Dicationic Imidazolium-based Ionic Liquids Research Articles

Ionic Liquid Coatings for Titanium Surfaces: Effect of IL Structure on Coating Profile.

Dicationic imidazolium-based ionic liquids (ILs) having bis(trifluoromethylsulfonyl)imide (NTf2) and amino acid-based (methionine and phenylalanine) anionic moieties were synthesized and used to coat titanium surfaces using a dip-coating technique. Dicationic moieties with varying alkyl chains (8 and 10 carbons) and anions with distinct characteristics were selected to understand the influence of IL structural features on deposition profile. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used in this study to help elucidate intermolecular interactions within ILs as well as between ILs and TiO2 surfaces and to investigate IL coating morphology. Charge concentration on IL moieties, as well as the presence of functional groups that can interact via hydrogen bond, such as carboxylate and amino groups, were observed to influence the deposition profile. ILs containing amino acids as the anionic moiety were observed to interact strongly with TiO2, which resulted in more pronounced changes in Ti 2p binding energy. The higher hydrophobicity of the IL having NTf2 as the anionic moiety resulted in higher adhesion strength between the IL coating and TiO2.

Anion effect on the aggregation behavior of the long-chain spacers dicationic imidazolium-based ionic liquids

This work reports the study of the anion effect on the aggregation behavior of the long-chain spacers of dicationic imidazolium-based ionic liquids (ILs) in a 4.75 % (v/v) ethanol-water solution as well as in ethanol (95 %). The anions studied were Br−, NO3 −, BF4 −, SCN− and NTf2 −. Aggregation behavior was investigated by differential scanning calorimetry (DSC), conductivity, surface tension, and fluorescence. In the ethanol-water solution, the critical aggregation concentration (CAC), free energy aggregation (∆G°a), and the ionization degree (α) all significantly decreased with the increase in anion hydrophobicity. In ethanol, the CAC and ∆G°a values also decreased with the increase in anion size and hydrophobicity. The free energy adsorption (∆G°ads) data showed that the dicationic ILs have good surfactant activity, and this property improved with the decrease in the hydration radius of the anions. The anion volumes calculated also showed a good correlation with the CAC values for aggregation in ethanol-water solution and ethanol.

Effect on aggregation behavior of long-chain spacers of dicationic imidazolium-based ionic liquids in aqueous solution

Abstract A systematic study was done in order to evaluate the aggregation behavior of long-chain spacers of dicationic imidazolium-based ionic liquids (ILs) in aqueous solution. The influence of spacer chain length on the self-aggregation of ILs was investigated with surface tension, conductivity, fluorescence, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and transmission electron microscopy (TEM) experiments. The critical aggregation concentration (CAC) of ILs obtained from the different techniques indicated good agreement. Surface tension measurements showed that increasing the length of the spacer group improves the surfactant properties, as previously hypothesized. Aggregates with different morphologies were detected. The aggregation behavior of dicationic ILs was also compared with analogous monocationic ILs. It was observed that dicationic ILs tended to form aggregates with more structured packing than analogous monocationic ILs.

When Chlorides are the Most Reactive: A Simple Route towards Diverse Mono- and Dicationic Dimethyl Phosphate Ionic Liquids

Structurally diverse aromatic and aliphatic ionic liquids have been prepared via anion metathesis utilizing alkylammonium chlorides and trimethyl phosphate. Excellent oxygen-containing functional-group tolerance in preparation of potentially greener dimethyl phosphate ionic liquids has been demonstrated. For the first time, this method has been employed in the synthesis of dicationic imidazolium-based ionic liquids possessing a dimethyl phosphate counterion, providing a simple, direct route towards structurally novel products of high purity.

Preparation of TiO₂ nanoparticles coated with ionic liquids: a supramolecular approach.

