Investigating Variation of the Pnicogen Nucleophilic Heteroatom on Ionic Liquid Solvent Effects in Bimolecular Nucleophilic Substitution Processes

A series of nucleophiles containing Group 15 nucleophilic heteroatoms has been used to expand and develop the current understanding of ionic liquid solvent effects on bimolecular nucleophilic substitution processes. It was found that when using arsenic-, antimony- and bismuth-based nucleophiles, rate constant enhancement was observed for all solvent compositions containing ionic liquids. This rate constant enhancement was driven by ionic liquid/transition state interactions, which contrasts with previous studies on earlier Group 15 nucleophiles. This study provides a holistic understanding and augments the predictive framework for the effects of ionic liquids on bimolecular nucleophilic substitution processes, with the potential for these periodic trends to be broadly applied.

The Dependence of Ionic Liquid Solvent Effects on the Nucleophilic Heteroatom in SN Ar Reactions. Highlighting the Potential for Control of Selectivity

Nucleophilic aromatic substitution (S_N Ar) reactions of 1-fluoro-4-nitrobenzene using similar nitrogen and sulfur nucleophiles were studied through extensive kinetic analysis in mixtures containing ionic liquids. The interactions of the ionic liquid components with the starting materials and transition state for each process were investigated in an attempt to construct a broad predictive framework for how ionic liquids affect reaction outcome. It was found that, based on the activation parameters, the microscopic interactions and thus the ionic liquid solvent effect were different for each of the nucleophiles considered. The results from this study suggest that it may be possible to rationally select a given ionic liquid mixture to selectively control reaction outcome of an S_N Ar reaction where multiple nucleophiles are present.

Ion-Reagent Interactions Contributing to Ionic Liquid Solvent Effects on a Condensation Reaction

Molecular dynamics simulations of solutions of hexan-1-amine or 4-methoxybenzaldehyde in acetonitrile, an ionic liquid/acetonitrile mixture (χIL =0.2), and a number of different (neat) ionic liquids were performed, to further understand the solvent effects on the condensation reaction of these species. This work indicates that, in the presence of an ionic liquid, the amine group of hexan-1-amine is exclusively solvated by the components of the ionic liquid, and not by acetonitrile, and that the anion interacts with the aldehyde group of 4-methoxybenzaldehyde. These interactions showed little dependence on the proportion of the ionic liquid present. When varying the cation of the ionic liquid there were changes in the cation-amine interaction, and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([Bm2 im][N(CF3 SO2 )2 ]) was found to order more than expected about the amine. This ordering is likely the origin of the large rate constant values determined in [Bm2 im][N(CF3 SO2 )2 ] for this condensation reaction and explains an anomaly seen previously. When changing the anion, changes were seen in the interactions between both the cation and anion with hexan-1-amine, and the anion with 4-methoxybenzaldehyde. The differing magnitude of these interactions likely causes subtle changes in the activation parameters for this condensation reaction, and provides an explanation for the anomalous rate constant values previously determined when varying the anion.

Rational selection of the cation of an ionic liquid to control the reaction outcome of a substitution reaction

Rational selection of ionic liquids to get the rate constant you want in a substitution process.

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.

Se reduction by CO/H2O in ionic liquid: acceleration effect by activating water molecules

The water molecules were activated by ionic liquid.

Rationalising the effects of ionic liquids on a nucleophilic aromatic substitution reaction

The nucleophilic aromatic substitution reaction between 1-fluoro-2,4-dinitrobenzene and ethanol was examined in a series of ionic liquids across a range of mole fractions.

Understanding the Effect of Solvent Structure on Organic Reaction Outcomes When Using Ionic Liquid/Acetonitrile Mixtures

The rate constant for the reaction between hexan-1-amine and 4-methoxybenzaldehyde was determined in ionic liquids containing an imidazolium cation. The effect on the rate constant of increasing the length of the alkyl substituent on the cation was examined in a number of ionic liquid/acetonitrile mixtures. In general it was found that there was no significant effect of changing the alkyl substituent on the rate constant of this process, suggesting that any nanodomains in these mixtures do not have a significant effect on the outcome of this process. A series of small-angle X-ray scattering and wide-angle X-ray scattering experiments were performed on mixtures of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][N(CF₃SO₂)₂]) and acetonitrile; this work indicated that the main structural changes in the mixtures occur by about a 0.2 mole fraction of ionic liquid in the mixture (χ_IL). This region at which the main changes in the solvent structuring occurs corresponds to the region at which the main changes in the rate constant and activation parameters occur for S_N2 and condensation reactions examined previously; this is the first time that such a correlation has been observed. To examine the ordering of the solvent about the nucleophile hexan-1-amine, WAXS experiments were performed on a number of [Bmim][N(CF₃SO₂)₂]/acetonitrile/hexan-1-amine mixtures, where it was found that some of the patterns featured asymmetric peaks as well as additional peaks not observed in the [Bmim][N(CF₃SO₂)₂]/acetonitrile mixtures; this suggests that the addition of hexan-1-amine to the mixture affects the bulk structure of the liquid. The SAXS/WAXS patterns of mixtures of 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([Bm₂im][N(CF₃SO₂)₂]) and acetonitrile were also determined, with the results suggesting that [Bm₂im][N(CF₃SO₂)₂] is more ordered than [Bmim][N(CF₃SO₂)₂] due to an enhancement in the short-range interactions.

Ionic liquid effects on a multistep process. Increased product formation due to enhancement of all steps

An ionic liquid is shown to increase the rate of all three steps in this imine formation and the microscopic origins of such are investigated. The magnitude of this enhancement varies with the nature of the substituent, though in all cases the rate of imine formation is increased.

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.

Ionic liquids: anion effect on the reaction of O,O-diethyl O-(2,4-dinitrophenyl) phosphate triester with piperidine

The ionic liquids can be considered as designer solvents in the titled reaction because by an appropriate choice of the anion it is possible to steer the selectivity of this reaction.