Macroscopic and microscopic properties of solutions of aromatic compounds in an ionic liquid

The effects of ionic liquids on the ethanolysis of a chloroacenaphthene. Evaluation of the effectiveness of nucleofugality data to predict reaction outcome

The reaction of a chlorobenzene in mixtures containing ethanol and eight different ionic liquids was investigated in order to understand the effects of varying proportions and constituent ions of an ionic liquid on the rate constant of the process. The results were found to be generally consistent with previously studied reactions of the same type, with small proportions of an ionic liquid resulting in a rate constant increase compared to ethanol and large proportions causing a rate constant decrease. Temperature dependent kinetic studies were used to interpret the changes in reaction outcome, particularly noting an entropic cost on moving to high proportions of ionic liquid, consistent with organisation of solvent around the transition state. While attempts to use empirical solvent parameters to correlate outcome with the ionic liquid used were unsuccessful, use of recently acquired nucleofugality data for chloride and estimations for the electrofuge allowed for excellent prediction of the effects of ionic liquids, with rate constants quantitatively predicted in systems containing both different proportions of ionic liquid (mean absolute error (MAE) log(k₁) = 0.11) and different ionic liquids (MAE log(k₁) = 0.33). Importantly, this demonstrates the ready application of these quantitative reactivity parameters.

Chemistry Dissolved in Ionic Liquids. A Theoretical Perspective

The theoretical treatment of ionic liquids must focus now on more realistic models while at the same time keeping an accurate methodology when following recent ionic liquids research trends or allowing predictability to come to the foreground. In this Perspective, we summarize in three cases of advanced ionic liquid research what methodological progress has been made and point out difficulties that need to be overcome. As particular examples to discuss we choose reactions, chirality, and radicals in ionic liquids. All these topics have in common that an explicit or accurate treatment of the electronic structure and/or intermolecular interactions is required (accurate methodology), while at the same time system size and complexity as well as simulation time (realistic model) play an important role and must be covered as well.

My Life in Changing Times: New Ideas and New Techniques

I describe some of the science that I have been involved in during the last 60 years and the changes in equipment that made it possible. Starting with an interest in spectroscopy and measurement of NMR parameters, I moved to work on theoretical aspects of spin systems and infrared and Raman line shapes. This morphed into using the new technique of computer simulation to study such problems. The last half of my working life has concentrated on the application of computer simulation to a number of problems culminating in pioneering investigations of the behavior of ionic liquids.

Understanding liquid–liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally. Experimentally, it is seen that excess toluene added to the IL forms two distinct liquid phases, an “ion-rich” phase of fixed composition and a phase that is nearly pure toluene. Conversely, n-heptane is observed to be essentially immiscible in the neat IL. Molecular dynamics simulations capture both of these behaviours. Furthermore, the simulated composition of the toluene-rich IL phase is within 10% of the experimentally determined composition. Additional simulations are performed on the binary mixtures of the IL and ten other small hydrocarbons having mixed aromatic/aliphatic character. It is found that hydrocarbons with a predominant aliphatic character are largely immiscible with the IL, while those with a predominant aromatic character readily mix with the IL. A detailed analysis of the structure and energetic changes that occur on mixing reveals the nature of the ion-rich phase. The simulations show a bicontinuous phase with hydrocarbon uptake akin to absorption and swelling by a porous absorbent. Aromatic hydrocarbons are driven into the neat IL via dispersion forces with the IL cations and, to a lesser extent, the IL anions. The ion–ion network expands to accommodate the hydrocarbons, yet maintains a core connective structure. At a certain loading, this network becomes stretched to its limit. The energetic penalty associated with breaking the core connective network outweighs the gain from new hydrocarbon–IL interactions, leaving additional hydrocarbons in the neat phase. The spatially alternating charge of the expanded IL network is shown to interact favourably with the stacked aromatic subphase, something not possible for aliphatic hydrocarbons.

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally.

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.

Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular Interactions

Hydrocarbon solubility and chemical interactions in ten imidazolium- and pyridinium-based ionic liquids (ILs) with four different anions (thiocyanate [SCN]^- , dicyanamide [DCA]^- , tricyanomethanide [TCM]^- , and bis(trifuoromethylsulfonyl)imide [NTf₂ ]^- ) have been studied by ¹ H and ¹³ C NMR spectroscopy. The anion structure has the main influence on the anion-aromatic chemical interaction strength; it is directly correlated to the NMR chemical shift deviations but not to the hydrocarbon solubility. The [TCM]^- anion shows the largest chemical shift deviations, but the [NTf₂ ]^- anion has the highest hydrocarbon solubility due to steric effects. Higher water contents decrease the hydrocarbon solubility in ILs. Ion-water solvation mainly occurs until 1 mol_water /mol_IL with the saturation limit at 10 mol_water /mol_IL . Toluene-ion interactions are stronger than water-ion interactions in [DCA]^- and [TCM]^- -based ILs, but they have a similar or even lower strength in [SCN]^- -based ILs.

Ionic liquid solvents: the importance of microscopic interactions in predicting organic reaction outcomes

Ionic liquids are attractive alternatives to molecular solvents as they have many favourable physical properties and can produce different organic reaction outcomes compared to molecular solvents. Thus far, interactions between the ionic liquid components and specific sites (such as charged centres, lone pairs and π systems) on the reagents and transition state have been identified as affecting reaction outcome; a comprehensive understanding of these interactions is necessary to allow prediction of ionic liquid solvent effects. This manuscript summarises our recent progress in the development of a framework for predicting the effect of an ionic liquid solvent on the outcome of organic processes. There will be a particular focus on the importance of the different interactions between the ionic liquid components and the species along the reaction coordinate that are responsible for the changes in reaction outcome observed in the cases described.

1-Alkyl-3-methylimidazolium 4-organyloxy-2,3,5,6-tetrafluorophenyltrifluoroborates as a new platform for ionic liquids with specific properties

A new synthetic platform for ionic liquids (ILs) with specific properties was suggested based on the polyfluorophenyltrifluoroborate anions, Q[4-XC₆F₄BF₃] (X = F, RO).

Nitrogen versus phosphorus nucleophiles – how changing the nucleophilic heteroatom affects ionic liquid solvent effects in bimolecular nucleophilic substitution processes

Changing the nucleophile gave different ionic liquid effects, showing the importance of interactions with all species along the reaction coordinate.

The importance of polarizability: comparison of models of carbon disulphide in the ionic liquids [C1C1im][NTf2] and [C4C1im][NTf2]

Three dimensional distribution of CS₂ around a [C₁C₁im]⁺ ion showing the difference in behaviour of polarizable (red) and unpolarizable (blue) models of CS₂.

The effects of an ionic liquid on unimolecular substitution processes: the importance of the extent of transition state solvation

An ionic liquid significantly increases benzylic carbocation formation due to favourable ionic liquid–transition state interactions. The magnitude of transition state solvation was shown to be critical, explaining the difference between this and previous cases.

Solubility of n-butane and 2-methylpropane (isobutane) in 1-alkyl-3-methylimidazolium-based ionic liquids with linear and branched alkyl side-chains

The solubility of n-butane and 2-methylpropane (isobutane) in three ionic liquids - 1-(2-methylpropyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [(2mC3)C1im][Ntf2], 1-(3-methylbutyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [(3mC4)C1im][Ntf2] and 1-methyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide [C5C1im][Ntf2] - has been measured at atmospheric pressure from 303 to 343 K. Isobutane is less soluble than n-butane in all the ionic liquids. Henry's constant values range from 13.8 × 10(5) Pa for n-butane in [C5C1im][Ntf2] at 303 K to 64.5 × 10(5) Pa for isobutane in [(2mC3)C1im][Ntf2] at 343 K. The difference in solubility between the two gases can be explained by a more negative enthalpy of solvation for n-butane. A structural analysis of the pure solvents and of the solutions of the gases, probed by molecular dynamics simulations, could explain the differences found in the systems: (i) the nonpolar domains of the ionic liquids accommodate better the long and more flexible n-butane solute; (ii) the small differences in solubility of each gas in the ionic liquids with the same number of carbon atoms in the alkyl side-chains are explained by the absence of large structural differences in the pure solvents. In all cases, the structural analysis of the four ionic liquids confirms that the studied gases can act as probes of the molecular structure of the ionic liquids, the simulations being always compatible with the experimental solubility data.