Coated TiO2 nanoparticles by dicationic imidazolium-based ionic liquids (ILs) were prepared and studied by differential scanning calorimetry (DSC), dynamic light scattering (DLS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Three ILs with different hydrophobicity degrees and structural characteristics were used (IL-1, IL-2, and IL-3). The interaction between IL molecules and the TiO2 surface was analyzed in both solid state and in solution. The physical and chemical properties of coated nanoparticles (TiO2 + IL-1, TiO2 + IL-2, and TiO2 + IL-3) were compared to pure materials (TiO2, IL-1, IL-2, and IL-3) in order to evaluate the interaction between both components. Thermal behavior, diffraction pattern, and morphologic characteristics were evaluated in the solid state. It was observed that all mixtures (TiO2 + IL) showed different behavior from that detected for pure substances, which is an evidence of film formation. DLS experiments were conducted to determine film thickness on the TiO2 surface comparing the size (hydrodynamic radius, Rh) of pure TiO2 with coated nanoparticles (TiO2 + IL). Results showed the thickness of the film increased with hydrophobicity of the IL compound. TEM images support this observation. Finally, X-ray diffraction patterns showed that, in coated samples, no structural changes in TiO2 diffraction peaks were observed, which is related to the maintenance of the crystalline structure. On the contrary, ILs showed different diffraction patterns, which confirms the hypothesis of interactions happening between IL and the TiO2 nanoparticles surface.

Structure Effect of Imidazolium-Based Dicationic Ionic Liquids on Claisen Rearrangement

A large group of imidazolium-based dicationic ionic liquids (DILs) has been prepared in good yields. Thermal stability of all DILs has been determined. The effects of the reaction time, cation, imidazolium C2–H acidity, and anion on the Claisen rearrangement of allyl phenyl ether have been investigated. Type of anion and the presence of the acidic C2–H bond in the imidazolium moieties have proven to be essential for this reaction. The simple procedure and the possibility of avoiding the use catalysts and volatile organic solvents make this synthetic method environmentally benign and adaptable for large-scale applications.

Dicationic imidazolium-based ionic liquids: a new strategy for non-toxic and antimicrobial materials

Dicationic imidazolium-based ILs: a potent strategy for applications requiring non-toxic materials with antimicrobial activity.

Microscopic Aspects in Dicationic Ionic Liquids through the Low-Frequency Spectra by Femtosecond Raman-Induced Kerr Effect Spectroscopy

The interionic vibrations in imidazolium-based dicationic ionic liquids (ILs) containing the bis(trifluoromethylsulfonyl)amide ([NTf(2)](-)) counteranion were investigated using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy. The microscopic nature of the dicationic ILs ([C(n)(MIm)(2)][NTf(2)](2), where n = 6, 10, and 12; MIm = N-methylimidazolium) was compared with that of the corresponding monocationic ILs ([C(n)MIm][NTf(2)], where n = 3, 5, and 6) used as reference samples. Low-frequency Kerr spectra within the frequency range 0-200 cm(-1) of the ILs revealed that (i) the spectral profile of the dicationic ILs as well as that of the corresponding monocationic ILs is bimodal; (ii) the difference in the spectral shapes of the dicationic and monocationic ILs is greater for [C(6)(MIm)(2)][NTf(2)](2) and [C(3)MIm][NTf(2)] than for the ILs with longer alkylene linker/alkyl groups, namely [C(10)(MIm)(2)][NTf(2)](2) and [C(5)MIm][NTf(2)], and [C(12)(MIm)(2)][NTf(2)](2) and [C(6)MIm][NTf(2)]; (iii) the small difference between the dicationic and monocationic ILs is confirmed by the relative intensity of the low-frequency component (ca. 17 cm(-1)) to the high-frequency component (ca. 70 cm(-1)); and (iv) the spectral profiles of the three dicationic ILs are not very different, but the line-shape of the low-frequency Kerr spectrum of 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide ([C(3)MIm][NTf(2)]) is significantly different from those of the other two monocationic ILs whose cations have a longer alkyl group. The distinguished line-shape of the low-frequency Kerr spectrum of [C(3)MIm][NTf(2)] from the other ILs can be accounted for by the homogeneous nature in the microstructure of the IL, but the other ILs indicate microsegregation structures due to the longer nonpolar alkylene linker or alkyl group in the cations.

Comparison between Dicationic and Monocationic Ionic Liquids: Liquid Density, Thermal Properties, Surface Tension, and Shear Viscosity

We report the data of liquid density, thermal properties including glass transition temperature, melting point, and decomposition temperature, surface tension, and shear viscosity for imidazolium-based dicationic ionic liquids with the anions of bis(trifluoromethylsulfonyl)amide, bis(pentafluoroethylsulfonyl)amide, tetrafluoroborate, and nitrate. To find the unique and general features of the dicationic ionic liquids, data of their corresponding monocationic ionic liquids are also summarized. The results of the dicationic ionic liquids showed that the density was high; the glass transition temperature and melting point were high, and they were thermally stable. Also the surface tension was large, and the shear viscosity was high in comparison with the reference monocationic ionic liquids. The data of the physical properties including liquid density, surface tension, and shear viscosity of the ionic liquids were also compared with that of alkanediols and alkyl alcohols to find the alkyene-linker and alkyl-...

