Structure–property relationships in protic ionic liquids: a study of solvent–solvent and solvent–solute interactions

Abstract

The ionic nature of a functionalized protic ionic liquid cannot be rationalized simply through the differences in aqueous proton dissociation constants between the acid precursor and the conjugate acid of the base precursor. The extent of proton transfer, i.e. the equilibrium ionicity, of a tertiary ammonium acetate protic ionic liquid can be significantly increased by introducing an hydroxyl functional group on the cation, compared to the alkyl or amino-functionalized analogues. This increase in apparent ionic nature correlates well with variations in solvent-solute and solvent-solvent interaction parameters, as well as with physicochemical properties such as viscosity.

Cellulose dissolution and regeneration using a non-aqueous, non-stoichiometric protic ionic liquid system

“…Viscosity of binary mixtures of 1,1,3,3tetramethylguanidine and propionic acid Prior to performing the trials of cellulose dissolution, we wanted to characterise the viscosity of the mixtures, as it is an important property for their application as solvents (Marcus 1998;Reid et al 2017a). Unfortunately, due to the high melting point of the equimolar PIL, we were unable to accurately measure its viscosity within the operating temperatures of our equipment.…”

“…By raising the temperature from 20°C to 120°C, we find the optimum temperature to be 80°C for all systems. Above this temperature, cellulose solubility decreases due probably to a shift in the proton transfer equilibrium, resulting in the formation of neutral species with subsequently lower hydrogen bond basicity (Reid et al 2017a).…”

“…In fact, ion accumulation has been observed in simulation studies of ILs; [Bmim]Cl shows anion accumulation around cellulose as a stabilisation interaction within the IL (Gross et al 2011). By lowering the temperature of the system, the proton exchange equilibrium will be shifted towards ionic species over neutral species, which in turn would promote greater ion accumulation around cellulose and thus stabilise the cellulose in solution (Reid et al 2017a;Abbott et al 2018).…”

Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives

“…The data obtained are summarized in Table 5. CT transitions usually display a large solvent-dependent effect [45], resulting in negative solvatochromism as observed in methanol and DMF when compared with DCM (Fig. 5).…”

Modelling biocompatible ionic liquids based on organic acids and amino acids: challenges for computational models and future perspectives

“…121 That the self-solvation properties of the final liquid towards the ions is a crucial, albeit difficult to predict, ingredient to understand the extent of equilibrium in reaction (1) has clearly emerged in a series of recent works. [122][123][124][125] An example of how simple molecular indicators can be misleading in understanding ionicity in a given PILs is triethylammonium acetate (TEAAc). Judging from pKa, one expects to find a majority of acetates and ammonium cations.…”