Organic reactions in ionic liquids: Knoevenagel condensation catalyzed by ethylenediammonium diacetate

The moisture and air stable ionic liquids 1-butyl-3-methylimidazonium tetrafluoroborate [bmim]BF4 and 1-butyl-3-methylimidazonium hexafluorophosphate [bmim]PF6 were used as ‘green' recyclable alternatives to volatile organic solvents (VOCs) for ethylenediammonium diacetate (EDDA) catalyzed Knoevenagel condensation between aldehydes or ketones with active methylene compounds. Both aldehydes and ketones gave satisfactory results. The ionic liquids containing catalyst EDDA were recycled several times with no decreases in yields and reaction rates. In the case of 2-hydroxybenzaldehyde, the reactions led to the formation of 3-substituted coumarins under standard reaction conditions.

Organic reactions in ionic liquids: alpha-tosyloxylation of ketones

The room temperature ionic liquid, n-butylpyridinium tetrafluoroborate (BPyBF4) is used as a "green" recyclable alternative to classical molecular solvents for the a-tosyloxylation of ketones.

Organic reactions in ionic liquids: ionic liquid-accelerated cyclocondensation of alpha-tosyloxyketones with 2-aminopyridine

The room temperature ionic liquid it-butylpyridinium tetrafluoroborate (BPyBF4) is used as a `green' recyclable alternative to classical molecular solvents for the cyclocondensation of alpha-tosyloxyketones with 2-aminopyridine. Significant rate enhancements and improved yields have been observed.

Solvation Structure of Uracil in Ionic Liquids

The local solvation environment of uracil dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate has been studied using neutron diffraction techniques. At solvent:solute ratios of 3:1 and 2:1 ionic liquid:uracil, little perturbation of the ion-ion correlations compared to those of the neat ionic liquid are observed. We find that solvation of the uracil is driven predominantly by the acetate anion of the solvent. While short distance correlations exist between uracil and the imidazolium cation, the geometry of these contacts suggest that they cannot be considered as hydrogen bonds, in contrast to other studies by Araújo et al. (J. M. Araújo, A. B. Pereiro, J. N. Canongia-Lopes, L. P. Rebelo, I. M. Marrucho, J. Phys. Chem. B 2013, 117, 4109-4120). Nevertheless, this combination of interactions of the solute with both the cation and anion components of the solvents helps explain the high solubility of the nucleobase in this media. In addition, favorable uracil-uracil contacts are observed, of similar magnitude to those between cation and uracil, and are also likely to aid dissolution

Evaluation of the conductor-like screening model for real solvents for the prediction of the water activity coefficient at infinite dilution in ionic liquids

Ionic liquids (ILs) have attracted great attention, from both industry and academia, as alternative fluids for very different types of applications. The large number of cations and anions allow a wide range of physical and chemical characteristics to be designed. However, the exhaustive measurement of all these systems is impractical, thus requiring the use of a predictive model for their study. In this work, the predictive capability of the conductor-like screening model for real solvents (COSMO-RS), a model based on unimolecular quantum chemistry calculations, was evaluated for the prediction water activity coefficient at infinite dilution, gamma(infinity)(w), in several classes of ILs. A critical evaluation of the experimental and predicted data using COSMO-RS was carried out. The global average relative deviation was found to be 27.2%, indicating that the model presents a satisfactory prediction ability to estimate gamma(infinity)(w) in a broad range of ILs. The results also showed that the basicity of the ILs anions plays an important role in their interaction with water, and it considerably determines the enthalpic behavior of the binary mixtures composed by Its and water. Concerning the cation effect, it is possible to state that generally gamma(infinity)(w) increases with the cation size, but it is shown that the cation-anion interaction strength is also important and is strongly correlated to the anion ability to interact with water. The results here reported are relevant in the understanding of ILs-water interactions and the impact of the various structural features of its on the gamma(infinity)(w) as these allow the development of guidelines for the choice of the most suitable lLs with enhanced interaction with water.

