Relative permittivity data of binary mixtures containing 2-butanol, 2-butanone, and cyclohexane
Introduction
Static dielectric constant (relative permittivity) of materials is an intrinsic property, which can play an important role in the solution properties. Measurement of relative permittivity has been shown to be a useful technique in characterizing molecular structure, solute–solute, and solvent–solute interactions in solutions [1], [2], [3].
Dielectric studies on the binary mixtures (both polar–polar and polar–apolar) are important for understanding the intermolecular interactions in the mixture due to the dipole–dipole interactions and hydrogen bonding. The dielectric investigations of binary polar liquid mixtures provide valuable information regarding intermolecular interactions and the consequent structural rearrangement of molecules in solution [4], [5], [6], [7], [8], [9]. The heterogeneous and homogeneous interactions in binary mixtures using dielectric measurements have been studied and reported by several investigators [10], [11], [12], [13].
Alcohols are among the most important organic compounds, because they are of central importance to organic chemistry and biochemistry. Due to the presence of the –OH group in the molecule, the solution chemistry of these compounds can be strongly influenced by the intermolecular hydrogen bond formation, which can play an important role in the physical properties of these molecules. Therefore, they have been subject of extensive practical and theoretical investigations to study intermolecular hydrogen bonding [14], [15], [16], [17], [18]. The aliphatic alcohols are excellent H-bond donors/acceptors, and therefore, are strongly associated through intermolecular H-bonding.
On the other hand, ketones are an important class of industrial chemicals with many scientific and industrial applications [14]. These compounds with a carbonyl group (CO) are strongly hydrogen-bond acceptors. The lower molar mass aliphatic ketones are stable, colourless liquids and generally have a pleasant, slightly aromatic odour.
A four carbon branched aliphatic alcohol containing one stereogenic centre, namely, 2-butanol (s-BuOH) is a secondary alcohol. It is a flammable colourless liquid, which is completely miscible in polar organic solvents. One of the most important aliphatic ketones is 2-butanone (namely methyl ethyl ketone, MEK), which is the second most important commercially produced ketone after acetone. The primary use of MEK is as a solvent in processes involving gums, resins, and cellulose acetate. It is also used in the manufacture of plastics, textiles, in the production of paraffin wax, glues, and as a cleaning agent. MEK is a colourless volatile liquid that is soluble in water.
Studies of molecular interactions of the polar liquids and their binary mixtures containing of s-BuOH, MEK and cyclohexane are very important in both theoretical and practical aspects [19], [20]. Some studies on the thermo-physical properties of non-aqueous binary mixtures containing (s-BuOH + MEK) have been recently carried out by Faranda et al. [21]. They have reported a useful collection of experimental data on this binary mixture.
In the present work, a binary system composed of MEK and s-BuOH was chosen. As far as the authors are aware, a detailed information about the dielectric behaviour of the (s-BuOH + MEK) binary mixture is not available in the literature, this work presents a useful dielectric data for this binary system. The investigation reported here is also concerned with the determination of the dielectric behaviour and the molecular association of these polar liquids in a non-polar solvent, i.e. (MEK + cyclohexane) and (s-BuOH + cyclohexane). Therefore, the present investigation comprises a study of intermolecular interactions in these binary systems. Some theoretical models [22], [23], [24] were also used to calculate the permittivity of these systems. These mixing rules are able to predict the permittivity of mixtures from those of their pure components.
Section snippets
Materials
The 2-butanol (sec-BuOH), 2-butanone (MEK) and cyclohexane (CX) for the dielectric investigations were purchased in high purity (spectroscopic and or HPLC grades) from Merck. All materials with stated purities were used as received without any further purification. The chemical structures of the compounds are given in table 1. Solutions of these materials were prepared by accurately weighing of appropriate amounts of the solute into 10 cm3 volumetric flasks. HPLC grade cyclohexane was used as
Molecular dipole moments, μ
The dipole moments, μ, of s-BuOH and MEK dissolved in cyclohexane were calculated using the Guggenheim–Debye equation [25]. The expression for the dipole moment is given bywhere ε1 is the static permittivity and n1 is the refractive index of pure non-polar solvent, k is the Boltzmann constant and NA is Avogadro’s number. The dielectric increment given by, , where the subscript 12 denotes a property of the solution. C is the molar concentration,
Conclusions
Electric permittivities for the binary mixtures of (s-BuOH or MEK + cyclohexane) and (s-BuOH + MEK) were measured over the whole composition range at T = (298.2, 308.2 and 318.2) K. For the mixtures of s-BuOH and MEK with cyclohexane, the permittivity results correspond to a dipole correlation factor, g > 1, and indicate a high degree of parallel dipole association. The origin of such behaviour in these materials is due to the several factors, but is mainly due to the strong polar group such as –OH
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