Proton Thermodynamics in a Protic Ionic Liquid, Ethylammonium Nitrate

Abstract

To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in aneat PIL, ethylammonium nitrate (EAN). Al inear relationship was found between the 14 pK a values of 12 compounds in EAN and in water.I no ther words,t he pK a value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds.Itispossible that this could be explained by the stronger acidity of HNO 3 in EAN than that of H 3 O + in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from À1t o9o nt he pH scale based on the pH value in water.

Enthalpy profile of pH-induced flocculation and redispersion of polyacrylic acid-coated nanoparticles in protic ionic liquid, N,N-diethylethanolammonium trifluoromethanesulfonate

“…Thus, the ΔS AP °value is thus less negative (favorable contribution to autoprotolysis) in the PIL than in water. This trend was observed in EAN; [33] however, the ΔS AP °value is much smaller in DEEAH + ⋅TfO − than that in EAN, indicating that the neutralized DEEA partly acts as a liquid structure maker. Thus, we propose a hydrogen bond formation between [38] 14.0 79.9 55.9 −24.0 −81 DEEA and the ubiquitously existing DEEAH + , as typically shown in Scheme 1.…”

“…From the least-squares fitting at B/Y > 0.65, the molar ionization enthalpy of Y is determined to be ΔH a °= 30 kJ/mol (note that the directly observed heat of reaction, 41 kJ/mol, is generated by the reaction HY + DEEA → Y − + DEEAH + , while ΔH a °corresponds to HY + TfO − → Y − + TfOH). This value resembles the ionization enthalpy of acetic acid in EAN (30.6 kJ/mol), [33] which is clearly larger than that in water, implying no specific behavior in CNp except for acid-base equilibrium in this pH region, however, the value in DEEAH + ⋅TfO − is currently unavailable due to experimental difficulties. Colloidal stability in ionic liquids has been previously proposed to highly depend on a matching between the surface charge density and the size of the solvent ions of ionic liquids.…”

“…Details of the equipment have been described elsewhere. [8,33] For each titration point, a few tens of mm 3 of titrant was injected over approximately 10-20 s into the sample solution (initial volume: 2.5 cm 3 ). After the solution is completely mixed, the heat generation stops, and the solution temperature returns to the equilibrium temperature according to Newton's law of cooling (exponential).…”

Effects of Ionic Liquids on the Cylindrical Self-Assemblies Formed by Poly(ethylene oxide)–Poly(propylene oxide)–Poly(ethylene oxide) Block Copolymers in Water

“…EAN is the most extensively investigated protic ionic liquid [37][38][39]. Protic ionic liquids (PILs) are formed by the transfer of a proton from a Brønsted acid to a Brønsted base [40].…”