Mean Activity Coefficients of NaCl in the Mixture of 2‑Hydroxyethylammonium Butyrate + H 2 O at 298.15 K Eliseo Amado-Gonza ́ lez,* Irina Lupita Gonza ́ lez-Gutierrez, and Wilfred Gome ́ z-Jaramillo Department of Chemistry, University of Pamplona, (57 + 7) 5685303-5685304, IBEAR FJ-207 Biofuels Laboratory, Pamplona, Colombia * S Supporting Information ABSTRACT: The main objective of this work is to continue with a series of electrochemistry studies of mixtures of ionic liquids and water as a solvent to provide accurate data for future particular applications [Amado-Gonzalez et al. J. Chem. Eng. Data 2017, 62, 752]. The mean activity coefficients for NaCl in [2-hydroxyethylammonium butyrate (2-HEAB) + H 2 O] as a solvent mixture were determined by cell potential measurements: Na-ion selective electrode (ISE)|NaCl (m), 2-HEAB (w), H 2 O (1 - w)|Cl-ion selective electrode (ISE) at molalities from 0.10 to 3.20 mol·kg -1 at 298.15 K. Different weight fractions (w) of 2-HEAB with w = 0.01, 0.05, 0.1, 0.2, 0.3, and 0.4 were used. At higher concentrations of w = 0.40, NaCl is salting out by 2- HEAB in water. The Pitzer ion interaction parameters β 0 , β 1 , and C γ were used to find the values of osmotic coefficients, solvent activity, and the excess Gibbs free energy for the mixed electrolyte system. The results may be interpreted by the clathrate-like formation of 2-HEAB + water. A qualitative description of the relation between water and the 2-HEAB was done using the general AMBER force field (GAFF). 1. INTRODUCTION Thermodynamic properties of mixtures of [ionic liquids (ILs) + H 2 O] are important to evaluate future applications. 1 Ionic liquids (ILs) or the future new solvents can be structurally designed as proposed by Lowe and Rendall. 2 Due to the physicochemical properties of ILs, 3-5 they may have many different industrial uses. 6 Activity coefficients and osmotic coefficients of electrolyte solutions are extremely useful to test new electrolyte solution theories. 7-15 Even though activity coefficients of ammonium ILs have been reported in aqueous solutions by the isopiestic method, 16-23 to our knowledge, research papers about the activity coefficients of NaCl in ILs + water are still scarce, and studies of mean ionic activity coefficients of NaCl reported in the literature for ternary liquid mixtures are still limited. 24-26 Because of the high costs of ILs and import restrictions, the synthesis of new ILs should be a goal. Protic ionic liquids offer a good possibility because they can be produced by a simple acid- base neutralization reaction. 27 2-Hydroxyethylammonium buty- rate (2-HEAB) is therefore evaluated for its potential abilities as a solvent. In this sense, our goal is to evaluate how the thermodynamic properties of salts like NaCl would be affected by the (2-HEAB + H 2 O) solvent mixture. In this work, we found the activity coefficients of NaCl in the mixture (2-HEAB + H 2 O) by cell potential measurements at 298.15 K. The results were fitted to the Pitzer model. Then, the osmotic coefficients, solvent mixture activities, and excess Gibbs free energies of these systems were calculated. A calculation of hydrogen interaction at w = 0.4 was completed using the general AMBER force field (GAFF). 2. EXPERIMENTAL SECTION 2.1. Materials, Synthesis, and Measurements. In Table 1 the chemicals, suppliers, and stated purity are shown. The IL, 2- HEAB was synthesized by acid-base neutralization reactions between ethanolamine and the organic acid as previously described. 26 The reagents monoethanolamine and butyric acid (Sigma-Aldrich, 99%) are analytical (AR grade) reagents. The synthesis of 2-HEAB was done as reported by literature. 28-30 Strong agitation was performed at heating at 323 K. The IL was dried under a vacuum of 20 kPa during 8 h until ΔpH (pH at the equivalent point - pH experimental) < 0.07. An ATR-FTIR spectra for 2-HEAB was done. The ammonium structure was found at 3200-2400 cm -1 . The OH stretching vibration was embedded in this band. The carbonyl stretching and N-H in- plane bending vibrations were at 1600 cm -1 . Water content was verified by a volumetric titroline KF (Schott instruments) as 6 × 10 -4 mass fraction. No phase change of ILs was observed. The analysis of 1 H NMR gave the next results for the 2-HEAB: (400 MHz, D 2 O) δ 4.72 (s, 4H, H3b y H4b), 3.75-3.66 (m, 2H, H2b), 3.06-2.97 (m, 2H, H1b), 2.05 (t, J = 7.3 Hz, 2H, H1a), 1.52-1.40 (m, 2H, H2a), 0.79 (t, J = 7.4 Hz, 3H, H3a) and a purity higher that 99% mass fraction (details available in the Supporting Information). Received: March 18, 2017 Accepted: July 10, 2017 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/acs.jced.7b00278 J. Chem. Eng. Data XXXX, XXX, XXX-XXX