Amphiphilic ionic liquid stabilizing palladium nanoparticles for highly efficient catalytic hydrogenation

The highly water-soluble palladium nanoparticles (NPs) were synthesized by using the amphiphilic poly(ethylene glycol)-functionalized dicationic imidazolium-based ionic liquid (C(12)Im-PEG IL) as a stabilizing agent. The aqueous dispersed palladium NPs in the range of 1.9 ± 0.3 nm were observed by transmission electron microscopy (TEM). The physicochemical properties of C(12)Im-PEG IL in aqueous phase have been characterized by electrical conductivity, surface tension and dynamic light scattering (DLS) measurements. It was demonstrated that the amphiphilic ionic liquid can form micelles above its critical micelle concentration (CMC) in aqueous solution and the micelles played a crucial role in stabilizing the palladium NPs and thus promoted catalytic hydrogenation. Furthermore, the dicationic ionic liquid can also act as a gemini surfactant and generated emulsion between hydrophobic substrates and the catalytic aqueous phase during the reaction. The aqueous dispersed palladium NPs showed efficient activity for the catalytic hydrogenation of various substrates under very mild conditions and the stabilizing Pd(0) nanoparticles (NPs) can be reused at least eight times with complete conservation of activity.

Dicationic imidazolium-based ionic liquids and ionic liquid crystals with variously positioned fluoro substituents

A series of new dicationic imidazolium-based organic salts bearing fluoro substituents on the bent-core unit and/or linker benzene-ring positions has been synthesized and characterized. The properties of these salts, including transition and decomposition temperatures, and density were determined, indicating that their performance is strongly dependent on the positions of the fluoro substituents, the number of carbon atoms in the alkyl group, and the anion present. Examination by polarized optical microscopy showed that the four salts (compounds 4c, 7a, 7b and 8b, where the alkyl group was C12H25–) were mesomorphic and these data were supported by DSC measurements.

Examination of analyte partitioning to monocationic and dicationic imidazolium-based ionic liquid aggregates using solid-phase microextraction–gas chromatography

Solid phase microextraction coupled to gas chromatography has been used to study the partitioning behaviour of several analytes to four monocationic and two dicationic imidazolium-based ionic liquid (IL) aggregates. The 14 different analytes studied consisted of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, phenols, and esters. The obtained partition coefficients for analytes that exhibited partitioning into the IL-aggregates ranged from 30 to 5200. Hydrophobic analytes (with octanol–water partition coefficients higher than 300) appear to be preferably extracted over more polar analytes revealing the possibility of carrying out selective extractions using these aggregate systems. Monocationic IL-aggregates generally exhibited higher partition coefficients compared to analogous dicationic ILs. The micellar shape of the IL-aggregates also influences the extent of analyte partitioning.

Interfacial and micellar properties of imidazolium-based monocationic and dicationic ionic liquids

The critical micelle concentration (CMC) values of an extensive class of 18 different monocationic and dicationic imidazolium-based ionic liquids (IL) were determined using surface tensiometry. An impressive correlation between the headgroup substituent chain length and the CMC value was obtained for a variety of structurally-related monocationic ILs. In one homologous series of ILs, a 3400-fold decrease in the CMC value was obtained by simply increasing the chain length of a fixed butylimidazolium headgroup. The CMC values of different classes of dicationic ionic liquids resembling gemini and bolaform surfactants were found to be highly dependent on the length of the employed linkage chain connecting the two headgroups as well as the nature of the free alkyl side chain. Dicationic ILs studied in this work containing longer alkyl linkage chains were found to produce modest decreases in the CMC whereas free alkyl chains appended onto the imidazolium cation provided over a 100-fold decrease in the CMC value. Dicationic ILs possessing hydrophilic and hydrophobic moieties analogous to structurally-related monocationic ILs exhibited much higher efficiencies at lowering the surface tension.