Article pubs.acs.org/jced
Determination of the Molar Enthalpy of Solution for Ionic Liquid [C5mim][OAc](1-pentyl-3-methylimidazolium acetate) in the Temperature Range from 288.15 to 308.15 K Zhiheng Zhang,† Qiubo Zhang,‡ Fang Tian,‡ Wei Guan,*,‡ and Jiazhen Yang‡ †
Pipeline R&D Center, PetroChina, Langfang, 065000, China College of Chemistry, Liaoning University, Shenyang, 110036, China
‡
ABSTRACT: The molar enthalpies of solution, ΔsolHm, for ionic liquid [C5mim][OAc] with different molalities were measured by the solutionreaction isoperibol calorimeter in the temperature range from 288.15 to 308.15 K with an interval of 5 K. According to Archer’s method, the standard molar enthalpies of solution, ΔsolHmθ, and the apparent relative molar enthalpy, ΦL, for [C5mim][OAc] were determined. In terms of Glasser’s theory of lattice energy, the hydration enthalpy of the cation, ΔH+ ([C5mim]+) = −178 kJ· mol−1 was obtained at 298.15 K. Compared with hydration enthalpy of [C2mim]+, ΔH+ ([C2mim]+) = −233 kJ·mol−1, the hydration of [C5mim]+ is weaker than [C2mim]+. The plot of ΔsolHmθ vs (T − 298.15) K is a good straight line and its slope is the standard molar heat capacity of solution, ΔCp,mθ = 231 J·K−1·mol−1, so that the specific heat capacity of solution, ΔCpθ = 1.09 J· g−1·K−1, was obtained for IL [C5mim][OAc].
1. INTRODUCTION Since ionic liquids (ILs) have minuscule vapor pressure, nonflammability, and dual natural polarity, that are environmental-friendly properties, they have been expected to be applied in many industrial processes.1 Acetic acid ionic liquids (AcAILs) are a new-generation “greener ionic liquids” and soft functional materials which have several unique properties including strong solubility and good catalytic properties. It can be predicted that they will have important application potential in many fields, for example, the pharmaceutical industry, biological substances dissolved process, and catalytic process, etc.2−6 As far as we know enthalpy of solution is the basic thermodynamic datum which is indispensable for theoretical research and practical application of AcAILs. As a continuation of our investigation,7−11 we report in this paper that (1) The enthalpies of solution for IL [C5mim][OAc] were measured at 288.15−308.15 K. (2) The values of the standard molar enthalpy of solution, ΔsolHmθ, for [C5mim][OAc] were obtained in terms of Archer’s method.12 (3) The standard molar heat capacity of solution, ΔCp,mθ, for [C5mim][OAc] was obtained from the slope of the straight line of ΔsolHmθ vs (T − 298.15) K.
Table 1. Source and Purity of the Materials mass fraction purity KCl (>0.9999) THAM (Tris(hydroxymethyl) aminomethane) (GR) purity of IL [C5mim][OAc] (≥0.99) halogen (
