(258g) On the Determination of the Dipole Moments of Solutes from Multi-Component Systems: Experimental and Model Development

The characterization of multi-component solutions is an important area in many branches of chemistry and chemical engineering. Moreover, the determination of the individual physico-chemical properties of solutes in multi-component solutions is a particularly difficult problem. A quaternary system consisting of three deuterated solutes, e.g. acetone-d6, acetonitrile-d3, dimethylformamide-d7 in cyclohexane at 298.15 K and 1.0125 x 10⁵ Pa was studied. Multi-component solutions in the range of concentration 0.0006 solute-i < 0.0085 were performed using a semi-batch procedure by injecting one solute at a time following a pre-experimental design protocol. On-line monitoring using IR spectroscopy and simultaneous measurements of densities, refractive indices, and dielectric constants of bulk solution were made for each solution. Two different approaches in determining dipole moment through solute partial molar polarization are used. The first approach is extending the relationships of dielectric constant, refractive index, and density versus mass (or mole) fractions as introduced by Hedestrand, Halverstadt-Kumler and Guggenheim-Smith for multi-component systems. The second approach is employing a response surface model for total molar polarization. The dipole moments of all species can thus be subsequently determined using the Debye formula. The dipole moment determinations from this multi-component system were consistent with literature values (obtained from binary system, if any) as well as those obtained from our separate binary studies.