Darja Rudan-Tasic

Structures of artificial sweeteners--cyclamic acid and sodium cyclamate with other cyclamates.

In the course of a study on artificial sweeteners, new crystal structures of cyclamic acid, sodium cyclamate, potassium cyclamate, ammonium cyclamate, rubidium cyclamate and tetra-n-propylammonium cyclamate have been determined. Cyclamic acid exists in its zwitterionic form in the crystalline state. The zwitterions are connected through hydrogen bonds of the N-H...O type to form two-dimensional sheets. The sodium, potassium, ammonium and rubidium cyclamates are isostructural, with the cyclamate moieties linked through hydrogen bonds into linear chains. Taking into account the connectivity through cations, two-dimensional layers with a hydrophobic surface are constructed. In tetra(n-propyl)ammonium cyclamate the large, non-coordinating cation apparently prevents the formation of chains and thereby facilitates the centrosymmetric head-to-head discrete dimeric arrangement of the cyclamate moieties.

Apparent Molar Volume and Expansibilityof Cyclohexanol in Benzene and Cyclohexane Solutions

Summary. The density of solutions of cyclohexanol in benzene and cyclohexane (up to 12.1 and 1.4 molċkg−1, respectively) was measured at 20, 25, 30, 40, 50, and 60°C. On the basis of the limiting partial molar volume and its temperature dependence, the apparent molar expansibility of cyclohexanol was estimated. The excess molar volume and the excess thermal expansion coefficient of the solute in the studied solvents as well as in water were derived and are discussed on the basis of solute-solvent interactions. In addition, the limiting partial molar volume of the solute is interpreted in terms of the scaled particle theory. The solvent effect on the partial molar volume of the solute was found to be due mainly to cavity formation and intermolecular dispersion forces..Zusammenfassung. Die Dichte von Lösungen von Cyclohexanol in Benzol und Cyclohexan (bis zu 12.1 bzw. 1.4 molċkg−1) wurde bei 20, 25, 30, 40, 50 und 60°C bestimmt. Aus dem partiellen Molvolumen und seiner Temperaturabhängigkeit wurde die scheinbare molare Expansibilität von Cyclohexanol abgeschätzt. Das Zusatzmolvolumen und der thermische Expansionskoeffizient von Cyclohexanol in den untersuchten Lösungsmitteln sowie in Wasser wurden hergeleitet und werden im Kontext mit Wechselwirkungen zwischen Lösungsmittel und gelöster Substanz diskutiert. Zusätzlich wird das partielle Molvolumen im Sinn der scaled particle theory interpretiert. Der Lösungsmitteleffekt auf das partielle Molvolumen ist hauptsächlich auf die Bildung von Kavitäten und auf intermolekulare Dispersionskräfte zurückzuführen..

Partial molar volumes of tetraalkylammonium hydroxides in aqueous solution at 25°C

The densities of aqueous solutions of tetramethylammonium, tetraethylammonium, tetra-n-propylammonium and tetra-n-butylammonium hydroxide have been measured at 25°C in the concentration range 0.1–1.0 mol-kg-1 . The apparent and partial molar volumes are calculated from the density measurements. The apparent molar volumes of the solutes show considerable deviation from the Debye-Hülckel limiting law, even at high dilution. The relation for the concentration dependence of the apparent molar volume is given in an analytical form. The limiting apparent molar volumes of the solutes are split into their ionic components by an extrathermodynamic approach and are discussed in terms of ion-solvent interactions. In this way, the limiting partial molar ionic volume for the hydroxide ion is found to be 2 cm3-mol-1.

Cryoscopic, infrared spectroscopic and dielectric studies of associated cyclohexanol + benzene mixtures

The practical osmotic coefficients and molal activity coefficients of benzene solutions of cyclohexanol over the concentration range 0.02–0.27 mol kg–1 have been determined by the cryoscopic method and infrared spectra of the systems investigated have been recorded in the OH stretching vibration region at 303.65 K. The non-ideal behaviour of the system has been interpreted by the excess Gibbs free energy and on the basis of an associated model including an extended series of multimers. The formation of oligomeric species has been described in term of one independent parameter, i.e. the constant K, which is equal to the stepwise association constants and is related to the self-association constant by βq=K(q–1). From experimental data obtained by the cryoscopic method, the constant K and the concentration of monomer at the lowest concentration studied have been determined by a curve-fitting method, while the concentration of monomer at any definite concentration has been obtained using Bjerrums integral. From i.r. measurements the fractions of monomer have been obtained for the concentration range studied, and thus the integrated band area of the free OH band of the cyclohexanol monomer has been obtained graphically. In the case of i.r. measurements, the constant K has also been obtained by a curve fitting method.The partial molar volumes, partial molar refraction, partial molar polarization and the apparent dipole moment of cyclohexanol in benzene have been determined at 298.15 K and found to be independent of concentration up to 1.30 mol kg–1. The negative solvent effect on the dipole moment of the cyclohexanol molecule in benzene has been elucidated using Higasis approach.