Enhanced extraction of phenol from model oils using ionic liquids elucidated with neutron diffraction.

Aromatic cation ionic liquids (ILs) based on alkylpyridiniums are shown to be good phenol extractants from model oils (hexane/toluene). ILs with hard basic anions are found to have best extraction efficiency consistent with tetraalkylammonium salts ([NR4]X). Key extraction interactions were analysed using small angle neutron diffraction. Trifluoromethanesulphonate ([OTf]- or triflate) anions provide the synergistic effects of reduced cation-phenol centre of mass (COM) distances and increased hydrogen bonding that are linked to the improved extraction efficiency. Increases in cation electron density (methylpyridinium ([Me-Py]+) vs. methylpicolinium ([Me-3-Pic]+)) also reduce cation-phenol COM interaction lengths consistent with small increases in extraction efficiency for the same ionic liquids.

Investigation of glycerol hydrogen-bonding networks in choline chloride/glycerol eutectic-forming liquids using neutron diffraction.

The structure of choline chloride/glycerol (ChCl : Gly) mixtures at two mole fractions (the eutectic χChCl = 0.33 (1 : 2), and a higher χChCl = 0.50 (1 : 1) composition) in the liquid state at 333 K and 1 atm. has been investigated using neutron diffraction coupled with hydrogen/deuterium isotopic substitution. Modelling using the empirical potential structure refinement (EPSR) technique, constrained to the experimental neutron diffraction data, produced structural models at both compositions consistent with the experimental data with an extensive, persistent homo-molecular glycerol hydrogen bonding network at χChCl = 0.33 similar to that present in pure glycerol and suggests that persistence of the latent glycerol hydrogen bonding network is key to formation of the ChCl : Gly deep eutectic solvent. In the choline chloride-rich χChCl = 0.50 composition, significant domain segregation is observed with a dramatic reduction in the extent of the homo-molecular glycerol hydrogen bond network which is replaced by a more homogeneous system-wide hydrogen bonded network incorporating glycerol, Cl-, and choline cations.

Rotation and translation dynamics of coumarin 153 in choline chloride-based deep eutectic solvents.

The equilibrium and dynamic solvation responses of coumarin 153 (C153) in a range of deep eutectic solvents (DESs) based on choline chloride with either urea (molar ratio 1:2, ChCl:U), glycerol (1:2, ChCl:G), ethylene glycol (1:2, ChCl:E), or malonic acid (1:1, ChCl:Mal) were investigated using both steady-state and time-resolved fluorescence emission spectroscopy at room temperature (298 K). From steady-state fluorescence data, "red-edge effects" were observed in all the DESs studied, attributed to spatial heterogeneity of the DES matrix. Time-resolved Stokes shifts were used to quantify dynamic solvation with the solvation response function in DES found to be a biexponential function of time, which were used to obtain average solvation times (⟨τ s ⟩) which are generally faster in DES than in ionic liquids of comparable viscosity. Average solvation times showed a partial correlation with viscosity between different DESs. The choline chloride-glycerol DES showed deviation from the viscosity trend observed in the other DES for both dynamic and steady-state results. Rotational reorientation times obtained from dynamic anisotropy (r(t)) measured for these DESs showed a partial correlation with viscosity between different DESs. Determination of the DES rotational coupling with C153 showed more "slip"-like behavior than the previously reported ionic liquids and dipolar solvents.

A comparison of choline:urea and choline:oxalic acid deep eutectic solvents at 338 K.

1:2 choline chloride:urea and 1:1 choline chloride:oxalic acid deep eutectic solvents are compared at 338 K using liquid-phase neutron diffraction with H/D isotopic substitution to obtain differential neutron scattering cross sections and fitting of models to the experimental data using Empirical Potential Structure Refinement. In comparison to the previously reported study of choline chloride:urea at 303 K, we observed significant weakening and lengthening of choline-OH⋯Cl- and choline-OH⋯hydrogen-bond acceptor correlations.

Applying neutron diffraction with isotopic substitution to the structure and proton-transport pathways in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids.

Neutron diffraction with isotopic substitution has been applied to examine the potential for complex-ion formation in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids. Strong cation-anion hydrogen-bonding in the 1 : 1 base : acid ionic liquid results in a high population of anions adopting a cis-conformation and, on adding excess imidazole (2 : 1 base : acid stoichiometry), cation-base and base-base correlations were identified, however, persistent hydrogen-bond associations were not 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 (ionic liquid:uracil) ratios of 3:1 and 2:1, 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, favourable uracil-uracil contacts are observed, of similar magnitude to those between cation and uracil, and are also likely to aid dissolution.

Association and liquid structure of pyridine-acetic acid mixtures determined from neutron scattering using a 'free proton' EPSR simulation model.

The liquid structure of pyridine-acetic acid mixtures have been investigated using neutron scattering at various mole fractions of acetic acid, χHOAc = 0.33, 0.50, and 0.67 and compared to the structures of neat pyridine and acetic acid. Data has been modelled using empirical potential structure refinement (EPSR) with a 'free proton' reference model, which has no prejudicial weighting towards either the existence of molecular or ionised species. Analysis of the neutron scattering results shows the existence of hydrogen-bonded acetic acid chains with pyridine inclusions, rather than the formation of an ionic liquid by proton transfer.