Thermodynamic investigation of room temperature ionic liquid: The heat capacity and standard enthalpy of formation of EMIES

doi:10.1016/j.tca.2006.04.022

Thermochimica Acta

Volume 447, Issue 2, 15 August 2006, Pages 141-146

https://doi.org/10.1016/j.tca.2006.04.022 Get rights and content

Abstract

The molar heat capacities of the room temperature ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES) were measured by an adiabatic calorimeter in temperature range from 78 to 390 K. The dependence of the molar heat capacity on temperature was given as a function of the reduced temperature X by polynomial equations, C_p,m (J K⁻¹ mol⁻¹) = 178.6 + 50.28X + 2.886X² − 1.362X³ + 0.6616X⁴ + 7.155X⁵ [X = (T − 132.5)/54.5] for the solid phase (78–187 K) and C_p,m (J K⁻¹ mol⁻¹) = 376.2 + 25.94X − 3.397X² − 0.6407X³ + 0.8091X⁴ + 0.9869X⁵ [X = (T − 292.5)/97.5] for the liquid phase (195–390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the EMIES relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass translation of EMIES was observed at 192.85 K. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of EMIES was determined to be $Δ_{c} H_{m}^{°} = - 5152.6 \pm 4.6 kJ mo l^{- 1}$ . The standard molar enthalpy of formation of EMIES was evaluated to be $Δ_{f} H_{m}^{°} = - 579.13 \pm 0.51 kJ mo l^{- 1}$ at T = 298.150 ± 0.001 K.

Introduction

Room temperature ionic liquids (RTILs) have emerged as a new kind of media alternative to the conventionally used organic solvents, which are generally volatile, flammable, and hazardous chemicals [1], [2], [3]. Even though ionic liquids such as [EtNH₃][NO₃], which have a melting point of 285 K, have been known since 1914 [4], it is only very recently that these systems have been explored as a new kind of media for synthetic electrochemical and catalytic applications [5], [6], [7], [8], [9], [10], [11]. Some of the properties that make the room temperature ionic liquids attractive media for various applications are the wide liquid range, non-volatility (negligible vapor pressure), non-flammable nature, less reactivity and the ability to dissolve a large variety of organic and inorganic substances including even the polymer materials in high concentration. Many of these properties have made the room temperature ionic liquids a nature-friendly “Green Solvent” [12]. The room temperature ionic liquids that are currently the focus of extensive investigation are generally a substituted imidazolium or a pyridinium salt. Even though the solvent properties of different halogenoaluminate (III) ionic liquids (ILs) were studied as early as in 1986 [13], very little is known about the various properties of the contemporary ionic liquids despite their extensive usage in synthetic applications. We refer, for instance, to that data of heat capacity, standard enthalpy of formation, thermodynamic functions and so on, which are paramount for the design of any technological processes, are even scarcer [14].

As a continuation of our previous investigations of RTILs [15], [16], [17], [18], in the present study, the molar heat capacities of EMIES were measured by an adiabatic calorimeter in temperature range from 78 to 390 K. Based on the measured heat capacity data and thermodynamic relationship, the values of thermodynamic function of the EMIES relative to 298.15 K were calculated. A glass translation of EMIES was observed at 192.85 K. Through oxygen-bomb combustion calorimetry, the molar enthalpies of combustion of EMIES were determined and the standard molar enthalpy of formation was further evaluated.

Section snippets

Chemicals

Diethyl sulfate (Academy of Military Medical Sciences, normal mass fraction purity, AR) was used as supplied, 1-methylimidazole (ACROS, normal mass fraction purity, AR) was vacuum distilled prior to use. Toluene (Tianjing Chemical Agent Factory, normal mass fraction purity, AR) was AR reagent and was purified by standard method. The 39i benzoic acid was purchased from NIST.

Synthesis of EMIES

1-Ethyl-3-methylimidazolium ethyl sulfate as a new ionic liquid was prepared through alkylation of 1-methylimidazole with

Molar heat capacity of EMIES

The molar heat capacities of the EMIES were determined by using the adiabatic calorimeter in temperature range from 78 to 390 K. The results of the molar heat capacities are listed in Table 2 and shown in Fig. 1. No thermal anomaly was observed or no phase transition took place in temperature range from 78 to 187 K for solid phase and from 195 to 390 K for liquid phase, respectively.

In order to fit heat capacity data as function of temperature well, the temperature T was replaced by the reduced

Acknowledgements

This work was financially supported by the National Nature Science Foundation of China under the contract NSFC no. 20373072.

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Thermodynamic investigation of room temperature ionic liquid: The heat capacity and standard enthalpy of formation of EMIES

Abstract

Introduction

Section snippets

Chemicals

Synthesis of EMIES

Molar heat capacity of EMIES

Acknowledgements

Fluid Phase Equilib.

J. Chem. Thermodyn.

Thermochim. Acta

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Mater. Chem.

J. Electrochem. Soc.

J. Phys. Chem. B.

Chem. Rev.

J. Phys. Org. Chem.

Chem. Commun.

Chem. Commun.

Chem. Commun.

Phys. Chem. Chem. Phys.

Phys. Chem. Chem. Phys.