The Equilibrium Structure of Lithium Salt Solutions in Ether-Functionalized Ammonium Ionic Liquids

Molecular dynamics simulations have been performed for ionic liquids based on a ternary mixture of lithium and ammonium cations and a common anion, bis(trifluoromethylsulfonyl)imide, [Tf2N](-). We address structural changes resulting from adding Li+ in ionic liquids with increasing length of an ether-functionalized chain in the ammonium cation. The calculation of static structure factors reveals the lithium effect on charge ordering and intermediate range order in comparison with the neat ionic liquids. The charge ordering is modified in the lithium solution because the coordination of [Tf2N](-) toward Li+ is much stronger than ammonium cations. Intermediate range order is observed in neat ionic liquids based on ammonium cations with a long chain, but in the lithium solutions, there is also a nonhomogenous distribution of Li+ cations. The presence of Li+ enhances interactions between the ammonium cations due to correlations between the oxygen atom of the ether chain and the nitrogen atom of another ammonium cation.

Intermolecular vibrations and fast relaxations in supercooled ionic liquids

Short-time dynamics of ionic liquids has been investigated by low-frequency Raman spectroscopy (4 < omega < 100 cm(-1)) within the supercooled liquid range. Raman spectra are reported for ionic liquids with the same anion, bis(trifluoromethylsulfonyl)imide, and different cations: 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-butyl-1-methylpiperidinium, trimethylbutylammonium, and tributylmethylammonium. It is shown that low-frequency Raman spectroscopy provides similar results as optical Kerr effect (OKE) spectroscopy, which has been used to study intermolecular vibrations in ionic liquids. The comparison of ionic liquids containing aromatic and non-aromatic cations identifies the characteristic feature in Raman spectra usually assigned to librational motion of the imidazolium ring. The strength of the fast relaxations (quasi-elastic scattering, QES) and the intermolecular vibrational contribution (boson peak) of ionic liquids with non-aromatic cations are significantly lower than imidazolium ionic liquids. A correlation length assigned to the boson peak vibrations was estimated from the frequency of the maximum of the boson peak and experimental data of sound velocity. The correlation length related to the boson peak (similar to 19 angstrom) does not change with the length of the alkyl chain in imidazolium cations, in contrast to the position of the first-sharp diffraction peak observed in neutron and X-ray scattering measurements of ionic liquids. The rate of change of the QES intensity in the supercooled liquid range is compared with data of excess entropy, free volume, and mean-squared displacement recently reported for ionic liquids. The temperature dependence of the QES intensity in ionic liquids illustrates relationships between short-time dynamics and long-time structural relaxation that have been proposed for glass-forming liquids. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3604533]

Revealing fungal activity in the presence of ionic liquids

Dissertation presented to obtain the Ph.D degree in Biochemistry

Immobilization of Burkholderia cepacia Lipase: Kinetic Resolution in Organic Solvents, Ionic Liquids and in Their Mixtures

