Sandra García-Garabal

The ternary system propyl propanoate+ hexane+chlorobenzene at 298.15 k

Excess molar enthalpies for the ternary mixture {propyl propanoate + hexane + chlorobenzene} and the binary mixtures {propyl propanoate + chlorobenzene} and {hexane + chlorobenzene} were determined at the temperature 298.15 K and normal atmospheric pressure. The experimental values were measured using a Calvet microcalorimeter. Excess molar enthalpies obtained were also used to test empirical expressions for estimating ternary properties from binary results.

Physical Properties of Binary Mixtures of ILs with Water and Ethanol. A Review.

The interest on ionic liquids (ILs) began in the present century, because these compounds have many physico-chemical interesting properties to be one of the most promising new materials family for the development of the novel Green Chemical industry, where generated pollution would be negligible (Rogers & Seddon, 2002; Rogers et al., 2002). To develop the novel green processes in the chemical industry using ILs it is necessary to know and to understand the physical properties of the fluids to be used, both pure ILs as mixed with other solvents (Rogers & Seddon, 2005; Danek, 2006). This last is particularly important to develop one of the most promising uses of the ILs, as electrolytes for lithium batteries, dye-sensitized solar cells (DSSC) and electrochemical processes (as deposition or metal recovery) (Ohno, 2005; Brennecke et al., 2007). Electrolytes are materials with free ions, which can move transporting electrical charge. They can be solid, liquid or even gaseous, but the most interesting for the chemical industries are liquid or gel. The use of a pure liquid as electrolyte is not very common, because the optimum efficiency in the charge transport process is given by a mixture of different substances, as it is well known for molten salt electrolytes (Danek, 2006). Furthermor, pure ILs have the problem of being very viscous at room temperature, and hence its electrical conductivity is relatively low. If we heat the IL those problems are minimized, because viscosity reduces and electrical conductivity increases, both exponentially. Usually pure ILs have a boiling temperature high enough to allow warming, although decomposition temperature is usually much lower (not higher than 400 K) (Rogers & Seddon, 2002). A much cheaper alternative to decrease viscosity and to increase electrical conductivity of the ionic liquid is to make a solution using a solvent. Thus, while viscosity decreases exponentially with the solvent molar fraction, electrical conductivity increases more than 10 times for a given IL + solvent concentration (Seddon et al., 2000). This last behaviour have been observed in aqueous solutions of metal salts, as aluminium halogen ones (Vila et al., 2005) and indicates that the increase of mobility of the IL ions is higher than the decrease of ion concentration when solvent is added, up to an optimum content. In spite of its interest, the measurement of the physical properties of IL mixtures begins in the present decade, and before 2005 the amount of papers published about it was scarce (Marsh et al., 2004). From that year the publication rhythm increased a lot, as can be

Imidazolium decyl sulfate: a very promising selfmade ionic hydrogel

In this paper, we show, for the first time, the synthesis, structural characterization, phase diagram and physical properties of the ionic liquid, 1-ethyl-3-methyl imidazolium decyl sulfate [EMIm][DSO4]. At 25 °C it is either a crystalline solid or a liquid depending on the thermal history as its melting point is about 33 °C and its point of solidification is about 22 °C. The interest of this new IL lies in its ability to become a rigid hydrogel when mixed with water. As observed in many ILs, the as-prepared IL is hygroscopic and it adsorbs about 14 wt% of water at usual laboratory conditions and up to 27 wt% in a 100% saturated atmosphere. Due to the H-bonds between water and the amphiphilic [DSO4] anions, a lyotropic HI liquid crystalline phase is formed in the hydrated state, which can be observed in micrographs recorded using white polarized light. The moisture adsorption is a completely reversible process; thus, the rigid-gel sample loses all adsorbed water when it is left in a dry atmosphere for a few hours, transitioning to the liquid state. Phase diagrams of the temperature-water concentration is presented and compared with that of the parent compound [EMIm] octyl sulfate, [OSO4]. X-ray diffraction revels that below 15 °C the hydrated compound crystallizes into a P2/m monoclinic structure. The structure of the new compound was confirmed by NMR, FTIR and mass spectroscopy (MS). In addition, the temperature behavior of ionic conductivity was experimentally measured and analyzed for the pure compound and for two samples hydrated with 10 wt% and 39 wt% of water. Viscosity and density were also measured vs. temperature for the pure sample. The as-prepared IL shows great potential for numerous practical applications.