Thermophysical properties of dimethyl sulfoxide + cyclic and linear ethers at 308.15 K: Application of an extended cell model
Introduction
The use of dimethyl sulfoxide (DMSO) has stimulated great interest in recent years because of its wide range of applicability as a solvent in chemical and biological processes, in pharmaceutical applications, in veterinary medicine and microbiology [1], [2], [3]. The importance of DMSO in medicine is various: in fact DMSO stabilizes membranes and cuts pain by blocking peripheral c fibres [4], it reduces inflammation by several mechanisms, it is an antioxidant, a scavenger of the free radical that gather at the site of injury [5]. DMSO was also successfully utilized in the treatment of several pathologies, including scleroderma [6], and arthritis [7]. Moreover, several properties of this substance have gained attention in relation to cancer [8].
As a part of our research of investigating the physical properties of binary liquid mixtures containing DMSO [9], [10], [11], in this paper we present experimental data of excess molar enthalpies, , and molar heat capacities, Cp, of DMSO + cyclic and linear ethers, namely 1,4-dioxane, 1,3-dioxolane, oxane, oxolane, 1,2-dimethoxyethane, and 1,2-diethoxyethane, respectively. The aim of this work is to provide information about the molecular interactions in the liquid state with a special attention focussed on the differences of the excess properties of cyclic and linear species.
DMSO is a highly polar aprotic solvent because of its SO group and has a large dipole moment and relative permittivity (μ = 4.06 D and ɛ = 46.45 at 298.15 K [12]). Cyclic and linear ethers, on the other hand, have relatively low values of relative permittivity and dipole moment. The thermodynamic properties of DMSO + cyclic and linear ethers should be related to the interactions between the SO group provided by DMSO and the OR group of the cyclic and linear ethers. However, just a few papers at 298.15 K are available in the literature [13], [14], [15], reporting thermo-chemical data.
Section snippets
Experimental
DMSO (analytical grade >99.5 mol%), 1,4-dioxane and 1,2-diethoxyethane (analytical grade 99.8 mol% for both products) were obtained from Fluka, while 1,3-dioxolane, tetrahydropyran (THP), and tetrahydrofuran (THF) ((analytical grade (99.8, 99, and 99.9) mol%, respectively)) were from Aldrich.
All liquids were used without further purification.
Before use, the components were degassed ultrasonically (ultrasonic bath, Hellma, type 460, Milan, Italy) and dried over molecular sieves (Aldrich, type 3A)
The cell model
An attempt to describe the systems studied in this paper by means of the cell model, elaborated by Prigogine and co-workers [34], [35], [36], Salsburg and Kirkwood [37] and Rowlinson [38], [39] was carried out, starting from the theoretical expression for wherewhere z is the number of nearest neighbours in the quasi-lattice model, Eij the interaction energy between molecules i and j, δ and θ the normalized
Results and conclusions
Fig. 1, Fig. 2 show the data for cyclic ethers and linear ethers, respectively. Linear diethers, 1,2-dimethoxyethane and 1,2-diethoxyethane make possible a comparison with the cyclic diether dioxolane, since the three molecules have two O groups separated by a CH2–CH2 chain.
A second useful comparison may be between cyclic mono ethers and cyclic diethers and, finally, also a comparison between 6-atom ring and 5-atom ring cyclic ethers, with the same number of ethereal atoms, may be of
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