Immobilization of Burkholderia cepacia Lipase: Kinetic Resolution in Organic Solvents, Ionic Liquids and in Their Mixtures Biocatalysis opens the door to green and sustainable processes in synthetic chemistry allowing the preparation of single enantiomers, since the enzymes are chiral and accordingly able to catalyze chemical reactions under mild conditions. Immobilization of enzymes enhances process robustness, often stabilizes and activates the enzyme, and enables reuse of the same enzyme preparation in multiple cycles. Although hundreds of variations of immobilization methods exist, there is no universal method to yield the highly active, selective and stable enzyme catalysts. Therefore, new methods need to be developed to obtain suitable catalysts for different substrates and reaction environments. Lipases are the most widely used enzymes in synthetic organic chemistry. The literature part together with the experimental part of this thesis discusses of the effects of immobilization methods mostly used to enhance lipase activity, stability and enantioselectivity. Moreover, the use of lipases in the kinetic resolution of secondary alcohols in organic solvents and in ionic liquids is discussed. The experimental work consists of the studies of immobilization of Burkholderia cepacia lipase (lipase PS) using three different methods: encapsulation in sol-gels, cross-linked enzyme aggregates (CLEAs) and supported ionic liquids enzyme catalysts (SILEs). In addition, adsorption of lipase PS on celite was studied to compare the results obtained with sol-gels, CLEAs and SILEs. The effects of immobilization on enzyme activity, enantioselectivity and hydrolysis side reactions were studied in kinetic resolution of three secondary alcohols in organic solvents, in ionic liquids (ILs), and in their mixtures. Lipase PS sol-gels were shown to be active and stable catalysts in organic solvents and solvent:IL mixtures. CLEAs and SILEs were highly active and enantioselective in organic solvents. Sol-gels and SILEs were reusable in several cycles. Hydrolysis side reaction was suppressed in the presence of sol-gels and CLEAs.

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids` polarity. This is accomplished by investigating the Raman bandshape of the nu (CN) band, corresponding to the CN stretching mode of CH(3)CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH(3)CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1-alkyl-3-methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the nu (CN) band of CH(3)CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the nu (CN) band were corroborated by the analysis of the symmetric nu(1) (CD(3)) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright (C) 2010 John Wiley & Sons, Ltd.

Ionic liquids in a multiscale study

Trotz des hohen Interesse an Ionischen Flüssigkeiten wird das zielgerichtete Design und die Anwendung Ionischer Flüssigkeiten durch fehlendes grundlegendes Verständnis erschwert. Deshalb wurde die Balance der molekularen Wechselwirkungen in Ionischen Flüssigkeiten studiert, um die Eigenschaften dieser zu verstehen und die Kraftfeldentwicklung im Rahmen des Multiskalenansatzes zu systematisieren. Es wurden reine Imidazolium-basierte Ionische Flüssigkeiten, Mischungen mit kleinen Molekülen und eine protische Ionische Flüssigkeit mit ab-initio-Methoden, hauptsächlich Car-Parrinello-Molekulardynamik, untersucht. Weiterhin wurden Eigenschaften der Flüssigphase mit denen von Ionenpaaren verglichen.rnIm Fokus standen die molekularen elektrostatischen Eigenschaften und es wurde gezeigt, dass Coulomb-Wechselwirkungen zu einzigartigen Charakteristika führten. So waren die Ionen-Nettoladungen stets reduziert, die molekularen Dipolmomentverteilungen sehr breit, elektronische Polarisation war entscheidend. Die elektrostatischen Eigenschaften waren allgemein lokal auf molekularen Größen- und Zeitskalen und hingen stark von Phasenzustand und Zusammensetzung ab. Für andere molekulare Eigenschaften, wie der Neigung zu dispersiven Kontakten oder Wasserstoffbrücken, wurde gezeigt, dass sie einen entscheidenden Einfluss auf die Feinstruktur Ionischer Flüssigkeiten hatten. Das Gleichgewicht der Wechselwirkungen zeigte sich auch in Leistungsspektren, die sich aus den ab-initio-Molekulardynamiksimulationen ergaben. Diese boten einen neuen Weg für den Vergleich zum Experiment und für einen Einblick in die schnelle Dynamik Ionischer Flüssigkeiten.

