provided 2-(3-fluoropropoxy)naphthalene (2a) in 38, 5, and 76% yields, respectively.