Imidazolium Salt Ion Pairs in Solution

Stassen, Hubert; Ludwig, Ralf; Wulf, Alexander; Dupont, Jaı̈rton

doi:10.1002/chem.201500239

Cited by 167 publications

(170 citation statements)

References 118 publications

(216 reference statements)

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“…Therefore, the oxidized palladium component increases with the decrease of the ionic bond strength between the imidazolium cation and anions, i.e., the stronger the ionic interaction between the cation and anion, the less "ionic" is the contact ion pair. Hence, the interaction of the IL with the metal surface is via IL contact pairs (or aggregates) 54,55 rather than by charged species, corroborating the proposed supramolecular model for formation and stabilization of M-NPs in ILs. [56][57][58] …”

Section: Chemical State and Local Atomic Order Of The Pd Atomssupporting

confidence: 73%

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

et al. 2016

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Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8-2.1 nm) Pd nanoparticles (PdNPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this "restricted" ionic environment. This suggests that ILhybrid organosilica/Pd-NPs under multiphase conditions ("dynamic asymmetric mixture") operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal ratedetermining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase.

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Section: Chemical State and Local Atomic Order Of The Pd Atomssupporting

confidence: 73%

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

et al. 2016

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“…The substances [MMIM][Ac] 12 show a transition from endothermic to an exothermic signal at a ratio of about 14:1 (a mole fraction of 93.28 %) At this extremely high concentration, this process corresponds rather to a solution of the water in the ionic liquid. 16 While the solution process of conventional salts such as LiCl or NaOH is usually strongly exothermic, the ILs investigated in our experiments (solid at RT) show an endothermic behavior. This process can be assigned to the cleavage of the lattice.…”

Section: Thermodynamic Measurementsmentioning

confidence: 66%

Investigations of structure property relationships of highly hygroscopic Imidazolium and Choline based ILs for the prediction of thermodynamic trends

Brünig

Pietschnig

2016

Proceedings of the 20th International Electronic Conference on Synthetic Organic Chemistry

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Abstract:1,3-alkyl-imidazolium-based ionic liquids show a wide range of applications from use as a "designer solvent", in catalysis 1-3 up to material science [4][5][6] . The interaction between cation and anion can be investigated by analyzing the crystal structure.7 In our work, we synthesized various 1,3-functionalized imidazolium and choline based Ils for the use as drying agent in sorption systems. Here especially substances with organic anion such as acetate, lactate and formate were quiet interesting because they expected, among other beneficial properties, a low melting point and a strongly pronounced hygroscopic behavior. However, the purification of the synthesized compounds showed a number of previously unknown crystal structures, which allowed to examine the interaction of cations and anions could be examined. In addition, the crystal structure data provided the molecular volume of the ions, which is used to predict thermodynamic aspects. Synthesis: Scheme 1For the use in our systems, it is necessary to have liquid media, which can be pumped and preferably does not crystallize during regeneration. As a result, especially RTILs are an interesting approach to avoid this problem. The known requirements reduce the possible anions mainly to the organic ones, esp. formate, acetate, lactate and oxalate. It is understandable, that the choice of the cations results from the same considerations as for the anions. This means a relative short alkyl chain length or hydrophilic groups like alcohols or carboxylic acids attached to the 3-position in 1-methyimidazole (Scheme 1).Chart 1

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“…[12] Additionally,a ny expectationf or complete salt dissociation, in thel ow polarity alcohols, would requireh ighly detailed assumptions, in contrast to those salts dissolvedi n water. [17] With aqueous [H 2 C=C 2 C 1 im]Cl solutions, acidity is unlikely af unction of impurities directly introducedd uring salt synthesis as all startingm aterials were distilleda nd dried. In any case, allyl chloride commonly contains olefins, chloropropanes and www.chemphyschem.org chloropropenes; [18] acidic impurities are still less probable with 1-methylimidazole.…”

Section: Resultsmentioning

confidence: 99%

Aqueous Brønsted–Lowry Chemistry of Ionic Liquid Ions

Driver

2015

ChemPhysChem

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Ionic liquids have become commonplace materials found in research laboratories the world over, and are increasingly utilised in studies featuring water as co-solvent. It is reported herein that proton activities, aH (+) , originating from auto-protolysis of H2O molecules, are significantly altered in mixtures with common ionic liquids comprised of Cl(-), [HSO4 ](-), [CH3SO4 ](-), [CH3COO](-), [BF4](-), relative to pure water. paH (+) values, recorded in partially aqueous media as -log(aH (+)), are observed over a wide range (∼0-13) as a result of hydrolysis (or acid dissociation) of liquid salt ions to their associated parent molecules (or conjugate bases). Brønsted-Lowry acid-base character of ionic liquid ions observed is rooted in equilibria known to govern the highly developed aqueous chemistry of classical organic and inorganic salts, as their well-known aqueous pKs dictate. Classical salt behaviour observed for both protic and aprotic ions in the presence of water suggests appropriate attention need be given to relevant chemical systems in order to exploit, or avoid, the nature of the medium formed.

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Imidazolium Salt Ion Pairs in Solution

Cited by 167 publications

References 118 publications

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

Investigations of structure property relationships of highly hygroscopic Imidazolium and Choline based ILs for the prediction of thermodynamic trends

Aqueous Brønsted–Lowry Chemistry of Ionic Liquid Ions

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