Probing the interactions between ionic liquids and water: experimental and quantum chemical approach

For an adequate choice or design of ionic liquids, the knowledge of their interaction with other solutes and solvents is an essential feature for predicting the reactivity and selectivity of systems involving these compounds. In this work, the activity coefficient of water in several imidazolium-based ionic liquids with the common cation 1-butyl-3-methylimidazolium was measured at 298.2 K. To contribute to a deeper insight into the interaction between ionic liquids and water, COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies. The results showed good agreement between experimental and predicted activity coefficient of water in ionic liquids and that the interaction of water and ionic liquids was strongly influenced by the hydrogen bonding of the anion with water. Accordingly, the intensity of interaction of the anions with water can be ranked as the following: [CF3SO3](-) < [SCN](-) < [TFA](-) < Br(-) < [TOS](-) < Cl(-) < [CH3SO3](-) [DMP](-) < [Ac](-). In addition, fluorination and aromatization of anions are shown to reduce their interaction with water. The effect of temperature on the activity coefficient of water at infinite dilution was measured by inverse gas chromatography and predicted by COSMO-RS. Further analysis based on COSMO-RS provided information on the nature of hydrogen bonding between water and anion as well as the possibility of anion-water complex formation.

Computational and experimental study of the behavior of cyano-based ionic liquids in aqueous solution

The solvation of cyano- (CN-) based ionic liquids (ILs) and their capacity to establish hydrogen bonds (H-bonds) with water was studied by means of experimental and computational approaches. Experimentally, water activity data were measured for aqueous solutions of ILs based on 1-butyl-3-methylimidazolium ([BMIM](+)) cation combined with one of the following anions: thiocyanate ([SCN](-)), dicyanamide ([DCA](-)), or tricyanomethanide ([TCM](-)), and of 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM][TCB]). From the latter data, water activity coefficients were estimated showing that [BMIM][SCN] and [BMIM][DCA], unlike [BMIM][TCM] and [EMIM][TCB], are able to establish favorable interactions with water. Computationally, the conductor like screening model for real solvents (COSMO-RS) was used to estimate the water activity coefficients which compare well with the experimental ones. From the COSMO-RS results, it is suggested that the polarity of each ion composing the ILs has a strong effect on the solvation phenomena. Furthermore, classical molecular dynamics (MD) simulations were performed for obtaining an atomic level picture of the local molecular neighborhood of the different species. From the experimental and computational data it is showed that increasing the number of CN groups in the ILs' anions does not enhance their ability to establish H-bonds with water but decreases their polarities, being [BMIM][DCA] and [BMIM][SCN] the ones presenting higher propensity to interact.

Tailored Media for Homogeneous Cellulose Chemistry: Ionic Liquid/Co-Solvent Mixtures

Co-solvents can minimize two of the major problems associated with the use of ionic liquids (ILs) as solvents for homogeneous derivatization of cellulose: high viscosity and limited miscibility with non-polar reagents or reaction products. Thus, the effects of 18 solvents and 3 binary solvent mixtures on cellulose solutions in three ILs were systematically studied with respect to the solution phase behavior. The applicable limits of these mixtures were evaluated and general guidelines for the use of co-solvents in cellulose chemistry could be advanced: Appropriate co-solvents should have EN T values (normalized empirical polarity) > 0.3, very low ``acidity`` (alpha < 0.5), and relatively high ""basicity`` (beta >= 0.4). Moreover, novel promising co-solvents and binary co-solvent mixtures were identified.

Effect of the chain length in the structure of imidazolic ionic liquids and dimethylformamide solutions probed by Raman spectroscopy

The Raman band assigned to the nu(C=O)mode in N,N-dimethylformamide (at ca. 1660 cm(-1)) was used as a probe to study a group of ionic liquids 1-alkyl-3-methylimidazolium bromide ([C(n)Mlm]Br) with different alkyl groups (n = 2, 4, 6, 8 and 10 carbons) in binary equimolar binary mixtures with dimethylformamide. Due to the high electric dipole moment of the group C=O, there is a substantial coupling between adjacent molecules in the solution, and the corresponding Raman band involves both vibrational and reorientational modes. Different chain lengths of the ILs lead to different extents of the uncoupling of adjacent molecules of dimethylformamide, resulting in different shifts for this band in the mixtures. Information about the organization of ionic liquids in solution was obtained and a model of aggregation for these systems is proposed. (C) 2010 Elsevier B.V. All rights reserved.