Densities and Viscosities of Binary Mixtures of 2-Ethyl-1,1,3,3-tetramethylguanidinium Ionic Liquids with Ethanol and 1-Propanol

Abstract

Two guanidinium-based ionic liquids (ILs), 2-ethyl-1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([TMGEt][NTf 2 ]) and ethyl sulfate ([TMGEt][C 2 OSO 3 ]) were synthesized and characterized. Experimental densities and viscosities for the binary mixtures of the ILs with ethanol and 1-propanol from (293.15 to 323.15) K were measured over the whole composition range and at the atmospheric pressure of 0.1 MPa. The excess molar volumes (V m E ) and the viscosity deviations (Δη) for the binary systems were calculated and fitted with the Redlich−Kister equation. It is found that the density of [TMGEt][NTf 2 ] is much higher than that of [TMGEt][C 2 OSO 3 ] at the same temperature, while the viscosity of the former with the value of 74.61 mPa·s is only 1 / 9 of that of the latter at 293.15 K. This indicates that the difference of the anions has a significant influence on the density and viscosity of the ILs with the same guanidinium cation. The addition of ethanol or 1-propanol leads to negative values of V m E and Δη, which result from the efficient packing of the constituents in the binary mixtures and the weakening of anion−cation interactions of the ILs. The partial molar volumes, excess partial molar volumes, Gibbs energy, and excess Gibbs energy of activation for viscous flow of the binary mixtures also have been calculated. It is hoped that the results provide useful information for the fundamental physicochemical properties of the guanidinium-based ILs and their further applications. ■ INTRODUCTIONOrganic salts with melting points lower than 373.15 K are generally considered as ionic liquids (ILs). 1−3 ILs have so many attractive features, such as low melting point, low volatility, nonflammability, and high thermal and chemical stabilities, that they have been studied extensively since the end of the 20th century. Nowadays, a large amount of scientific works have been carried out with ILs as alternative solvents for dissolution of various substances (acidic gases, 4−8 cellulose, 9−11 metals, and metallic compounds, 12−14 etc.) and extraction of different target compounds (hydrocarbons, 15−19 organic sulfurs, 20−24 and proteins, 25,26 etc.) from liquids. The ILs are also treated as specific reaction media in some cases. 27−30 As the cations and anions are both switchable, new species of ILs are continuously synthesized in the laboratory for various purposes. By far, the most favored cation and anion are the imidazolium cation and the bis(trifluoromethylsulfonyl)imide ([NTf 2 ] − ) anion. In most cases, the ILs containing these ionic moieties are low-viscous, low-melting, and stable to heat and moisture, and they are often inert in terms of chemical changes. However, the disadvantage of the higher viscosity of the pure IL compared with traditional solvents is considerable. Thus, a combination of the IL with other low-viscous and low-toxic liquid components such as ethanol can be considered as an alternative to the pure IL. This approach may also alleviate the cost problem for expensive ILs such...

Volumetric Properties and Viscosity B-Coefficients for the Ternary Systems Epigallocatechin Gallate + MCl + H2O (M = Li, Na, K) at Temperatures 288.15–308.15 K

“…The viscosity data with solvent concentration at various temperatures are useful in understanding the solute–solute, solute–solvent interactions. , The experimental viscosities of ternary systems of EGCG + aqueous solutions at T = 288.15–308.15 K are given in Table and all the viscosity data are depicted in Figure S3 in Supporting Information. The relative expanded uncertainty ( k = 2) in η was estimated to be 0.004 mPa·s according to the law of propagation of error.…”

Density and Viscosity for Binary Mixtures of the Ionic Liquid 2,2-Diethyl-1,1,3,3-Tetramethylguanidinium Ethyl Sulfate with Water, Methanol, or Ethanol

“…Thermal transition behaviors of the IL were investigated by differential scanning calorimetry (DSC, Q2000, TA Instruments) with the scanning rate of 5 K·min –1 at the range from 183.15 to 363.15 K and by thermal gravimetric analysis (TGA, Q50, TA Instruments) with the heating rate of 5 K·min –1 from 293.15 to 773.15 K. The DSC and TGA curves of the IL are shown in Figure S8. As shown in Figure S8a, glass-transition ( T g ) temperature is T g = 202 K, while no melting point is found for the IL from 190 to 360 K . In Figure S8b, the onset ( T onset ) and maximum ( T max ) temperatures of thermal decomposition of the IL are T onset = 432 K and T max = 632 K, respectively.…”

“…It indicates that the IL has satisfactory thermal stability. The weight loss of 10.0% at about 520 K probably represents the decomposition of ethyl sulfate anion. , …”

“…As shown in Figure S8a, glass-transition (T g ) temperature is T g = 202 K, while no melting point is found for the IL from 190 to 360 K. 35 In Figure S8b, the onset (T onset ) .0% at about 520 K probably represents the decomposition of ethyl sulfate anion. 35,36 Apparatus and Procedure for Density and Viscosity Measurements. The binary mixtures were prepared by mass using an analytical balance (Mettler Toledo, AL204, Switzerland) with a precision of 1 × 10 −4 g in a 20 mL special glass vial sealed with a polytetrafluoroethylene cap.…”

Guanidinium Ionic Liquids

“…Table 2 lists 1 H NMR, 13 CNMR, IR, and MS characterization data of some reported GBILs. According to the literature, NMR technique can be used to evaluate the purity of ionic liquids [37,41]. For example, in the 1 H NMR of [TMGEt][Tf 2 N] (Table 2, C2), the two peaks (5.94 ppm and 6.06 ppm) for the hydrogen atom attached to N + are integrated separately, and they are used for purity estimation (total peak area ¼ 1.00).…”