An OHD-RIKES and simulation study comparing a benzylmethylimidazolium ionic liquid with an equimolar mixture of dimethylimidazolium and benzene

The Kerr spectra of a mixture of benzene and an ionic liquid are compared to the corresponding benzylated ionic liquid and found to be surprisingly similar.

Computational approaches to understanding reaction outcomes of organic processes in ionic liquids

The utility of using a combined experimental and computational approach for understanding ionic liquid media, and their effect on reaction outcome, is highlighted through a number of case studies.

Effect of Modifying the Anion of an Ionic Liquid on the Outcome of an SN2 Process

The effect of a series of ionic liquids containing different anions (bis(trifluoromethanesulfonyl)imide, dicyanimide, hexafluorophosphate, tetrafluoroborate, and bromide) on the rate constant of a bimolecular substitution process was investigated. A general ionic liquid effect was noted, with increases in the rate constant observed in all ionic liquids used when compared with that in acetonitrile. Temperature-dependent kinetic data allowed calculation of activation parameters in each of the reaction mixtures considered; these parameters showed that the microscopic origins of the rate enhancements observed were not the same for all of the ionic liquids used, demonstrating the importance of the nature of the anion.

Towards solvent-controlled reactivity in ionic liquids

Ionic liquids are frequently touted as alternatives to traditional molecular solvents but are limited in their applicability as the outcome of reactions may be altered on moving from a molecular to an ionic solvent. This manuscript summarizes our progress towards a predictive framework through understanding how ionic solvents affect organic processes, with an emphasis on how these findings might be applied. Particularly, we will consider the importance of the mole fraction of the ionic liquid used, including some hitherto undisclosed results, as well as the importance of understanding the key interactions of the solvent with the components along the reaction coordinate.

Further investigation of the intermolecular interactions and component distributions in a [Bmim][BF4]-based polystyrene composite membranes using two-dimensional correlation infrared spectroscopy

The intermolecular interaction and distribution of components in [Bmim][BF(4)]-based polystyrene composite membrane which is composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), poly(1-(2-methyl acryloyloxyundecyl)-3-methylimidazolium bromide) (poly(MAUM-Br)) and polystyrene is investigated by in situ Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation infrared spectroscopy (2DIR) in this study. A proposed model about the structure of this composite material is presented, and a sketch map about the local distributions of components is provided. In this model, alkyl chains in [Bmim][BF(4)], poly(MAUM-Br), and polystyrene in this system were supposed to form a polymeric network through aggregation or copolymerization. Cations of ionic liquids separate into the polymer network, while anions are kept mainly through the Coulomb force and partially by the hydrogen bonding between cations and anions. To support this model, FTIR has provided some hints on the pi-pi interaction existing in this complex material between the imidazole ring of ionic liquids and the benzene ring of polystyrene, based on the discovery of the shifts of IR absorption bands assigned to the C-C stretching vibrational mode. The sequential order of the responses from different chemical groups toward the variation of temperature is calculated by 2DIR, and the results suggest how different components distributed in this [Bmim][BF(4)]-based polystyrene composite membrane.

Ionic liquids: just Molten salts after all?

While there has been much effort in recent years to characterise ionic liquids in terms of parameters that are well described for molecular solvents, using these to explain reaction outcomes remains problematic. Herein we propose that many reaction outcomes in ionic liquids may be explained by considering the electrostatic interactions present in the solution; that is, by recognising that ionic liquids are salts. This is supported by evidence in the literature, along with studies presented here.